=head1 NAME
-perldelta - what is new for perl v5.18.0
+[ this is a template for a new perldelta file. Any text flagged as XXX needs
+to be processed before release. ]
-=head1 DESCRIPTION
-
-This document describes differences between the v5.16.0 release and the v5.18.0
-release.
-
-If you are upgrading from an earlier release such as v5.14.0, first read
-L<perl5160delta>, which describes differences between v5.14.0 and v5.16.0.
-
-=head1 Core Enhancements
-
-=head2 New mechanism for experimental features
-
-Newly-added experimental features will now require this incantation:
-
- no warnings "experimental::feature_name";
- use feature "feature_name"; # would warn without the prev line
-
-There is a new warnings category, called "experimental", containing
-warnings that the L<feature> pragma emits when enabling experimental
-features.
-
-Newly-added experimental features will also be given special warning IDs,
-which consist of "experimental::" followed by the name of the feature. (The
-plan is to extend this mechanism eventually to all warnings, to allow them
-to be enabled or disabled individually, and not just by category.)
-
-By saying
-
- no warnings "experimental::feature_name";
-
-you are taking responsibility for any breakage that future changes to, or
-removal of, the feature may cause.
-
-Since some features (like C<~~> or C<my $_>) now emit experimental warnings,
-and you may want to disable them in code that is also run on perls that do not
-recognize these warning categories, consider using the C<if> pragma like this:
-
- no if $] >= 5.018, 'warnings', "experimental::feature_name";
-
-Existing experimental features may begin emitting these warnings, too. Please
-consult L<perlexperiment> for information on which features are considered
-experimental.
-
-=head2 Hash overhaul
-
-Changes to the implementation of hashes in perl v5.18.0 will be one of the most
-visible changes to the behavior of existing code.
-
-By default, two distinct hash variables with identical keys and values may now
-provide their contents in a different order where it was previously identical.
-
-When encountering these changes, the key to cleaning up from them is to accept
-that B<hashes are unordered collections> and to act accordingly.
-
-=head3 Hash randomization
-
-The seed used by Perl's hash function is now random. This means that the
-order which keys/values will be returned from functions like C<keys()>,
-C<values()>, and C<each()> will differ from run to run.
-
-This change was introduced to make Perl's hashes more robust to algorithmic
-complexity attacks, and also because we discovered that it exposes hash
-ordering dependency bugs and makes them easier to track down.
-
-Toolchain maintainers might want to invest in additional infrastructure to
-test for things like this. Running tests several times in a row and then
-comparing results will make it easier to spot hash order dependencies in
-code. Authors are strongly encouraged not to expose the key order of
-Perl's hashes to insecure audiences.
-
-Further, every hash has its own iteration order, which should make it much
-more difficult to determine what the current hash seed is.
-
-=head3 New hash functions
-
-Perl v5.18 includes support for multiple hash functions, and changed
-the default (to ONE_AT_A_TIME_HARD), you can choose a different
-algorithm by defining a symbol at compile time. For a current list,
-consult the F<INSTALL> document. Note that as of Perl v5.18 we can
-only recommend use of the default or SIPHASH. All the others are
-known to have security issues and are for research purposes only.
-
-=head3 PERL_HASH_SEED environment variable now takes a hex value
-
-C<PERL_HASH_SEED> no longer accepts an integer as a parameter;
-instead the value is expected to be a binary value encoded in a hex
-string, such as "0xf5867c55039dc724". This is to make the
-infrastructure support hash seeds of arbitrary lengths, which might
-exceed that of an integer. (SipHash uses a 16 byte seed.)
-
-=head3 PERL_PERTURB_KEYS environment variable added
-
-The C<PERL_PERTURB_KEYS> environment variable allows one to control the level of
-randomization applied to C<keys> and friends.
-
-When C<PERL_PERTURB_KEYS> is 0, perl will not randomize the key order at all. The
-chance that C<keys> changes due to an insert will be the same as in previous
-perls, basically only when the bucket size is changed.
-
-When C<PERL_PERTURB_KEYS> is 1, perl will randomize keys in a non-repeatable
-way. The chance that C<keys> changes due to an insert will be very high. This
-is the most secure and default mode.
-
-When C<PERL_PERTURB_KEYS> is 2, perl will randomize keys in a repeatable way.
-Repeated runs of the same program should produce the same output every time.
-
-C<PERL_HASH_SEED> implies a non-default C<PERL_PERTURB_KEYS> setting. Setting
-C<PERL_HASH_SEED=0> (exactly one 0) implies C<PERL_PERTURB_KEYS=0> (hash key
-randomization disabled); settng C<PERL_HASH_SEED> to any other value implies
-C<PERL_PERTURB_KEYS=2> (deterministic and repeatable hash key randomization).
-Specifying C<PERL_PERTURB_KEYS> explicitly to a different level overrides this
-behavior.
-
-=head3 Hash::Util::hash_seed() now returns a string
-
-Hash::Util::hash_seed() now returns a string instead of an integer. This
-is to make the infrastructure support hash seeds of arbitrary lengths
-which might exceed that of an integer. (SipHash uses a 16 byte seed.)
-
-=head3 Output of PERL_HASH_SEED_DEBUG has been changed
-
-The environment variable PERL_HASH_SEED_DEBUG now makes perl show both the
-hash function perl was built with, I<and> the seed, in hex, in use for that
-process. Code parsing this output, should it exist, must change to accommodate
-the new format. Example of the new format:
-
- $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
- HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
-
-=head2 Upgrade to Unicode 6.2
-
-Perl now supports Unicode 6.2. A list of changes from Unicode
-6.1 is at L<http://www.unicode.org/versions/Unicode6.2.0>.
-
-=head2 Character name aliases may now include non-Latin1-range characters
-
-It is possible to define your own names for characters for use in
-C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
-comprised of characters from the whole Unicode range. This allows for
-names to be in your native language, and not just English. Certain
-restrictions apply to the characters that may be used (you can't define
-a name that has punctuation in it, for example). See L<charnames/CUSTOM
-ALIASES>.
-
-=head2 New DTrace probes
-
-The following new DTrace probes have been added:
-
-=over 4
-
-=item *
-
-C<op-entry>
-
-=item *
-
-C<loading-file>
-
-=item *
-
-C<loaded-file>
-
-=back
-
-=head2 C<${^LAST_FH}>
-
-This new variable provides access to the filehandle that was last read.
-This is the handle used by C<$.> and by C<tell> and C<eof> without
-arguments.
-
-=head2 Regular Expression Set Operations
-
-This is an B<experimental> feature to allow matching against the union,
-intersection, etc., of sets of code points, similar to
-L<Unicode::Regex::Set>. It can also be used to extend C</x> processing
-to [bracketed] character classes, and as a replacement of user-defined
-properties, allowing more complex expressions than they do. See
-L<perlrecharclass/Extended Bracketed Character Classes>.
-
-=head2 Lexical subroutines
-
-This new feature is still considered B<experimental>. To enable it:
-
- use 5.018;
- no warnings "experimental::lexical_subs";
- use feature "lexical_subs";
-
-You can now declare subroutines with C<state sub foo>, C<my sub foo>, and
-C<our sub foo>. (C<state sub> requires that the "state" feature be
-enabled, unless you write it as C<CORE::state sub foo>.)
-
-C<state sub> creates a subroutine visible within the lexical scope in which
-it is declared. The subroutine is shared between calls to the outer sub.
-
-C<my sub> declares a lexical subroutine that is created each time the
-enclosing block is entered. C<state sub> is generally slightly faster than
-C<my sub>.
-
-C<our sub> declares a lexical alias to the package subroutine of the same
-name.
-
-For more information, see L<perlsub/Lexical Subroutines>.
-
-=head2 Computed Labels
-
-The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
-operator, now allow arbitrary expressions to be used to compute labels at run
-time. Previously, any argument that was not a constant was treated as the
-empty string.
-
-=head2 More CORE:: subs
-
-Several more built-in functions have been added as subroutines to the
-CORE:: namespace - namely, those non-overridable keywords that can be
-implemented without custom parsers: C<defined>, C<delete>, C<exists>,
-C<glob>, C<pos>, C<protoytpe>, C<scalar>, C<split>, C<study>, and C<undef>.
-
-As some of these have prototypes, C<prototype('CORE::...')> has been
-changed to not make a distinction between overridable and non-overridable
-keywords. This is to make C<prototype('CORE::pos')> consistent with
-C<prototype(&CORE::pos)>.
-
-=head2 C<kill> with negative signal names
-
-C<kill> has always allowed a negative signal number, which kills the
-process group instead of a single process. It has also allowed signal
-names. But it did not behave consistently, because negative signal names
-were treated as 0. Now negative signals names like C<-INT> are supported
-and treated the same way as -2 [perl #112990].
-
-=head1 Security
-
-=head2 See also: hash overhaul
-
-Some of the changes in the L<hash overhaul|/"Hash overhaul"> were made to
-enhance security. Please read that section.
-
-=head2 C<Storable> security warning in documentation
-
-The documentation for C<Storable> now includes a section which warns readers
-of the danger of accepting Storable documents from untrusted sources. The
-short version is that deserializing certain types of data can lead to loading
-modules and other code execution. This is documented behavior and wanted
-behavior, but this opens an attack vector for malicious entities.
-
-=head2 C<Locale::Maketext> allowed code injection via a malicious template
-
-If users could provide a translation string to Locale::Maketext, this could be
-used to invoke arbitrary Perl subroutines available in the current process.
-
-This has been fixed, but it is still possible to invoke any method provided by
-C<Locale::Maketext> itself or a subclass that you are using. One of these
-methods in turn will invoke the Perl core's C<sprintf> subroutine.
-
-In summary, allowing users to provide translation strings without auditing
-them is a bad idea.
-
-This vulnerability is documented in CVE-2012-6329.
-
-=head2 Avoid calling memset with a negative count
-
-Poorly written perl code that allows an attacker to specify the count to perl's
-C<x> string repeat operator can already cause a memory exhaustion
-denial-of-service attack. A flaw in versions of perl before v5.15.5 can escalate
-that into a heap buffer overrun; coupled with versions of glibc before 2.16, it
-possibly allows the execution of arbitrary code.
-
-The flaw addressed to this commit has been assigned identifier CVE-2012-5195
-and was researched by Tim Brown.
-
-=head1 Incompatible Changes
-
-=head2 See also: hash overhaul
-
-Some of the changes in the L<hash overhaul|/"Hash overhaul"> are not fully
-compatible with previous versions of perl. Please read that section.
-
-=head2 An unknown character name in C<\N{...}> is now a syntax error
-
-Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
-substituted. Unicode now recommends that this situation be a syntax
-error. Also, the previous behavior led to some confusing warnings and
-behaviors, and since the REPLACEMENT CHARACTER has no use other than as
-a stand-in for some unknown character, any code that has this problem is
-buggy.
-
-=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
-
-Since v5.12.0, it has been deprecated to use certain characters in
-user-defined C<\N{...}> character names. These now cause a syntax
-error. For example, it is now an error to begin a name with a digit,
-such as in
-
- my $undraftable = "\N{4F}"; # Syntax error!
-
-or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>.
-
-=head2 C<\N{BELL}> now refers to U+1F514 instead of U+0007
-
-Unicode 6.0 reused the name "BELL" for a different code point than it
-traditionally had meant. Since Perl v5.14, use of this name still
-referred to U+0007, but would raise a deprecation warning. Now, "BELL"
-refers to U+1F514, and the name for U+0007 is "ALERT". All the
-functions in L<charnames> have been correspondingly updated.
-
-=head2 New Restrictions in Multi-Character Case-Insensitive Matching in Regular Expression Bracketed Character Classes
-
-Unicode has now withdrawn their previous recommendation for regular
-expressions to automatically handle cases where a single character can
-match multiple characters case-insensitively, for example, the letter
-LATIN SMALL LETTER SHARP S and the sequence C<ss>. This is because
-it turns out to be impracticable to do this correctly in all
-circumstances. Because Perl has tried to do this as best it can, it
-will continue to do so. (We are considering an option to turn it off.)
-However, a new restriction is being added on such matches when they
-occur in [bracketed] character classes. People were specifying
-things such as C</[\0-\xff]/i>, and being surprised that it matches the
-two character sequence C<ss> (since LATIN SMALL LETTER SHARP S occurs in
-this range). This behavior is also inconsistent with using a
-property instead of a range: C<\p{Block=Latin1}> also includes LATIN
-SMALL LETTER SHARP S, but C</[\p{Block=Latin1}]/i> does not match C<ss>.
-The new rule is that for there to be a multi-character case-insensitive
-match within a bracketed character class, the character must be
-explicitly listed, and not as an end point of a range. This more
-closely obeys the Principle of Least Astonishment. See
-L<perlrecharclass/Bracketed Character Classes>. Note that a bug [perl
-#89774], now fixed as part of this change, prevented the previous
-behavior from working fully.
-
-=head2 Explicit rules for variable names and identifiers
-
-Due to an oversight, single character variable names in v5.16 were
-completely unrestricted. This opened the door to several kinds of
-insanity. As of v5.18, these now follow the rules of other identifiers,
-in addition to accepting characters that match the C<\p{POSIX_Punct}>
-property.
-
-There is no longer any difference in the parsing of identifiers
-specified by using braces versus without braces. For instance, perl
-used to allow C<${foo:bar}> (with a single colon) but not C<$foo:bar>.
-Now that both are handled by a single code path, they are both treated
-the same way: both are forbidden. Note that this change is about the
-range of permissible literal identifiers, not other expressions.
-
-=head2 Vertical tabs are now whitespace
-
-No one could recall why C<\s> didn't match C<\cK>, the vertical tab.
-Now it does. Given the extreme rarity of that character, very little
-breakage is expected. That said, here's what it means:
-
-C<\s> in a regex now matches a vertical tab in all circumstances.
-
-Literal vertical tabs in a regex literal are ignored when the C</x>
-modifier is used.
-
-Leading vertical tabs, alone or mixed with other whitespace, are now
-ignored when interpreting a string as a number. For example:
-
- $dec = " \cK \t 123";
- $hex = " \cK \t 0xF";
-
- say 0 + $dec; # was 0 with warning, now 123
- say int $dec; # was 0, now 123
- say oct $hex; # was 0, now 15
-
-=head2 C</(?{})/> and C</(??{})/> have been heavily reworked
-
-The implementation of this feature has been almost completely rewritten.
-Although its main intent is to fix bugs, some behaviors, especially
-related to the scope of lexical variables, will have changed. This is
-described more fully in the L</Selected Bug Fixes> section.
-
-=head2 Stricter parsing of substitution replacement
-
-It is no longer possible to abuse the way the parser parses C<s///e> like
-this:
-
- %_=(_,"Just another ");
- $_="Perl hacker,\n";
- s//_}->{_/e;print
-
-=head2 C<given> now aliases the global C<$_>
-
-Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
-global C<$_> an alias for its argument, just like C<foreach>. However, it
-still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
-C<foreach>) [perl #114020].
-
-=head2 The smartmatch family of features are now experimental
-
-Smart match, added in v5.10.0 and significantly revised in v5.10.1, has been
-a regular point of complaint. Although there are a number of ways in which
-it is useful, it has also proven problematic and confusing for both users and
-implementors of Perl. There have been a number of proposals on how to best
-address the problem. It is clear that smartmatch is almost certainly either
-going to change or go away in the future. Relying on its current behavior
-is not recommended.
-
-Warnings will now be issued when the parser sees C<~~>, C<given>, or C<when>.
-To disable these warnings, you can add this line to the appropriate scope:
-
- no if $] >= 5.018, "experimental::smartmatch";
-
-Consider, though, replacing the use of these features, as they may change
-behavior again before becoming stable.
-
-=head2 Lexical C<$_> is now experimental
-
-Since it was introduced in Perl v5.10, it has caused much confusion with no
-obvious solution:
-
-=over
-
-=item *
-
-Various modules (e.g., List::Util) expect callback routines to use the
-global C<$_>. C<use List::Util 'first'; my $_; first { $_ == 1 } @list>
-does not work as one would expect.
-
-=item *
-
-A C<my $_> declaration earlier in the same file can cause confusing closure
-warnings.
-
-=item *
-
-The "_" subroutine prototype character allows called subroutines to access
-your lexical C<$_>, so it is not really private after all.
-
-=item *
-
-Nevertheless, subroutines with a "(@)" prototype and methods cannot access
-the caller's lexical C<$_>, unless they are written in XS.
-
-=item *
-
-But even XS routines cannot access a lexical C<$_> declared, not in the
-calling subroutine, but in an outer scope, iff that subroutine happened not
-to mention C<$_> or use any operators that default to C<$_>.
-
-=back
-
-It is our hope that lexical C<$_> can be rehabilitated, but this may
-cause changes in its behavior. Please use it with caution until it
-becomes stable.
-
-=head2 readline() with C<$/ = \N> now reads N characters, not N bytes
-
-Previously, when reading from a stream with I/O layers such as
-C<encoding>, the readline() function, otherwise known as the C<< <> >>
-operator, would read I<N> bytes from the top-most layer. [perl #79960]
-
-Now, I<N> characters are read instead.
-
-There is no change in behaviour when reading from streams with no
-extra layers, since bytes map exactly to characters.
-
-=head2 Overridden C<glob> is now passed one argument
-
-C<glob> overrides used to be passed a magical undocumented second argument
-that identified the caller. Nothing on CPAN was using this, and it got in
-the way of a bug fix, so it was removed. If you really need to identify
-the caller, see L<Devel::Callsite> on CPAN.
-
-=head2 Here doc parsing
-
-The body of a here document inside a quote-like operator now always begins
-on the line after the "<<foo" marker. Previously, it was documented to
-begin on the line following the containing quote-like operator, but that
-was only sometimes the case [perl #114040].
-
-=head2 Alphanumeric operators must now be separated from the closing
-delimiter of regular expressions
-
-You may no longer write something like:
-
- m/a/and 1
-
-Instead you must write
-
- m/a/ and 1
-
-with whitespace separating the operator from the closing delimiter of
-the regular expression. Not having whitespace has resulted in a
-deprecation warning since Perl v5.14.0.
-
-=head2 qw(...) can no longer be used as parentheses
-
-C<qw> lists used to fool the parser into thinking they were always
-surrounded by parentheses. This permitted some surprising constructions
-such as C<foreach $x qw(a b c) {...}>, which should really be written
-C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
-the wrong state, so they didn't fully work, and the similar C<foreach qw(a
-b c) {...}> that one might expect to be permitted never worked at all.
-
-This side effect of C<qw> has now been abolished. It has been deprecated
-since Perl v5.13.11. It is now necessary to use real parentheses
-everywhere that the grammar calls for them.
-
-=head2 Interaction of lexical and default warnings
-
-Turning on any lexical warnings used first to disable all default warnings
-if lexical warnings were not already enabled:
-
- $*; # deprecation warning
- use warnings "void";
- $#; # void warning; no deprecation warning
-
-Now, the C<debugging>, C<deprecated>, C<glob>, C<inplace> and C<malloc> warnings
-categories are left on when turning on lexical warnings (unless they are
-turned off by C<no warnings>, of course).
-
-This may cause deprecation warnings to occur in code that used to be free
-of warnings.
-
-Those are the only categories consisting only of default warnings. Default
-warnings in other categories are still disabled by C<< use warnings "category" >>,
-as we do not yet have the infrastructure for controlling
-individual warnings.
-
-=head2 C<state sub> and C<our sub>
-
-Due to an accident of history, C<state sub> and C<our sub> were equivalent
-to a plain C<sub>, so one could even create an anonymous sub with
-C<our sub { ... }>. These are now disallowed outside of the "lexical_subs"
-feature. Under the "lexical_subs" feature they have new meanings described
-in L<perlsub/Lexical Subroutines>.
-
-=head2 Defined values stored in environment are forced to byte strings
-
-A value stored in an environment variable has always been stringified. In this
-release, it is converted to be only a byte string. First, it is forced to be
-only a string. Then if the string is utf8 and the equivalent of
-C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
-C<utf8::encode()> is used, and a warning is issued about wide characters
-(L</Diagnostics>).
-
-=head2 C<require> dies for unreadable files
-
-When C<require> encounters an unreadable file, it now dies. It used to
-ignore the file and continue searching the directories in C<@INC>
-[perl #113422].
-
-=head2 C<gv_fetchmeth_*> and SUPER
-
-The various C<gv_fetchmeth_*> XS functions used to treat a package whose
-named ended with C<::SUPER> specially. A method lookup on the C<Foo::SUPER>
-package would be treated as a C<SUPER> method lookup on the C<Foo> package. This
-is no longer the case. To do a C<SUPER> lookup, pass the C<Foo> stash and the
-C<GV_SUPER> flag.
-
-=head2 C<split>'s first argument is more consistently interpreted
-
-After some changes earlier in v5.17, C<split>'s behavior has been
-simplified: if the PATTERN argument evaluates to a string
-containing one space, it is treated the way that a I<literal> string
-containing one space once was.
-
-=head1 Deprecations
-
-=head2 Module removals
-
-The following modules will be removed from the core distribution in a future
-release, and will at that time need to be installed from CPAN. Distributions
-on CPAN which require these modules will need to list them as prerequisites.
-
-The core versions of these modules will now issue C<"deprecated">-category
-warnings to alert you to this fact. To silence these deprecation warnings,
-install the modules in question from CPAN.
-
-Note that these are (with rare exceptions) fine modules that you are encouraged
-to continue to use. Their disinclusion from core primarily hinges on their
-necessity to bootstrapping a fully functional, CPAN-capable Perl installation,
-not usually on concerns over their design.
-
-=over
-
-=item L<encoding>
-
-The use of this pragma is now strongly discouraged. It conflates the encoding
-of source text with the encoding of I/O data, reinterprets escape sequences in
-source text (a questionable choice), and introduces the UTF-8 bug to all runtime
-handling of character strings. It is broken as designed and beyond repair.
-
-For using non-ASCII literal characters in source text, please refer to L<utf8>.
-For dealing with textual I/O data, please refer to L<Encode> and L<open>.
-
-=item L<Archive::Extract>
-
-=item L<B::Lint>
-
-=item L<B::Lint::Debug>
-
-=item L<CPANPLUS> and all included C<CPANPLUS::*> modules
-
-=item L<Devel::InnerPackage>
-
-=item L<Log::Message>
-
-=item L<Log::Message::Config>
-
-=item L<Log::Message::Handlers>
-
-=item L<Log::Message::Item>
-
-=item L<Log::Message::Simple>
-
-=item L<Module::Pluggable>
-
-=item L<Module::Pluggable::Object>
-
-=item L<Object::Accessor>
-
-=item L<Pod::LaTeX>
-
-=item L<Term::UI>
-
-=item L<Term::UI::History>
-
-=back
-
-=head2 Deprecated Utilities
-
-The following utilities will be removed from the core distribution in a
-future release as their associated modules have been deprecated. They
-will remain available with the applicable CPAN distribution.
-
-=over
-
-=item L<cpanp>
-
-=item C<cpanp-run-perl>
-
-=item L<cpan2dist>
-
-These items are part of the C<CPANPLUS> distribution.
-
-=item L<pod2latex>
-
-This item is part of the C<Pod::LaTeX> distribution.
-
-=back
-
-=head2 PL_sv_objcount
-
-This interpreter-global variable used to track the total number of
-Perl objects in the interpreter. It is no longer maintained and will
-be removed altogether in Perl v5.20.
-
-=head2 Five additional characters should be escaped in patterns with C</x>
-
-When a regular expression pattern is compiled with C</x>, Perl treats 6
-characters as white space to ignore, such as SPACE and TAB. However,
-Unicode recommends 11 characters be treated thusly. We will conform
-with this in a future Perl version. In the meantime, use of any of the
-missing characters will raise a deprecation warning, unless turned off.
-The five characters are:
-
- U+0085 NEXT LINE
- U+200E LEFT-TO-RIGHT MARK
- U+200F RIGHT-TO-LEFT MARK
- U+2028 LINE SEPARATOR
- U+2029 PARAGRAPH SEPARATOR
-
-=head2 User-defined charnames with surprising whitespace
-
-A user-defined character name with trailing or multiple spaces in a row is
-likely a typo. This now generates a warning when defined, on the assumption
-that uses of it will be unlikely to include the excess whitespace.
-
-=head2 Various XS-callable functions are now deprecated
-
-All the functions used to classify characters will be removed from a
-future version of Perl, and should not be used. With participating C
-compilers (e.g., gcc), compiling any file that uses any of these will
-generate a warning. These were not intended for public use; there are
-equivalent, faster, macros for most of them.
-
-See L<perlapi/Character classes>. The complete list is:
-
-C<is_uni_alnum>, C<is_uni_alnumc>, C<is_uni_alnumc_lc>,
-C<is_uni_alnum_lc>, C<is_uni_alpha>, C<is_uni_alpha_lc>,
-C<is_uni_ascii>, C<is_uni_ascii_lc>, C<is_uni_blank>,
-C<is_uni_blank_lc>, C<is_uni_cntrl>, C<is_uni_cntrl_lc>,
-C<is_uni_digit>, C<is_uni_digit_lc>, C<is_uni_graph>,
-C<is_uni_graph_lc>, C<is_uni_idfirst>, C<is_uni_idfirst_lc>,
-C<is_uni_lower>, C<is_uni_lower_lc>, C<is_uni_print>,
-C<is_uni_print_lc>, C<is_uni_punct>, C<is_uni_punct_lc>,
-C<is_uni_space>, C<is_uni_space_lc>, C<is_uni_upper>,
-C<is_uni_upper_lc>, C<is_uni_xdigit>, C<is_uni_xdigit_lc>,
-C<is_utf8_alnum>, C<is_utf8_alnumc>, C<is_utf8_alpha>,
-C<is_utf8_ascii>, C<is_utf8_blank>, C<is_utf8_char>,
-C<is_utf8_cntrl>, C<is_utf8_digit>, C<is_utf8_graph>,
-C<is_utf8_idcont>, C<is_utf8_idfirst>, C<is_utf8_lower>,
-C<is_utf8_mark>, C<is_utf8_perl_space>, C<is_utf8_perl_word>,
-C<is_utf8_posix_digit>, C<is_utf8_print>, C<is_utf8_punct>,
-C<is_utf8_space>, C<is_utf8_upper>, C<is_utf8_xdigit>,
-C<is_utf8_xidcont>, C<is_utf8_xidfirst>.
-
-In addition these three functions that have never worked properly are
-deprecated:
-C<to_uni_lower_lc>, C<to_uni_title_lc>, and C<to_uni_upper_lc>.
-
-=head2 Certain rare uses of backslashes within regexes are now deprecated
-
-There are three pairs of characters that Perl recognizes as
-metacharacters in regular expression patterns: C<{}>, C<[]>, and C<()>.
-These can be used as well to delimit patterns, as in:
-
- m{foo}
- s(foo)(bar)
-
-Since they are metacharacters, they have special meaning to regular
-expression patterns, and it turns out that you can't turn off that
-special meaning by the normal means of preceding them with a backslash,
-if you use them, paired, within a pattern delimited by them. For
-example, in
-
- m{foo\{1,3\}}
-
-the backslashes do not change the behavior, and this matches
-S<C<"f o">> followed by one to three more occurrences of C<"o">.
-
-Usages like this, where they are interpreted as metacharacters, are
-exceedingly rare; we think there are none, for example, in all of CPAN.
-Hence, this deprecation should affect very little code. It does give
-notice, however, that any such code needs to change, which will in turn
-allow us to change the behavior in future Perl versions so that the
-backslashes do have an effect, and without fear that we are silently
-breaking any existing code.
-
-=head2 Splitting the tokens C<(?> and C<(*> in regular expressions
-
-A deprecation warning is now raised if the C<(> and C<?> are separated
-by white space or comments in C<(?...)> regular expression constructs.
-Similarly, if the C<(> and C<*> are separated in C<(*VERB...)>
-constructs.
-
-=head2 Pre-PerlIO IO implementations
-
-In theory, you can currently build perl without PerlIO. Instead, you'd use a
-wrapper around stdio or sfio. In practice, this isn't very useful. It's not
-well tested, and without any support for IO layers or (thus) Unicode, it's not
-much of a perl. Building without PerlIO will most likely be removed in the
-next version of perl.
-
-PerlIO supports a C<stdio> layer if stdio use is desired. Similarly a
-sfio layer could be produced in the future, if needed.
-
-=head1 Future Deprecations
-
-=over
-
-=item *
-
-Platforms without support infrastructure
-
-Both Windows CE and z/OS have been historically under-maintained, and are
-currently neither successfully building nor regularly being smoke tested.
-Efforts are underway to change this situation, but it should not be taken for
-granted that the platforms are safe and supported. If they do not become
-buildable and regularly smoked, support for them may be actively removed in
-future releases. If you have an interest in these platforms and you can lend
-your time, expertise, or hardware to help support these platforms, please let
-the perl development effort know by emailing C<perl5-porters@perl.org>.
-
-Some platforms that appear otherwise entirely dead are also on the short list
-for removal between now and v5.20.0:
-
-=over
-
-=item DG/UX
-
-=item NeXT
-
-=back
-
-We also think it likely that current versions of Perl will no longer
-build AmigaOS, DJGPP, NetWare (natively), OS/2 and Plan 9. If you
-are using Perl on such a platform and have an interest in ensuring
-Perl's future on them, please contact us.
-
-We believe that Perl has long been unable to build on mixed endian
-architectures (such as PDP-11s), and intend to remove any remaining
-support code. Similarly, code supporting the long umaintained GNU
-dld will be removed soon if no-one makes themselves known as an
-active user.
-
-=item *
-
-Swapping of $< and $>
-
-Perl has supported the idiom of swapping $< and $> (and likewise $( and
-$)) to temporarily drop permissions since 5.0, like this:
-
- ($<, $>) = ($>, $<);
-
-However, this idiom modifies the real user/group id, which can have
-undesirable side-effects, is no longer useful on any platform perl
-supports and complicates the implementation of these variables and list
-assignment in general.
-
-As an alternative, assignment only to C<< $> >> is recommended:
-
- local $> = $<;
-
-See also: L<Setuid Demystified|http://www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf>.
-
-=item *
-
-C<microperl>, long broken and of unclear present purpose, will be removed.
-
-=item *
-
-Revamping C<< "\Q" >> semantics in double-quotish strings when combined with
-other escapes.
-
-There are several bugs and inconsistencies involving combinations
-of C<\Q> and escapes like C<\x>, C<\L>, etc., within a C<\Q...\E> pair.
-These need to be fixed, and doing so will necessarily change current
-behavior. The changes have not yet been settled.
-
-=item *
-
-Use of C<$x>, where C<x> stands for any actual (non-printing) C0 control
-character will be disallowed in a future Perl version. Use C<${x}>
-instead (where again C<x> stands for a control character),
-or better, C<$^A> , where C<^> is a caret (CIRCUMFLEX ACCENT),
-and C<A> stands for any of the characters listed at the end of
-L<perlebcdic/OPERATOR DIFFERENCES>.
-
-=back
-
-=head1 Performance Enhancements
-
-=over 4
-
-=item *
-
-Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
-down to a single op and are hence faster than before.
-
-=item *
-
-A new C preprocessor define C<NO_TAINT_SUPPORT> was added that, if set,
-disables Perl's taint support altogether. Using the -T or -t command
-line flags will cause a fatal error. Beware that both core tests as
-well as many a CPAN distribution's tests will fail with this change. On
-the upside, it provides a small performance benefit due to reduced
-branching.
-
-B<Do not enable this unless you know exactly what you are getting yourself
-into.>
-
-=item *
-
-C<pack> with constant arguments is now constant folded in most cases
-[perl #113470].
-
-=item *
-
-Speed up in regular expression matching against Unicode properties. The
-largest gain is for C<\X>, the Unicode "extended grapheme cluster." The
-gain for it is about 35% - 40%. Bracketed character classes, e.g.,
-C<[0-9\x{100}]> containing code points above 255 are also now faster.
-
-=item *
-
-On platforms supporting it, several former macros are now implemented as static
-inline functions. This should speed things up slightly on non-GCC platforms.
-
-=item *
-
-The optimisation of hashes in boolean context has been extended to
-affect C<scalar(%hash)>, C<%hash ? ... : ...>, and C<sub { %hash || ... }>.
-
-=item *
-
-Filetest operators manage the stack in a fractionally more efficient manner.
-
-=item *
-
-Globs used in a numeric context are now numified directly in most cases,
-rather than being numified via stringification.
-
-=item *
-
-The C<x> repetition operator is now folded to a single constant at compile
-time if called in scalar context with constant operands and no parentheses
-around the left operand.
-
-=back
-
-=head1 Modules and Pragmata
-
-=head2 New Modules and Pragmata
-
-=over 4
-
-=item *
-
-L<Config::Perl::V> version 0.16 has been added as a dual-lifed module.
-It provides structured data retrieval of C<perl -V> output including
-information only known to the C<perl> binary and not available via L<Config>.
-
-=back
-
-=head2 Updated Modules and Pragmata
-
-For a complete list of updates, run:
-
- $ corelist --diff 5.16.0 5.18.0
-
-You can substitute your favorite version in place of C<5.16.0>, too.
-
-=over
-
-=item *
-
-L<Archive::Extract> has been upgraded to 0.68.
-
-Work around an edge case on Linux with Busybox's unzip.
-
-=item *
-
-L<Archive::Tar> has been upgraded to 1.90.
-
-ptar now supports the -T option as well as dashless options
-[rt.cpan.org #75473], [rt.cpan.org #75475].
-
-Auto-encode filenames marked as UTF-8 [rt.cpan.org #75474].
-
-Don't use C<tell> on L<IO::Zlib> handles [rt.cpan.org #64339].
-
-Don't try to C<chown> on symlinks.
-
-=item *
-
-L<autodie> has been upgraded to 2.13.
-
-C<autodie> now plays nicely with the 'open' pragma.
-
-=item *
-
-L<B> has been upgraded to 1.42.
-
-The C<stashoff> method of COPs has been added. This provides access to an
-internal field added in perl 5.16 under threaded builds [perl #113034].
-
-C<B::COP::stashpv> now supports UTF-8 package names and embedded NULs.
-
-All C<CVf_*> and C<GVf_*>
-and more SV-related flag values are now provided as constants in the C<B::>
-namespace and available for export. The default export list has not changed.
-
-This makes the module work with the new pad API.
-
-=item *
-
-L<B::Concise> has been upgraded to 0.95.
-
-The C<-nobanner> option has been fixed, and C<format>s can now be dumped.
-When passed a sub name to dump, it will check also to see whether it
-is the name of a format. If a sub and a format share the same name,
-it will dump both.
-
-This adds support for the new C<OpMAYBE_TRUEBOOL> and C<OPpTRUEBOOL> flags.
-
-=item *
-
-L<B::Debug> has been upgraded to 1.18.
-
-This adds support (experimentally) for C<B::PADLIST>, which will be
-added in Perl 5.17.4.
-
-=item *
-
-L<B::Deparse> has been upgraded to 1.20.
-
-Avoid warning when run under C<perl -w>.
-
-It now deparses
-loop controls with the correct precedence, and multiple statements in a
-C<format> line are also now deparsed correctly.
-
-This release suppresses trailing semicolons in formats.
-
-This release adds stub deparsing for lexical subroutines.
-
-It no longer dies when deparsing C<sort> without arguments. It now
-correctly omits the comma for C<system $prog @args> and C<exec $prog
-@args>.
-
-=item *
-
-L<bignum>, L<bigint> and L<bigrat> have been upgraded to 0.33.
-
-The overrides for C<hex> and C<oct> have been rewritten, eliminating
-several problems, and making one incompatible change:
-
-=over
-
-=item *
-
-Formerly, whichever of C<use bigint> or C<use bigrat> was compiled later
-would take precedence over the other, causing C<hex> and C<oct> not to
-respect the other pragma when in scope.
-
-=item *
-
-Using any of these three pragmata would cause C<hex> and C<oct> anywhere
-else in the program to evalute their arguments in list context and prevent
-them from inferring $_ when called without arguments.
-
-=item *
-
-Using any of these three pragmata would make C<oct("1234")> return 1234
-(for any number not beginning with 0) anywhere in the program. Now "1234"
-is translated from octal to decimal, whether within the pragma's scope or
-not.
-
-=item *
-
-The global overrides that facilitate lexical use of C<hex> and C<oct> now
-respect any existing overrides that were in place before the new overrides
-were installed, falling back to them outside of the scope of C<use bignum>.
-
-=item *
-
-C<use bignum "hex">, C<use bignum "oct"> and similar invocations for bigint
-and bigrat now export a C<hex> or C<oct> function, instead of providing a
-global override.
-
-=back
-
-=item *
-
-L<Carp> has been upgraded to 1.29.
-
-Carp is no longer confused when C<caller> returns undef for a package that
-has been deleted.
-
-The C<longmess()> and C<shortmess()> functions are now documented.
-
-=item *
-
-L<CGI> has been upgraded to 3.63.
-
-Unrecognized HTML escape sequences are now handled better, problematic
-trailing newlines are no longer inserted after E<lt>formE<gt> tags
-by C<startform()> or C<start_form()>, and bogus "Insecure Dependency"
-warnings appearing with some versions of perl are now worked around.
-
-=item *
-
-L<Class::Struct> has been upgraded to 0.64.
-
-The constructor now respects overridden accessor methods [perl #29230].
-
-=item *
-
-L<Compress::Raw::Bzip2> has been upgraded to 2.060.
-
-The misuse of Perl's "magic" API has been fixed.
-
-=item *
-
-L<Compress::Raw::Zlib> has been upgraded to 2.060.
-
-Upgrade bundled zlib to version 1.2.7.
-
-Fix build failures on Irix, Solaris, and Win32, and also when building as C++
-[rt.cpan.org #69985], [rt.cpan.org #77030], [rt.cpan.org #75222].
-
-The misuse of Perl's "magic" API has been fixed.
-
-C<compress()>, C<uncompress()>, C<memGzip()> and C<memGunzip()> have
-been speeded up by making parameter validation more efficient.
-
-=item *
-
-L<CPAN::Meta::Requirements> has been upgraded to 2.122.
-
-Treat undef requirements to C<from_string_hash> as 0 (with a warning).
-
-Added C<requirements_for_module> method.
-
-=item *
-
-L<CPANPLUS> has been upgraded to 0.9135.
-
-Allow adding F<blib/script> to PATH.
-
-Save the history between invocations of the shell.
-
-Handle multiple C<makemakerargs> and C<makeflags> arguments better.
-
-This resolves issues with the SQLite source engine.
-
-=item *
-
-L<Data::Dumper> has been upgraded to 2.145.
-
-It has been optimized to only build a seen-scalar hash as necessary,
-thereby speeding up serialization drastically.
-
-Additional tests were added in order to improve statement, branch, condition
-and subroutine coverage. On the basis of the coverage analysis, some of the
-internals of Dumper.pm were refactored. Almost all methods are now
-documented.
-
-=item *
-
-L<DB_File> has been upgraded to 1.827.
-
-The main Perl module no longer uses the C<"@_"> construct.
-
-=item *
-
-L<Devel::Peek> has been upgraded to 1.11.
-
-This fixes compilation with C++ compilers and makes the module work with
-the new pad API.
-
-=item *
-
-L<Digest::MD5> has been upgraded to 2.52.
-
-Fix C<Digest::Perl::MD5> OO fallback [rt.cpan.org #66634].
-
-=item *
-
-L<Digest::SHA> has been upgraded to 5.84.
-
-This fixes a double-free bug, which might have caused vulnerabilities
-in some cases.
-
-=item *
-
-L<DynaLoader> has been upgraded to 1.18.
-
-This is due to a minor code change in the XS for the VMS implementation.
-
-This fixes warnings about using C<CODE> sections without an C<OUTPUT>
-section.
-
-=item *
-
-L<Encode> has been upgraded to 2.49.
-
-The Mac alias x-mac-ce has been added, and various bugs have been fixed
-in Encode::Unicode, Encode::UTF7 and Encode::GSM0338.
-
-=item *
-
-L<Env> has been upgraded to 1.04.
-
-Its SPLICE implementation no longer misbehaves in list context.
-
-=item *
-
-L<ExtUtils::CBuilder> has been upgraded to 0.280210.
-
-Manifest files are now correctly embedded for those versions of VC++ which
-make use of them. [perl #111782, #111798].
-
-A list of symbols to export can now be passed to C<link()> when on
-Windows, as on other OSes [perl #115100].
-
-=item *
-
-L<ExtUtils::ParseXS> has been upgraded to 3.18.
-
-The generated C code now avoids unnecessarily incrementing
-C<PL_amagic_generation> on Perl versions where it's done automatically
-(or on current Perl where the variable no longer exists).
-
-This avoids a bogus warning for initialised XSUB non-parameters [perl
-#112776].
-
-=item *
-
-L<File::Copy> has been upgraded to 2.26.
-
-C<copy()> no longer zeros files when copying into the same directory,
-and also now fails (as it has long been documented to do) when attempting
-to copy a file over itself.
-
-=item *
-
-L<File::DosGlob> has been upgraded to 1.10.
-
-The internal cache of file names that it keeps for each caller is now
-freed when that caller is freed. This means
-C<< use File::DosGlob 'glob'; eval 'scalar <*>' >> no longer leaks memory.
-
-=item *
-
-L<File::Fetch> has been upgraded to 0.38.
-
-Added the 'file_default' option for URLs that do not have a file
-component.
-
-Use C<File::HomeDir> when available, and provide C<PERL5_CPANPLUS_HOME> to
-override the autodetection.
-
-Always re-fetch F<CHECKSUMS> if C<fetchdir> is set.
-
-=item *
-
-L<File::Find> has been upgraded to 1.23.
-
-This fixes inconsistent unixy path handling on VMS.
-
-Individual files may now appear in list of directories to be searched
-[perl #59750].
-
-=item *
-
-L<File::Glob> has been upgraded to 1.20.
-
-File::Glob has had exactly the same fix as File::DosGlob. Since it is
-what Perl's own C<glob> operator itself uses (except on VMS), this means
-C<< eval 'scalar <*>' >> no longer leaks.
-
-A space-separated list of patterns return long lists of results no longer
-results in memory corruption or crashes. This bug was introduced in
-Perl 5.16.0. [perl #114984]
-
-=item *
-
-L<File::Spec::Unix> has been upgraded to 3.40.
-
-C<abs2rel> could produce incorrect results when given two relative paths or
-the root directory twice [perl #111510].
-
-=item *
-
-L<File::stat> has been upgraded to 1.07.
-
-C<File::stat> ignores the L<filetest> pragma, and warns when used in
-combination therewith. But it was not warning for C<-r>. This has been
-fixed [perl #111640].
-
-C<-p> now works, and does not return false for pipes [perl #111638].
-
-Previously C<File::stat>'s overloaded C<-x> and C<-X> operators did not give
-the correct results for directories or executable files when running as
-root. They had been treating executable permissions for root just like for
-any other user, performing group membership tests I<etc> for files not owned
-by root. They now follow the correct Unix behaviour - for a directory they
-are always true, and for a file if any of the three execute permission bits
-are set then they report that root can execute the file. Perl's builtin
-C<-x> and C<-X> operators have always been correct.
-
-=item *
-
-L<File::Temp> has been upgraded to 0.23
-
-Fixes various bugs involving directory removal. Defers unlinking tempfiles if
-the initial unlink fails, which fixes problems on NFS.
-
-=item *
-
-L<GDBM_File> has been upgraded to 1.15.
-
-The undocumented optional fifth parameter to C<TIEHASH> has been
-removed. This was intended to provide control of the callback used by
-C<gdbm*> functions in case of fatal errors (such as filesystem problems),
-but did not work (and could never have worked). No code on CPAN even
-attempted to use it. The callback is now always the previous default,
-C<croak>. Problems on some platforms with how the C<C> C<croak> function
-is called have also been resolved.
-
-=item *
-
-L<Hash::Util> has been upgraded to 0.15.
-
-C<hash_unlocked> and C<hashref_unlocked> now returns true if the hash is
-unlocked, instead of always returning false [perl #112126].
-
-C<hash_unlocked>, C<hashref_unlocked>, C<lock_hash_recurse> and
-C<unlock_hash_recurse> are now exportable [perl #112126].
-
-Two new functions, C<hash_locked> and C<hashref_locked>, have been added.
-Oddly enough, these two functions were already exported, even though they
-did not exist [perl #112126].
-
-=item *
-
-L<HTTP::Tiny> has been upgraded to 0.025.
-
-Add SSL verification features [github #6], [github #9].
-
-Include the final URL in the response hashref.
-
-Add C<local_address> option.
-
-This improves SSL support.
-
-=item *
-
-L<IO> has been upgraded to 1.28.
-
-C<sync()> can now be called on read-only file handles [perl #64772].
-
-L<IO::Socket> tries harder to cache or otherwise fetch socket
-information.
-
-=item *
-
-L<IPC::Cmd> has been upgraded to 0.80.
-
-Use C<POSIX::_exit> instead of C<exit> in C<run_forked> [rt.cpan.org #76901].
-
-=item *
-
-L<IPC::Open3> has been upgraded to 1.13.
-
-The C<open3()> function no longer uses C<POSIX::close()> to close file
-descriptors since that breaks the ref-counting of file descriptors done by
-PerlIO in cases where the file descriptors are shared by PerlIO streams,
-leading to attempts to close the file descriptors a second time when
-any such PerlIO streams are closed later on.
-
-=item *
-
-L<Locale::Codes> has been upgraded to 3.25.
-
-It includes some new codes.
-
-=item *
-
-L<Memoize> has been upgraded to 1.03.
-
-Fix the C<MERGE> cache option.
-
-=item *
-
-L<Module::Build> has been upgraded to 0.4003.
-
-Fixed bug where modules without C<$VERSION> might have a version of '0' listed
-in 'provides' metadata, which will be rejected by PAUSE.
-
-Fixed bug in PodParser to allow numerals in module names.
-
-Fixed bug where giving arguments twice led to them becoming arrays, resulting
-in install paths like F<ARRAY(0xdeadbeef)/lib/Foo.pm>.
-
-A minor bug fix allows markup to be used around the leading "Name" in
-a POD "abstract" line, and some documentation improvements have been made.
-
-=item *
-
-L<Module::CoreList> has been upgraded to 2.90
-
-Version information is now stored as a delta, which greatly reduces the
-size of the F<CoreList.pm> file.
-
-This restores compatibility with older versions of perl and cleans up
-the corelist data for various modules.
-
-=item *
-
-L<Module::Load::Conditional> has been upgraded to 0.54.
-
-Fix use of C<requires> on perls installed to a path with spaces.
-
-Various enhancements include the new use of Module::Metadata.
-
-=item *
-
-L<Module::Metadata> has been upgraded to 1.000011.
-
-The creation of a Module::Metadata object for a typical module file has
-been sped up by about 40%, and some spurious warnings about C<$VERSION>s
-have been suppressed.
-
-=item *
-
-L<Module::Pluggable> has been upgraded to 4.7.
-
-Amongst other changes, triggers are now allowed on events, which gives
-a powerful way to modify behaviour.
-
-=item *
-
-L<Net::Ping> has been upgraded to 2.41.
-
-This fixes some test failures on Windows.
-
-=item *
-
-L<Opcode> has been upgraded to 1.25.
-
-Reflect the removal of the boolkeys opcode and the addition of the
-clonecv, introcv and padcv opcodes.
-
-=item *
-
-L<overload> has been upgraded to 1.22.
-
-C<no overload> now warns for invalid arguments, just like C<use overload>.
-
-=item *
-
-L<PerlIO::encoding> has been upgraded to 0.16.
-
-This is the module implementing the ":encoding(...)" I/O layer. It no
-longer corrupts memory or crashes when the encoding back-end reallocates
-the buffer or gives it a typeglob or shared hash key scalar.
-
-=item *
-
-L<PerlIO::scalar> has been upgraded to 0.16.
-
-The buffer scalar supplied may now only contain code pounts 0xFF or
-lower. [perl #109828]
-
-=item *
-
-L<Perl::OSType> has been upgraded to 1.003.
-
-This fixes a bug detecting the VOS operating system.
-
-=item *
-
-L<Pod::Html> has been upgraded to 1.18.
-
-The option C<--libpods> has been reinstated. It is deprecated, and its use
-does nothing other than issue a warning that it is no longer supported.
-
-Since the HTML files generated by pod2html claim to have a UTF-8 charset,
-actually write the files out using UTF-8 [perl #111446].
-
-=item *
-
-L<Pod::Simple> has been upgraded to 3.28.
-
-Numerous improvements have been made, mostly to Pod::Simple::XHTML,
-which also has a compatibility change: the C<codes_in_verbatim> option
-is now disabled by default. See F<cpan/Pod-Simple/ChangeLog> for the
-full details.
-
-=item *
-
-L<re> has been upgraded to 0.23
-
-Single character [class]es like C</[s]/> or C</[s]/i> are now optimized
-as if they did not have the brackets, i.e. C</s/> or C</s/i>.
-
-See note about C<op_comp> in the L</Internal Changes> section below.
-
-=item *
-
-L<Safe> has been upgraded to 2.35.
-
-Fix interactions with C<Devel::Cover>.
-
-Don't eval code under C<no strict>.
-
-=item *
-
-L<Scalar::Util> has been upgraded to version 1.27.
-
-Fix an overloading issue with C<sum>.
-
-C<first> and C<reduce> now check the callback first (so C<&first(1)> is
-disallowed).
-
-Fix C<tainted> on magical values [rt.cpan.org #55763].
-
-Fix C<sum> on previously magical values [rt.cpan.org #61118].
-
-Fix reading past the end of a fixed buffer [rt.cpan.org #72700].
-
-=item *
-
-L<Search::Dict> has been upgraded to 1.07.
-
-No longer require C<stat> on filehandles.
-
-Use C<fc> for casefolding.
-
-=item *
-
-L<Socket> has been upgraded to 2.009.
-
-Constants and functions required for IP multicast source group membership
-have been added.
-
-C<unpack_sockaddr_in()> and C<unpack_sockaddr_in6()> now return just the IP
-address in scalar context, and C<inet_ntop()> now guards against incorrect
-length scalars being passed in.
-
-This fixes an uninitialized memory read.
-
-=item *
-
-L<Storable> has been upgraded to 2.41.
-
-Modifying C<$_[0]> within C<STORABLE_freeze> no longer results in crashes
-[perl #112358].
-
-An object whose class implements C<STORABLE_attach> is now thawed only once
-when there are multiple references to it in the structure being thawed
-[perl #111918].
-
-Restricted hashes were not always thawed correctly [perl #73972].
-
-Storable would croak when freezing a blessed REF object with a
-C<STORABLE_freeze()> method [perl #113880].
-
-It can now freeze and thaw vstrings correctly. This causes a slight
-incompatible change in the storage format, so the format version has
-increased to 2.9.
-
-This contains various bugfixes, including compatibility fixes for older
-versions of Perl and vstring handling.
-
-=item *
-
-L<Sys::Syslog> has been upgraded to 0.32.
-
-This contains several bug fixes relating to C<getservbyname()>,
-C<setlogsock()>and log levels in C<syslog()>, together with fixes for
-Windows, Haiku-OS and GNU/kFreeBSD. See F<cpan/Sys-Syslog/Changes>
-for the full details.
-
-=item *
-
-L<Term::ANSIColor> has been upgraded to 4.02.
-
-Add support for italics.
-
-Improve error handling.
-
-=item *
-
-L<Term::ReadLine> has been upgraded to 1.10. This fixes the
-use of the B<cpan> and B<cpanp> shells on Windows in the event that the current
-drive happens to contain a F<\dev\tty> file.
-
-=item *
-
-L<Test::Harness> has been upgraded to 3.26.
-
-Fix glob semantics on Win32 [rt.cpan.org #49732].
-
-Don't use C<Win32::GetShortPathName> when calling perl [rt.cpan.org #47890].
-
-Ignore -T when reading shebang [rt.cpan.org #64404].
-
-Handle the case where we don't know the wait status of the test more
-gracefully.
-
-Make the test summary 'ok' line overridable so that it can be changed to a
-plugin to make the output of prove idempotent.
-
-Don't run world-writable files.
-
-=item *
-
-L<Text::Tabs> and L<Text::Wrap> have been upgraded to
-2012.0818. Support for Unicode combining characters has been added to them
-both.
-
-=item *
-
-L<threads::shared> has been upgraded to 1.31.
-
-This adds the option to warn about or ignore attempts to clone structures
-that can't be cloned, as opposed to just unconditionally dying in
-that case.
-
-This adds support for dual-valued values as created by
-L<Scalar::Util::dualvar|Scalar::Util/"dualvar NUM, STRING">.
-
-=item *
-
-L<Tie::StdHandle> has been upgraded to 4.3.
-
-C<READ> now respects the offset argument to C<read> [perl #112826].
-
-=item *
-
-L<Time::Local> has been upgraded to 1.2300.
-
-Seconds values greater than 59 but less than 60 no longer cause
-C<timegm()> and C<timelocal()> to croak.
-
-=item *
-
-L<Unicode::UCD> has been upgraded to 0.53.
-
-This adds a function L<all_casefolds()|Unicode::UCD/all_casefolds()>
-that returns all the casefolds.
-
-=item *
-
-L<Win32> has been upgraded to 0.47.
-
-New APIs have been added for getting and setting the current code page.
-
-=back
-
-
-=head2 Removed Modules and Pragmata
-
-=over
-
-=item *
-
-L<Version::Requirements> has been removed from the core distribution. It is
-available under a different name: L<CPAN::Meta::Requirements>.
-
-=back
-
-=head1 Documentation
-
-=head2 Changes to Existing Documentation
-
-=head3 L<perlcheat>
-
-=over 4
-
-=item *
-
-L<perlcheat> has been reorganized, and a few new sections were added.
-
-=back
-
-=head3 L<perldata>
-
-=over 4
-
-=item *
-
-Now explicitly documents the behaviour of hash initializer lists that
-contain duplicate keys.
-
-=back
-
-=head3 L<perldiag>
-
-=over 4
-
-=item *
-
-The explanation of symbolic references being prevented by "strict refs"
-now doesn't assume that the reader knows what symbolic references are.
-
-=back
-
-=head3 L<perlfaq>
-
-=over 4
-
-=item *
-
-L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
-
-=back
-
-=head3 L<perlfunc>
-
-=over 4
-
-=item *
-
-The return value of C<pipe> is now documented.
-
-=item *
-
-Clarified documentation of C<our>.
-
-=back
-
-=head3 L<perlop>
-
-=over 4
-
-=item *
-
-Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
-had the same precedence as assignment operators, but this was not documented
-until now.
-
-=back
-
-=head3 Diagnostics
-
-The following additions or changes have been made to diagnostic output,
-including warnings and fatal error messages. For the complete list of
-diagnostic messages, see L<perldiag>.
-
-=head2 New Diagnostics
-
-=head3 New Errors
-
-=over 4
-
-=item *
-
-L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
-
-This message now occurs when a here document label has an initial quotation
-mark but the final quotation mark is missing.
-
-This replaces a bogus and misleading error message about not finding the label
-itself [perl #114104].
-
-=item *
-
-L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
-
-This error is thrown when a child pseudo-process in the ithreads implementation
-on Windows was not scheduled within the time period allowed and therefore was
-not able to initialize properly [perl #88840].
-
-=item *
-
-L<Group name must start with a non-digit word character in regex; marked by <-- HERE in mE<sol>%sE<sol>|perldiag/"Group name must start with a non-digit word character in regex; marked by <-- HERE in m/%s/">
-
-This error has been added for C<(?&0)>, which is invalid. It used to
-produce an incomprehensible error message [perl #101666].
-
-=item *
-
-L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
-
-Calling an undefined value as a subroutine now produces this error message.
-It used to, but was accidentally disabled, first in Perl 5.004 for
-non-magical variables, and then in Perl v5.14 for magical (e.g., tied)
-variables. It has now been restored. In the mean time, undef was treated
-as an empty string [perl #113576].
-
-=item *
-
-L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
-
-To use lexical subs, you must first enable them:
-
- no warnings 'experimental::lexical_subs';
- use feature 'lexical_subs';
- my sub foo { ... }
-
-=back
-
-=head3 New Warnings
-
-=over 4
-
-=item *
-
-L<'Strings with code points over 0xFF may not be mapped into in-memory file handles'|perldiag/"Strings with code points over 0xFF may not be mapped into in-memory file handles">
-
-=item *
-
-L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
-
-=item *
-
-L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
-
-=item *
-
-L<'A sequence of multiple spaces in a charnames alias definition is deprecated'|perldiag/"A sequence of multiple spaces in a charnames alias definition is deprecated">
-
-=item *
-
-L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
-
-=item *
-
-L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
-
-(W closure) During compilation, an inner named subroutine or eval is
-attempting to capture an outer lexical subroutine that is not currently
-available. This can happen for one of two reasons. First, the lexical
-subroutine may be declared in an outer anonymous subroutine that has not
-yet been created. (Remember that named subs are created at compile time,
-while anonymous subs are created at run-time.) For example,
-
- sub { my sub a {...} sub f { \&a } }
-
-At the time that f is created, it can't capture the current the "a" sub,
-since the anonymous subroutine hasn't been created yet. Conversely, the
-following won't give a warning since the anonymous subroutine has by now
-been created and is live:
-
- sub { my sub a {...} eval 'sub f { \&a }' }->();
-
-The second situation is caused by an eval accessing a variable that has
-gone out of scope, for example,
-
- sub f {
- my sub a {...}
- sub { eval '\&a' }
- }
- f()->();
-
-Here, when the '\&a' in the eval is being compiled, f() is not currently
-being executed, so its &a is not available for capture.
-
-=item *
-
-L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
-
-(W misc) A "my" or "state" subroutine has been redeclared in the
-current scope or statement, effectively eliminating all access to
-the previous instance. This is almost always a typographical error.
-Note that the earlier subroutine will still exist until the end of
-the scope or until all closure references to it are destroyed.
-
-=item *
-
-L<The %s feature is experimental|perldiag/"The %s feature is experimental">
-
-(S experimental) This warning is emitted if you enable an experimental
-feature via C<use feature>. Simply suppress the warning if you want
-to use the feature, but know that in doing so you are taking the risk
-of using an experimental feature which may change or be removed in a
-future Perl version:
-
- no warnings "experimental::lexical_subs";
- use feature "lexical_subs";
-
-=item *
-
-L<sleep(%u) too large|perldiag/"sleep(%u) too large">
-
-(W overflow) You called C<sleep> with a number that was larger than it can
-reliably handle and C<sleep> probably slept for less time than requested.
-
-=item *
-
-L<Wide character in setenv|perldiag/"Wide character in %s">
-
-Attempts to put wide characters into environment variables via C<%ENV> now
-provoke this warning.
-
-=item *
-
-"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
-
-C<chr()> now warns when passed a negative value [perl #83048].
-
-=item *
-
-"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
-
-C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
-value will be truncated rather than overflowing) [perl #40605].
-
-=item *
-
-"L<-i used with no filenames on the command line, reading from STDIN|perldiag/"-i used with no filenames on the command line, reading from STDIN">"
-
-Running perl with the C<-i> flag now warns if no input files are provided on
-the command line [perl #113410].
-
-=back
-
-=head2 Changes to Existing Diagnostics
-
-=over 4
-
-=item *
-
-L<$* is no longer supported|perldiag/"$* is no longer supported">
-
-The warning that use of C<$*> and C<$#> is no longer supported is now
-generated for every location that references them. Previously it would fail
-to be generated if another variable using the same typeglob was seen first
-(e.g. C<@*> before C<$*>), and would not be generated for the second and
-subsequent uses. (It's hard to fix the failure to generate warnings at all
-without also generating them every time, and warning every time is
-consistent with the warnings that C<$[> used to generate.)
-
-=item *
-
-The warnings for C<\b{> and C<\B{> were added. They are a deprecation
-warning which should be turned off by that category. One should not
-have to turn off regular regexp warnings as well to get rid of these.
-
-=item *
-
-L<Constant(%s): Call to &{$^H{%s}} did not return a defined value|perldiag/Constant(%s): Call to &{$^H{%s}} did not return a defined value>
-
-Constant overloading that returns C<undef> results in this error message.
-For numeric constants, it used to say "Constant(undef)". "undef" has been
-replaced with the number itself.
-
-=item *
-
-The error produced when a module cannot be loaded now includes a hint that
-the module may need to be installed: "Can't locate hopping.pm in @INC (you
-may need to install the hopping module) (@INC contains: ...)"
-
-=item *
-
-L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
-
-This warning was not suppressable, even with C<no warnings>. Now it is
-suppressible, and has been moved from the "internal" category to the
-"printf" category.
-
-=item *
-
-C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
-
-This fatal error has been turned into a warning that reads:
-
-L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
-
-(W regexp) Minima should be less than or equal to maxima. If you really want
-your regexp to match something 0 times, just put {0}.
-
-=item *
-
-The "Runaway prototype" warning that occurs in bizarre cases has been
-removed as being unhelpful and inconsistent.
-
-=item *
-
-The "Not a format reference" error has been removed, as the only case in
-which it could be triggered was a bug.
-
-=item *
-
-The "Unable to create sub named %s" error has been removed for the same
-reason.
-
-=item *
-
-The 'Can't use "my %s" in sort comparison' error has been downgraded to a
-warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
-for state variables). In addition, the heuristics for guessing whether
-lexical $a or $b has been misused have been improved to generate fewer
-false positives. Lexical $a and $b are no longer disallowed if they are
-outside the sort block. Also, a named unary or list operator inside the
-sort block no longer causes the $a or $b to be ignored [perl #86136].
-
-=back
-
-=head1 Utility Changes
-
-=head3 L<h2xs>
-
-=over 4
-
-=item *
-
-F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
-
-=back
-
-=head1 Configuration and Compilation
-
-=over 4
-
-=item *
-
-Added C<useversionedarchname> option to Configure
-
-When set, it includes 'api_versionstring' in 'archname'. E.g.
-x86_64-linux-5.13.6-thread-multi. It is unset by default.
-
-This feature was requested by Tim Bunce, who observed that
-C<INSTALL_BASE> creates a library structure that does not
-differentiate by perl version. Instead, it places architecture
-specific files in "$install_base/lib/perl5/$archname". This makes
-it difficult to use a common C<INSTALL_BASE> library path with
-multiple versions of perl.
-
-By setting C<-Duseversionedarchname>, the $archname will be
-distinct for architecture I<and> API version, allowing mixed use of
-C<INSTALL_BASE>.
-
-=item *
-
-Add a C<PERL_NO_INLINE_FUNCTIONS> option
-
-If C<PERL_NO_INLINE_FUNCTIONS> is defined, don't include "inline.h"
-
-This permits test code to include the perl headers for definitions without
-creating a link dependency on the perl library (which may not exist yet).
-
-=item *
-
-Configure will honour the external C<MAILDOMAIN> environment variable, if set.
-
-=item *
-
-C<installman> no longer ignores the silent option
-
-=item *
-
-Both C<META.yml> and C<META.json> files are now included in the distribution.
-
-=item *
-
-F<Configure> will now correctly detect C<isblank()> when compiling with a C++
-compiler.
-
-=item *
-
-The pager detection in F<Configure> has been improved to allow responses which
-specify options after the program name, e.g. B</usr/bin/less -R>, if the user
-accepts the default value. This helps B<perldoc> when handling ANSI escapes
-[perl #72156].
-
-=back
-
-=head1 Testing
-
-=over 4
-
-=item *
-
-The test suite now has a section for tests that require very large amounts
-of memory. These tests won't run by default; they can be enabled by
-setting the C<PERL_TEST_MEMORY> environment variable to the number of
-gibibytes of memory that may be safely used.
-
-=back
-
-=head1 Platform Support
-
-=head2 Discontinued Platforms
-
-=over 4
-
-=item BeOS
-
-BeOS was an operating system for personal computers developed by Be Inc,
-initially for their BeBox hardware. The OS Haiku was written as an open
-source replacement for/continuation of BeOS, and its perl port is current and
-actively maintained.
-
-=item UTS Global
-
-Support code relating to UTS global has been removed. UTS was a mainframe
-version of System V created by Amdahl, subsequently sold to UTS Global. The
-port has not been touched since before Perl v5.8.0, and UTS Global is now
-defunct.
-
-=item VM/ESA
-
-Support for VM/ESA has been removed. The port was tested on 2.3.0, which
-IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
-was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
-for end of service on 2015/04/30.
-
-=item MPE/IX
-
-Support for MPE/IX has been removed.
-
-=item EPOC
-
-Support code relating to EPOC has been removed. EPOC was a family of
-operating systems developed by Psion for mobile devices. It was the
-predecessor of Symbian. The port was last updated in April 2002.
-
-=item Rhapsody
-
-Support for Rhapsody has been removed.
-
-=back
-
-=head2 Platform-Specific Notes
-
-=head3 AIX
-
-Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
-using xlC. This will make it easier to compile a number of XS-based modules
-that assume C99 [perl #113778].
-
-=head3 clang++
-
-There is now a workaround for a compiler bug that prevented compiling
-with clang++ since Perl v5.15.7 [perl #112786].
-
-=head3 C++
-
-When compiling the Perl core as C++ (which is only semi-supported), the
-mathom functions are now compiled as C<extern "C">, to ensure proper
-binary compatibility. (However, binary compatibility isn't generally
-guaranteed anyway in the situations where this would matter.)
-
-=head3 Darwin
-
-Stop hardcoding an alignment on 8 byte boundaries to fix builds using
--Dusemorebits.
-
-=head3 Haiku
-
-Perl should now work out of the box on Haiku R1 Alpha 4.
-
-=head3 MidnightBSD
-
-C<libc_r> was removed from recent versions of MidnightBSD and older versions
-work better with C<pthread>. Threading is now enabled using C<pthread> which
-corrects build errors with threading enabled on 0.4-CURRENT.
-
-=head3 Solaris
-
-In Configure, avoid running sed commands with flags not supported on Solaris.
-
-=head3 VMS
-
-=over
-
-=item *
-
-Where possible, the case of filenames and command-line arguments is now
-preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
-C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
-when extended parse is enabled in the process from which Perl is run.
-
-=item *
-
-The character set for Extended Filename Syntax (EFS) is now enabled by default
-on VMS. Among other things, this provides better handling of dots in directory
-names, multiple dots in filenames, and spaces in filenames. To obtain the old
-behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
-
-=item *
-
-Fixed linking on builds configured with C<-Dusemymalloc=y>.
-
-=item *
-
-Experimental support for building Perl with the HP C++ compiler is available
-by configuring with C<-Dusecxx>.
-
-=item *
-
-All C header files from the top-level directory of the distribution are now
-installed on VMS, providing consistency with a long-standing practice on other
-platforms. Previously only a subset were installed, which broke non-core
-extension builds for extensions that depended on the missing include files.
-
-=item *
-
-Quotes are now removed from the command verb (but not the parameters) for
-commands spawned via C<system>, backticks, or a piped C<open>. Previously,
-quotes on the verb were passed through to DCL, which would fail to recognize
-the command. Also, if the verb is actually a path to an image or command
-procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
-
-=item *
-
-The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
-
-=back
-
-=head3 Win32
-
-=over
-
-=item *
-
-Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
-CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
-Windows Desktop) in F<win32/Makefile>.
-
-=item *
-
-The option to build without C<USE_SOCKETS_AS_HANDLES> has been removed.
-
-=item *
-
-Fixed a problem where perl could crash while cleaning up threads (including the
-main thread) in threaded debugging builds on Win32 and possibly other platforms
-[perl #114496].
-
-=item *
-
-A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
-time than requested, and possibly even hanging, has been fixed [perl #33096].
-
-=item *
-
-C<link> on Win32 now attempts to set C<$!> to more appropriate values
-based on the Win32 API error code. [perl #112272]
-
-Perl no longer mangles the environment block, e.g. when launching a new
-sub-process, when the environment contains non-ASCII characters. Known
-problems still remain, however, when the environment contains characters
-outside of the current ANSI codepage (e.g. see the item about Unicode in
-C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
-[perl #113536]
-
-=item *
-
-Building perl with some Windows compilers used to fail due to a problem
-with miniperl's C<glob> operator (which uses the C<perlglob> program)
-deleting the PATH environment variable [perl #113798].
-
-=item *
-
-A new makefile option, C<USE_64_BIT_INT>, has been added to the Windows
-makefiles. Set this to "define" when building a 32-bit perl if you want
-it to use 64-bit integers.
-
-Machine code size reductions, already made to the DLLs of XS modules in
-Perl v5.17.2, have now been extended to the perl DLL itself.
-
-Building with VC++ 6.0 was inadvertently broken in Perl v5.17.2 but has
-now been fixed again.
-
-=back
-
-=head3 WinCE
-
-Building on WinCE is now possible once again, although more work is required
-to fully restore a clean build.
-
-=head1 Internal Changes
-
-=over
-
-=item *
-
-Synonyms for the misleadingly named C<av_len()> have been created:
-C<av_top_index()> and C<av_tindex>. All three of these return the
-number of the highest index in the array, not the number of elements it
-contains.
-
-=item *
-
-SvUPGRADE() is no longer an expression. Originally this macro (and its
-underlying function, sv_upgrade()) were documented as boolean, although
-in reality they always croaked on error and never returned false. In 2005
-the documentation was updated to specify a void return value, but
-SvUPGRADE() was left always returning 1 for backwards compatibility. This
-has now been removed, and SvUPGRADE() is now a statement with no return
-value.
-
-So this is now a syntax error:
-
- if (!SvUPGRADE(sv)) { croak(...); }
-
-If you have code like that, simply replace it with
-
- SvUPGRADE(sv);
-
-or to avoid compiler warnings with older perls, possibly
-
- (void)SvUPGRADE(sv);
-
-=item *
-
-Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
-upgraded to a copy-on-write scalar. A reference count on the string buffer
-is stored in the string buffer itself. This feature is B<not enabled by
-default>.
-
-It can be enabled in a perl build by running F<Configure> with
-B<-Accflags=-DPERL_NEW_COPY_ON_WRITE>, and we would encourage XS authors
-to try their code with such an enabled perl, and provide feedback.
-Unfortunately, there is not yet a good guide to updating XS code to cope
-with COW. Until such a document is available, consult the perl5-porters
-mailing list.
-
-It breaks a few XS modules by allowing copy-on-write scalars to go
-through code paths that never encountered them before.
-
-=item *
-
-Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
-SvREADONLY indicates a true read-only SV.
-
-Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
-
-=item *
-
-C<PL_glob_index> is gone.
-
-=item *
-
-The private Perl_croak_no_modify has had its context parameter removed. It is
-now has a void prototype. Users of the public API croak_no_modify remain
-unaffected.
-
-=item *
-
-Copy-on-write (shared hash key) scalars are no longer marked read-only.
-C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
-true.
-
-=item *
-
-A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
-optimiser will, where possible, substitute a single padrange op for a
-pushmark followed by one or more pad ops, and possibly also skipping list
-and nextstate ops. In addition, the op can carry out the tasks associated
-with the RHS of a C<< my(...) = @_ >> assignment, so those ops may be optimised
-away too.
-
-=item *
-
-Case-insensitive matching inside a [bracketed] character class with a
-multi-character fold no longer excludes one of the possibilities in the
-circumstances that it used to. [perl #89774].
-
-=item *
-
-C<PL_formfeed> has been removed.
-
-=item *
-
-The regular expression engine no longer reads one byte past the end of the
-target string. While for all internally well-formed scalars this should
-never have been a problem, this change facilitates clever tricks with
-string buffers in CPAN modules. [perl #73542]
-
-=item *
-
-Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
-subroutine, rather than the BEGIN block itself.
-
-=item *
-
-C<mg_length> has been deprecated.
-
-=item *
-
-C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
-count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
-sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
-assumes that its argument is in UTF-8. Neither of these creates UTF-8 caches
-for tied or overloaded values or for non-PVs any more.
-
-=item *
-
-C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
-called from XS modules [perl #79824].
-
-=item *
-
-C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
-#defined as 0.
-
-=item *
-
-The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
-engines to indicate that the execution of the regular expression may cause
-variables to be modified. This lets C<s///> know to skip certain
-optimisations. Perl's own regular expression engine sets this flag for the
-special backtracking verbs that set $REGMARK and $REGERROR.
-
-=item *
-
-The APIs for accessing lexical pads have changed considerably.
-
-C<PADLIST>s are now longer C<AV>s, but their own type instead.
-C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
-rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
-C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
-newly added pad API instead of the plain C<AV> and C<SV> APIs. See
-L<perlapi> for details.
-
-=item *
-
-In the regex API, the numbered capture callbacks are passed an index
-indicating what match variable is being accessed. There are special
-index values for the C<$`, $&, $&> variables. Previously the same three
-values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
-too, but these have now been assigned three separate values. See
-L<perlreapi/Numbered capture callbacks>.
-
-=item *
-
-C<PL_sawampersand> was previously a boolean indicating that any of
-C<$`, $&, $&> had been seen; it now contains three one-bit flags
-indicating the presence of each of the variables individually.
-
-=item *
-
-The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
-just like C<&{...}> [perl #96872].
-
-=item *
-
-The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
-object. It is now set automatically whenever a method or @ISA changes, so
-its meaning has changed, too. It now means "potentially overloaded". When
-the overload table is calculated, the flag is automatically turned off if
-there is no overloading, so there should be no noticeable slowdown.
-
-The staleness of the overload tables is now checked when overload methods
-are invoked, rather than during C<bless>.
-
-"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
-eliminate the need for it.
-
-C<PL_amagic_generation> has been removed as no longer necessary. For XS
-modules, it is now a macro alias to C<PL_na>.
-
-The fallback overload setting is now stored in a stash entry separate from
-overloadedness itself.
-
-=item *
-
-The character-processing code has been cleaned up in places. The changes
-should be operationally invisible.
-
-=item *
-
-The C<study> function was made a no-op in v5.16. It was simply disabled via
-a C<return> statement; the code was left in place. Now the code supporting
-what C<study> used to do has been removed.
-
-=item *
-
-Under threaded perls, there is no longer a separate PV allocated for every
-COP to store its package name (C<< cop->stashpv >>). Instead, there is an
-offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
-holds stash pointers.
-
-=item *
-
-In the pluggable regex API, the C<regexp_engine> struct has acquired a new
-field C<op_comp>, which is currently just for perl's internal use, and
-should be initialized to NULL by other regex plugin modules.
-
-=item *
-
-A new function C<alloccopstash> has been added to the API, but is considered
-experimental. See L<perlapi>.
-
-=item *
-
-Perl used to implement get magic in a way that would sometimes hide bugs in
-code that could call mg_get() too many times on magical values. This hiding of
-errors no longer occurs, so long-standing bugs may become visible now. If
-you see magic-related errors in XS code, check to make sure it, together
-with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
-values.
-
-=item *
-
-OP allocation for CVs now uses a slab allocator. This simplifies
-memory management for OPs allocated to a CV, so cleaning up after a
-compilation error is simpler and safer [perl #111462][perl #112312].
-
-=item *
-
-C<PERL_DEBUG_READONLY_OPS> has been rewritten to work with the new slab
-allocator, allowing it to catch more violations than before.
-
-=item *
-
-The old slab allocator for ops, which was only enabled for C<PERL_IMPLICIT_SYS>
-and C<PERL_DEBUG_READONLY_OPS>, has been retired.
-
-=back
-
-=head1 Selected Bug Fixes
-
-=over 4
-
-=item *
-
-Here document terminators no longer require a terminating newline character when
-they occur at the end of a file. This was already the case at the end of a
-string eval [perl #65838].
-
-=item *
-
-C<-DPERL_GLOBAL_STRUCT> builds now free the global struct B<after>
-they've finished using it.
-
-=item *
-
-A trailing '/' on a path in @INC will no longer have an additional '/'
-appended.
-
-=item *
-
-The C<:crlf> layer now works when unread data doesn't fit into its own
-buffer. [perl #112244].
-
-=item *
-
-C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
-
-=item *
-
-A bug in the core typemap caused any C types that map to the T_BOOL core
-typemap entry to not be set, updated, or modified when the T_BOOL variable was
-used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
-section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
-was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
-in the OUTPUT: section (which previous did nothing to the SV), and a read only
-SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
-value attempted" will happen. [perl #115796]
-
-=item *
-
-On many platforms, providing a directory name as the script name caused perl
-to do nothing and report success. It should now universally report an error
-and exit nonzero. [perl #61362]
-
-=item *
-
-C<sort {undef} ...> under fatal warnings no longer crashes. It had
-begun crashing in Perl v5.16.
-
-=item *
-
-Stashes blessed into each other
-(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
-frees. This bug started happening in Perl v5.16.
-
-=item *
-
-Numerous memory leaks have been fixed, mostly involving fatal warnings and
-syntax errors.
-
-=item *
-
-Some failed regular expression matches such as C<'f' =~ /../g> were not
-resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
-it, too, when invoked a second time [perl #23180].
-
-=item *
-
-Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
-MRO caches have been fixed.
-
-=item *
-
-Defining a subroutine when its typeglob has been aliased no longer results
-in stale method caches. This bug was introduced in Perl v5.10.
-
-=item *
-
-Localising a typeglob containing a subroutine when the typeglob's package
-has been deleted from its parent stash no longer produces an error. This
-bug was introduced in Perl v5.14.
-
-=item *
-
-Under some circumstances, C<local *method=...> would fail to reset method
-caches upon scope exit.
-
-=item *
-
-C</[.foo.]/> is no longer an error, but produces a warning (as before) and
-is treated as C</[.fo]/> [perl #115818].
-
-=item *
-
-C<goto $tied_var> now calls FETCH before deciding what type of goto
-(subroutine or label) this is.
-
-=item *
-
-Renaming packages through glob assignment
-(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
-C<reset> no longer makes threaded builds crash.
-
-=item *
-
-A number of bugs related to assigning a list to hash have been fixed. Many of
-these involve lists with repeated keys like C<(1, 1, 1, 1)>.
-
-=over 4
-
-=item *
-
-The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
-
-=item *
-
-The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
-this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
-
-=item *
-
-Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
-C<(%h) = ({})>, "Reference found where even-sized list expected".
-
-=item *
-
-A number of additional edge cases in list assignment to hashes were
-corrected. For more details see commit 23b7025ebc.
-
-=back
-
-=item *
-
-Attributes applied to lexical variables no longer leak memory.
-[perl #114764]
-
-=item *
-
-C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
-bareword (or version) and then an infix operator is no longer a syntax
-error. It used to be for those infix operators (like C<+>) that have a
-different meaning where a term is expected. [perl #105924]
-
-=item *
-
-C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
-ambiguity warnings. [perl #107002]
-
-=item *
-
-Class method calls are now allowed on any string, and not just strings
-beginning with an alphanumeric character. [perl #105922]
-
-=item *
-
-An empty pattern created with C<qr//> used in C<m///> no longer triggers
-the "empty pattern reuses last pattern" behaviour. [perl #96230]
-
-=item *
-
-Tying a hash during iteration no longer results in a memory leak.
-
-=item *
-
-Freeing a tied hash during iteration no longer results in a memory leak.
-
-=item *
-
-List assignment to a tied array or hash that dies on STORE no longer
-results in a memory leak.
-
-=item *
-
-If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
-the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
-
-=item *
-
-Constant folding no longer inappropriately triggers the special
-C<split " "> behaviour. [perl #94490]
-
-=item *
-
-C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
-now treat the argument to C<defined> as a simple scalar. [perl #97466]
-
-=item *
-
-Running a custom debugging that defines no C<*DB::DB> glob or provides a
-subroutine stub for C<&DB::DB> no longer results in a crash, but an error
-instead. [perl #114990]
-
-=item *
-
-C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
-patterns when called with no argument. An empty string for an argument now
-does nothing. (It used to be treated as no argument.) [perl #97958]
-
-=item *
-
-C<printf> with an argument returning an empty list no longer reads past the
-end of the stack, resulting in erratic behaviour. [perl #77094]
-
-=item *
-
-C<--subname> no longer produces erroneous ambiguity warnings.
-[perl #77240]
-
-=item *
-
-C<v10> is now allowed as a label or package name. This was inadvertently
-broken when v-strings were added in Perl v5.6. [perl #56880]
-
-=item *
-
-C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
-overloading, references and typeglobs if the stringification of such
-changed the internal representation to or from UTF-8. [perl #114410]
-
-=item *
-
-utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
-calls STORE (it was already calling FETCH).
-
-=item *
-
-C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
-variable returns a Latin-1 string, shared hash key scalar, or reference or
-typeglob that stringifies as ASCII or Latin-1. This was a regression from
-v5.12.
-
-=item *
-
-C<s///> without /e is now better at detecting when it needs to forego
-certain optimisations, fixing some buggy cases:
-
-=over
-
-=item *
-
-Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
-the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
-
-=item *
-
-Aliases to match variables in the replacement.
-
-=item *
-
-C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
-
-=item *
-
-An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
-be used, when that pattern contains code blocks that modify the variables
-in the replacement.
-
-=back
-
-=item *
-
-The taintedness of the replacement string no longer affects the taintedness
-of the return value of C<s///e>.
-
-=item *
-
-The C<$|> autoflush variable is created on-the-fly when needed. If this
-happened (e.g., if it was mentioned in a module or eval) when the
-currently-selected filehandle was a typeglob with an empty IO slot, it used
-to crash. [perl #115206]
-
-=item *
-
-Line numbers at the end of a string eval are no longer off by one.
-[perl #114658]
-
-=item *
-
-@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
-copy-on-write scalar no longer cause the parser to modify that string
-buffer in place.
-
-=item *
-
-C<length($object)> no longer returns the undefined value if the object has
-string overloading that returns undef. [perl #115260]
-
-=item *
-
-The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
-been restored,
-
-Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
-up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
-carried on working without it.
-
-=item *
-
-The error "Can't localize through a reference" had disappeared in v5.16.0
-when C<local %$ref> appeared on the last line of an lvalue subroutine.
-This error disappeared for C<\local %$ref> in perl v5.8.1. It has now
-been restored.
-
-=item *
-
-The parsing of here-docs has been improved significantly, fixing several
-parsing bugs and crashes and one memory leak, and correcting wrong
-subsequent line numbers under certain conditions.
-
-=item *
-
-Inside an eval, the error message for an unterminated here-doc no longer
-has a newline in the middle of it [perl #70836].
-
-=item *
-
-A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
-confuses the parser.
-
-=item *
-
-It may be an odd place to allow comments, but C<s//"" # hello/e> has
-always worked, I<unless> there happens to be a null character before the
-first #. Now it works even in the presence of nulls.
-
-=item *
-
-An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
-
-=item *
-
-String eval no longer treats a semicolon-delimited quote-like operator at
-the very end (C<eval 'q;;'>) as a syntax error.
-
-=item *
-
-C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
-get confused with certain list operators followed by an anonymous hash and
-then an infix operator that shares its form with a unary operator.
-
-=item *
-
-C<(caller $n)[6]> (which gives the text of the eval) used to return the
-actual parser buffer. Modifying it could result in crashes. Now it always
-returns a copy. The string returned no longer has "\n;" tacked on to the
-end. The returned text also includes here-doc bodies, which used to be
-omitted.
-
-=item *
-
-The UTF-8 position cache is now reset when accessing magical variables, to
-avoid the string buffer and the UTF-8 position cache getting out of sync
-[perl #114410].
+perldelta - what is new for perl v5.19.1
-=item *
-
-Various cases of get magic being called twice for magical UTF-8
-strings have been fixed.
-
-=item *
-
-This code (when not in the presence of C<$&> etc)
-
- $_ = 'x' x 1_000_000;
- 1 while /(.)/;
-
-used to skip the buffer copy for performance reasons, but suffered from C<$1>
-etc changing if the original string changed. That's now been fixed.
-
-=item *
-
-Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
-might attempt to allocate more memory.
-
-=item *
-
-In a regular expression, if something is quantified with C<{n,m}> where
-C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
-error, but now is merely a warning (and that something won't match).
-[perl #82954].
-
-=item *
-
-It used to be possible for formats defined in subroutines that have
-subsequently been undefined and redefined to close over variables in the
-wrong pad (the newly-defined enclosing sub), resulting in crashes or
-"Bizarre copy" errors.
-
-=item *
-
-Redefinition of XSUBs at run time could produce warnings with the wrong
-line number.
-
-=item *
-
-The %vd sprintf format does not support version objects for alpha versions.
-It used to output the format itself (%vd) when passed an alpha version, and
-also emit an "Invalid conversion in printf" warning. It no longer does,
-but produces the empty string in the output. It also no longer leaks
-memory in this case.
-
-=item *
-
-C<< $obj->SUPER::method >> calls in the main package could fail if the
-SUPER package had already been accessed by other means.
-
-=item *
-
-Stash aliasing (C<< *foo:: = *bar:: >>) no longer causes SUPER calls to ignore
-changes to methods or @ISA or use the wrong package.
-
-=item *
-
-Method calls on packages whose names end in ::SUPER are no longer treated
-as SUPER method calls, resulting in failure to find the method.
-Furthermore, defining subroutines in such packages no longer causes them to
-be found by SUPER method calls on the containing package [perl #114924].
-
-=item *
-
-C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
-(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
-Unicode corrected their definition of what C<\w> should match.
-
-=item *
-
-C<dump LABEL> no longer leaks its label.
-
-=item *
-
-Constant folding no longer changes the behaviour of functions like C<stat()>
-and C<truncate()> that can take either filenames or handles.
-C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
-arbitrary expression), rather than the handle "foo".
-
-=item *
-
-C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
-the filehandle has been deleted. This was broken in Perl v5.16.0.
-
-=item *
-
-Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
-longer cause double frees or panic messages.
-
-=item *
-
-C<s///> now turns vstrings into plain strings when performing a substitution,
-even if the resulting string is the same (C<s/a/a/>).
-
-=item *
-
-Prototype mismatch warnings no longer erroneously treat constant subs as having
-no prototype when they actually have "".
-
-=item *
-
-Constant subroutines and forward declarations no longer prevent prototype
-mismatch warnings from omitting the sub name.
-
-=item *
-
-C<undef> on a subroutine now clears call checkers.
-
-=item *
-
-The C<ref> operator started leaking memory on blessed objects in Perl v5.16.0.
-This has been fixed [perl #114340].
-
-=item *
-
-C<use> no longer tries to parse its arguments as a statement, making
-C<use constant { () };> a syntax error [perl #114222].
-
-=item *
-
-On debugging builds, "uninitialized" warnings inside formats no longer cause
-assertion failures.
-
-=item *
-
-On debugging builds, subroutines nested inside formats no longer cause
-assertion failures [perl #78550].
-
-=item *
-
-Formats and C<use> statements are now permitted inside formats.
+=head1 DESCRIPTION
-=item *
+This document describes differences between the 5.19.0 release and the 5.19.1
+release.
-C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
-It was possible for the latter to refuse to close over $x if the variable was
-not active; e.g., if it was defined outside a currently-running named
-subroutine.
+=head1 Notice
-=item *
+XXX Any important notices here
-Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
-This also allows "my $x if 0" variables to be seen in the debugger [perl
-#114018].
+=head1 Core Enhancements
-=item *
+XXX New core language features go here. Summarize user-visible core language
+enhancements. Particularly prominent performance optimisations could go
+here, but most should go in the L</Performance Enhancements> section.
-Formats called recursively no longer stomp on their own lexical variables, but
-each recursive call has its own set of lexicals.
+[ List each enhancement as a =head2 entry ]
-=item *
+=head1 Security
-Attempting to free an active format or the handle associated with it no longer
-results in a crash.
+XXX Any security-related notices go here. In particular, any security
+vulnerabilities closed should be noted here rather than in the
+L</Selected Bug Fixes> section.
-=item *
+[ List each security issue as a =head2 entry ]
-Format parsing no longer gets confused by braces, semicolons and low-precedence
-operators. It used to be possible to use braces as format delimiters (instead
-of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
-in format argument lines no longer confuse the parser into ignoring the line's
-return value. In format argument lines, braces can now be used for anonymous
-hashes, instead of being treated always as C<do> blocks.
+=head1 Incompatible Changes
-=item *
+XXX For a release on a stable branch, this section aspires to be:
-Formats can now be nested inside code blocks in regular expressions and other
-quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
+ There are no changes intentionally incompatible with 5.XXX.XXX
+ If any exist, they are bugs, and we request that you submit a
+ report. See L</Reporting Bugs> below.
-=item *
+[ List each incompatible change as a =head2 entry ]
-Formats are no longer created after compilation errors.
+=head1 Deprecations
-=item *
+XXX Any deprecated features, syntax, modules etc. should be listed here.
-Under debugging builds, the B<-DA> command line option started crashing in Perl
-v5.16.0. It has been fixed [perl #114368].
+=head2 Module removals
-=item *
+XXX Remove this section if inapplicable.
-A potential deadlock scenario involving the premature termination of a pseudo-
-forked child in a Windows build with ithreads enabled has been fixed. This
-resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
-#88840].
+The following modules will be removed from the core distribution in a future
+release, and will at that time need to be installed from CPAN. Distributions
+on CPAN which require these modules will need to list them as prerequisites.
-=item *
+The core versions of these modules will now issue C<"deprecated">-category
+warnings to alert you to this fact. To silence these deprecation warnings,
+install the modules in question from CPAN.
-The code which generates errors from C<require()> could potentially read one or
-two bytes before the start of the filename for filenames less than three bytes
-long and ending C</\.p?\z/>. This has now been fixed. Note that it could
-never have happened with module names given to C<use()> or C<require()> anyway.
+Note that these are (with rare exceptions) fine modules that you are encouraged
+to continue to use. Their disinclusion from core primarily hinges on their
+necessity to bootstrapping a fully functional, CPAN-capable Perl installation,
+not usually on concerns over their design.
-=item *
+XXX Note that deprecated modules should be listed here even if they are listed
+as an updated module in the L</Modules and Pragmata> section.
-The handling of pathnames of modules given to C<require()> has been made
-thread-safe on VMS.
+=over
=item *
-Non-blocking sockets have been fixed on VMS.
+L<DB> has been updated from 1.05 to 1.06 and L<perl5db.pl> from 1.39_10
+to 1.40. The call depth allowed by default in the debugger is now 1000
+rather than 100.
-=item *
+=back
-Pod can now be nested in code inside a quoted construct outside of a string
-eval. This used to work only within string evals [perl #114040].
+[ List each other deprecation as a =head2 entry ]
-=item *
+=head1 Performance Enhancements
-C<goto ''> now looks for an empty label, producing the "goto must have
-label" error message, instead of exiting the program [perl #111794].
+XXX Changes which enhance performance without changing behaviour go here.
+There may well be none in a stable release.
-=item *
+[ List each enhancement as a =item entry ]
-C<goto "\0"> now dies with "Can't find label" instead of "goto must have
-label".
+=over 4
=item *
-The C function C<hv_store> used to result in crashes when used on C<%^H>
-[perl #111000].
+Perl has a new copy-on-write mechanism that avoids the need to copy the
+internal string buffer when assigning from one scalar to another. This
+makes copying large strings appear much faster. Modifying one of the two
+(or more) strings after an assignment will force a copy internally. This
+makes it unnecessary to pass strings by reference for efficiency.
-=item *
+This feature was already available in 5.18.0, but wasn't enabled by
+default. It is the default now, and so you no longer need build perl with
+the F<Configure> argument:
-A call checker attached to a closure prototype via C<cv_set_call_checker>
-is now copied to closures cloned from it. So C<cv_set_call_checker> now
-works inside an attribute handler for a closure.
+ -Accflags=PERL_NEW_COPY_ON_WRITE
-=item *
+It can be disabled (for now) in a perl build with:
-Writing to C<$^N> used to have no effect. Now it croaks with "Modification
-of a read-only value" by default, but that can be overridden by a custom
-regular expression engine, as with C<$1> [perl #112184].
+ -Accflags=PERL_NO_COW
-=item *
+=back
-C<undef> on a control character glob (C<undef *^H>) no longer emits an
-erroneous warning about ambiguity [perl #112456].
+=head1 Modules and Pragmata
-=item *
+XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
+go here. If Module::CoreList is updated, generate an initial draft of the
+following sections using F<Porting/corelist-perldelta.pl>, which prints stub
+entries to STDOUT. Results can be pasted in place of the '=head2' entries
+below. A paragraph summary for important changes should then be added by hand.
+In an ideal world, dual-life modules would have a F<Changes> file that could be
+cribbed.
-For efficiency's sake, many operators and built-in functions return the
-same scalar each time. Lvalue subroutines and subroutines in the CORE::
-namespace were allowing this implementation detail to leak through.
-C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
-would happen with an lvalue subroutine returning the return value of C<uc>.
-Now the value is copied in such cases.
+[ Within each section, list entries as a =item entry ]
-=item *
+=head2 New Modules and Pragmata
-C<method {}> syntax with an empty block or a block returning an empty list
-used to crash or use some random value left on the stack as its invocant.
-Now it produces an error.
+=over 4
=item *
-C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
+XXX
-=item *
+=back
-Changes to overload settings now take effect immediately, as do changes to
-inheritance that affect overloading. They used to take effect only after
-C<bless>.
+=head2 Updated Modules and Pragmata
-Objects that were created before a class had any overloading used to remain
-non-overloaded even if the class gained overloading through C<use overload>
-or @ISA changes, and even after C<bless>. This has been fixed
-[perl #112708].
+=over 4
=item *
-Classes with overloading can now inherit fallback values.
-
-=item *
+B::Deparse has been upgraded from version 1.20 to 1.21.
-Overloading was not respecting a fallback value of 0 if there were
-overloaded objects on both sides of an assignment operator like C<+=>
-[perl #111856].
+C<foreach my $lexical> is now deparsed correctly with the B<-p> option.
+[RT #117081]
-=item *
+The B<-l> option no longer puts form feeds in the middle of a line when
+outputting C<map> and C<grep> blocks. [RT #117311]
-C<pos> now croaks with hash and array arguments, instead of producing
-erroneous warnings.
+Elements of C<%#>, such as C<$# {foo}> and C<${#}{foo}> are now deparsed
+correctly. [RT #117531]
=item *
-C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
-C<readline> and C<readdir>.
+File::Spec has been upgraded from version 3.40 to 3.41.
-=item *
-
-Subs in the CORE:: namespace no longer crash after C<undef *_> when called
-with no argument list (C<&CORE::time> with no parentheses).
+C<tmpdir> now respects changes to environment variables from which the
+temporary directory is derived. [RT #88940]
=item *
-C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
-error when it is the data that are at fault [perl #60204].
+Test::Harness has been upgraded from version 3.26 to 3.28
-=item *
+Memory usage is dramatically reduced. t/harness now uses about 10% of the
+memory used by 3.26 and earlier.
-C<join> and C<"@array"> now call FETCH only once on a tied C<$">
-[perl #8931].
+C<PERL5LIB> is always propagated to a test's C<@INC>, even under C<-T>.
=item *
-Some subroutine calls generated by compiling core ops affected by a
-C<CORE::GLOBAL> override had op checking performed twice. The checking
-is always idempotent for pure Perl code, but the double checking can
-matter when custom call checkers are involved.
-
-=item *
+Unicode::UCD has been upgraded from version 0.51 to 0.52.
-A race condition used to exist around fork that could cause a signal sent to
-the parent to be handled by both parent and child. Signals are now blocked
-briefly around fork to prevent this from happening [perl #82580].
+A function, L<Unicode::UCD/search_invlist()> is now available to do
+search an inversion list or map for a code point.
-=item *
+=back
-The implementation of code blocks in regular expressions, such as C<(?{})>
-and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
-The main user-visible changes are:
+=head2 Removed Modules and Pragmata
=over 4
=item *
-Code blocks within patterns are now parsed in the same pass as the
-surrounding code; in particular it is no longer necessary to have balanced
-braces: this now works:
-
- /(?{ $x='{' })/
-
-This means that this error message is no longer generated:
-
- Sequence (?{...}) not terminated or not {}-balanced in regex
-
-but a new error may be seen:
-
- Sequence (?{...}) not terminated with ')'
-
-In addition, literal code blocks within run-time patterns are only
-compiled once, at perl compile-time:
-
- for my $p (...) {
- # this 'FOO' block of code is compiled once,
- # at the same time as the surrounding 'for' loop
- /$p{(?{FOO;})/;
- }
-
-=item *
-
-Lexical variables are now sane as regards scope, recursion and closure
-behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
-exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
-C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
-expect, creating three regexes that match 0, 1, and 2:
+XXX
- for my $i (0..2) {
- push @r, qr/^(??{$i})$/;
- }
- "1" =~ $r[1]; # matches
-
-=item *
+=back
-The C<use re 'eval'> pragma is now only required for code blocks defined
-at runtime; in particular in the following, the text of the C<$r> pattern is
-still interpolated into the new pattern and recompiled, but the individual
-compiled code-blocks within C<$r> are reused rather than being recompiled,
-and C<use re 'eval'> isn't needed any more:
+=head1 Documentation
- my $r = qr/abc(?{....})def/;
- /xyz$r/;
+XXX Changes to files in F<pod/> go here. Consider grouping entries by
+file and be sure to link to the appropriate page, e.g. L<perlfunc>.
-=item *
+=head2 New Documentation
-Flow control operators no longer crash. Each code block runs in a new
-dynamic scope, so C<next> etc. will not see
-any enclosing loops. C<return> returns a value
-from the code block, not from any enclosing subroutine.
+XXX Changes which create B<new> files in F<pod/> go here.
-=item *
+=head3 L<XXX>
-Perl normally caches the compilation of run-time patterns, and doesn't
-recompile if the pattern hasn't changed, but this is now disabled if
-required for the correct behavior of closures. For example:
+XXX Description of the purpose of the new file here
- my $code = '(??{$x})';
- for my $x (1..3) {
- # recompile to see fresh value of $x each time
- $x =~ /$code/;
- }
+=head2 Changes to Existing Documentation
-=item *
+XXX Changes which significantly change existing files in F<pod/> go here.
+However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
+section.
-The C</msix> and C<(?msix)> etc. flags are now propagated into the return
-value from C<(??{})>; this now works:
+=head3 L<perltrap>
- "AB" =~ /a(??{'b'})/i;
+=over 4
=item *
-Warnings and errors will appear to come from the surrounding code (or for
-run-time code blocks, from an eval) rather than from an C<re_eval>:
-
- use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
- /(?{ warn "foo" })/;
-
-formerly gave:
-
- foo at (re_eval 1) line 1.
- foo at (re_eval 2) line 1.
-
-and now gives:
-
- foo at (eval 1) line 1.
- foo at /some/prog line 2.
+There is now a L<JavaScript|perltrap/JavaScript Traps> section.
=back
-=item *
-
-Perl now can be recompiled to use any Unicode version. In v5.16, it
-worked on Unicodes 6.0 and 6.1, but there were various bugs if earlier
-releases were used; the older the release the more problems.
-
-=item *
-
-C<vec> no longer produces "uninitialized" warnings in lvalue context
-[perl #9423].
-
-=item *
-
-An optimization involving fixed strings in regular expressions could cause
-a severe performance penalty in edge cases. This has been fixed
-[perl #76546].
-
-=item *
-
-In certain cases, including empty subpatterns within a regular expression (such
-as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
+=head1 Diagnostics
-=item *
-
-The "Can't find an opnumber" message that C<prototype> produces when passed
-a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
-NULs through unchanged [perl #97478].
-
-=item *
+The following additions or changes have been made to diagnostic output,
+including warnings and fatal error messages. For the complete list of
+diagnostic messages, see L<perldiag>.
-C<prototype> now treats magical variables like C<$1> the same way as
-non-magical variables when checking for the CORE:: prefix, instead of
-treating them as subroutine names.
+XXX New or changed warnings emitted by the core's C<C> code go here. Also
+include any changes in L<perldiag> that reconcile it to the C<C> code.
-=item *
+=head2 New Diagnostics
-Under threaded perls, a runtime code block in a regular expression could
-corrupt the package name stored in the op tree, resulting in bad reads
-in C<caller>, and possibly crashes [perl #113060].
+XXX Newly added diagnostic messages go under here, separated into New Errors
+and New Warnings
-=item *
+=head3 New Errors
-Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
-closure) no longer results in a copy of the subroutine (or assertion
-failures on debugging builds).
+=over 4
=item *
-C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
-the current package has been assigned over (as in
-C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
+XXX L<message|perldiag/"message">
-=item *
-
-If a package is deleted by code that it calls, it is possible for C<caller>
-to see a stack frame belonging to that deleted package. C<caller> could
-crash if the stash's memory address was reused for a scalar and a
-substitution was performed on the same scalar [perl #113486].
+=back
-=item *
+=head3 New Warnings
-C<UNIVERSAL::can> no longer treats its first argument differently
-depending on whether it is a string or number internally.
+=over 4
=item *
-C<open> with C<< <& >> for the mode checks to see whether the third argument is
-a number, in determining whether to treat it as a file descriptor or a handle
-name. Magical variables like C<$1> were always failing the numeric check and
-being treated as handle names.
+L<A sequence of multiple spaces in a charnames alias definition is deprecated|perldiag/"A sequence of multiple spaces in a charnames alias definition is deprecated">
-=item *
+L<Trailing white-space in a charnames alias definition is deprecated|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
-C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
-fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
-[perl #97480]. Tied variables returning objects that stringify as "" are
-no longer ignored. A tied C<$@> that happened to return a reference the
-I<previous> time it was used is no longer ignored.
+These two deprecation warnings involving C<\N{...}> were incorrectly
+implemented. They did not warn by default (now they do) and could not be
+made fatal via C<use warnings FATAL => 'deprecated'> (now they can).
-=item *
+=back
-C<warn ""> now treats C<$@> with a number in it the same way, regardless of
-whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
-former. Now it appends "\t...caught", as it has always done with
-C<$@="3">.
+=head2 Changes to Existing Diagnostics
-=item *
+XXX Changes (i.e. rewording) of diagnostic messages go here
-Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
-floating point operations even where integer operations were more appropriate,
-resulting in loss of accuracy on 64-bit platforms [perl #109542].
+=over 4
=item *
-Unary negation no longer treats a string as a number if the string happened
-to be used as a number at some point. So, if C<$x> contains the string "dogs",
-C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
+XXX Describe change here
-=item *
-
-In Perl v5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
-variables (C<$1>, ties) were not fixed till now [perl #57706].
+=back
-=item *
+=head1 Utility Changes
-Unary negation now treats strings consistently, regardless of the internal
-C<UTF8> flag.
+XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go here.
+Most of these are built within the directories F<utils> and F<x2p>.
-=item *
+[ List utility changes as a =head3 entry for each utility and =item
+entries for each change
+Use L<XXX> with program names to get proper documentation linking. ]
-A regression introduced in Perl v5.16.0 involving
-C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
-instance is supposed to be meaningful if a character appears more than
-once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
-was overriding all earlier ones. [perl #113584]
+=head3 F<bisect.pl> enhancements
-=item *
+The git bisection tool F<Porting/bisect.pl> has had many enhancements.
-Regular expressions like C<qr/\87/> previously silently inserted a NUL
-character, thus matching as if it had been written C<qr/\00087/>. Now it
-matches as if it had been written as C<qr/87/>, with a message that the
-sequence C<"\8"> is unrecognized.
+=over 4
=item *
-C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
+Can optionally run the test case with a timeout.
=item *
-Thread creation on Windows could theoretically result in a crash if done
-inside a C<BEGIN> block. It still does not work properly, but it no longer
-crashes [perl #111610].
+Can now run in-place in a clean git checkout.
=item *
-C<\&{''}> (with the empty string) now autovivifies a stub like any other
-sub name, and no longer produces the "Unable to create sub" error
-[perl #94476].
+Can run the test case under C<valgrind>.
=item *
-A regression introduced in v5.14.0 has been fixed, in which some calls
-to the C<re> module would clobber C<$_> [perl #113750].
+Can apply user supplied patches and fixes to the source checkout before
+building.
=item *
-C<do FILE> now always either sets or clears C<$@>, even when the file can't be
-read. This ensures that testing C<$@> first (as recommended by the
-documentation) always returns the correct result.
+Now has fixups to enable building several more historical ranges of bleadperl,
+which can be useful for pinpointing the origins of bugs or behaviour changes.
-=item *
-
-The array iterator used for the C<each @array> construct is now correctly
-reset when C<@array> is cleared [perl #75596]. This happens, for example, when
-the array is globally assigned to, as in C<@array = (...)>, but not when its
-B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
-will now reset the iterator.
+=back
-This mirrors the behaviour of the hash iterator when the hash is cleared.
+It is provided as part of the source distribution but not installed because
+it is not self-contained as it relies on being run from within a git
+checkout. Note also that it makes no attempt to fix tests, correct runtime
+bugs or make something useful to install - its purpose is to make minimal
+changes to get any historical revision of interest to build and run as close
+as possible to "as-was", and thereby make C<git bisect> easy to use.
-=item *
+=head1 Configuration and Compilation
-C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
-correct results, regardless of whether that package referred to by C<$class>
-exists [perl #47113].
+XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
+go here. Any other changes to the Perl build process should be listed here.
+However, any platform-specific changes should be listed in the
+L</Platform Support> section, instead.
-=item *
+[ List changes as a =item entry ].
-Arriving signals no longer clear C<$@> [perl #45173].
+=over 4
=item *
-Allow C<my ()> declarations with an empty variable list [perl #113554].
-
-=item *
+XXX
-During parsing, subs declared after errors no longer leave stubs
-[perl #113712].
+=back
-=item *
+=head1 Testing
-Closures containing no string evals no longer hang on to their containing
-subroutines, allowing variables closed over by outer subroutines to be
-freed when the outer sub is freed, even if the inner sub still exists
-[perl #89544].
+XXX Any significant changes to the testing of a freshly built perl should be
+listed here. Changes which create B<new> files in F<t/> go here as do any
+large changes to the testing harness (e.g. when parallel testing was added).
+Changes to existing files in F<t/> aren't worth summarizing, although the bugs
+that they represent may be covered elsewhere.
-=item *
+[ List each test improvement as a =item entry ]
-Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
-stopped working properly in v5.16.0. It was causing the new handle to
-reference a different scalar variable. This has been fixed [perl #113764].
+=over 4
=item *
-C<qr//> expressions no longer crash with custom regular expression engines
-that do not set C<offs> at regular expression compilation time
-[perl #112962].
-
-=item *
+XXX
-C<delete local> no longer crashes with certain magical arrays and hashes
-[perl #112966].
+=back
-=item *
+=head1 Platform Support
-C<local> on elements of certain magical arrays and hashes used not to
-arrange to have the element deleted on scope exit, even if the element did
-not exist before C<local>.
+XXX Any changes to platform support should be listed in the sections below.
-=item *
+[ Within the sections, list each platform as a =item entry with specific
+changes as paragraphs below it. ]
-C<scalar(write)> no longer returns multiple items [perl #73690].
+=head2 New Platforms
-=item *
+XXX List any platforms that this version of perl compiles on, that previous
+versions did not. These will either be enabled by new files in the F<hints/>
+directories, or new subdirectories and F<README> files at the top level of the
+source tree.
-String to floating point conversions no longer misparse certain strings under
-C<use locale> [perl #109318].
+=over 4
-=item *
+=item XXX-some-platform
-C<@INC> filters that die no longer leak memory [perl #92252].
+XXX
-=item *
+=back
-The implementations of overloaded operations are now called in the correct
-context. This allows, among other things, being able to properly override
-C<< <> >> [perl #47119].
+=head2 Discontinued Platforms
-=item *
+XXX List any platforms that this version of perl no longer compiles on.
-Specifying only the C<fallback> key when calling C<use overload> now behaves
-properly [perl #113010].
+=over 4
-=item *
+=item XXX-some-platform
-C<< sub foo { my $a = 0; while ($a) { ... } } >> and
-C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
+XXX
-=item *
+=back
-String negation now behaves the same under C<use integer;> as it does
-without [perl #113012].
+=head2 Platform-Specific Notes
-=item *
+XXX List any changes for specific platforms. This could include configuration
+and compilation changes or changes in portability/compatibility. However,
+changes within modules for platforms should generally be listed in the
+L</Modules and Pragmata> section.
-C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
-regardless of the internal representation. -1 used to wrap if the argument
-was tied or a string internally.
+=over 4
-=item *
+=item Mixed-endian platforms
-Using a C<format> after its enclosing sub was freed could crash as of
-perl v5.12.0, if the format referenced lexical variables from the outer sub.
+The code supporting C<pack> and C<unpack> operations on mixed endian
+platforms has been removed. We believe that Perl has long been unable to
+build on mixed endian architectures (such as PDP-11s), so we don't think
+that this change will affect any platforms which are able to build v5.18.0.
-=item *
+=back
-Using a C<format> after its enclosing sub was undefined could crash as of
-perl v5.10.0, if the format referenced lexical variables from the outer sub.
+=head1 Internal Changes
-=item *
+XXX Changes which affect the interface available to C<XS> code go here. Other
+significant internal changes for future core maintainers should be noted as
+well.
-Using a C<format> defined inside a closure, which format references
-lexical variables from outside, never really worked unless the C<write>
-call was directly inside the closure. In v5.10.0 it even started crashing.
-Now the copy of that closure nearest the top of the call stack is used to
-find those variables.
+=over 4
=item *
-Formats that close over variables in special blocks no longer crash if a
-stub exists with the same name as the special block before the special
-block is compiled.
+Perl's new copy-on-write mechanism (which is now enabled by default),
+allows any C<SvPOK> scalar to be automatically upgraded to a copy-on-write
+scalar when copied. A reference count on the string buffer is stored in
+the string buffer itself.
-=item *
+For example:
-The parser no longer gets confused, treating C<eval foo ()> as a syntax
-error if preceded by C<print;> [perl #16249].
+ $ perl -MDevel::Peek -e'$a="abc"; $b = $a; Dump $a; Dump $b'
+ SV = PV(0x260cd80) at 0x2620ad8
+ REFCNT = 1
+ FLAGS = (POK,IsCOW,pPOK)
+ PV = 0x2619bc0 "abc"\0
+ CUR = 3
+ LEN = 16
+ COW_REFCNT = 1
+ SV = PV(0x260ce30) at 0x2620b20
+ REFCNT = 1
+ FLAGS = (POK,IsCOW,pPOK)
+ PV = 0x2619bc0 "abc"\0
+ CUR = 3
+ LEN = 16
+ COW_REFCNT = 1
-=item *
+Note that both scalars share the same PV buffer and have a COW_REFCNT
+greater than zero.
-The return value of C<syscall> is no longer truncated on 64-bit platforms
-[perl #113980].
+This means that XS code which wishes to modify the C<SvPVX()> buffer of an
+SV should call C<SvPV_force()> or similar first, to ensure a valid (and
+unshared) buffer, and to call C<SvSETMAGIC()> afterwards. This in fact has
+always been the case (for example hash keys were already copy-on-write);
+this change just spreads the COW behaviour to a wider variety of SVs.
-=item *
+One important difference is that before 5.18.0, shared hash-key scalars
+used to have the C<SvREADONLY> flag set; this is no longer the case.
-Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
-FOO handle [perl #78064].
+This new behaviour can still be disabled by running F<Configure> with
+B<-Accflags=-DPERL_NO_COW>. This option will probably be removed in Perl
+5.22.
=item *
-C<do subname> now calls the named subroutine and uses the file name it
-returns, instead of opening a file named "subname".
-
-=item *
+C<PL_sawampersand> is now a constant. The switch this variable provided
+(to enable/disable the pre-match copy depending on whether C<$&> had been
+seen) has been removed and replaced with copy-on-write, eliminating a few
+bugs.
-Subroutines looked up by rv2cv check hooks (registered by XS modules) are
-now taken into consideration when determining whether C<foo bar> should be
-the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
+The previous behaviour can still be enabled by running F<Configure> with
+B<-Accflags=-DPERL_SAWAMPERSAND>.
=item *
-C<CORE::foo::bar> is no longer treated specially, allowing global overrides
-to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
+The functions C<my_swap>, C<my_htonl> and C<my_ntohl> have been removed.
+It is unclear why these functions were ever marked as I<A>, part of the
+API. XS code can't call them directly, as it can't rely on them being
+compiled. Unsurprisingly, no code on CPAN references them.
=item *
-Calling an undefined sub whose typeglob has been undefined now produces the
-customary "Undefined subroutine called" error, instead of "Not a CODE
-reference".
-
-=item *
+The signature of the C<Perl_re_intuit_start()> regex function has changed;
+the function pointer C<intuit> in the regex engine plugin structure
+has also changed accordingly. A new parameter, C<strbeg> has been added;
+this has the same meaning as the same-named parameter in
+C<Perl_regexec_flags>. Previously intuit would try to guess the start of
+the string from the passed SV (if any), and would sometimes get it wrong
+(e.g. with an overloaded SV).
-Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
-C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
-updating the internal caches used to look up methods. The
-*glob_without_array case was a regression from Perl v5.12.
+=back
-=item *
+=head1 Selected Bug Fixes
-Regular expression optimisations sometimes caused C<$> with C</m> to
-produce failed or incorrect matches [perl #114068].
+XXX Important bug fixes in the core language are summarized here. Bug fixes in
+files in F<ext/> and F<lib/> are best summarized in L</Modules and Pragmata>.
-=item *
+[ List each fix as a =item entry ]
-C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
-predeclared with C<sub foo;> syntax [perl #113710].
+=over 4
=item *
-Unicode properties only apply to Unicode code points, which leads to
-some subtleties when regular expressions are matched against
-above-Unicode code points. There is a warning generated to draw your
-attention to this. However, this warning was being generated
-inappropriately in some cases, such as when a program was being parsed.
-Non-Unicode matches such as C<\w> and C<[:word:]> should not generate the
-warning, as their definitions don't limit them to apply to only Unicode
-code points. Now the message is only generated when matching against
-C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
-few properties in Unicode that match just a single code point. The
-warning is not generated if they are matched against an above-Unicode
-code point.
+The OP allocation code now returns correctly aligned memory in all cases
+for C<struct pmop>. Previously it could return memory only aligned to a
+4-byte boundary, which is not correct for an ithreads build with 64 bit IVs
+on some 32 bit platforms. Notably, this caused the build to fail completely
+on sparc GNU/Linux. [RT #118055]
=item *
-Uninitialized warnings mentioning hash elements would only mention the
-element name if it was not in the first bucket of the hash, due to an
-off-by-one error.
+The debugger's C<man> command been fixed. It was broken in the v5.18.0
+release. The C<man> command is aliased to the names C<doc> and C<perldoc> -
+all now work again.
=item *
-A regular expression optimizer bug could cause multiline "^" to behave
-incorrectly in the presence of line breaks, such that
-C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
+Evaluating large hashes in scalar context is now much faster, as the number
+of used chains in the hash is now cached for larger hashes. Smaller hashes
+continue not to store it and calculate it when needed, as this saves one IV.
+That would be 1 IV overhead for every object built from a hash. [RT #114576]
=item *
-Failed C<fork> in list context no longer corrupts the stack.
-C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
-if the C<fork> call failed.
+Fixed a small number of regexp constructions that could either fail to
+match or crash perl when the string being matched against was
+allocated above the 2GB line on 32-bit systems. [RT #118175]
=item *
-Numerous memory leaks have been fixed, mostly involving tied variables that
-die, regular expression character classes and code blocks, and syntax
-errors.
+Perl v5.16 inadvertently introduced a bug whereby calls to XSUBs that were
+not visible at compile time were treated as lvalues and could be assigned
+to, even when the subroutine was not an lvalue sub. This has been fixed.
+[RT #117947]
=item *
-Assigning a regular expression (C<${qr//}>) to a variable that happens to
-hold a floating point number no longer causes assertion failures on
-debugging builds.
+In Perl v5.18.0 dualvars that had an empty string for the string part but a
+non-zero number for the number part starting being treated as true. In
+previous versions they were treated as false, the string representation
+taking precedeence. The old behaviour has been restored. [RT #118159]
=item *
-Assigning a regular expression to a scalar containing a number no longer
-causes subsequent numification to produce random numbers.
+Since Perl v5.12, inlining of constants that override built-in keywords of
+the same name had countermanded C<use subs>, causing subsequent mentions of
+the constant to use the built-in keyword instead. This has been fixed.
=item *
-Assigning a regular expression to a magic variable no longer wipes away the
-magic. This was a regression from v5.10.
+Lexical constants (C<my sub a() { 42 }>) no longer crash when inlined.
=item *
-Assigning a regular expression to a blessed scalar no longer results in
-crashes. This was also a regression from v5.10.
+Parameter prototypes attached to lexical subroutines are now respected when
+compiling sub calls without parentheses. Previously, the prototypes were
+honoured only for calls I<with> parentheses. [RT #116735]
=item *
-Regular expression can now be assigned to tied hash and array elements with
-flattening into strings.
+Syntax errors in lexical subroutines in combination with calls to the same
+subroutines no longer cause crashes at compile time.
=item *
-Numifying a regular expression no longer results in an uninitialized
-warning.
+The warning produced by C<-l $handle> now applies to IO refs and globs, not
+just to glob refs. That warning is also now UTF8-clean. [RT #117595]
=item *
-Negative array indices no longer cause EXISTS methods of tied variables to
-be ignored. This was a regression from v5.12.
+Various memory leaks involving the parsing of the C<(?[...])> regular
+expression construct have been fixed.
=item *
-Negative array indices no longer result in crashes on arrays tied to
-non-objects.
+C<(?[...])> now allows interpolation of precompiled patterns consisting of
+(?[...])> with bracket character classes inside (C<$pat =
+S<qr/(?[ [a] ])/;> S</(?[ $pat ])/>>). Formerly, the brackets would
+confuse the regular expression parser.
=item *
-C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF-8 if the
-left-hand scalar happened to have produced a UTF-8 string the last time
-overloading was invoked.
+C<delete local $ENV{nonexistent_env_var}> no longer leaks memory.
=item *
-C<goto &sub> now uses the current value of @_, instead of using the array
-the subroutine was originally called with. This means
-C<local @_ = (...); goto &sub> now works [perl #43077].
+C<sort> and C<require> followed by a keyword prefixed with C<CORE::> now
+treat it as a keyword, and not as a subroutine or module name. [RT #24482]
=item *
-If a debugger is invoked recursively, it no longer stomps on its own
-lexical variables. Formerly under recursion all calls would share the same
-set of lexical variables [perl #115742].
+Through certain conundrums, it is possible to cause the current package to
+be freed. Certain operators (C<bless>, C<reset>, C<open>, C<eval>) could
+not cope and would crash. They have been made more resilient. [RT #117941]
=item *
-C<*_{ARRAY}> returned from a subroutine no longer spontaneously
-becomes empty.
+Aliasing filehandles through glob-to-glob assignment would not update
+internal method caches properly if a package of the same name as the
+filehandle existed, resulting in filehandle method calls going to the
+package instead. This has been fixed.
=back
=head1 Known Problems
+XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
+tests that had to be C<TODO>ed for the release would be noted here. Unfixed
+platform specific bugs also go here.
+
+[ List each fix as a =item entry ]
+
=over 4
=item *
-UTF8-flagged strings in C<%ENV> on HP-UX 11.00 are buggy
-
-The interaction of UTF8-flagged strings and C<%ENV> on HP-UX 11.00 is
-currently dodgy in some not-yet-fully-diagnosed way. Expect test
-failures in F<t/op/magic.t>, followed by unknown behavior when storing
-wide characters in the environment.
+XXX
=back
=head1 Obituary
-Hojung Yoon (AMORETTE), 24, of Seoul, South Korea, went to his long rest
-on May 8, 2013 with llama figurine and autographed TIMTOADY card. He
-was a brilliant young Perl 5 & 6 hacker and a devoted member of
-Seoul.pm. He programmed Perl, talked Perl, ate Perl, and loved Perl. We
-believe that he is still programming in Perl with his broken IBM laptop
-somewhere. He will be missed.
+XXX If any significant core contributor has died, we've added a short obituary
+here.
=head1 Acknowledgements
-Perl v5.18.0 represents approximately 12 months of development since
-Perl v5.16.0 and contains approximately 400,000 lines of changes across
-2,100 files from 113 authors.
-
-Perl continues to flourish into its third decade thanks to a vibrant
-community of users and developers. The following people are known to
-have contributed the improvements that became Perl v5.18.0:
-
-Aaron Crane, Aaron Trevena, Abhijit Menon-Sen, Adrian M. Enache, Alan
-Haggai Alavi, Alexandr Ciornii, Andrew Tam, Andy Dougherty, Anton Nikishaev,
-Aristotle Pagaltzis, Augustina Blair, Bob Ernst, Brad Gilbert, Breno G. de
-Oliveira, Brian Carlson, Brian Fraser, Charlie Gonzalez, Chip Salzenberg, Chris
-'BinGOs' Williams, Christian Hansen, Colin Kuskie, Craig A. Berry, Dagfinn
-Ilmari Mannsåker, Daniel Dragan, Daniel Perrett, Darin McBride, Dave Rolsky,
-David Golden, David Leadbeater, David Mitchell, David Nicol, Dominic
-Hargreaves, E. Choroba, Eric Brine, Evan Miller, Father Chrysostomos, Florian
-Ragwitz, François Perrad, George Greer, Goro Fuji, H.Merijn Brand, Herbert
-Breunung, Hugo van der Sanden, Igor Zaytsev, James E Keenan, Jan Dubois,
-Jasmine Ahuja, Jerry D. Hedden, Jess Robinson, Jesse Luehrs, Joaquin Ferrero,
-Joel Berger, John Goodyear, John Peacock, Karen Etheridge, Karl Williamson,
-Karthik Rajagopalan, Kent Fredric, Leon Timmermans, Lucas Holt, Lukas Mai,
-Marcus Holland-Moritz, Markus Jansen, Martin Hasch, Matthew Horsfall, Max
-Maischein, Michael G Schwern, Michael Schroeder, Moritz Lenz, Nicholas Clark,
-Niko Tyni, Oleg Nesterov, Patrik Hägglund, Paul Green, Paul Johnson, Paul
-Marquess, Peter Martini, Rafael Garcia-Suarez, Reini Urban, Renee Baecker,
-Rhesa Rozendaal, Ricardo Signes, Robin Barker, Ronald J. Kimball, Ruslan
-Zakirov, Salvador Fandiño, Sawyer X, Scott Lanning, Sergey Alekseev, Shawn M
-Moore, Shirakata Kentaro, Shlomi Fish, Sisyphus, Smylers, Steffen Müller,
-Steve Hay, Steve Peters, Steven Schubiger, Sullivan Beck, Sven Strickroth,
-Sébastien Aperghis-Tramoni, Thomas Sibley, Tobias Leich, Tom Wyant, Tony Cook,
-Vadim Konovalov, Vincent Pit, Volker Schatz, Walt Mankowski, Yves Orton,
-Zefram.
-
-The list above is almost certainly incomplete as it is automatically generated
-from version control history. In particular, it does not include the names of
-the (very much appreciated) contributors who reported issues to the Perl bug
-tracker.
-
-Many of the changes included in this version originated in the CPAN modules
-included in Perl's core. We're grateful to the entire CPAN community for
-helping Perl to flourish.
-
-For a more complete list of all of Perl's historical contributors, please see
-the F<AUTHORS> file in the Perl source distribution.
+XXX Generate this with:
+
+ perl Porting/acknowledgements.pl v5.19.1..HEAD
=head1 Reporting Bugs
https://perl5.git.perl.org / perl5.git / blobdiff