-=for todo
-
-869747506f/00051dd553 (merijn) - gcc 4.9 by default does some optimizations that break perl / -fwrapv is broken prior to gcc-4.3 (#121505)
-
=encoding utf8
=head1 NAME
-perldelta - what is new for perl v5.19.11
+[ this is a template for a new perldelta file. Any text flagged as XXX needs
+to be processed before release. ]
+
+perldelta - what is new for perl v5.21.1
=head1 DESCRIPTION
-This document describes differences between the 5.19.10 release and the 5.19.11
+This document describes differences between the 5.21.0 release and the 5.21.1
release.
-If you are upgrading from an earlier release such as 5.19.9, first read
-L<perl51910delta>, which describes differences between 5.19.9 and 5.19.10.
+If you are upgrading from an earlier release such as 5.20.0, first read
+L<perl5210delta>, which describes differences between 5.20.0 and 5.21.0.
+
+=head1 Notice
+
+XXX Any important notices here
+
+=head1 Core Enhancements
+
+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.
+
+[ List each enhancement as a =head2 entry ]
+
+=head2 Unicode 7.0 is now supported
+
+For details on what is in this release, see
+L<http://www.unicode.org/versions/Unicode7.0.0/>.
+
+=head2 Experimental C Backtrace API
+
+Starting from Perl 5.21.1, on some platforms Perl supports retrieving
+the C level backtrace (similar to what symbolic debuggers like gdb do).
+
+The backtrace returns the stack trace of the C call frames,
+with the symbol names (function names), the object names (like "perl"),
+and if it can, also the source code locations (file:line).
+
+The supported platforms are Linux and OS X (some *BSD might work at
+least partly, but they have not yet been tested).
+
+The feature needs to be enabled with C<Configure -Dusecbacktrace>.
+
+Also included is a C API to retrieve backtraces.
+
+See L<perlhacktips/"C backtrace"> for more information.
+
+=head2 C<qr/foo/x> now ignores any Unicode pattern white space
+
+The C</x> regular expression modifier allows the pattern to contain
+white space and comments, both of which are ignored, for improved
+readability. Until now, not all the white space characters that Unicode
+designates for this purpose were handled. The additional ones now
+recognized are
+U+0085 NEXT LINE,
+U+200E LEFT-TO-RIGHT MARK,
+U+200F RIGHT-TO-LEFT MARK,
+U+2028 LINE SEPARATOR,
+and
+U+2029 PARAGRAPH SEPARATOR.
+
+=head2 S<C<use locale>> can restrict which locale categories are affected
+
+It is now possible to pass a parameter to S<C<use locale>> to specify
+a subset of locale categories to be locale-aware, with the remaining
+ones unaffected. See L<perllocale/The "use locale" pragma> for details.
+
+=head1 Security
+
+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.
+
+[ List each security issue as a =head2 entry ]
+
+=head1 Incompatible Changes
+
+XXX For a release on a stable branch, this section aspires to be:
+
+ 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.
+
+=head2 C<\N{}> with a sequence of multiple spaces is now a fatal error.
+
+This has been deprecated since v5.18.
+
+=head2 In double-quotish C<\cI<X>>, I<X> must now be a printable ASCII character
+
+In prior releases, failure to do this raised a deprecation warning.
+
+=head2 Splitting the tokens C<(?> and C<(*> in regular expressions is
+now a fatal compilation error.
+
+These had been deprecated since v5.18.
+
+=head2 5 additional characters are treated as white space under C</x> in
+regex patterns (unless escaped)
+
+The use of these characters with C</x> outside bracketed character
+classes and when not preceeded by a backslash has raised a deprecation
+warning since v5.18. Now they will be ignored. See L</qrE<sol>fooE<sol>x>
+for the list of the five characters.
+
+=head2 Comment lines within S<C<(?[ ])>> now are ended only by a C<\n>
+
+S<C<(?[ ])>> is an experimental feature, introduced in v5.18. It operates
+as if C</x> is always enabled. But there was a difference, comment
+lines (following a C<#> character) were terminated by anything matching
+C<\R> which includes all vertical whitespace, such as form feeds. For
+consistency, this is now changed to match what terminates comment lines
+outside S<C<(?[ ])>>, namely a C<\n> (even if escaped), which is the
+same as what terminates a heredoc string and formats.
+
+=head2 Omitting % and @ on hash and array names is no longer permitted
+
+Really old Perl let you omit the @ on array names and the % on hash
+names in some spots. This has issued a deprecation warning since Perl
+5.0, and is no longer permitted.
+
+=head2 C<"$!"> text is now in English outside C<"use locale"> scope
+
+Previously, the text, unlike almost everything else, always came out
+based on the current underlying locale of the program. (Also affected
+on some systems is C<"$^E>".) For programs that are unprepared to
+handle locale, this can cause garbage text to be displayed. It's better
+to display text that is translatable via some tool than garbage text
+which is much harder to figure out.
+
+=head2 C<"$!"> text will be returned in UTF-8 when appropriate
+
+The stringification of C<$!> and C<$^E> will have the UTF-8 flag set
+when the text is actually non-ASCII UTF-8. This will enable programs
+that are set up to be locale-aware to properly output messages in the
+user's native language. Code that needs to continue the 5.20 and
+earlier behavior can do the stringification within the scopes of both
+'use bytes' and 'use locale ":messages". No other Perl operations will
+be affected by locale; only C<$!> and C<$^E> stringification. The
+'bytes' pragma causes the UTF-8 flag to not be set, just as in previous
+Perl releases. This resolves [perl #112208].
+
+=head2 Support for C<?PATTERN?> without explicit operator has been removed
+
+Starting regular expressions matching only once directly with the
+question mark delimiter is now a syntax error, so that the question mark
+can be available for use in new operators. Write C<m?PATTERN?> instead,
+explicitly using the C<m> operator: the question mark delimiter still
+invokes match-once behaviour.
+
+=head1 Deprecations
+
+XXX Any deprecated features, syntax, modules etc. should be listed here.
+
+=head2 Using a NO-BREAK space in a character alias for C<\N{...}> is now
+deprecated
+
+This non-graphic character is essentially indistinguishable from a
+regular space, and so should not be allowed. See
+L<charnames/CUSTOM ALIASES>.
+
+=head2 A literal C<"{"> should now be escaped in a pattern
+
+If you want a literal left curly bracket (also called a left brace) in a
+regular expression pattern, you should now escape it by either
+preceding it with a backslash (C<"\{">) or enclosing it within square
+brackets C<"[{]">, or by using C<\Q>; otherwise a deprecation warning
+will be raised. This was first announced as forthcoming in the v5.16
+release; it will allow future extensions to the language to happen.
+
+=head2 Module removals
+
+XXX Remove this section if inapplicable.
+
+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 XXX
+
+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.
+
+=back
+
+[ List each other deprecation as a =head2 entry ]
+
+=head1 Performance Enhancements
+
+XXX Changes which enhance performance without changing behaviour go here.
+There may well be none in a stable release.
+
+[ List each enhancement as a =item entry ]
+
+=over 4
+
+=item *
+
+Many internal functions have been refactored to improve performance and reduce
+their memory footprints.
+
+L<[perl #121436]|https://rt.perl.org/Ticket/Display.html?id=121436>
+L<[perl #121906]|https://rt.perl.org/Ticket/Display.html?id=121906>
+L<[perl #121969]|https://rt.perl.org/Ticket/Display.html?id=121969>
+
+=item *
+
+C<-T> and C<-B> filetests will return sooner when an empty file is detected.
+
+L<perl #121489|https://rt.perl.org/Ticket/Display.html?id=121489>
+
+=back
=head1 Modules and Pragmata
+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>. 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.
+
+[ Within each section, list entries as a =item entry ]
+
=head2 New Modules and Pragmata
=over 4
=item *
-L<experimental> version 0.007 has been added.
-
-This pragma provides an easy and convenient way to enable or disable
-experimental features.
+XXX
=back
=item *
-L<Carp> has been upgraded from version 1.33 to 1.3301.
+L<Carp> has been upgraded from version 1.3301 to 1.34.
+
+Carp::Heavy now ignores version mismatches with Carp if Carp is newer
+than 1.12, since Carp::Heavy's guts were merged into Carp at that
+point.
+L<[perl #121574]|https://rt.perl.org/Ticket/Display.html?id=121574>
+
+=item *
+
+L<Data::Dumper> has been upgraded from version 2.151 to 2.152.
+
+Changes to resolve Coverity issues.
+
+XS dumps incorrectly stored the name of code references stored in a
+GLOB.
+L<[perl #122070]|https://rt.perl.org/Ticket/Display.html?id=122070>
+
+=item *
+
+L<Encode> has been upgraded from version 2.60_01 to 2.62.
+
+B<piconv> now has better error handling when the encoding name is nonexistent,
+and a build breakage when upgrading L<Encode> in perl-5.8.2 and earlier has
+been fixed.
+
+=item *
+
+L<Hash::Util> has been upgraded from version 0.16 to 0.17.
+
+Minor bug fixes and documentation fixes to Hash::Util::hash_stats()
+
+=item *
+
+The libnet collection of modules has been upgraded from version 1.25 to 1.27.
+
+There are only whitespace changes to the installed files.
+
+=item *
+
+The Locale-Codes collection of modules has been upgraded from vesion 3.30 to 3.31.
+
+Fixed a bug in the scripts used to extract data from spreadsheets that
+prevented the SHP currency code from being found.
+L<[cpan #94229]|https://rt.cpan.org/Ticket/Display.html?id=94229>
+
+=item *
+
+L<Math::BigInt> has been upgraded from version 1.9993 to 1.9994.
+
+Synchronize POD changes from the CPAN release.
+
+C<< Math::BigFloat->blog(x) >> would sometimes return blog(2*x) when
+the accuracy was greater than 70 digits.
+
+The result of C<< Math::BigFloat->bdiv() >> in list context now
+satisfies C<< x = quotient * divisor + remainder >>.
+
+=item *
+
+L<Math::BigRat> has been upgraded from version 0.2606 to 0.2607.
+
+Synchronize POD changes from the CPAN release.
+
+=item *
+
+L<Module::Metadata> has been upgraded from version 1.000022 to 1.000024.
+
+Support installations on older perls with an L<ExtUtils::MakeMaker> earlier
+than 6.63_03
+
+=item *
+
+L<OS2::Process> has been upgraded from version 1.09 to 1.10.
+
+=item *
+
+L<perl5db.pl> has been upgraded from version 1.44 to 1.45.
+
+fork() in the debugger under C<tmux> will now create a new window for
+the forked process. L<[perl
+#121333]|https://rt.perl.org/Ticket/Display.html?id=121333>
+
+The debugger now saves the current working directory on startup and
+restores it when you restart your program with C<R> or <rerun>. L<[perl
+#121509]|https://rt.perl.org/Ticket/Display.html?id=121509>
+
+=item *
+
+L<PerlIO::encoding> has been upgraded from version 0.18 to 0.19.
+
+No changes in behaviour.
+
+=item *
+
+L<PerlIO::mmap> has been upgraded from version 0.012 to 0.013.
+
+No changes in behaviour.
+
+=item *
+
+L<PerlIO::scalar> has been upgraded from version 0.18 to 0.19.
+
+No changes in behaviour.
+
+=item *
+
+L<Unicode::Collate> has been upgraded from version 1.04 to 1.07.
+
+Version 0.67's improved discontiguous contractions is invalidated by default
+and is supported as a parameter 'long_contraction'.
+
+=item *
+
+L<Unicode::Normalize> has been upgraded from version 1.17 to 1.18.
+
+The XSUB implementation has been removed in favour of pure Perl.
+
+=item *
+
+A mismatch between the documentation and the code in utf8::downgrade()
+was fixed in favour of the documentation. The optional second argument
+is now correctly treated as a perl boolean (true/false semantics) and
+not as an integer.
-No changes have been made to the installed code other than the version bump to
-keep in sync with the latest CPAN release.
+=back
+
+=head2 Removed Modules and Pragmata
+
+=over 4
=item *
-L<CPAN> has been upgraded from version 2.04-TRIAL to 2.05.
+XXX
+
+=back
+
+=head1 Documentation
+
+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>.
+
+=head2 New Documentation
+
+XXX Changes which create B<new> files in F<pod/> go here.
+
+=head3 L<XXX>
+
+XXX Description of the purpose of the new file here
-This fixes L<local::lib> shell variable string output and prevents an endless
-loop when running "notest test Module" for some Module having dependencies.
+=head2 Changes to Existing Documentation
+
+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.
+
+=head3 L<perlfunc>
+
+=over 4
=item *
-L<DB> has been upgraded from version 1.43 to 1.44.
+C<-l> now notes that it will return false if symlinks aren't supported by the
+file system.
-The debugger now correctly restores its input and output filehandles after
-using the pager command.
-[L<perl #121456|https://rt.perl.org/Public/Bug/Display.html?id=121456>]
+L<[perl #121523]|https://rt.perl.org/Ticket/Display.html?id=121523>
=item *
-L<ExtUtils::Install> has been upgraded from version 1.63 to 1.67.
+Note that C<exec LIST> and C<system LIST> may fall back to the shell on
+Win32. Only C<exec PROGRAM LIST> and C<system PROGRAM LIST> indirect object
+syntax will reliably avoid using the shell.
+
+This has also been noted in L<perlport>.
-When upgrading an already-installed file, L<ExtUtils::Install> could mess up
-the permissions of files if the old versions of files were hard or symbolic
-links. This has now been fixed.
-[L<perl #72028|https://rt.perl.org/Public/Bug/Display.html?id=72028>]
+L<[perl #122046]|https://rt.perl.org/Ticket/Display.html?id=122046>
-The MM_TEST_ROOT feature has been removed from the tests.
+=back
+
+=head3 L<perlapi>
+
+=over 4
+
+=item *
+
+Note that C<SvSetSV> doesn't do set magic.
=item *
-L<ExtUtils::MakeMaker> has been upgraded from version 6.92 to 6.94.
+C<sv_usepvn_flags> - Fix documentation to mention the use of C<NewX> instead of
+C<malloc>.
-A regression in MM_Unix.pm has been resolved.
-[L<Issue #96|https://github.com/Perl-Toolchain-Gang/ExtUtils-MakeMaker/issues/96>]
+L<[perl #121869]|https://rt.perl.org/Ticket/Display.html?id=121869>
=item *
-L<Module::CoreList> has been upgraded from version 3.09 to 3.10.
+Clarify where C<NUL> may be embedded or is required to terminate a string.
-The list of Perl versions covered has been updated.
+=item *
+
+Previously missing documentation due to formatting errors are now included.
+
+=item *
+
+Entries are now organized into groups rather than by file where they are found.
=item *
-L<PerlIO> has been upgraded from version 1.08 to 1.09.
+Alphabetical sorting of entries is now handled by the POD generator to make
+entries easier to find when scanning.
-The warning about the use of the C<:utf8> layer has been made more prominent.
+=back
+
+=head3 L<perlhacktips>
+
+=over 4
=item *
-L<Storable> has been upgraded from version 2.48 to 2.49.
+Updated documentation for the C<test.valgrind> C<make> target.
+
+L<[perl #121431]|https://rt.perl.org/Ticket/Display.html?id=121431>
+
+=back
-Recognition of tied SVs has been tightened up.
+=head3 L<perlre>
+
+=over 4
=item *
-L<Win32> has been upgraded from version 0.48 to 0.49.
+The C</x> modifier has been clarified to note that comments cannot be continued
+onto the next line by escaping them.
+
+=back
+
+=head3 L<Unicode::UCD>
-This fixes a problem when building with B<gcc> version 4.8.1 from
-L<http://www.mingw.org>.
-[L<cpan #94730|https://rt.cpan.org/Public/Bug/Display.html?id=94730>]
+=over 4
+
+=item *
+
+The documentation includes many clarifications and fixes.
=back
including warnings and fatal error messages. For the complete list of
diagnostic messages, see L<perldiag>.
+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.
+
+=head2 New Diagnostics
+
+XXX Newly added diagnostic messages go under here, separated into New Errors
+and New Warnings
+
+=head3 New Errors
+
+=over 4
+
+=item *
+
+L<In '(?...)', the '(' and '?' must be adjacent in regex; marked by S<<-- HERE> in mE<sol>%sE<sol>|perldiag/"In '(?...)', the '(' and '?' must be adjacent in regex; marked by <-- HERE in m/%s/">
+
+(F) The two-character sequence C<"(?"> in
+this context in a regular expression pattern should be an
+indivisible token, with nothing intervening between the C<"(">
+and the C<"?">, but you separated them.
+
+=item *
+
+L<In '(*VERB...)', the '(' and '*' must be adjacent in regex; marked by S<<-- HERE> in mE<sol>%sE<sol>|perldiag/"In '(*VERB...)', the '(' and '*' must be adjacent in regex; marked by <-- HERE in m/%s/">
+
+(F) The two-character sequence C<"(*"> in
+this context in a regular expression pattern should be an
+indivisible token, with nothing intervening between the C<"(">
+and the C<"*">, but you separated them.
+
+=item *
+
+L<charnames alias definitions may not contain a sequence of multiple spaces|perldiag/"charnames alias definitions may not contain a sequence of multiple spaces">
+
+(F) You defined a character name which had multiple space
+ characters in a row. Change them to single spaces. Usually these
+ names are defined in the C<:alias> import argument to C<use charnames>, but
+ they could be defined by a translator installed into C<$^H{charnames}>.
+ See L<charnames/CUSTOM ALIASES>.
+
+=item *
+
+L<charnames alias definitions may not contain trailing white-space|perldiag/"charnames alias definitions may not contain trailing white-space">
+
+(F) You defined a character name which ended in a space
+character. Remove the trailing space(s). Usually these names are
+defined in the C<:alias> import argument to C<use charnames>, but they
+could be defined by a translator installed into C<$^H{charnames}>.
+See L<charnames/CUSTOM ALIASES>.
+
+=item *
+
+L<Can't use a hash as a reference|perldiag/"Can't use a hash as a reference">
+
+(F) You tried to use a hash as a reference, as in
+C<< %foo->{"bar"} >> or C<< %$ref->{"hello"} >>. Versions of perl <= 5.6.1
+used to allow this syntax, but shouldn't have.
+
+=item *
+
+L<Can't use an array as a reference|perldiag/"Can't use an array as a reference">
+
+(F) You tried to use an array as a reference, as in
+C<< @foo->[23] >> or C<< @$ref->[99] >>. Versions of perl <= 5.6.1 used to
+allow this syntax, but shouldn't have.
+
+=item *
+
+L<Can't use 'defined(@array)' (Maybe you should just omit the defined()?)|perldiag/"Can't use 'defined(@array)' (Maybe you should just omit the defined()?)">
+
+(F) defined() is not useful on arrays because it
+checks for an undefined I<scalar> value. If you want to see if the
+array is empty, just use C<if (@array) { # not empty }> for example.
+
+=item *
+
+L<Can't use 'defined(%hash)' (Maybe you should just omit the defined()?)|perldiag/"Can't use 'defined(%hash)' (Maybe you should just omit the defined()?)">
+
+(F) C<defined()> is not usually right on hashes.
+
+Although C<defined %hash> is false on a plain not-yet-used hash, it
+becomes true in several non-obvious circumstances, including iterators,
+weak references, stash names, even remaining true after C<undef %hash>.
+These things make C<defined %hash> fairly useless in practice, so it now
+generates a fatal error.
+
+If a check for non-empty is what you wanted then just put it in boolean
+context (see L<perldata/Scalar values>):
+
+ if (%hash) {
+ # not empty
+ }
+
+If you had C<defined %Foo::Bar::QUUX> to check whether such a package
+variable exists then that's never really been reliable, and isn't
+a good way to enquire about the features of a package, or whether
+it's loaded, etc.
+
+=item *
+
+L<Illegal suidscript|perldiag/"Illegal suidscript">
+
+(F) The script run under suidperl was somehow illegal.
+
+=back
+
+=head3 New Warnings
+
+=over 4
+
+=item *
+
+L<Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in mE<sol>%sE<sol>|perldiag/"Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/%s/">
+
+(D deprecated, regexp) You used a literal C<"{"> character in a regular
+expression pattern. You should change to use C<"\{"> instead, because a future
+version of Perl (tentatively v5.26) will consider this to be a syntax error. If
+the pattern delimiters are also braces, any matching right brace
+(C<"}">) should also be escaped to avoid confusing the parser, for
+example,
+
+ qr{abc\{def\}ghi}
+
+=item *
+
+L<NO-BREAK SPACE in a charnames alias definition is deprecated|perldiag/"NO-BREAK SPACE in a charnames alias definition is deprecated">
+
+(D deprecated) You defined a character name which contained a no-break
+space character. Change it to a regular space. Usually these names are
+defined in the C<:alias> import argument to C<use charnames>, but they
+could be defined by a translator installed into C<$^H{charnames}>. See
+L<charnames/CUSTOM ALIASES>.
+
+=item *
+
+L<PerlIO layer ':win32' is experimental|perldiag/"PerlIO layer ':win32' is experimental">
+
+(S experimental::win32_perlio) The C<:win32> PerlIO layer is
+experimental. If you want to take the risk of using this layer,
+simply disable this warning:
+
+ no warnings "experimental::win32_perlio";
+
+=item *
+
+L<Negative repeat count does nothing|perldiag/"Negative repeat count does nothing">
+
+(W numeric) You tried to execute the
+L<C<x>|perlop/Multiplicative Operators> repetition operator fewer than 0
+times, which doesn't make sense.
+
+=item *
+
+L<localtime(%f) failed|perldiag/"localtime(%f) failed">
+
+(W overflow) You called C<localtime> with a number that it could not handle:
+too large, too small, or NaN. The returned value is C<undef>.
+
+=item *
+
+L<gmtime(%f) failed|perldiag/"gmtime(%f) failed">
+
+(W overflow) You called C<gmtime> with a number that it could not handle:
+too large, too small, or NaN. The returned value is C<undef>.
+
+=item *
+
+L<PerlIO layer ':win32' is experimental|perldiag/"PerlIO layer ':win32' is experimental">:
+
+(S experimental::win32_perlio) The C<:win32> PerlIO layer is
+experimental. If you want to take the risk of using this layer,
+simply disable this warning:
+
+ no warnings "experimental::win32_perlio";
+
+=item *
+
+L<Negative repeat count does nothing|perldiag/Negative repeat count does nothing>
+
+(W numeric) This warns when the repeat count of the
+L<C<x>|perlop/Multiplicative Operators> repetition operator is
+negative.
+
+This warning may be changed or removed if it turn out that it was
+unwise to have added it.
+
+=back
+
=head2 Changes to Existing Diagnostics
+XXX Changes (i.e. rewording) of diagnostic messages go here
+
=over 4
=item *
-The now fatal error message C<Character following "\c" must be ASCII> has been
-reworded as C<Character following "\c" must be printable ASCII> to emphasize
-that in C<\cI<X>>, I<X> must be a I<printable (non-control)> ASCII character.
+L<Variable length lookbehind not implemented in regex mE<sol>%sE<sol>|perldiag/"Variable length lookbehind not implemented in regex m/%s/">
+
+Information about Unicode behaviour has been added.
+
+=item *
+
+<> should be quotes
+
+This warning has been changed to
+L<< <> at require-statement should be quotes|perldiag/"<> at require-statement should be quotes" >>
+to make the issue more identifiable.
+
+=item *
+
+L<Unsuccessful %s on filename containing newline|perldiag/"Unsuccessful %s on filename containing newline">
+
+This warning is now only produced when the newline is at the end of
+the filename.
=back
=head1 Utility Changes
-=head2 L<perlbug>
+XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go here.
+Most of these are built within the directory F<utils>.
+
+[ List utility changes as a =head2 entry for each utility and =item
+entries for each change
+Use L<XXX> with program names to get proper documentation linking. ]
+
+=head2 F<x2p/>
=over 4
=item *
-L<perlbug> has been modified to supply the report template with CRLF line
-endings on Windows.
-[L<perl #121277|https://rt.perl.org/Public/Bug/Display.html?id=121277>]
+The F<x2p/> directory has been removed from the Perl core.
+
+This removes find2perl, s2p and a2p. They have all been released to CPAN as
+separate distributions (App::find2perl, App::s2p, App::a2p).
+
+=back
+
+=head1 Configuration and Compilation
+
+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.
+
+[ List changes as a =item entry ].
+
+=over 4
=item *
-L<perlbug> now makes as few assumptions as possible about the encoding of the
-report. This will likely change in the future to assume UTF-8 by default but
-allow a user override.
+C<make test.valgrind> now supports parallel testing.
+
+For example:
+
+ TEST_JOBS=9 make test.valgrind
+
+See L<perlhacktips/valgrind> for more information.
+
+L<[perl #121431]|https://rt.perl.org/Ticket/Display.html?id=121431>
+
+=item *
+
+The MAD (Misc Attribute Decoration) build option has been removed
+
+This was an unmaintained attempt at preserving
+the Perl parse tree more faithfully so that automatic conversion of
+Perl 5 to Perl 6 would have been easier.
+
+This build-time configuration option had been unmaintained for years,
+and had probably seriously diverged on both Perl 5 and Perl 6 sides.
+
+=back
+
+=head1 Testing
+
+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.
+
+[ List each test improvement as a =item entry ]
+
+=over 4
+
+=item *
+
+XXX
=back
=head1 Platform Support
+XXX Any changes to platform support should be listed in the sections below.
+
+[ Within the sections, list each platform as a =item entry with specific
+changes as paragraphs below it. ]
+
+=head2 New Platforms
+
+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.
+
+=over 4
+
+=item XXX-some-platform
+
+XXX
+
+=back
+
+=head2 Discontinued Platforms
+
+XXX List any platforms that this version of perl no longer compiles on.
+
+=over 4
+
+=item NeXTSTEP/OPENSTEP
+
+NeXTSTEP was proprietary OS bundled with NeXT's workstations in the early
+to mid 90's; OPENSTEP was an API specification that provided a NeXTSTEP-like
+environment on a non-NeXTSTEP system. Both are now long dead, so support
+for building Perl on them has been removed.
+
+=back
+
=head2 Platform-Specific Notes
+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.
+
=over 4
-=item VMS
-
-On VMS only, a check for glob metacharacters in a path returned by the
-L<C<glob()>|perlfunc/glob> operator has been replaced with a check for VMS
-wildcard characters. This saves a significant number of unnecessary
-L<C<lstat()>|perlfunc/lstat> calls such that some simple glob operations become
-60-80% faster.
-
-=item Win32
-
-The time taken to build perl on Windows has been reduced quite significantly
-(time savings in the region of 30-40% are typically seen) by reducing the
-number of, usually failing, I/O calls for each L<C<require()>|perlfunc/require>
-(for B<miniperl.exe> only).
-[L<perl #121119|https://rt.perl.org/Public/Bug/Display.html?id=121119>]
-
-About 15 minutes of idle sleeping was removed from running C<make test> due to
-a bug in which the timeout monitor used for tests could not be cancelled once
-the test completes, and the full timeout period elapsed before running the next
-test file.
-[L<perl #121395|https://rt.perl.org/Public/Bug/Display.html?id=121395>]
-
-On a perl built without psuedo-fork (psuedo-fork builds were not affected by
-this bug), killing a process tree with L<C<kill()>|perlfunc/kill> and a negative
-signal resulted in C<kill()> inverting the returned value. For example, if
-C<kill()> killed 1 process tree PID then it returned 0 instead of 1, and if
-C<kill()> was passed 2 invalid PIDs then it returned 2 instead of 0. This has
-probably been the case since the process tree kill feature was implemented on
-Win32. It has now been corrected to follow the documented behaviour.
-[L<perl #121230|https://rt.perl.org/Public/Bug/Display.html?id=121230>]
-
-When building a 64-bit perl, an uninitialized memory read in B<miniperl.exe>,
-used during the build process, could lead to a 4GB B<wperl.exe> being created.
-This has now been fixed. (Note that B<perl.exe> itself was unaffected, but
-obviously B<wperl.exe> would have been completely broken.)
-[L<perl #121471|https://rt.perl.org/Public/Bug/Display.html?id=121471>]
-
-Perl can now be built with B<gcc> version 4.8.1 from L<http://www.mingw.org>.
-This was previously broken due to an incorrect definition of DllMain() in one
-of perl's source files. Earlier B<gcc> versions were also affected when using
-version 4 of the w32api package. Versions of B<gcc> available from
-L<http://mingw-w64.sourceforge.net/> were not affected.
-[L<perl #121643|https://rt.perl.org/Public/Bug/Display.html?id=121643>]
-
-The test harness now has no failures when perl is built on a FAT drive with the
-Windows OS on an NTFS drive.
-[L<perl #21442|https://rt.perl.org/Public/Bug/Display.html?id=21442>]
+=item XXX-some-platform
+
+XXX
+
+=item OpenBSD
+
+On OpenBSD, Perl will now default to using the system C<malloc> due to the
+security features it provides. Perl's own malloc wrapper has been in use
+since v5.14 due to performance reasons, but the OpenBSD project believes
+the tradeoff is worth it and would prefer that users who need the speed
+specifically ask for it.
+
+L<[perl #122000]|https://rt.perl.org/Ticket/Display.html?id=122000>.
=back
=head1 Internal Changes
+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.
+
=over 4
=item *
-C<LC_NUMERIC> is now initialized to the C locale. This affects only XS
-modules, as the Perl core usages always make sure this locale category is
-correctly set for their purposes. XS code remains vulnerable to other code
-changing this category's locale. Further fixes are planned in Perl 5.22 to
-reduce these long-standing vulnerabilities.
-[L<perl #121317|https://rt.perl.org/Public/Bug/Display.html?id=121317>]
+The deprecated variable C<PL_sv_objcount> has been removed.
+
+=item *
+
+Perl now tries to keep the locale category C<LC_NUMERIC> set to "C"
+except around operations that need it to be set to the program's
+underlying locale. This protects the many XS modules that cannot cope
+with the decimal radix character not being a dot. Prior to this
+release, Perl initialized this category to "C", but a call to
+C<POSIX::setlocale()> would change it. Now such a call will change the
+underlying locale of the C<LC_NUMERIC> category for the program, but the
+locale exposed to XS code will remain "C". There is an API under
+development for those relatively few modules that need to use the
+underlying locale. This API will be nailed down during the course of
+developing v5.21. Send email to L<mailto:perl5-porters@perl.org> for
+guidance.
+
+=item *
+
+A new macro L<C<isUTF8_CHAR>|perlapi/isUTF8_CHAR> has been written which
+efficiently determines if the string given by its parameters begins
+with a well-formed UTF-8 encoded character.
=back
=head1 Selected Bug Fixes
+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>.
+
+[ List each fix as a =item entry ]
+
=over 4
=item *
-A regression involving the string value of L<C<$!>|perlvar/$!> introduced in
-Perl 5.19.2 has been reverted for Perl 5.20.
-[L<perl #119499|https://rt.perl.org/Public/Bug/Display.html?id=119499>]
+index() and rindex() no longer crash when used on strings over 2GB in
+size.
+L<[perl #121562]|https://rt.perl.org/Ticket/Display.html?id=121562>.
-This re-breaks the bugs it fixed,
-L<perl #112208|https://rt.perl.org/Public/Bug/Display.html?id=112208>, so an
-alternative fix is planned for Perl 5.22
+=item *
+
+A small previously intentional memory leak in PERL_SYS_INIT/PERL_SYS_INIT3 on
+Win32 builds was fixed. This might affect embedders who repeatedly create and
+destroy perl engines within the same process.
+
+=item *
+
+C<POSIX::localeconv()> now returns the data for the program's underlying
+locale even when called from outside the scope of S<C<use locale>>.
+
+=item *
+
+C<POSIX::localeconv()> now works properly on platforms which don't have
+C<LC_NUMERIC> and/or C<LC_MONETARY>, or for which Perl has been compiled
+to disregard either or both of these locale categories. In such
+circumstances, there are now no entries for the corresponding values in
+the hash returned by C<localeconv()>.
+
+=item *
+
+C<POSIX::localeconv()> now marks appropriately the values it returns as
+UTF-8 or not. Previously they were always returned as a bytes, even if
+they were supposed to be encoded as UTF-8.
=item *
-A regression was introduced in Perl 5.19.10 that under some circumstances
-caused C<//m> matches to falsely fail. Now fixed.
-[L<perl #121484|https://rt.perl.org/Public/Bug/Display.html?id=121484>]
+On Microsoft Windows, within the scope of C<S<use locale>>, the following
+POSIX character classes gave results for many locales that did not
+conform to the POSIX standard:
+C<[[:alnum:]]>,
+C<[[:alpha:]]>,
+C<[[:blank:]]>,
+C<[[:digit:]]>,
+C<[[:graph:]]>,
+C<[[:lower:]]>,
+C<[[:print:]]>,
+C<[[:punct:]]>,
+C<[[:upper:]]>,
+C<[[:word:]]>,
+and
+C<[[:xdigit:]]>.
+These are because the underlying Microsoft implementation does not
+follow the standard. Perl now takes special precautions to correct for
+this.
=item *
-A regression was introduced in the fix for
-L<perl #116192|https://rt.perl.org/Public/Bug/Display.html?id=116192> that
-prevented C<perl -I /somedir/> (with a trailing slash) from finding .pmc files.
-This has been fixed.
-[L<perl #121512|https://rt.perl.org/Public/Bug/Display.html?id=121512>].
+Many issues have been detected by L<Coverity|http://www.coverity.com/> and
+fixed.
=item *
-Fixed a bug detected by valgrind where sv_pvn_force_flags() would check SvPVX()
-even when the SV hadn't been upgraded to a SVt_PV. SvPVX() is only initialized
-when the SV is upgraded to a SVt_PV or higher.
-[L<perl #121366|https://rt.perl.org/Public/Bug/Display.html?id=121366>]
+system() and friends should now work properly on more Android builds.
+
+Due to an oversight, the value specified through -Dtargetsh to Configure
+would end up being ignored by some of the build process. This caused perls
+cross-compiled for Android to end up with defective versions of system(),
+exec() and backticks: the commands would end up looking for C</bin/sh>
+instead of C</system/bin/sh>, and so would fail for the vast majority
+of devices, leaving C<$!> as C<ENOENT>.
=item *
-Fixed a bug in L<C<caller()>|perlfunc/caller> introduced in Perl 5.18.0. In
-some circumstances when C<caller()> was called on an C<eval STRING> stack frame
-it would attempt to allocate the limit of the address space minus one, which
-would croak with an out of memory error, which would be caught by the eval. A
-change in Perl 5.19.1 which increased allocation sizes to allow COW to operate
-more often rounded that allocation size up and wrapped to a zero allocation
-size, resulting in a crash when the source string was copied over.
-[L<perl #120998|https://rt.perl.org/Public/Bug/Display.html?id=120998>].
+C<qr(...\(...\)...)>,
+C<qr[...\[...\]...]>,
+and
+C<qr{...\{...\}...}>
+now work. Previously it was impossible to escape these three
+left-characters with a backslash within a regular expression pattern
+where otherwise they would be considered metacharacters, and the pattern
+opening delimiter was the character, and the closing delimiter was its
+mirror character.
=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 *
-One test in F<ext/POSIX/t/time.t> is known to fail on Windows when building
-with certain versions of B<gcc> from L<http://www.mingw.org> due to a known bug
-in the MinGW build, which is logged here:
-L<http://sourceforge.net/p/mingw/bugs/2152/>.
+XXX
=back
+=head1 Errata From Previous Releases
+
+=over 4
+
+=item *
+
+XXX Add anything here that we forgot to add, or were mistaken about, in
+the perldelta of a previous release.
+
+=back
+
+=head1 Obituary
+
+XXX If any significant core contributor has died, we've added a short obituary
+here.
+
=head1 Acknowledgements
XXX Generate this with:
- perl Porting/acknowledgements.pl v5.19.10..HEAD
+ perl Porting/acknowledgements.pl v5.21.1..HEAD
=head1 Reporting Bugs
If you find what you think is a bug, you might check the articles recently
posted to the comp.lang.perl.misc newsgroup and the perl bug database at
-https://rt.perl.org/ . There may also be information at http://www.perl.org/ ,
-the Perl Home Page.
+https://rt.perl.org/ . There may also be information at
+http://www.perl.org/ , the Perl Home Page.
If you believe you have an unreported bug, please run the L<perlbug> program
included with your release. Be sure to trim your bug down to a tiny but
https://perl5.git.perl.org / perl5.git / blobdiff