[ List each enhancement as a =head2 entry ]
+=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
If any exist, they are bugs, and we request that you submit a
report. See L</Reporting Bugs> below.
+=head2 S<C<"use encoding">> now is a fatal error
+
+The C<encoding> pragma has been deprecated since v5.18, and its use now
+is a fatal error.
+
+=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 MAD build option has been removed
+
+MAD = Misc Attribute Decoration; 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.
+
=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.
=item *
-XXX
+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
=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.
=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
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
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.
+
=back
=head2 Removed Modules and Pragmata
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.
-=head3 L<XXX>
+=head3 L<perlfunc>
+
+=over 4
+
+=item *
+
+C<-l> now notes that it will return false if symlinks aren't supported by the
+file system.
+
+L<[perl #121523]|https://rt.perl.org/Ticket/Display.html?id=121523>
+
+=item *
+
+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>.
+
+L<[perl #122046]|https://rt.perl.org/Ticket/Display.html?id=122046>
+
+=back
+
+=head3 L<perlapi>
=over 4
=item *
-XXX Description of the change here
+C<sv_usepvn_flags> - Fix documentation to mention the use of C<NewX> instead of
+C<malloc>.
+
+L<[perl #121869]|https://rt.perl.org/Ticket/Display.html?id=121869>
+
+=item *
+
+Clarify where C<NUL> may be embedded or is required to terminate a string.
+
+=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 *
+
+Alphabetical sorting of entries is now handled by the POD generator to make
+entries easier to find when scanning.
+
+=back
+
+=head3 L<perlhacktips>
+
+=over 4
+
+=item *
+
+Updated documentation for the C<test.valgrind> C<make> target.
+
+L<[perl #121431]|https://rt.perl.org/Ticket/Display.html?id=121431>
+
+=back
+
+=head3 L<perlre>
+
+=over 4
+
+=item *
+
+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>
+
+=over 4
+
+=item *
+
+The documentation includes many clarifications and fixes.
=back
=item *
-XXX L<message|perldiag/"message">
+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";
=back
=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
=head1 Utility Changes
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>.
+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 L<XXX>
+=head2 F<x2p/>
=over 4
=item *
-XXX
+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
=item *
-XXX
+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>
=back
=over 4
-=item XXX-some-platform
+=item NeXTSTEP/OPENSTEP
-XXX
+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
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
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
size.
L<[perl #121562]|https://rt.perl.org/Ticket/Display.html?id=121562>.
+=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 *
+
+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 *
+
+Many issues have been detected by L<Coverity|http://www.coverity.com/> and
+fixed.
+
+=item *
+
+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 *
+
+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
https://perl5.git.perl.org / perl5.git / blobdiff