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=encoding utf8

=head1 NAME

[ 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 v5.17.3

=head1 DESCRIPTION

This document describes differences between the 5.17.2 release and the 5.17.3
release.

If you are upgrading from an earlier release such as 5.17.1, first read
L<perl5172delta>, which describes differences between 5.17.1 and 5.17.2.

=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 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.

=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

[ List each incompatible change as a =head2 entry ]

=head2 C<$ENV{foo} = undef> deletes value from environ, like C<delete $ENV{foo}>

This facilitates use of C<local()> with C<%ENV> entries.  In previous
versions of Perl, C<undef> was converted to the empty string.

=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 a 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<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>).

=head1 Deprecations

XXX Any deprecated features, syntax, modules etc. should be listed here.  In
particular, deprecated modules should be listed here even if they are listed as
an updated module in the L</Modules and Pragmata> section.

[ List each 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 *

XXX

=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>, 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.

[ Within each section, list entries as a =item entry ]

=head2 New Modules and Pragmata

=over 4

=item *

XXX

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<B> has been upgraded from version 1.36 to 1.37.  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.

=item *

L<B::Concise> has been upgraded from version 0.91 to 0.92.  The C<-nobanner>
option has been fixed, and C<format>s can now be dumped.

=item *

L<B::Deparse> has been upgraded from version 1.15 to 1.16.  It now deparses
loop controls with the correct precedence, and multiple statements in a
C<format> line are also now deparsed correctly.

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.05201 to 2.055.  The
misuse of Perl's "magic" API has been fixed.

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.05401 to 2.056.  The
misuse of Perl's "magic" API has been fixed.

=item *

L<Compress::Zlib> has been upgraded from version 2.052 to 2.055.
C<compress()>, C<uncompress()>, C<memGzip()> and C<memGunzip()> have been
speeded up by making parameter validation more efficient.

=item *

L<Data::Dumper> has been upgraded from version 2.135_06 to 2.135_07.  It has
been optimized to only build a seen-scalar hash as necessary, thereby speeding
up serialization drastically.

=item *

L<Devel::Peek> has been upgraded from version 1.08 to 1.09.  The only change has
been to the test script, to account for changes to some flags in perl's
internals.

=item *

L<Encode> has been upgraded from version 2.44 to 2.46.  The Mac alias x-mac-ce
has been added, and various bugs have been fixed in Encode::Unicode and
Encode::UTF7.

=item *

L<Module::Build> has been upgraded from version 0.40 to 0.4002.  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 from version 2.69 to 2.70.  Version
information is now stored as a delta, which greatly reduces the size of the
F<CoreList.pm> file.

=item *

L<Module::Load::Conditional> has been upgraded from version 0.50 to 0.54.
Various enhancements include the new use of Module::Metadata.

=item *

L<Module::Metadata> has been upgraded from version 1.000009 to 1.000010.  The
creation of a Module::Metadata object for a typical module file has been sped up
by about 40%.

=item *

L<Pod::Simple> has been upgraded from version 3.20 to 3.23.  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 from version 0.21 to 0.22.  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>.

=item *

L<Storable> has been upgraded from version 2.37 to 2.38.  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.

=item *

L<Time::Local> has been upgraded from version 1.2000 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 from version 0.44 to 0.45.  This has been
modified slightly for reasons of perl internal use only.

=item *

L<Win32CORE> has been upgraded from version 0.02 to 0.03.  The use of
PERL_NO_GET_CONTEXT here has resulted in smaller machine code.

=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

=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>, 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 never
documented until now.

=back

=head1 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>.

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<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].

=back

=head3 New Warnings

=over 4

=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.

=back

=head2 Changes to Existing Diagnostics

XXX Changes (i.e. rewording) of diagnostic messages go here

=over 4

=item *

XXX Describe change here

=back

=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>.

[ 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. ]

=head3 L<XXX>

=over 4

=item *

XXX

=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 *

XXX

=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 XXX-some-platform

XXX

=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 XXX-some-platform

XXX

=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.

[ List each change as a =item entry ]

=over 4

=item *

XXX

=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 *

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 5.16.0.

=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
5.16.0.  This has been fixed [perl #114340].

=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 *

XXX

=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 v5.17.2..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
http://rt.perl.org/perlbug/ .  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
sufficient test case.  Your bug report, along with the output of C<perl -V>,
will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

If the bug you are reporting has security implications, which make it
inappropriate to send to a publicly archived mailing list, then please send it
to perl5-security-report@perl.org.  This points to a closed subscription
unarchived mailing list, which includes all the core committers, who will be
able to help assess the impact of issues, figure out a resolution, and help
co-ordinate the release of patches to mitigate or fix the problem across all
platforms on which Perl is supported.  Please only use this address for
security issues in the Perl core, not for modules independently distributed on
CPAN.

=head1 SEE ALSO

The F<Changes> file for an explanation of how to view exhaustive details on
what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut