two perldelta fixes

[perl5.git] / pod / perldelta.pod

=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 v5.15.0

=for comment
This has been completed up to 3ed94dc04.

=head1 DESCRIPTION

This document describes differences between the 5.15.0 release and
the 5.14.0 release.

If you are upgrading from an earlier release such as 5.YYY.YYY, first read
L<perl5YYYdelta>, which describes differences between 5.ZZZ.ZZZ and
5.YYY.YYY.

Some of the changes have been included in Perl 5.14.1.  These are
indicated with a "(5.14.1)" marker.

XXX compare this perldelta to 5.14.1 and double check the notation

=head1 Notice

XXX Any important notices here

=head1 Core Enhancements

XXX New core language features go here. Summarise 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 C<CORE::> works on all keywords

The C<CORE::> prefix can now be used on keywords enabled by
L<feature.pm|feature>, even outside the scope of C<use feature>.

=head2 C<continue> no longer requires the "switch" feature

The C<continue> keyword has two meanings.  It can introduce a C<continue>
block after a loop, or it can exit the current C<when> block.  Up till now,
the latter meaning was only valid with the "switch" feature enabled, and
was a syntax error otherwise.  Since the main purpose of feature.pm is to
avoid conflicts with user-defined subroutines, there is no reason for
C<continue> to depend on it.

=head2 C<$$> can be assigned to

C<$$> was made read-only in Perl 5.8.0.  But only sometimes: C<local $$>
would make it writable again.  Some CPAN modules were using C<local $$> or
XS code to bypass the read-only check, so there is no reason to keep C<$$>
read-only.  (This change also allowed a bug to be fixed while maintaining
backward compatibility.)

=head2 Features inside the debugger

The current Perl's feature bundle is now enabled for commands entered in
the interactive debugger.

=head2 C<\N{...}> can now have Unicode loose name matching

This is described in the C<charnames> item in
L</Updated Modules and Pragmata> below.

=head2 Breakpoints with file names

The debugger's "b" command for setting breakpoints now allows a line number
to be prefixed with a file name.  See
L<perldebug/"b [file]:[line] [condition]">.

=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 Tying scalars that hold typeglobs

Attempting to tie a scalar after a typeglob was assigned to it would
instead tie the handle in the typeglob's IO slot.  This meant that it was
impossible to tie the scalar itself.  Similar problems affected C<tied> and
C<untie>: C<tied $scalar> would return false on a tied scalar if the last
thing returned was a typeglob, and C<untie $scalar> on such a tied scalar
would do nothing.

We fixed this problem before Perl 5.14.0, but it caused problems with some
CPAN modules, so we put in a deprecation cycle instead.

Now the deprecation has been removed and this bug has been fixed.  So
C<tie $scalar> will always tie the scalar, not the handle it holds.  To tie
the handle, use C<tie *$scalar> (with an explicit asterisk).  The same
applies to C<tied *$scalar> and C<untie *$scalar>.

=head2 IPC::Open3 no longer provides C<xfork()>, C<xclose_on_exec()>
and C<xpipe_anon()>

All three functions were private, undocumented and unexported.  They do
not appear to be used by any code on CPAN.  Two have been inlined and one
deleted entirely.

=head2 C<$$> no longer caches PID

Previously, if one embeds Perl or uses XS and calls fork(3) from C, Perls
notion of C<$$> could go out of sync with what getpid() returns. By always
fetching the value of C<$$> via getpid(), this potential bug is eliminated.
Code that depends on the caching behavior will break.  As described in
L</Core Enhancements>, C<$$> is now writable, but it will be reset during a
fork.

=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<constant> has been updated from version 1.21 to 1.22.

=item *

L<Archive::Extract> has been upgraded from version 0.48 to version 0.52

Includes a fix for FreeBSD to only use C<unzip> if it is located in
C</usr/local/bin>, as FreeBSD 9.0 will ship with a limited C<unzip> in
C</usr/bin>.

=item *

L<Attribute::Handlers> updated from version 0.88 to 0.91

=item *

L<B> has been upgraded from version 1.29 to version 1.30.

=item *

L<B::Deparse> has been upgraded from version 1.03 to 1.05.

It addresses two regressions in Perl 5.14.0:

=over

=item *

Deparsing of the C<glob> operator and its diamond (C<< <> >>) form now
works again [RT #90898] (5.14.1).

=item *

The presence of subroutines named C<::::> or C<::::::> no longer causes
B::Deparse to hang (5.14.1).

=back

Plus a few other bugs:

=over

=item *

Deparsing of handle C<keys>, C<each> and C<value> with a scalar argument
now works [RT #91008].

=item *

C<readpipe> followed by a complex expression (as opposed to a simple scalar
variable) now works.

=item *

It now puts C<CORE::> in front of overridable core keywords if they
conflict with user-defined subroutines.

=item *

Deparsing assignment to an lvalue method specified as a variable
(C<< $obj->$method = ... >>) used not to work [RT #62498].

=back

=item *

L<CGI> has been upgraded from version 3.52 to version 3.54

The DELETE HTTP verb is now supported.

=item *

L<Compress::Zlib> has been upgraded from version 2.033 to version 2.035

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.033 to version 2.035

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.033 to version 2.035

=item *

L<CPAN::Meta> has been upgraded from version 2.110440 to version 2.110930

=item *

L<CPANPLUS> has been upgraded from version 0.9103 to version 0.9105

Now understands specifying modules to install in the format 'Module/Type.pm'

=item *

L<CPANPLUS::Dist::Build> has been upgraded from version 0.54 to version 0.56

=item *

L<Data::Dumper> has been upgraded from version 2.128 to 2.131.

=item *

L<DB_File> has been upgraded from version 1.821 to version 1.822

Warnings are now in sync with perl's

=item *

L<Digest::SHA> has been upgraded from version 5.61 to version 5.62

No longer loads L<MIME::Base64> as this was unnecessary.

=item *

L<Devel::Peek> has been upgraded from version 1.07 to 1.08.

Its C<fill_mstats> function no longer refuses to write to copy-on-write
scalars.

=item *

L<Encode> has been upgraded from version 2.42 to version 2.43

Missing aliases added, a deep recursion error fixed and various
documentation updates.

=item *

L<ExtUtils::CBuilder> updated from version 0.280203 to 0.280204.  The new version
append CFLAGS and LDFLAGS to their Config.pm counterparts.

=item *

L<Filter::Util::Call> has been upgraded from version 1.08 to version 1.39

C<decrypt> fixed to work with v5.14.0

=item *

L<Filter::Simple> updated from version 0.85 to 0.87

=item *

L<FindBin> updated from version 1.50 to 1.51.

It no longer returns a wrong result if a script of the same name as the
current one exists in the path and is executable.

=item *

L<JSON::PP> has been upgraded from version 2.27105 to version 2.27200

Fixed C<incr_parse> decoding string more correctly.

=item *

L<I18N::LangTags> has been upgraded from version 0.35_01 to version 0.36.

Fix broken URLs for RFCs.

=item *

L<IPC::Open3> has been upgraded from version 1.10 to version 1.11.

=over 4

=item *

Fixes a bug which prevented use of C<open3> on Windows when C<*STDIN>,
C<*STDOUT> or C<*STDERR> had been localized.

=item *

Fixes a bug which prevented duplicating numeric file descriptors on Windows.

=back

=item *

L<Math::BigFloat> has been upgraded from version 1.993 to 1.994.

The C<numify> method has been corrected to return a normalised Perl number
(the result of C<0 + $thing>), instead of a string [rt.cpan.org #66732].

=item *

L<Math::BigInt> has been upgraded from version 1.994 to 1.995.

It provides a new C<bsgn> method that complements the C<babs> method.

It fixes the internal C<objectify> function's handling of "foreign objects"
so they are converted to the appropriate class (Math::BigInt or
Math::BigFloat).

=item *

L<Math::Complex> has been upgraded from version 1.56 to version 1.57.

Correct copy constructor usage.
Fix polarwise formatting with numeric format specifier.
More stable C<great_circle_direction> algorithm.

=item *

L<Module::CoreList> has been upgraded from version 2.49 to 2.50.

Updated for v5.12.4.

=item *

L<mro> has been updated to remove two broken URLs in the documentation.

=item *

L<Object::Accessor> has been upgraded from version 0.38 to version 0.42

Eliminated use of C<exists> on array elements which has been deprecated.

=item *

L<ODBM_File> has been upgraded from version 1.10 to version 1.11.

The XS code is now compiled with C<PERL_NO_GET_CONTEXT>, which will aid
performance under ithreads.

=item *

L<PerlIO::encoding> has been upgraded from version 0.14 to 0.15

=item *

L<PerlIO::scalar> has been upgraded from version 0.11 to 0.12.

It fixes a problem with C<< open my $fh, ">", \$scalar >> not working if
C<$scalar> is a copy-on-write scalar.

It also fixes a hang that occurs with C<readline> or C<< <$fh> >> if a
typeglob has been assigned to $scalar [RT #92258].

=item *

L<Pod::Perldoc> has been upgraded from version 3.15_03 to 3.15_05.

It corrects the search paths on VMS [RT #90640].

=item *

L<Storable> has been upgraded from version 2.27 to version 2.28.

It no longer turns copy-on-write scalars into read-only scalars when
freezing and thawing.

=item *

L<Sys::Syslog> has been upgraded from version 0.27 to version 0.29

Large number of Request Tickets resolved.

=item *

L<Time::HiRes> has been upgraded from version 1.9721_01 to version 1.9722.

Portability fix, and avoiding some compiler warnings.

=item *

L<Unicode::Collate> has been upgraded from version 0.73 to version 0.76

Updated to CLDR 1.9.1

=item *

L<Unicode::Normalize> has been upgraded from version 1.10 to version 1.12

Fixes for the removal of F<unicore/CompositionExclusions.txt> from core.

=item *

L<XSLoader> has been upgraded from version 0.13 to version 0.15

Integrated changes from bleadperl

=item *

L<charnames> can now be invoked with a new option, C<:loose>,
which is like the existing C<:full> option, but enables Unicode loose
name matching.  This means that instead of
having to get the name of the code point or sequence you want exactly right,
you can fudge things somewhat.  This is especially useful when
you don't remember if the official Unicode name uses hyphens or
blanks between words.  Details are in L<charnames/LOOSE MATCHES>.

XXX

=back

=head2 Removed Modules and Pragmata

As promised in Perl 5.14.0's release notes, the following modules have
been removed from the core distribution, and if needed should be installed
from CPAN instead.

=over

=item *

L<Devel::DProf> has been removed from the Perl core.  Prior version was 20110228.00.

=item *

L<Shell> has been removed from the Perl core.  Prior version was 0.72_01.

=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<perlfork>

=over

=item *

Added portability caveats related to using C<kill> on forked process.

=back

=head3 L<perlfunc>

=over

=item *

C<given>, C<when> and C<default> are now listed in L<perlfunc> (5.14.1).

=item *

The examples for the C<select> function no longer use strings for file
handles.

=back

=head3 L<perlguts>

=over

=item *

Some of the function descriptions in L<perlguts> were confusing, as it was
not clear whether they referred to the function above or below the
description.  This has been clarified [RT #91790].

=back

=head3 L<perllol>

=over

=item *

L<perllol> has been expanded with examples using the new C<push $scalar>
syntax introduced in Perl 5.14.0 (5.14.1).

=back

=head3 L<perlmod>

=over

=item *

L<perlmod> now states explicitly that some types of explicit symbol table
manipulation are not supported.  This codifies what was effectively already
the case [RT #78074].

=back

=head3 L<perlop>

=over 4

=item *

The explanation of bitwise operators has been expanded to explain how they
work on Unicode strings (5.14.1).

=item *

The section on the triple-dot or yada-yada operator has been moved up, as
it used to separate two closely related sections about the comma operator
(5.14.1).

=item *

More examples for C<m//g> have been added (5.14.1).

=item *

The C<<< <<\FOO >>> here-doc syntax has been documented (5.14.1).

=back

=head3 L<perlpodstyle>

=over 4

=item *

The tips on which formatting codes to use have been corrected and greatly
expanded.

=item *

There are now a couple of example one-liners for previewing POD files after
they have been edited.

=back

=head3 L<perlre>

=over

=item *

The C<(*COMMIT)> directive is now listed in the right section
(L<Verbs without an argument|perlre/Verbs without an argument>).

=back

=head3 L<perlrun>

=over

=item *

L<perlrun> has undergone a significant clean-up.  Most notably, the
B<-0x...> form of the B<-0> flag has been clarified, and the final section
on environment variables has been corrected and expanded (5.14.1).

=back

=head3 L<perlvar>

=over

=item *

The documentation for L<$!|perlvar/$!> has been corrected and clarified.
It used to state that $! could be C<undef>, which is not the case.  It was
also unclear as to whether system calls set C's C<errno> or Perl's C<$!>
[RT #91614].

=back

=head3 L<POSIX>

=over

=item *

The invocation documentation for C<WIFEXITED>, C<WEXITSTATUS>,
C<WIFSIGNALED>, C<WTERMSIG>, C<WIFSTOPPED>, and C<WSTOPSIG> has been
corrected (5.14.1).

=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.

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

=head2 New Diagnostics

XXX Newly added diagnostic messages go here

=head3 New Warnings

=over 4

=item L<Useless assignment to a temporary|perldiag/"Useless assignment to a temporary">

Assigning to a temporary returned from an XS lvalue subroutine now produces a
warning [RT #31946].

=back

=head2 Changes to Existing Diagnostics

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

=over 4

=item *

XXX

=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 *

F<regexp.h> has been modified for compatibility with GCC's B<-Werror>
option, as used by some projects that include perl's header files (5.14.1).

=item *

USE_LOCALE{,_COLLATE,_CTYPE,_NUMERIC} have been added the output of perl -V
as they have affect the behaviour of the interpreter binary (albeit only
in a small area).

=item *

The code and tests for L<IPC::Open2> have been moved from F<ext/IPC-Open2>
into F<ext/IPC-Open3>, as C<IPC::Open2::open2()> is implemented as a thin
wrapper around C<IPC::Open3::_open3()>, and hence is very tightly coupled to
it.

=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 summarising, 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 GNU/Hurd

=over

=item *

No longer overrides possible extra $ccflags values given to Configure
on GNU/Hurd.  C.f. Bug-Debian: http://bugs.debian.org/587901

=back

=item Mac OS X

Clarified Apple Developer Tools requirements in F<README.macosx>

=item MSWin32

Supplied F<makefile.mk> patched to support gcc-4.x.x and README.win32
updated accordingly. [RT #91354]

=item Solaris

Updated the list of required packages for building perl to reflect Solaris 9
and 10 in README.solaris [RT #90850]

=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.

=head3 Ubuntu Linux

=over 4

=item *

The L<ODBM_File> installation process has been updated with the new library
paths on Ubuntu natty [RT #90106].

=item *

I<h2ph> now gets the include paths from gcc correctly.  This stopped
working when Ubuntu switched to a "multiarch" setup [RT #90122].

=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 *

When empting a hash of its elements (e.g. via undef(%h), or %h=()), HvARRAY
field is no longer temporarily zeroed.  Any destructors called on the freed
elements see the remaining elements. Thus, %h=() becomes more like C<delete
$h{$_} for keys %h>.

=item *

The compiled representation of formats is now stored via the C<mg_ptr> of
their C<PERL_MAGIC_fm>. Previously it was stored in the string buffer,
beyond C<SvLEN()>, the regular end of the string. C<SvCOMPILED()> and
C<SvCOMPILED_{on,off}()> now exist solely for compatibility for XS code.
The first is always 0, the other two now no-ops.

=item *

Boyer-Moore compiled scalars are now PVMGs, and the Boyer-Moore tables are now
stored via the mg_ptr of their C<PERL_MAGIC_bm>. Previously they were PVGVs,
with the tables stored in the string buffer, beyond C<SvLEN()>. This eliminates
the last place where the core stores data beyond C<SvLEN()>.

=item *

Simplified logic in C<Perl_sv_magic()> introduces a small change of
behaviour for error cases involving unknown magic types. Previously, if
C<Perl_sv_magic()> was passed a magic type unknown to it, it would

=over

=item 1.

Croak "Modification of a read-only value attempted" if read only

=item 2.

Return without error if the SV happened to already have this magic

=item 3.

otherwise croak "Don't know how to handle magic of type \\%o"

=back

Now it will always croak "Don't know how to handle magic of type \\%o", even
on read only values, or SVs which already have the unknown magic type.

=back

=head1 Selected Bug Fixes

XXX Important bug fixes in the core language are summarised here.
Bug fixes in files in F<ext/> and F<lib/> are best summarised in
L</Modules and Pragmata>.

[ List each fix as a =item entry ]

=head2 Regular expressions and character classes

=over 4

=item *

The new (in 5.14.0) regular expression modifier C</a> when repeated like
C</aa> forbids the characters outside the ASCII range that match
characters inside that range from matching under C</i>.  This did not
work under some circumstances, all involving alternation, such as:

 "\N{KELVIN SIGN}" =~ /k|foo/iaa;

succeeded inappropriately.  This is now fixed.

=item *

5.14.0 introduced some memory leaks in regular expression character
classes such as C<[\w\s]>, which have now been fixed

=item *

An edge case in regular expression matching could potentially loop.
This happened only under C</i> in bracketed character classes that have
characters with multi-character folds, and the target string to match
against includes the first portion of the fold, followed by another
character that has a multi-character fold that begins with the remaining
portion of the fold, plus some more.

 "s\N{U+DF}" =~ /[\x{DF}foo]/i

is one such case.  C<\xDF> folds to C<"ss">

=item *

A few characters in regular expression pattern matches did not
match correctly in some circumstances, all involving C</i>.  The
affected characters are:
COMBINING GREEK YPOGEGRAMMENI,
GREEK CAPITAL LETTER IOTA,
GREEK CAPITAL LETTER UPSILON,
GREEK PROSGEGRAMMENI,
GREEK SMALL LETTER IOTA WITH DIALYTIKA AND OXIA,
GREEK SMALL LETTER IOTA WITH DIALYTIKA AND TONOS,
GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND OXIA,
GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND TONOS,
LATIN SMALL LETTER LONG S,
LATIN SMALL LIGATURE LONG S T,
and
LATIN SMALL LIGATURE ST.

=item *

Fixed memory leak regression in regular expression compilation
under threading

=back

=head2 Formats

=over

=item *

A number of edge cases have been fixed with formats and C<formline>;
in particular, where the format itself is potentially variable (such as
with ties and overloading), and where the format and data differ in their
encoding. In both these cases, it used to possible for the output to be
corrupted [RT #91032].

=item *

C<formline> no longer converts its argument into a string in-place.  So
passing a reference to C<formline> no longer destroys the reference
[RT #79532].

=back

=head2 Copy-on-write scalars

Copy-on-write scalars were introduced in 5.8.0, but most Perl code
did not encounter them (they were used mostly internally).  Perl
5.10.0 extended them, such that assigning C<__PACKAGE__> or a
hash key to a scalar would make it copy-on-write.  Several parts
of Perl were not updated to account for them, but have now been fixed.

=over

=item *

C<utf8::decode> had a nasty bug that would modify copy-on-write scalars'
string buffers in place (i.e., skipping the copy).  This could result in
hashes having two elements with the same key [RT #91834].

=item *

Lvalue subroutines were not allowing COW scalars to be returned.  This was
fixed for lvalue scalar context in Perl 5.12.3 and 5.14.0, but list context
was not fixed until this release.

=item *

Elements of restricted hashes (see the L<fields> pragma) containing
copy-on-write values couldn't be deleted, nor could such hashes be cleared
(C<%hash = ()>).

=item *

Localising a tied variable used to make it read-only if it contained a
copy-on-write string.

=item *

L<Storable>, L<Devel::Peek> and L<PerlIO::scalar> had similar problems.
See L</Updated Modules and Pragmata>, above.

=back

=head2 lvalue subroutines

There have been various fixes to lvalue subroutines.

=over

=item *

Explicit return now returns the actual argument passed to return, instead
of copying it [RT #72724] [RT #72706].

B<Note:> There are still some discrepancies between explicit and implicit
return, which will hopefully be resolved soon.  So the exact behaviour is
not set in stone yet.

=item *

Lvalue subroutines used to enforce lvalue syntax (i.e., whatever can go on
the left-hand side of C<=>) for the last statement and the arguments to
return.  Since lvalue subroutines are not always called in lvalue context,
this restriction has been lifted.

=item *

Lvalue subroutines are less restrictive as to what values can be returned.
It used to croak on values returned by C<shift> and C<delete> and from
other subroutines, but no longer does so [RT #71172].

=item *

Empty lvalue subroutines (C<sub :lvalue {}>) used to return C<@_> in list
context.  In fact, all subroutines used to, but regular subs were fixed in
Perl 5.8.2.  Now lvalue subroutines have been likewise fixed.

=item *

Lvalue subroutines used to copy their return values in rvalue context.  Not
only was this a waste of CPU cycles, but it also caused bugs.  A C<($)>
prototype would cause an lvalue sub to copy its return value [RT #51408],
and C<while(lvalue_sub() =~ m/.../g) { ... }> would loop endlessly
[RT #78680].

=item *

Autovivification now works on values returned from lvalue subroutines
[RT #7946].

=item *

When called in pass-by-reference context (e.g., subroutine arguments or a list
passed to C<for>), an lvalue subroutine returning arrays or hashes used to bind
the arrays (or hashes) to scalar variables--something that is not supposed to
happen.  This could result in "Bizarre copy of ARRAY" errors or C<print>
ignoring its arguments.  It also made nonsensical code like C<@{\$_}> "work".
This was fixed in 5.14.0 if an array were the first thing returned from the
subroutine (but not for C<$scalar, @array> or hashes being returned).  Now a
more general fix has been applied [RT #23790].

=item *

When called in pass-by-reference context, lvalue subroutines used to copy
any read-only value that were returned.  E.g., C< sub :lvalue { $] } >
would not return C<$]>, but a copy of it.

=item *

Assignment to C<keys> returned from an lvalue sub used not to work, but now
it does.

=item *

Applying the C<:lvalue> attribute to an XSUB or to an aliased subroutine
stub with C<< sub foo :lvalue; >> syntax stopped working in Perl 5.12.
This has been fixed.

=back

=head2 Fixes related to hashes

=over

=item *

A bug has been fixed that would cause a "Use of freed value in iteration"
error if the next two hash elements that would be iterated over are
deleted [RT #85026].

=item *

Freeing deeply nested hashes no longer crashes [RT #44225].

=item *

Deleting the current hash iterator (the hash element that would be returend
by the next call to C<each>) in void context used not to free it.  The hash
would continue to reference it until the next iteration.  This has been
fixed [RT #85026].

=back

=head2 Other notable fixes

=over

=item *

Passing the same constant subroutine to both C<index> and C<formline> no
longer causes one or the other to fail [RT #89218].

=item *

List assignment to lexical variables declared with attributes in the same
statement (C<my ($x,@y) : blimp = (72,94)>) stopped working in Perl 5.8.0.
It has now been fixed.

=item *

Perl 5.10.0 introduced some faulty logic that made "U*" in the middle of
a pack template equivalent to "U0" if the input string was empty.  This has
been fixed [RT #90160].

=item *

Destructors on objects were not called during global destruction on objects
that were not referenced by any scalars.  This could happen if an array
element were blessed (e.g., C<bless \$a[0]>) or if a closure referenced a
blessed variable (C<bless \my @a; sub foo { @a }>).

Now there is an extra pass during global destruction to fire destructors on
any objects that might be left after the usual passes that check for
objects referenced by scalars [RT #36347].

This bug fix was added in Perl 5.13.9, but caused problems with some CPAN
modules that were relying on the bug.  Since it was so close to Perl
5.14.0, the fix was reverted in 5.13.10, to allow more time for the modules
to adapt.  Hopefully they will be fixed soon (see L</Known Problems>,
below).

=item *

C<given> was not calling set-magic on the implicit lexical C<$_> that it
uses.  This meant, for example, that C<pos> would be remembered from one
execution of the same C<given> block to the next, even if the input were a
different variable [RT #84526].

=item *

The "R" command for restarting a debugger session has been fixed to work on
Windows, or any other system lacking a C<POSIX::_SC_OPEN_MAX> constant
[RT #87740].

=item *

Fixed a case where it was possible that a freed buffer may have been read
from when parsing a here document [RT #90128].

=item *

The C<study> function could become confused if fed a string longer than
2**31 characters.  Now it simply skips such strings.

=item *

C<each(I<ARRAY>)> is now wrapped in C<defined(...)>, like C<each(I<HASH>)>,
inside a C<while> condition [RT #90888].

=item *

In @INC filters (subroutines returned by subroutines in @INC), $_ used to
misbehave: If returned from a subroutine, it would not be copied, but the
variable itself would be returned; and freeing $_ (e.g., with C<undef *_>)
would cause perl to crash.  This has been fixed [RT #91880].

=item *

An ASCII single quote (') in a symbol name is meant to be equivalent to a
double colon (::) except at the end of the name.  It was not equivalent if
followed by a null character, but now it is [RT #88138].

=item *

The abbreviations for four C1 control characters
C<MW>
C<PM>,
C<RI>,
and
C<ST>
were previously unrecognized by C<\N{}>,
vianame(), and string_vianame().

=item *

Some cases of threads crashing due to memory allocation during cloning have
been fixed [RT #90006].

=item *

Attempting to C<goto> out of a tied handle method used to cause memory
corruption or crashes.  Now it produces an error message instead
[RT #8611].

=item *

Perl skips copying values returned from a subroutine if it thinks the value
is not in use elsewhere.  Due to faulty logic, this would happen with the
result of C<delete>, C<shift> or C<splice>, even if the result was
referenced elsewhere.  So C<< \sub { delete $_[0] }->($x) >> would return a
reference to C<$x>.  This has been fixed [RT #91844].

=back

=head2 Additional fixes by ticket number

XXX Prefix these with "\n=item *\n" once the list is final

Fixed RT #88822: Test failure t/re_fold_grind.t with bleadperl
Fixed RT #89896: Locale::Maketext test failure

XXX Comments from FC: I do not think these two are necessary.

=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, unless
they were specific to a particular platform (see below).

This is a list of some significant unfixed bugs, which are regressions
from either 5.XXX.XXX or 5.XXX.XXX.

[ List each fix as a =item entry ]

=over 4

=item *

The fix for RT #36347 causes test failures for C<Gtk2> and C<Tk> on some
systems [RT #82542].

=item *

The changes to C<tie> cause test failures for the C<JS> module.

=back

=head1 Obituary

XXX If any significant core contributor has died, we've added a short obituary
here.

=head1 Acknowledgements

XXX The list of people to thank goes here.

=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 are 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