perldelta for #113932 (UNIVERSAL::can)

[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 v5.19.2

=head1 DESCRIPTION

This document describes differences between the 5.19.1 release and the 5.19.2
release.

If you are upgrading from an earlier release such as 5.19.0, first read
L<perl5191delta>, which describes differences between 5.19.0 and 5.19.1.

=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.

=head2 More consistent prototype parsing

Multiple semicolons in subroutine prototypes have long been tolerated and
treated as a single semicolon.  There was one case where this did not
happen.  A subroutine whose prototype begins with "*" or ";*" can affect
whether a bareword is considered a method name or sub call.  This now
applies also to ";;;*".

Whitespace has long been allowed inside subroutine prototypes, so
C<sub( $ $ )> is equivalent to C<sub($$)>.  But it was stripped when the
subroutine was parse.  Hence, whitespace was I<not> allowed in prototypes
set by C<Scalar::Util::set_prototype>.  Now it is permitted, and the parser
no longer strips whitespace.  This means C<prototype &mysub> returns the
original prototype, whitespace and all.

=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.

[ List each incompatible change as a =head2 entry ]

=head1 Deprecations

XXX Any deprecated features, syntax, modules etc. should be listed here.

=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

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 *

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<ExtUtils::Embed> has been upgraded from version 1.30 to 1.31

The generated C<C> code now incorporates bug fixes present in
F<miniperlmain.c>, and has whitespace changes. It now uses
C<#include "..."> for header files instead of C<< #include <...> >>.
This should not make any difference, unless programs embedding C<libperl>
happen to have local and incompatible files named F<EXTERN.h>, F<XSUB.h> or
F<perl.h>, as these will now be picked up instead of the installed Perl
headers.

=item *

L<ExtUtils::Miniperl> has been upgraded and given a version of 1.
Previously it did not have a version number.

C<writemain()> now takes an optional first argument. A reference to a scalar
is treated as a filename to be opened and written to. Any other reference is
used as the filehandle to write to. Otherwise the existing default remains,
to write to C<STDOUT>.

C<writemain()> has been refactored to use functions from L<ExtUtils::Embed>,
reducing code size and duplication. The internal function C<canon()> has been
deleted.

=item *

L<POSIX> has been upgraded from version 1.33 to 1.34.

C<POSIX::AUTOLOAD> will no longer infinitely recurse if the shared
object fails to load.

=item *

L<Storable> has been upgraded from version 2.43 to 2.44.

Calling C<STORABLE_attach> hooks no longer leaks memory. [perl #118829]

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

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

=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<perlexperiment>

=over 4

=item *

Code in regular expressions, regular expression backtracking verbs,
and lvalue subroutines are no longer listed as experimental.  (This
also affects L<perlre> and L<perlsub>.)

=back

=head3 L<perlfunc>

=over 4

=item *

Since Perl v5.10, it has been possible for subroutines in @INC to return
a reference to a scalar holding initial source code to prepend to the file.
This is now documented.

=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 *

XXX L<message|perldiag/"message">

=back

=head3 New Warnings

=over 4

=item *

XXX L<message|perldiag/"message">

=back

=head2 Changes to Existing Diagnostics

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

=over 4

=item *

Under rare circumstances, one could get a "Can't coerce readonly REF to
string" instead of the customary "Modification of a read-only value".  This
alternate error message has been removed.

=item *

"Ambiguous use of * resolved as operator *": This and similar warnings
about "%" and "&" used to occur in some circumstances where there was no
operator of the type cited, so the warning was completely wrong.  This has
been fixed [perl #117535, #76910].

=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<installperl> and F<installman>'s option handling has been refactored to use
L<Getopt::Long>. Both are used by the F<Makefile> C<install> targets, and
are not installed, so these changes are only likely to affect custom
installation scripts.

=over 4

=item *

single letter options now also have long names

=item *

invalid options are now rejected

=item *

command line arguments that are not options are now rejected

=item *

Each now has a C<--help> option to display the usage message.

=back

The behaviour for all valid documented invocations is unchanged.

=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 MidnightBSD

C<objformat> was removed from version 0.4-RELEASE of MidnightBSD and had been
deprecated on earlier versions.  This caused the build environment to be
erroneously configured for C<a.out> rather than C<elf>.  This has been now
been corrected.

=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 *

The Makefile shortcut targets for many rarely (or never) used testing and
profiling targets have been removed, or merged into the only other Makefile
target that uses them.  Specifically, these targets are gone, along with
documentation that referenced them or explained how to use them:

    check.third check.utf16 check.utf8 coretest minitest.prep
    minitest.utf16 perl.config.dashg perl.config.dashpg
    perl.config.gcov perl.gcov perl.gprof perl.gprof.config
    perl.pixie perl.pixie.atom perl.pixie.config perl.pixie.irix
    perl.third perl.third.config perl.valgrind.config purecovperl
    pureperl quantperl test.deparse test.taintwarn test.third
    test.torture test.utf16 test.utf8 test_notty.deparse
    test_notty.third test_notty.valgrind test_prep.third
    test_prep.valgrind torturetest ucheck ucheck.third ucheck.utf16
    ucheck.valgrind utest utest.third utest.utf16 utest.valgrind

It's still possible to run the relevant commands by "hand" - no underlying
functionality has been removed.

=item *

It is now possible to keep Perl from initializing locale handling.
For the most part, Perl doesn't pay attention to locale.  (See
L<perllocale>.)  Nonetheless, until now, on startup, it has always
initialized locale handling to the system default, just in case the
program being executed ends up using locales.  (This is one of the first
things a locale-aware program should do, long before Perl knows if it
will actually be needed or not.)  This works well except when Perl is
embedded in another application which wants a locale that isn't the
system default.  Now, if the environment variable
C<PERL_SKIP_LOCALE_INIT> is set at the time Perl is started, this
initialization step is skipped.  Prior to this, on Windows platforms,
the only workaround for this deficiency was to use a hacked-up copy of
internal Perl code.  Applications that need to use older Perls can
discover if the embedded Perl they are using needs the workaround by
testing that the C preprocessor symbol C<HAS_SKIP_LOCALE_INIT> is not
defined.  (RT #38193)

=item *

C<BmRARE> and C<BmPREVIOUS> have been removed.  They were not used anywhere
and are not part of the API.  For XS modules, they are now #defined as 0.

=item *

C<sv_force_normal>, which usually croaks on read-only values, used to allow
read-only values to be modified at compile time.  This has been changed to
croak on read-only values regardless.  This change uncovered several core
bugs.

=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 *

There have been several fixes related to Perl's handling of locales.  perl
#38193 was described above in L</Internal Changes>.
Also fixed is #112208 in which the error string in C<$!> displayed as
garbage in many UTF-8 locales;
#118197, where the radix (decimal point) character had to be an ASCII
character (which doesn't work for some non-Western languages);
and #115808, in which C<POSIX::setlocale()> on failure returned an
C<undef> which didn't warn about not being defined even if those
warnings were enabled.

=item *

The dtrace sub-entry probe now works with lexical subs, instead of
crashing [perl #118305].

=item *

Compiling a C<split> operator whose third argument is a named constant
evaulating to 0 no longer causes the constant's value to change.

=item *

A named constant used as the second argument to C<index> no longer gets
coerced to a string if it is a reference, regular expression, dualvar, etc.

=item *

A named constant evaluating to the undefined value used as the second
argument to C<index> no longer produces "uninitialized" warnings at compile
time.  It will still produce them at run time.

=item *

When a scalar was returned from a subroutine in @INC, the referenced scalar
was magically converted into an IO thingy, possibly resulting in "Bizarre
copy" errors if that scalar continued to be used elsewhere.  Now Perl uses
an internal copy of the scalar instead.

=item *

Undefining an inlinable lexical subroutine (C<my sub foo() { 42 } undef
&foo>) would result in a crash if warnings were turned on.

=item *

Certain uses of the C<sort> operator are optimised to modify an array in
place, such as C<@a = sort @a>.  During the sorting, the array is made
read-only.  If a sort block should happen to die, then the array remained
read-only even outside the C<sort>.  This has been fixed.

=item *

C<$a> and C<$b> inside a sort block are aliased to the actual arguments to
C<sort>, so they can be modified through those two variables.  This did not
always work, e.g., for lvalue subs and C<$#ary>, and probably many other
operators.  It works now.

=item *

The arguments to C<sort> are now all in list context.  If the C<sort>
itself were called in void or scalar context, then I<some>, but not all, of
the arguments used to be in void or scalar context.

=item *

Subroutine prototypes with Unicode characters above U+00FF were getting
mangled during closure cloning.  This would happen with subroutines closing
over lexical variables declared outside, and with lexical subs.

=item *

In regular expressions containing multiple code blocks, the values of
C<$1>, C<$2>, etc., set by nested regular expression calls would leak from
one block to the next.  Now these variables always refer to the outer
regular expression at the start of an embedded block [perl #117917].

=item *

C<UNIVERSAL::can> now treats its first argument the same way that method
calls do: Typeglobs and glob references with non-empty IO slots are treated
as handles, and strings are treated as filehandles, rather than packages,
if a handle with that name exists [perl #113932].

=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 v5.19.1..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
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