path: root/pod/perldelta.pod

=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.13.5

=head1 DESCRIPTION

This document describes differences between the 5.13.4 release and
the 5.13.5 release.

If you are upgrading from an earlier release such as 5.13.3, first read
L<perl5134delta>, which describes differences between 5.13.3 and
5.13.4.

=head1 Core Enhancements

=head2 Adjacent pairs of nextstate opcodes are now optimized away

Previously, in code such as

    use constant DEBUG => 0;

    sub GAK {
        warn if DEBUG;
        print "stuff\n";
    }

the ops for C<warn if DEBUG;> would be folded to a C<null> op (C<ex-const>), but
the C<nextstate> op would remain, resulting in a runtime op dispatch of
C<nextstate>, C<nextstate>, ...

The execution of a sequence of C<nextstate> ops is indistinguishable from just
the last C<nextstate> op so the peephole optimizer now eliminates the first of
a pair of C<nextstate> ops, except where the first carries a label, since labels
must not be eliminated by the optimizer and label usage isn't conclusively known
at compile time.

=head2 API function to parse statements

The C<parse_fullstmt> function has been added to allow parsing of a single
complete Perl statement.  See L<perlapi> for details.

=head2 API functions for accessing the runtime hinthash

A new C API for introspecting the hinthash C<%^H> at runtime has been added.
See C<cop_hints_2hv>, C<cop_hints_fetchpvn>, C<cop_hints_fetchpvs>,
C<cop_hints_fetchsv>, and C<hv_copy_hints_hv> in L<perlapi> for details.

=head2 C interface to C<caller()>

The C<caller_cx> function has been added as an XSUB-writer's equivalent of
C<caller()>.  See L<perlapi> for details.

=head1 Incompatible Changes

=head2 Magic variables outside the main package

In previous versions of Perl, magic variables like C<$!>, C<%SIG>, etc. would
'leak' into other packages.  So C<%foo::SIG> could be used to access signals,
C<${"foo::!"}> (with strict mode off) to access C's C<errno>, etc.

This was a bug, or an 'unintentional' feature, which caused various ill effects,
such as signal handlers being wiped when modules were loaded, etc.

This has been fixed (or the feature has been removed, depending on how you see
it).

=head2 Smart-matching against array slices

Previously, the following code resulted in a successful match:

    my @a = qw(a y0 z);
    my @b = qw(a x0 z);
    $a[0 .. $#b] ~~ @b;

This odd behaviour has now been fixed
L<[perl #77468]|http://rt.perl.org/rt3//Public/Bug/Display.html?id=77468>.

=head2 C API changes

The first argument of the C API function C<Perl_fetch_cop_label> has changed
from C<struct refcounted he *> to C<COP *>, to better insulate the user from
implementation details.

This API function was marked as "may change", and likely isn't in use outside
the core.  (Neither an unpacked CPAN, nor Google's codesearch, finds any other
references to it.)

=head1 Deprecations

=head2 Use of qw(...) as parentheses

Historically the parser fooled itself into thinking that C<qw(...)> literals
were always enclosed in parentheses, and as a result you could sometimes omit
parentheses around them:

    for $x qw(a b c) { ... }

The parser no longer lies to itself in this way.  Wrap the list literal in
parentheses, like:

    for $x (qw(a b c)) { ... }

=head1 Performance Enhancements

=over 4

=item *

Scalars containing regular expressions now only allocate the part of the C<SV>
body they actually use, saving some space.

=item *

Compiling regular expressions has been made faster for the case where upgrading
the regex to utf8 is necessary but that isn't known when the compilation begins.

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item C<bignum>

Upgraded from version 0.23 to 0.25.

=item C<blib>

Upgraded from version 1.05 to 1.06.

=item C<open>

Upgraded from version 1.07 to 1.08.

=item C<threads-shared>

Upgraded from version 1.33_02 to 1.33_03.

=item C<warnings> and C<warnings::register>

Upgraded from version 1.10 to 1.11 and from version 1.01 to 1.02 respectively.

It is now possible to register warning categories other than the names of
packages using C<warnings::register>.  See L<perllexwarn> for more information.

=item C<B::Debug>

Upgraded from version 1.12 to 1.16.

=item C<CPANPLUS::Dist::Build>

Upgraded from version 0.46 to 0.48.

=item C<Data::Dumper>

Upgraded from version 2.126 to 2.128.

This fixes a crash when using custom sort functions that might cause the stack
to change.

=item C<Encode>

Upgraded from version 2.39 to 2.40.

=item C<Errno>

Upgraded from version 1.12 to 1.13.

On some platforms with unusual header files, like Win32/gcc using mingw64
headers, some constants which weren't actually error numbers have been exposed
by C<Errno>.  This has been fixed
L<[perl #77416]|http://rt.perl.org/rt3//Public/Bug/Display.html?id=77416>.

=item C<ExtUtils::MakeMaker>

Upgraded from version 6.5601 to 6.57_05.

=item C<Filter::Simple>

Upgraded from version 0.84 to 0.85.

=item C<Hash::Util>

Upgraded from version 0.08 to 0.09.

=item C<Math::BigInt>

Upgraded from version 1.89_01 to 1.95.

This fixes, among other things, incorrect results when computing binomial
coefficients
L<[perl #77640]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=77640>.

=item C<Math::BigInt::FastCalc>

Upgraded from version 0.19 to 0.22.

=item C<Math::BigRat>

Upgraded from version 0.24 to 0.26.

=item C<Module::CoreList>

Upgraded from version 2.37 to 2.38.

=item C<PerlIO::scalar>

Upgraded from version 0.08 to 0.09.

=item C<POSIX>

Upgraded from version 1.19 to 1.20.

It now includes constants for POSIX signal constants.

=item C<Safe>

Upgraded from version 2.27 to 2.28.

This fixes a possible infinite loop when looking for coderefs.

=item C<Test::Simple>

Upgraded from version 0.96 to 0.97_01.

=item C<Tie::Hash>

Upgraded from version 1.03 to 1.04.

Calling C<< Tie::Hash-E<gt>TIEHASH() >> used to loop forever.  Now it C<croak>s.

=item C<Unicode::Collate>

Upgraded from version 0.56 to 0.59.

=item C<XSLoader>

Upgraded from version 0.10 to 0.11.

=back

=head1 Documentation

=head2 Changes to Existing Documentation

=head3 L<perlapi>

=over 4

=item *

Many of the optree construction functions are now documented.

=back

=head3 L<perlbook>

=over 4

=item *

Expanded to cover many more popular books.

=back

=head3 L<perlfaq>

=over 4

=item *

L<perlfaq>, L<perlfaq2>, L<perlfaq4>, L<perlfaq5>, L<perlfaq6>, L<perlfaq8>, and
L<perlfaq9> have seen various updates and modernizations.

=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>.

=head2 New Diagnostics

=over 4

=item *

Parsing code internal error (%s)

New fatal error produced when parsing code supplied by an extension violated the
parser's API in a detectable way.

=item *

Use of qw(...) as parentheses is deprecated

See L</"Use of qw(...) as parentheses"> for details.

=back

=head1 Utility Changes

=head3 L<h2ph>

=over 4

=item *

The use of a deprecated C<goto> construct has been removed
L<[perl #74404]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=74404>.

=back

=head1 Testing

=over 4

=item *

The new F<t/lib/universal.t> script tests the Internal::* functions and other
things in F<universal.c>.

=item *

A rare race condition in F<t/op/while_readdir.t> has been fixed, stopping it
from failing randomly when running tests in parallel.

=item *

The new F<t/op/leaky-magic.t> script tests that magic applied to variables in
the main packages does not affect other packages.

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item VMS

=over 4

=item *

Make C<PerlIOUnix_open> honour default permissions on VMS.

When C<perlio> became the default and C<unixio> became the default bottom layer,
the most common path for creating files from Perl became C<PerlIOUnix_open>,
which has always explicitly used C<0666> as the permission mask.

To avoid this, C<0777> is now passed as the permissions to C<open()>.  In the
VMS CRTL, C<0777> has a special meaning over and above intersecting with the
current umask; specifically, it allows Unix syscalls to preserve native default
permissions.

=back

=back

=head1 Internal Changes

=over 4

=item *

C<CALL_FPTR> and C<CPERLscope> have been deprecated.

Those are left from an old implementation of C<MULTIPLICITY> using C++ objects,
which was removed in Perl 5.8.  Nowadays these macros do exactly nothing, so
they shouldn't be used anymore.

For compatibility, they are still defined for external C<XS> code.  Only
extensions defining C<PERL_CORE> must be updated now.

=item *

C<lex_stuff_pvs()> has been added as a convenience macro wrapping
C<lex_stuff_pvn()> for literal strings.

=item *

The recursive part of the peephole optimizer is now hookable.

In addition to C<PL_peepp>, for hooking into the toplevel peephole optimizer, a
C<PL_rpeepp> is now available to hook into the optimizer recursing into
side-chains of the optree.

=back

=head1 Selected Bug Fixes

=over 4

=item *

A regression introduced in Perl 5.12.0, making
C<< my $x = 3; $x = length(undef) >> result in C<$x> set to C<3> has been
fixed.  C<$x> will now be C<undef>.

=item *

A fatal error in regular expressions when processing UTF-8 data has been fixed
L<[perl #75680]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=75680>.

=item *

An erroneous regular expression engine optimization that caused regex verbs like
C<*COMMIT> to sometimes be ignored has been removed.

=item *

The Perl debugger now also works in taint mode
L<[perl #76872]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=76872>.

=item *

Several memory leaks in cloning and freeing threaded Perl interpreters have been
fixed L<[perl #77352]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=77352>.

=item *

A possible string corruption when doing regular expression matches on overloaded
objects has been fixed
L<[perl #77084]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=77084>.

=item *

Magic applied to variables in the main package no longer affects other packages.
See L</Magic variables outside the main package> above
L<[perl #76138]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=76138>.

=item *

Opening a glob reference via C<< open $fh, "E<gt>", \*glob >> will no longer
cause the glob to be corrupted when the filehandle is printed to.  This would
cause perl to crash whenever the glob's contents were accessed
L<[perl #77492]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=77492>.

=item *

The postincrement and postdecrement operators, C<++> and C<-->, used to cause
leaks when being used on references.  This has now been fixed.

=item *

A bug when replacing the glob of a loop variable within the loop has been fixed
L<[perl #21469]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=21469>.  This
means the following code will no longer crash:

    for $x (...) {
        *x = *y;
    }

=item *

Perl would segfault if the undocumented C<Internals> functions that used
reference prototypes were called with the C<&foo()> syntax, e.g.
C<&Internals::SvREADONLY(undef)>
L<[perl #77776]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=77776>.

These functions now call C<SvROK> on their arguments before dereferencing them
with C<SvRV>, and we test for this case in F<t/lib/universal.t>.

=item *

When assigning a list with duplicated keys to a hash, the assignment used to
return garbage and/or freed values:

    @a = %h = (list with some duplicate keys);

This has now been fixed
L<[perl #31865]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=31865>.

=item *

An earlier release of the 5.13 series of Perl changed the semantics of opening a
reference to a copy of a glob:

    my $var = *STDOUT;
    open my $fh, '>', \$var;

This was a mistake, and the previous behaviour from Perl 5.10 and 5.12, which is
to treat \$var as a scalar reference, has now been restored.

=item *

The regular expression bracketed character class C<[\8\9]> was effectively the
same as C<[89\000]>, incorrectly matching a NULL character.  It also gave
incorrect warnings that the C<8> and C<9> were ignored.  Now C<[\8\9]> is the
same as C<[89]> and gives legitimate warnings that C<\8> and C<\9> are
unrecognized escape sequences, passed-through.

=item *

C<warn()> now respects utf8-encoded scalars
L<[perl #45549]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=45549>.

=back

=head1 Known Problems

=over 4

=item *

The upgrade to Encode-2.40 has caused some tests in the libwww-perl distribution
on CPAN to fail. (Specifically, F<base/message-charset.t> tests 33-36 in version
5.836 of that distribution currently fail.)

=back

=head1 Acknowledgements

Perl 5.13.5 represents approximately one month of development since
Perl 5.13.4 and contains 74558 lines of changes across 549 files
from 45 authors and committers:

Abigail, Alexander Alekseev, Aristotle Pagaltzis, Ben Morrow, Bram, brian d foy,
Chas. Owens, Chris 'BinGOs' Williams, Craig A. Berry, Curtis Jewell, Dagfinn
Ilmari Mannsåker, David Golden, David Leadbeater, David Mitchell, Eric Brine,
Father Chrysostomos, Florian Ragwitz, Gisle Aas, Jan Dubois, Jerry D. Hedden,
Jesse Vincent, Jim Cromie, Jirka Hruška, Karl Williamson, Michael G. Schwern,
Nicholas Clark, Paul Johnson, Philippe Bruhat (BooK), Piotr Fusik, Rafael
Garcia-Suarez, Rainer Tammer, Reini Urban, Ricardo Signes, Rob Hoelz, Robin
Barker, Steffen Mueller, Steve Hay, Steve Peters, Todd Rinaldo, Tony Cook,
Vincent Pit, Yves Orton, Zefram, Zsbán Ambrus, Ævar Arnfjörð Bjarmason.

Many of the changes included in this version originated in the CPAN
modules included in Perl's core. We're grateful to the entire CPAN
community for helping Perl to flourish.

=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 B<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 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