perldelta update

[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 v5.17.2

=head1 DESCRIPTION

This document describes differences between the 5.17.1 release and
the 5.17.2 release.

If you are upgrading from an earlier release such as 5.17.0, first read
L<perl5171delta>, which describes differences between 5.17.0 and
5.17.1.

=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<kill> with negative signal names

C<kill> has always allowed a negative signal number, which kills the
process group instead of a single process.  It has also allowed signal
names.  But it did not behave consistently, because negative signal names
were treated as 0.  Now negative signals names like C<-INT> are supported
and treated the same way as -2 [perl #112990].

=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.
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<File::stat> has been upgraded from version 1.06 to 1.07.

Previously C<File::stat>'s overloaded C<-x> and C<-X> operators did not give
the correct results for directories or executable files when running as
root. They had been treating executable permissions for root just like for
any other user, performing group membership tests I<etc> for files not owned
by root. They now follow the correct Unix behaviour - for a directory they
are always true, and for a file if any of the three execute permission bits
are set then they report that root can execute the file. Perl's builtin
C<-x> and C<-X> operators have always been correct.

=item *

L<Tie::StdHandle> has been upgraded from version 4.2 to 4.3.

C<READ> now respects the offset argument to C<read> [perl #112826].

=item *

L<IO> has been upgraded from version 1.25_07 to 1.25_08.

L<IO::Socket> tries harder to cache or otherwise fetch socket
information.

=item *

L<Storable> has been upgraded from version 2.36 to 2.37.

Restricted hashes were not always thawed correctly [perl #73972].

Storable would croak when freezing a blessed REF object with a
C<STORABLE_freeze()> method [perl #113880].

=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<perlfunc>

=over 4

=item *

Clarified documentation of C<our>.

=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 that links to perldiag,
  e.g.

  =item *

  L<Invalid version object|perldiag/"Invalid version object">
]

=head2 New Diagnostics

XXX Newly added diagnostic messages go here

=head3 New Errors

=over 4

=item *

L<Group name must start with a non-digit word character in regex; marked by <-- HERE in mE<sol>%sE<sol>|perldiag/"Group name must start with a non-digit word character in regex; marked by <-- HERE in m/%s/">

This error has been added for C<(?&0)>, which is invalid.  It used to
produce an incomprehensible error message [perl #101666].

=back

=head3 New Warnings

=over 4

=item *

C<chr()> now warns when passed a negative value [perl #83048].

=item *

C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
value will be truncated rather than overflowing) [perl #40605].

=item *

Running perl with the C<-i> flag now warns if no input files are provided on
the command line [perl #113410].

=back

=head2 Changes to Existing Diagnostics

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

=over 4

=item *

The 'Can't use "my %s" in sort comparison' error has been downgraded to a
warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
for state variables).  In addition, the heuristics for guessing whether
lexical $a or $b has been misused have been improved to generate fewer
false positives.  Lexical $a and $b are no longer disallowed if they are
outside the sort block.  Also, a named unary or list operator inside the
sort block no longer causes the $a or $b to be ignored [perl #86136].

=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 *

Building perl with some Windows compilers used to fail due to a problem
with miniperl's C<glob> operator (which uses the C<perlglob> program)
deleting the PATH environment variable [perl #113798].

=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 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 VMS

Quotes are now removed from the command verb (but not the parameters) for commands
spawned via C<system>, backticks, or a piped C<open>.  Previously, quotes on the verb 
were passed through to DCL, which would fail to recognize the command.  Also, if the
verb is actually a path to an image or command procedure on an ODS-5 volume, quoting it
now allows the path to contain spaces.

=item AIX

Configure now always adds -qlanglvl=extc99 to the CC flags on AIX when
using xlC.  This will make it easier to compile a number of XS-based modules
that assume C99 [perl #113778].

=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 *

OP allocation for CVs now uses a slab allocator.  This simplifies
memory management for OPs allocated to a CV, so cleaning up after a
compilation error is simpler and safer [perl #111462][perl #112312].

=item *

PERL_DEBUG_READONLY_OPS has been rewritten to work with the new slab
allocator, allowing it to catch more violations that befor.

=item *

The old slab allocator for ops, which was only enabled for PERL_IMPLICIT_SYS and PERL_DEBUG_READONLY_OPS, has been retired.

=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 ]

=over 4

=item *

A regression introduced in v5.14.0 has been fixed, in which some calls
to the C<re> module would clobber C<$_> [perl #113750].

=item *

C<do FILE> now always either sets or clears C<$@>, even when the file can't be
read. This ensures that testing C<$@> first (as recommended by the
documentation) always returns the correct result.

=item *

The array iterator used for the C<each @array> construct is now correctly
reset when C<@array> is cleared (RT #75596). This happens for example when the
array is globally assigned to, as in C<@array = (...)>, but not when its
B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
will now reset the iterator.

This mirrors the behaviour of the hash iterator when the hash is cleared.

=item *

C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
correct results, regardless of whether that package referred to by C<$class>
exists [perl #47113].

=item *

Arriving signals no longer clear C<$@> [perl #45173].

=item *

Allow C<my ()> declarations with an empty variable list [perl #113554].

=item *

During parsing, subs declared after errors no longer leave stubs
[perl #113712].

=item *

Closures containing no string evals no longer hang on to their containing
subroutines, allowing variables closed over by outer subroutines to be
freed when the outer sub is freed, even if the inner sub still exists
[perl #89544].

=item *

Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
stopped working properly in 5.16.0.  It was causing the new handle to
reference a different scalar variable.  This has been fixed [perl #113764].

=item *

C<qr//> expressions no longer crash with custom regular expression engines
that do not set C<offs> at regular expression compilation time
[perl #112962].

=item *

C<delete local> no longer crashes with certain magical arrays and hashes
[perl #112966].

=item *

C<local> on elements of certain magical arrays and hashes used not to
arrange to have the element deleted on scope exit, even if the element did
not exist before C<local>.

=item *

C<scalar(write)> no longer returns multiple items [perl #73690].

=item *

String to floating point conversions no longer misparse certain strings under
C<use locale> [perl #109318].

=item *

C<@INC> filters that die no longer leak memory [perl #92252].

=item *

The implementations of overloaded operations are now called in the correct
context. This allows, among other things, being able to properly override
C<< <> >> [perl #47119].

=item *

Specifying only the C<fallback> key when calling C<use overload> now behaves
properly [perl #113010].

=item *

C<< sub foo { my $a = 0; while ($a) { ... } } >> and
C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].

=item *

Fixed the debugger C<l> and C<M> commands, and other debugger
functionality which was broken in 5.17.0 [perl #113918].

=item *

String negation now behaves the same under C<use integer;> as it does
without [perl #113012].

=item *

C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
regardless of the internal representation.  -1 used to wrap if the argument
was tied or a string internally.

=item *

Using a C<format> after its enclosing sub was freed could crash as of
perl 5.12.0, if the format referenced lexical variables from the outer sub.

=item *

Using a C<format> after its enclosing sub was undefined could crash as of
perl 5.10.0, if the format referenced lexical variables from the outer sub.

=item *

Using a C<format> defined inside a closures, which format references
lexical variables from outside, never really worked unless the C<write>
call was directly inside the closure.  In 5.10.0 it even started crashing.
Now the copy of that closure nearest the top of the call stack is used to
find those variables.

=item *

Formats that close over variables in special blocks no longer crash if a
stub exists with the same name as the special block before the special
block is compiled.

=item *

The parser no longer gets confused, treating C<eval foo ()> as a syntax
error if preceded by C<print;> [perl #16249].

=item *

The return value of C<syscall> is no longer truncated on 64-bit platforms
[perl #113980].

=item *

Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
FOO handle [perl #78064].

=item *

C<do subname> now calls the named subroutine and uses the file name it
returns, instead of opening a file named "subname".

=item *

Subroutines looked up by rv2cv check hooks (registered by XS modules) are
now taken into consideration when determining whether C<foo bar> should be
the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.

=item *

C<CORE::foo::bar> is no longer treated specially, allowing global overrides
to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].

=item *

Calling an undefined sub whose typeglob has been undefined now produces the
customary "Undefined subroutine called" error, instead of "Not a CODE
reference".

=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 v5.17.1..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