path: root/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 v5.19.1

=head1 DESCRIPTION

This document describes differences between the 5.19.0 release and the 5.19.1
release.

=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 ]

=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.

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.

=over

=item *

L<DB> has been updated from 1.05 to 1.06 and L<perl5db.pl> from 1.39_10
to 1.40.  The call depth allowed by default in the debugger is now 1000
rather than 100.

=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 *

Perl has a new copy-on-write mechanism that avoids the need to copy the
internal string buffer when assigning from one scalar to another. This
makes copying large strings appear much faster.  Modifying one of the two
(or more) strings after an assignment will force a copy internally. This
makes it unnecessary to pass strings by reference for efficiency.

This feature was already available in 5.18.0, but wasn't enabled by
default. It is the default now, and so you no longer need build perl with
the F<Configure> argument:

    -Accflags=PERL_NEW_COPY_ON_WRITE

It can be disabled (for now) in a perl build with:

    -Accflags=PERL_NO_COW

=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 *

B::Deparse has been upgraded from version 1.20 to 1.21.

C<foreach my $lexical> is now deparsed correctly with the B<-p> option.
[RT #117081]

The B<-l> option no longer puts form feeds in the middle of a line when
outputting C<map> and C<grep> blocks. [RT #117311]

Elements of C<%#>, such as C<$# {foo}> and C<${#}{foo}> are now deparsed
correctly. [RT #117531]

=item *

Test::Harness has been upgraded from version 3.26 to 3.28

Memory usage is dramatically reduced. t/harness now uses about 10% of the
memory used by 3.26 and earlier.

C<PERL5LIB> is always propagated to a test's C<@INC>, even under C<-T>.

=item *

Unicode::UCD has been upgraded from version 0.51 to 0.52.

A function, L<Unicode::UCD/search_invlist()> is now available to do
search an inversion list or map for a code point.

=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<perltrap>

=over 4

=item *

There is now a L<JavaScript|perltrap/JavaScript Traps> section.

=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 *

L<A sequence of multiple spaces in a charnames alias definition is deprecated|perldiag/"A sequence of multiple spaces in a charnames alias definition is deprecated">

L<Trailing white-space in a charnames alias definition is deprecated|perldiag/"Trailing white-space in a charnames alias definition is deprecated">

These two deprecation warnings involving C<\N{...}> were incorrectly
implemented.  They did not warn by default (now they do) and could not be
made fatal via C<use warnings FATAL => 'deprecated'> (now they can).

=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 F<bisect.pl> enhancements

The git bisection tool F<Porting/bisect.pl> has had many enhancements.

=over 4

=item *

Can optionally run the test case with a timeout.

=item *

Can now run in-place in a clean git checkout.

=item *

Can run the test case under C<valgrind>.

=item *

Can apply user supplied patches and fixes to the source checkout before
building.

=item *

Now has fixups to enable building several more historical ranges of bleadperl,
which can be useful for pinpointing the origins of bugs or behaviour changes.

=back

It is provided as part of the source distribution but not installed because
it is not self-contained as it relies on being run from within a git
checkout. Note also that it makes no attempt to fix tests, correct runtime
bugs or make something useful to install - its purpose is to make minimal
changes to get any historical revision of interest to build and run as close
as possible to "as-was", and thereby make C<git bisect> easy to use.

=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 Mixed-endian platforms

The code supporting C<pack> and C<unpack> operations on mixed endian
platforms has been removed. We believe that Perl has long been unable to
build on mixed endian architectures (such as PDP-11s), so we don't think
that this change will affect any platforms which are able to build v5.18.0.

=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 *

Perl's new copy-on-write mechanism  (which is now enabled by default),
allows any C<SvPOK> scalar to be automatically upgraded to a copy-on-write
scalar when copied. A reference count on the string buffer is stored in
the string buffer itself.

For example:

    $ perl -MDevel::Peek -e'$a="abc"; $b = $a; Dump $a; Dump $b'
    SV = PV(0x260cd80) at 0x2620ad8
      REFCNT = 1
      FLAGS = (POK,IsCOW,pPOK)
      PV = 0x2619bc0 "abc"\0
      CUR = 3
      LEN = 16
      COW_REFCNT = 1
    SV = PV(0x260ce30) at 0x2620b20
      REFCNT = 1
      FLAGS = (POK,IsCOW,pPOK)
      PV = 0x2619bc0 "abc"\0
      CUR = 3
      LEN = 16
      COW_REFCNT = 1

Note that both scalars share the same PV buffer and have a COW_REFCNT
greater than zero.

This means that XS code which wishes to modify the C<SvPVX()> buffer of an
SV should call C<SvPV_force()> or similar first, to ensure a valid (and
unshared) buffer, and to call C<SvSETMAGIC()> afterwards. This in fact has
always been the case (for example hash keys were already copy-on-write);
this change just spreads the COW behaviour to a wider variety of SVs.

One important difference is that before 5.18.0, shared hash-key scalars
used to have the C<SvREADONLY> flag set; this is no longer the case.

This new behaviour can still be disabled by running F<Configure> with
B<-Accflags=-DPERL_NO_COW>.  This option will probably be removed in Perl
5.22.

=item *

C<PL_sawampersand> is now a constant.  The switch this variable provided
(to enable/disable the pre-match copy depending on whether C<$&> had been
seen) has been removed and replaced with copy-on-write, eliminating a few
bugs.

The previous behaviour can still be enabled by running F<Configure> with
B<-Accflags=-DPERL_SAWAMPERSAND>.

=item *

The functions C<my_swap>, C<my_htonl> and C<my_ntohl> have been removed.
It is unclear why these functions were ever marked as I<A>, part of the
API. XS code can't call them directly, as it can't rely on them being
compiled. Unsurprisingly, no code on CPAN references them.

=item *

The signature of the C<Perl_re_intuit_start()> regex function has changed;
the function pointer C<intuit> in the regex engine plugin structure
has also changed accordingly. A new parameter, C<strbeg> has been added;
this has the same meaning as the same-named parameter in
C<Perl_regexec_flags>. Previously intuit would try to guess the start of
the string from the passed SV (if any), and would sometimes get it wrong
(e.g. with an overloaded SV).

=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 *

The OP allocation code now returns correctly aligned memory in all cases
for C<struct pmop>. Previously it could return memory only aligned to a
4-byte boundary, which is not correct for an ithreads build with 64 bit IVs
on some 32 bit platforms. Notably, this caused the build to fail completely
on sparc GNU/Linux. [RT #118055]

=item *

The debugger's C<man> command been fixed. It was broken in the v5.18.0
release. The C<man> command is aliased to the names C<doc> and C<perldoc> -
all now work again.

=item *

Evaluating large hashes in scalar context is now much faster, as the number
of used chains in the hash is now cached for larger hashes. Smaller hashes
continue not to store it and calculate it when needed, as this saves one IV.
That would be 1 IV overhead for every object built from a hash. [RT #114576]

=item *

Fixed a small number of regexp constructions that could either fail to
match or crash perl when the string being matched against was
allocated above the 2GB line on 32-bit systems. [RT #118175]

=item *

Perl v5.16 inadvertently introduced a bug whereby calls to XSUBs that were
not visible at compile time were treated as lvalues and could be assigned
to, even when the subroutine was not an lvalue sub.  This has been fixed.
[RT #117947]

=item *

In Perl v5.18.0 dualvars that had an empty string for the string part but a
non-zero number for the number part starting being treated as true.  In
previous versions they were treated as false, the string representation
taking precedeence.  The old behaviour has been restored. [RT #118159]

=item *

Since Perl v5.12, inlining of constants that override built-in keywords of
the same name had countermanded C<use subs>, causing subsequent mentions of
the constant to use the built-in keyword instead.  This has been fixed.

=item *

Lexical constants (C<my sub a() { 42 }>) no longer crash when inlined.

=item *

Parameter prototypes attached to lexical subroutines are now respected when
compiling sub calls without parentheses.  Previously, the prototypes were
honoured only for calls I<with> parentheses. [RT #116735]

=item *

Syntax errors in lexical subroutines in combination with calls to the same
subroutines no longer cause crashes at compile time.

=item *

The warning produced by C<-l $handle> now applies to IO refs and globs, not
just to glob refs.  That warning is also now UTF8-clean. [RT #117595]

=item *

Various memory leaks involving the parsing of the C<(?[...])> regular
expression construct have been fixed.

=item *

C<(?[...])> now allows interpolation of precompiled patterns consisting of
(?[...])> with bracket character classes inside (C<$pat =
S<qr/(?[ [a] ])/;> S</(?[ $pat ])/>>).  Formerly, the brackets would
confuse the regular expression parser.

=item *

C<delete local $ENV{nonexistent_env_var}> no longer leaks memory.

=item *

C<sort> and C<require> followed by a keyword prefixed with C<CORE::> now
treat it as a keyword, and not as a subroutine or module name. [RT #24482]

=item *

Through certain conundrums, it is possible to cause the current package to
be freed.  Certain operators (C<bless>, C<reset>, C<open>, C<eval>) could
not cope and would crash.  They have been made more resilient. [RT #117941]

=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