Add epigraph for 5.15.8

[perl5.git] / pod / perldelta.pod

=encoding utf8

=for comment
This has been completed up to 0aae26c14, except for:
d9298c1	rurban	mymalloc isn't thread safe

=head1 NAME

perldelta - what is new for perl v5.15.8

=head1 DESCRIPTION

This document describes differences between the 5.15.7 release and
the 5.15.8 release.

If you are upgrading from an earlier release such as 5.15.6, first read
L<perl5157delta>, which describes differences between 5.15.6 and
5.15.7.

=head1 Notice

This space intentionally left blank.

=head1 Core Enhancements

=head2 Improved ability to mix locales and Unicode, including UTF-8 locales

An optional parameter has been added to C<use locale>

 use locale ':not_characters';

which tells Perl to use all but the C<LC_CTYPE> and C<LC_COLLATE>
portions of the current locale.  Instead, the character set is assumed
to be Unicode.  This allows locales and Unicode to be seamlessly mixed,
including the increasingly frequent UTF-8 locales.  When using this
hybrid form of locales, the C<:locale> layer to the L<open> pragma can
be used to interface with the file system, and there are CPAN modules
available for ARGV and environment variable conversions.

Full details are in L<perllocale>.

=head2 New function C<fc> and corresponding escape sequence C<\F> for Unicode foldcase

Unicode foldcase is an extension to lowercase that gives better results
when comparing two strings case-insensitively.  It has long been used
internally in regular expression C</i> matching.  Now it is available
explicitly through the new C<fc> function call (enabled by
S<C<"use feature 'fc'">>, or C<use v5.16>, or explicitly callable via
C<CORE::fc>) or through the new C<\F> sequence in double-quotish
strings.

Full details are in L<perlfunc/fc>.

=head2 C<_> in subroutine prototypes

The C<_> character in subroutine prototypes is now allowed before C<@> or
C<%>.

=head2 Supports (I<almost>) Unicode 6.1

Besides the addition of whole new scripts, and new characters in
existing scripts, this new version of Unicode, as always, makes some
changes to existing characters.  One change that may trip up some
applications is that the General Category of two characters in the
Latin-1 range, PILCROW SIGN and SECTION SIGN, has been changed from
Other_Symbol to Other_Punctuation.  The same change has been made for
a character in each of Tibetan, Ethiopic, and Aegean.
The code points U+3248..U+324F (CIRCLED NUMBER TEN ON BLACK SQUARE
through CIRCLED NUMBER EIGHTY ON BLACK SQUARE) have had their General
Category changed from Other_Symbol to Other_Numeric.  The Line Break
property has changes for Hebrew and Japanese; and as a consequence of
other changes in 6.1, the Perl regular expression construct C<\X> now
works differently for some characters in Thai and Lao.

New aliases (synonyms) have been defined for many property values;
these, along with the previously existing ones, are all cross indexed in
L<perluniprops>.

The return value of C<charnames::viacode()> is affected by other
changes:

 Code point      Old Name             New Name
   U+000A    LINE FEED (LF)        LINE FEED
   U+000C    FORM FEED (FF)        FORM FEED
   U+000D    CARRIAGE RETURN (CR)  CARRIAGE RETURN
   U+0085    NEXT LINE (NEL)       NEXT LINE
   U+008E    SINGLE-SHIFT 2        SINGLE-SHIFT-2
   U+008F    SINGLE-SHIFT 3        SINGLE-SHIFT-3
   U+0091    PRIVATE USE 1         PRIVATE USE-1
   U+0092    PRIVATE USE 2         PRIVATE USE-2
   U+2118    SCRIPT CAPITAL P      WEIERSTRASS ELLIPTIC FUNCTION

Perl will accept any of these names as input, but
C<charnames::viacode()> now returns the new name of each pair.  The
change for U+2118 is considered by Unicode to be a correction, that is
the original name was a mistake (but again, it will remain forever valid
to use it to refer to U+2118).  But most of these changes are the
fallout of the mistake Unicode 6.0 made in naming a character used in
Japanese cell phones to be "BELL", which conflicts with the long
standing industry use of (and Unicode's recommendation to use) that name
to mean the ASCII control character at U+0007.  As a result, that name
has been deprecated in Perl since v5.14; and any use of it will raise a
warning message (unless turned off).  The name "ALERT" is now the
preferred name for this code point, with "BEL" being an acceptable short
form.  The name for the new cell phone character, at code point U+1F514,
remains undefined in this version of Perl (hence we don't quite
implement all of Unicode 6.1), but starting in v5.18, BELL will mean
this character, and not U+0007.

Unicode has taken steps to make sure that this sort of mistake does not
happen again.  The Standard now includes all the generally accepted
names and abbreviations for control characters, whereas previously it
didn't (though there were recommended names for most of them, which Perl
used).  This means that most of those recommended names are now
officially in the Standard.  Unicode did not recommend names for the
four code points listed above between U+008E and U+008F, and in
standardizing them Unicode subtly changed the names that Perl had
previously given them, by replacing the final blank in each name by a
hyphen.  Unicode also officially accepts names that Perl had deprecated,
such as FILE SEPARATOR.  Now the only deprecated name is BELL.
Finally, Perl now uses the new official names instead of the old
(now considered obsolete) names for the first four code points in the
list above (the ones which have the parentheses in them).

Now that the names have been placed in the Unicode standard, these kinds
of changes should not happen again, though corrections, such as to
U+2118, are still possible.

Unicode also added some name abbreviations, which Perl now accepts:
SP for SPACE;
TAB for CHARACTER TABULATION;
NEW LINE, END OF LINE, NL, and EOL for LINE FEED;
LOCKING-SHIFT ONE for SHIFT OUT;
LOCKING-SHIFT ZERO for SHIFT IN;
and ZWNBSP for ZERO WIDTH NO-BREAK SPACE.

More details on this version of Unicode are provided in
L<http://www.unicode.org/versions/Unicode6.1.0/>.

=head2 Added C<is_utf8_char_buf()>

This function is designed to replace the deprecated L</is_utf8_char()>
function.  It includes an extra parameter to make sure it doesn't read
past the end of the input buffer.

=head1 Security

=head2 Use C<is_utf8_char_buf()> and not C<is_utf8_char()>

The latter function is now deprecated because its API is insufficient to
guarantee that it doesn't read (up to 12 bytes in the worst case) beyond
the end of its input string.  See
L<is_utf8_char_buf()|/Added is_utf8_char_buf()>.

=head1 Incompatible Changes

[ List each incompatible change as a =head2 entry ]

=head2 Special blocks called in void context

Special blocks (C<BEGIN>, C<CHECK>, C<INIT>, C<UNITCHECK>, C<END>) are now
called in void context.  This avoids wasteful copying of the result of the
last statement [perl #108794].

=head2 The C<overloading> pragma and regexp objects

With C<no overloading>, regular expression objects returned by C<qr//> are
now stringified as "Regexp=REGEXP(0xbe600d)" instead of the regular
expression itself [perl #108780].

=head2 Two XS typemap Entries removed

Two presumably unused XS typemap entries have been removed from the
core typemap: T_DATAUNIT and T_CALLBACK. If you are, against all odds,
a user of these, please see the instructions on how to regain them
in L<perlxstypemap>.

=head2 Unicode 6.1 has incompatibilities with Unicode 6.0

These are detailed in L</Supports (almost) Unicode 6.1> above.

=head2 Changed returns for some properties in C<Unicode::UCD::prop_invmap()>

The return values for C<prop_invmap> have been changed for some
properties to make the returned lists significantly smaller.  This
allows those lists to be searched faster.

This function was introduced earlier in the v5.15 series of releases,
and the API will not be considered stable until v5.16.

See L<Unicode::UCD/prop_invmap()> for details on the new interface.

=head2 C<$$> and C<getppid()> no longer emulate POSIX semantics under LinuxThreads

The POSIX emulation of C<$$> and C<getppid()> under the obsolete
LinuxThreads implementation has been removed (the C<$$> emulation was
actually removed in v5.15.0). This only impacts users of Linux 2.4 and
users of Debian GNU/kFreeBSD up to and including 6.0, not the vast
majority of Linux installations that use NPTL threads.

This means that C<getppid()> like C<$$> is now always guaranteed to
return the OS's idea of the current state of the process, not perl's
cached version of it.

See the documentation for L<$$|perlvar/$$> for details.

=head2 C<< $< >>, C<< $> >>, C<$(> and C<$)> are no longer cached

Similarly to the changes to C<$$> and C<getppid()> the internal
caching of C<< $< >>, C<< $> >>, C<$(> and C<$)> has been removed.

When we cached these values our idea of what they were would drift out
of sync with reality if someone (e.g. someone embedding perl) called
sete?[ug]id() without updating C<PL_e?[ug]id>. Having to deal with
this complexity wasn't worth it given how cheap the C<gete?[ug]id()>
system call is.

This change will break a handful of CPAN modules that use the XS-level
C<PL_uid>, C<PL_gid>, C<PL_euid> or C<PL_egid> variables.

The fix for those breakages is to use C<PerlProc_gete?[ug]id()> to
retrieve them (e.g. C<PerlProc_getuid()>), and not to assign to
C<PL_e?[ug]id> if you change the UID/GID/EUID/EGID. There is no longer
any need to do so since perl will always retrieve the up-to-date
version of those values from the OS.

=head2 Which Non-ASCII characters get quoted by C<quotemeta> and C<\Q> has changed

This is unlikely to result in a real problem, as Perl does not attach
special meaning to any non-ASCII character, so it is currently
irrelevant which are quoted or not.  This change fixes bug [perl #77654] and
bring Perl's behavior more into line with Unicode's recommendations.
See L<perlfunc/quotemeta>.

=head1 Deprecations

=head2 C<is_utf8_char()>

This function is deprecated because it could read beyond the end of the
input string.  Use the new L<is_utf8_char_buf()|/Added is_utf8_char_buf()>
instead.

=head1 Modules and Pragmata

=head2 New Modules and Pragmata

=over 4

=item *

C<PerlIO::mmap> 0.010 has been added to the Perl core.

The C<mmap> PerlIO layer is no longer implemented by perl itself, but has
been moved out into the new L<PerlIO::mmap> module.

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<arybase> has been upgraded from version 0.03 to version 0.04.

List slices no longer modify items on the stack belonging to outer lists
[perl #109570].

=item *

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

C<B::COP> now has a C<stashflags> method, corresponding to a new internal
field added in 5.15.4 [perl #108860].

=item *

C<B::Deparse> has been upgraded from version 1.11 to 1.12.

=item *

L<Carp> has been upgraded from version 1.24 to version 1.25.

It now puts a dot after the file and line number, just like errors from
C<die> [perl #106538].

=item *

C<Compress::Raw::Bzip2> has been upgraded from version 2.045 to 2.048.

=item *

C<Compress::Raw::Zlib> has been upgraded from version 2.045 to 2.048.

=item *

L<Compress::Zlib> has been upgraded from version 2.046 to version 2.048.

=item *

C<CPAN::Meta> has been upgraded from version 2.113640 to 2.120351.

Work around a memory leak bug involving version objects in boolean context.

=item *

C<CPAN::Meta::YAML> has been upgraded from version 0.005 to 0.007.

=item *

C<CPANPLUS> has been upgraded from version 0.9116 to 0.9118.

=item *

C<CPANPLUS::Dist::Build> has been upgraded from version 0.60 to 0.62.

=item *

C<Data::Dumper> has been upgraded from version 2.135_04 to 2.135_05.

=item *

C<DB_File> has been upgraded from version 1.824 to 1.826.

=item *

C<diagnostics> has been upgraded from version 1.27 to 1.28.

When searching for F<perldiag.pod>, it no longer uses paths that were only
relevant on Perl 5.004 and earlier.

=item *

C<English> has been upgraded from version 1.04 to 1.05.

=item *

C<ExtUtils::Install> has been upgraded from version 1.57 to 1.58.

=item *

C<ExtUtils::ParseXS> has been upgraded from version 3.12 to 3.16.

The new version comes with important tools for sharing typemaps between
different CPAN distributions.

=item *

C<File::Copy> has been upgraded from version 2.21 to 2.23.

It no longer emits warnings when copying files with newlines in their names
[perl #109104].

=item *

C<File::Glob> has been upgraded from version 1.16 to 1.17.

=item *

C<Filter::Util::Call> has been upgraded from version 1.39 to 1.40.

=item *

C<IPC::Cmd> has been upgraded from version 0.72 to 0.76.

=item *

C<Math::Complex> has been upgraded from version 1.58 to 1.59.

This avoids a new core warning.

=item *

C<Module::Metadata> has been upgraded from version 1.000007 to 1.000009.

Adds C<provides> method to generate a CPAN META provides data structure
correctly; use of C<package_versions_from_directory> is discouraged.

=item *

C<Opcode> has been upgraded from version 1.22 to 1.23.

=item *

C<overload> has been upgraded from version 1.17 to 1.18.

=item *

C<Parse::CPAN::Meta> has been upgraded from version 1.4401 to 1.4402.

=item *

C<perlfaq> has been upgraded from version 5.0150038 to 5.0150039.

=item *

C<Pod::Functions> has been upgraded from version 1.04 to 1.05.

F<Functions.pm> is now generated at perl build time from annotations in
F<perlfunc.pod>. This will ensure that L<Pod::Functions> and L<perlfunc>
remain in synchronisation.

=item *

C<Pod::Html> has been upgraded from version 1.13 to 1.14.

=item *

C<Pod::Parser> has been upgraded from version 1.37 to 1.51.

=item *

C<POSIX> has been upgraded from version 1.28 to 1.30.

=item *

C<re> has been upgraded from version 0.18 to 0.19.

=item *

C<Safe> has been upgraded from version 2.30 to 2.31.

=item *

C<Socket> has been upgraded from version 1.97 to 1.98.

=item *

C<Term::Cap> has been upgraded from version 1.12 to 1.13.

=item *

C<Term::ReadLine> has been upgraded from version 1.07 to 1.08.

Term::ReadLine now supports any event loop, including unpublished ones and
simple L<IO::Select> loops without the need to rewrite existing code for
any particular framework [perl #108470].

=item *

C<Time::HiRes> has been upgraded from version 1.9724 to 1.9725.

C<Time::HiRes::stat()> no longer corrupts the Perl stack.

=item *

C<Unicode::UCD> has been upgraded from version 0.39 to 0.41.

The only change is to fix a formatting error in the Pod.

=item *

C<Version::Requirements> has been upgraded from version 0.101021 to 0.101022.

=item *

C<warnings> has been upgraded from version 1.12 to 1.13.

=item *

C<XS::Typemap> has been upgraded from version 0.07 to 0.08.

=back

=head1 Documentation

=head2 New Documentation

=head3 L<perlxstypemap>

The new manual describes the XS typemapping mechanism in unprecedented
detail and combines new documentation with information extracted from
L<perlxs> and the previously unofficial list of all core typemaps.

=head1 Testing

=over 4

=item *

F<t/porting/pending-author.t> has been added, to avoid the problem of
C<make test> passing 100%, but the subsequent git commit causing
F<t/porting/authors.t> to fail, because it uses a "new" e-mail address.

This test is only run if one is building inside a git checkout, B<and> one
has made local changes. Otherwise it's skipped.

=item *

F<t/porting/perlfunc.t> has been added, to test that changes to
F<pod/perlfunc.pod> do not inadvertently break the build of L<Pod::Functions>.

=item *

The test suite for typemaps has been extended to cover a larger fraction of
the core typemaps.

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item Cygwin

Since version 1.7, Cygwin supports native UTF-8 paths. If Perl is built
under that environment, directory and filenames will be UTF-8 encoded.

Cygwin does not initialize all original Win32 environment variables. See
F<README.cygwin> for a discussion of C<Cygwin::sync_winenv()> and
further links.

=item VMS

The build on VMS now allows names of the resulting
symbols in C code for Perl longer than 31 characters.
Symbols like C<Perl__it_was_the_best_of_times_it_was_the_worst_of_times>
can now be created freely without causing the VMS linker to seize up.

=back

=head1 Selected Bug Fixes

=over 4

=item *

C<~~> now correctly handles the precedence of Any~~Object, and is not tricked
by an overloaded object on the left-hand side.

=item *

C<stat _> no longer warns about unopened filehandles [perl #71002].

=item *

C<stat> on an unopened filehandle now warns consistently, instead of
skipping the warning at times.

=item *

A change in an earlier 5.15 release caused warning hints to propagate into
C<do $file>.  This has been fixed [rt.cpan.org #72767].

=item *

Starting with 5.12.0, Perl used to get its internal bookkeeping muddled up
after assigning C<${ qr// }> to a hash element and locking it with
L<Hash::Util>.  This could result in double frees, crashes or erratic
behaviour.

=item *

In 5.15.7, some typeglobs in the CORE namespace were made read-only by
mistake.  This has been fixed [rt.cpan.org #74289].

=item *

C<-t> now works when stacked with other filetest operators [perl #77388].

=item *

Stacked filetest operators now only call FETCH once on a tied argument.

=item *

C</.*/g> would sometimes refuse to match at the end of a string that ends
with "\n".  This has been fixed [perl #109206].

=item *

C<m/[[:ascii:]]/i> and C</\p{ASCII}/i> now match identically (when not
under a differing locale).  This fixes a regression introduced in 5.14
in which the first expression could match characters outside of ASCII,
such as the KELVIN SIGN.

=item *

Method calls whose arguments were all surrounded with C<my()> or C<our()>
(as in C<< $object->method(my($a,$b)) >>) used to force lvalue context on
the subroutine.  This would prevent lvalue methods from returning certain
values.  Due to lvalue fixes earlier in the 5.15.x series, it would also
prevent non-lvalue methods from being called [perl #109264].

=for comment
This bug I<did> affect earlier stable releases.  It is just the last
sentence that does not apply to 5.14.

=item *

The C<SvPVutf8> C function no longer tries to modify its argument,
resulting in errors [perl #108994].

=item *

C<SvPVutf8> now works properly with magical variables.

=item *

C<SvPVbyte> now works properly non-PVs.

=item *

C</[[:ascii:]]/> and C</[[:blank:]]/> now use locale rules under
C<use locale> when the platform supports that.  Previously, they used
the platform's native character set.

=item *

A regression introduced in 5.13.6 was fixed.  This involved an inverted
bracketed character class in a regular expression that consisted solely
of a Unicode property, that property wasn't getting inverted outside the
Latin1 range.

=item *

C<quotemeta> now quotes consistently the same non-ASCII characters under
C<use feature 'unicode_strings'>, regardless of whether the string is
encoded in UTF-8 or not, hence fixing the last vestiges (we hope) of the
infamous L<perlunicode/The "Unicode Bug">.  [perl #77654].

Which of these code points is quoted has changed, based on Unicode's
recommendations.  See L<perlfunc/quotemeta> for details.

=back

=head1 Known Problems

This is a list of some significant unfixed bugs, which are regressions
from either 5.14.0 or 5.15.7.

=over 4

=item * C<eval { 'fork()' }> is broken on Windows [perl #109718]

This is a known test failure to be fixed before 5.16.0.

=back

=head1 Acknowledgements

Perl 5.15.8 represents approximately 4 weeks of development since Perl 5.15.7
and contains approximately 61,000 lines of changes across 480 files from 36
authors.

Perl continues to flourish into its third decade thanks to a vibrant community
of users and developers. The following people are known to have contributed the
improvements that became Perl 5.15.8:

Abhijit Menon-Sen, Alan Haggai Alavi, Alexandr Ciornii, Andy Dougherty, Brian
Fraser, Chris 'BinGOs' Williams, Craig A. Berry, Darin McBride, Dave Rolsky,
David Golden, David Leadbeater, David Mitchell, Dominic Hargreaves, Eric Brine,
Father Chrysostomos, Florian Ragwitz, H.Merijn Brand, Juerd Waalboer, Karl
Williamson, Leon Timmermans, Marc Green, Max Maischein, Nicholas Clark, Paul
Evans, Rafael Garcia-Suarez, Rainer Tammer, Reini Urban, Ricardo Signes, Robin
Barker, Shlomi Fish, Steffen Müller, Todd Rinaldo, Tony Cook, Yves Orton,
Zefram, Ævar Arnfjörð Bjarmason.

The list above is almost certainly incomplete as it is automatically generated
from version control history. In particular, it does not include the names of
the (very much appreciated) contributors who reported issues to the Perl bug
tracker.

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.

For a more complete list of all of Perl's historical contributors, please see
the F<AUTHORS> file in the Perl source distribution.

=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