perldelta - 'nonexistent' should be 'non-existent'

[perl5.git] / pod / perldelta.pod

=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.19.4

=head1 DESCRIPTION

This document describes differences between the 5.19.3 release and the 5.19.4
release.

If you are upgrading from an earlier release such as 5.19.2, first read
L<perl5193delta>, which describes differences between 5.19.2 and 5.19.3.

=head1 Core Enhancements

=head2 C<rand> now uses a consistent random number generator

Previously perl would use a platform specific random number generator, varying
between the libc rand(), random() or drand48().

This meant that the quality of perl's random numbers would vary from platform
to platform, from the 15 bits of rand() on Windows to 48-bits on POSIX
platforms such as Linux with drand48().

Perl now uses its own internal drand48() implementation on all platforms.  This
does not make perl's C<rand> cryptographically secure.  [perl #115928]

=head2 Better 64-bit support

On 64-bit platforms, the internal array functions now use 64-bit offsets,
allowing Perl arrays to hold more than 2**31 elements, if you have the memory
available.

The regular expression engine now supports strings longer than 2**31
characters.  [perl #112790, #116907]

The functions PerlIO_get_bufsiz, PerlIO_get_cnt, PerlIO_set_cnt and
PerlIO_set_ptrcnt now have SSize_t, rather than int, return values and
parameters.

=head2 New slice syntax

The new C<%hash{...}> and C<%array[...]> syntax returns a list of key/value (or
index/value) pairs.

=head2 EBCDIC support

Core Perl now mostly works on EBCDIC platforms.  This is not true of many
modules, including some which are shipped with this release.  If you have
resources to help continue this process, including test machines, send email to
L<mailto:perl-mvs@perl.org>.

As a result of this, certain XS functions are now deprecated; see L</Internal
Changes>.

=head1 Incompatible Changes

=head2 Locale decimal point character no longer leaks outside of
S<C<use locale>> scope (with the exception of $!)

This is actually a bug fix, but some code has come to rely on the bug being
present, so this change is listed here.  The current locale that the program is
running under is not supposed to be visible to Perl code except within the
scope of a S<C<use locale>>.  However, until now under certain circumstances,
the character used for a decimal point (often a comma) leaked outside the
scope.

This continues the work released in Perl 5.19.1.  It turns out that that did
not catch all the leaks, including C<printf> and C<sprintf> not respecting
S<C<use locale>>.  If your code is affected by this change, simply add a
S<C<use locale>>.

Now, the only known place where S<C<use locale>> is not respected is in the
stringification of L<$!|perlvar/$!>.

=head2 Assignments of Windows sockets error codes to $! now prefer F<errno.h> values over WSAGetLastError() values

In previous versions of Perl, Windows sockets error codes as returned by
WSAGetLastError() were assigned to $!, and some constants such as ECONNABORTED,
not in F<errno.h> in VC++ (or the various Windows ports of gcc) were defined to
corresponding WSAE* values to allow $! to be tested against the E* constants
exported by L<Errno> and L<POSIX>.

This worked well until VC++ 2010 and later, which introduced new E* constants
with values E<gt> 100 into F<errno.h>, including some being (re)defined by perl
to WSAE* values.  That caused problems when linking XS code against other
libraries which used the original definitions of F<errno.h> constants.

To avoid this incompatibility, perl now maps WSAE* error codes to E* values
where possible, and assigns those values to $!.  The E* constants exported by
L<Errno> and L<POSIX> are updated to match so that testing $! against them,
wherever previously possible, will continue to work as expected, and all E*
constants found in F<errno.h> are now exported from those modules with their
original F<errno.h> values

In order to avoid breakage in existing Perl code which assigns WSAE* values to
$!, perl now intercepts the assignment and performs the same mapping to E*
values as it uses internally when assigning to $! itself.

However, one backwards-incompatibility remains: existing Perl code which
compares $! against the numeric values of the WSAE* error codes that were
previously assigned to $! will now be broken in those cases where a
corresponding E* value has been assigned instead.  This is only an issue for
those E* values E<lt> 100, which were always exported from L<Errno> and
L<POSIX> with their original F<errno.h> values, and therefore could not be used
for WSAE* error code tests (e.g. WSAEINVAL is 10022, but the corresponding
EINVAL is 22).  (E* values E<gt> 100, if present, were redefined to WSAE*
values anyway, so compatibility can be achieved by using the E* constants,
which will work both before and after this change, albeit using different
numeric values under the hood.)

=head1 Deprecations

=head2 Literal control characters in variable names

This deprecation affects things like $\cT, where \cT is a literal control in
the source code.  Surprisingly, it appears that originally this was intended as
the canonical way of accessing variables like $^T, with the caret form only
being added as an alternative.

The literal control form is being deprecated for two main reasons.  It has what
are likely unfixable bugs, such as $\cI not working as an alias for $^I, and
their usage not being portable to non-ASCII platforms: While $^T will work
everywhere, \cT is whitespace in EBCDIC.  [perl #119123]

=head1 Performance Enhancements

=over 4

=item *

The trie performance enhancement for regular expressions has now been extended
to those compiled under C</iaa>.

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<autodie> has been upgraded from version 2.20 to 2.21.

Numerous improvements have been made, many speed-related.  See the F<Changes>
file in the CPAN distribution for full details.

=item *

L<B> has been upgraded from version 1.45 to 1.46.

The fix for [perl #118525] introduced a regression in the behaviour of
C<B::CV::GV>, changing the return value from a C<B::SPECIAL> object on a
C<NULL> C<CvGV> to C<undef>.  C<B::CV::GV> again returns a C<B::SPECIAL> object
in this case.  [perl #119351]

B version 1.44 (Perl 5.19.2) introduced four new B::OP methods, C<slabbed>,
C<savefree>, C<static> and C<folded>, but these have never actually worked
until now.  They used to croak.

=item *

L<B::Concise> has been upgraded from version 0.98 to 0.99.

The handling of the C<glob> operator, broken since Perl 5.17.6, has been fixed
and handling of the new kvaslice and kvhslice operators have been added.

=item *

L<B::Deparse> has been upgraded from version 1.22 to 1.23.

The new kvaslice and kvhslice operators have been added.

=item *

L<Carp> has been upgraded from version 1.31 to 1.32.

=over 4

=item *

In stack traces, subroutine arguments that are strings are now quoted in a
consistent manner, regardless of what characters they contain and how they're
internally represented.

=item *

C<Carp> also now shows subroutine arguments that are references to regexp
objects in a consistent manner in stack traces.

=item *

C<Carp> now takes care not to clobber the status variables $! and $^E.

=item *

C<Carp> now won't vivify the C<overload::StrVal> glob or subroutine or the
C<overload> stash.

=item *

C<Carp> now avoids some unwanted Unicode warnings on older Perls.  This doesn't
affect behaviour with current Perls.

=item *

C<Carp::Heavy> detects version mismatch with C<Carp>, to give a good error
message if a current (stub) C<Carp::Heavy> gets loaded by an old C<Carp> that
expects C<Carp::Heavy> to provide subroutines.

=back

=item *

L<charnames> has been upgraded from version 1.38 to 1.39.

This module now works on EBCDIC platforms.

=item *

L<CPAN> has been upgraded from version 2.00 to 2.03-TRIAL.

Numerous updates and bug fixes are incorporated.  See the F<Changes> file for
full details.

=item *

L<CPAN::Meta> has been upgraded from version 2.132140 to 2.132510.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<CPAN::Meta::Requirements> has been upgraded from version 2.122 to 2.123.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<Data::Dumper> has been upgraded from version 2.148 to 2.149.

This upgrade is part of a larger change to make the array interface 64-bit safe
by using SSize_t instead of I32 for array indices.

In addition, an EBCDIC fix has been applied.

=item *

L<Devel::Peek> has been upgraded from version 1.13 to 1.14.

This upgrade is part of a larger change to preserve referential identity when
passing C<undef> to a subroutine by using NULL rather than &PL_sv_undef for
non-existent array elements.

In addition, C<Dump> with no args was broken in Perl 5.19.3, but has now been
fixed.

=item *

L<diagnostics> has been upgraded from version 1.32 to 1.33.

C<=back> is now treated as the end of a warning description, thus keeping any
trailing data in the file from showing up as part of the last warning's
description.  [perl #119817]

=item *

L<DynaLoader> has been upgraded from version 1.19 to 1.20.

The documentation now makes it clear, as has always been the case, that
C<dl_unload_file> is only called automatically to unload all loaded shared
objects if the perl interpreter was built with the C macro
DL_UNLOAD_ALL_AT_EXIT defined.  Support for GNU DLD has also been removed.

=item *

L<Encode> has been upgraded from version 2.52 to 2.55.

An erroneous early return in C<decode_utf8> has been removed, and a bug in
C<_utf8_on> under COW has been fixed.  Encode also now uses L<parent> rather
than L<base> throughout.

=item *

L<Errno> has been upgraded from version 1.19 to 1.20.

The list of E* constants exported on Windows has been updated to reflect the
changes made in the assignment of sockets error codes to $! (see
L</Incompatible Changes>).

=item *

L<Exporter> has been upgraded from version 5.69 to 5.70.

A number of typos have been corrected in the documentation.

=item *

L<ExtUtils::CBuilder> has been upgraded from version 0.280205 to 0.280212.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<ExtUtils::Command> has been upgraded from version 1.17 to 1.18.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<ExtUtils::MakeMaker> has been upgraded from version 6.72 to 6.76.

Numerous updates and bug fixes are incorporated.  See the F<Changes> file for
full details.

=item *

L<ExtUtils::ParseXS> has been upgraded from version 3.21 to 3.23.

Unquoted "here-doc" markers for typemaps can now be optionally followed by a
semicolon, just like quoted markers.  [perl #119761]

=item *

L<File::Copy> has been upgraded from version 2.27 to 2.28.

The documentation of C<copy> now makes it clear that trying to copy a file into
a non-existent directory is not supported.  [perl #119539]

=item *

L<File::Find> has been upgraded from version 1.24 to 1.25.

Better diagnostics are now provided in the case of a failed C<chdir>.

=item *

L<File::Glob> has been upgraded from version 1.20 to 1.21.

C<glob> now warns in the context of C<use warnings "syscalls";> if the supplied
pattern has an internal NUL (C<"\0">) character.

=item *

L<FileCache> has been upgraded from version 1.08 to 1.09.

This upgrade is part of a larger change to use L<parent> rather than L<base>.

=item *

L<Hash::Util::FieldHash> has been upgraded from version 1.12 to 1.13.

This upgrade is part of a larger change to use L<parent> rather than L<base>.

=item *

L<HTTP::Tiny> has been upgraded from version 0.034 to 0.035.

Encoded data from C<post_form> now preserves term order if data is provided as
an array reference.  (They are still sorted for consistency if provided as a
hash reference.)

=item *

L<I18N::LangTags> has been upgraded from version 0.39 to 0.40.

Bosnian has now joined Croatian and Serbian in the lists of mutually
intelligible Slavic languages.  [perl #72594]

=item *

L<IO> has been upgraded from version 1.28 to 1.29.

A minor internals-only change has been made to the XS code.

=item *

L<IO::Socket> has been upgraded from version 1.36 to 1.37.

The C<connect> method has been updated in the light of changes made in the
assignment of sockets error codes to $! on Windows (see L</Incompatible
Changes>).

=item *

L<IPC::Open3> has been upgraded from version 1.15 to 1.16.

This upgrade is part of a larger change to preserve referential identity when
passing C<undef> to a subroutine by using NULL rather than &PL_sv_undef for
non-existent array elements.

=item *

L<JSON::PP> has been patched from version 2.27202 to 2.27202_01.

A precedence issue has been fixed in the return value of a private subroutine.

=item *

L<Locale::Codes> has been upgraded from version 3.26 to 3.27.

New codes have been added and the (deprecated) set of FIPS-10 country codes has
been removed.

=item *

L<Math::BigInt> has been upgraded from version 1.9992 to 1.9993.

Cleaned up the L<Math::BigInt> and L<Math::BigFloat> documentation to be more
consistent with other Perl documentation.  [perl #86686]

Added a C<bint> method for rounding towards zero.  [perl #85296]

=item *

L<Math::BigInt::FastCalc> has been upgraded from version 0.30 to 0.31.

This upgrade is part of a larger change to make the array interface 64-bit safe
by using SSize_t instead of I32 for array indices.

=item *

L<Module::CoreList> has been upgraded from version 2.97 to 2.99.

The list of Perl versions covered has been updated.

A function C<is_core> has been added, which returns true if the specified
module was bundled with Perl.  Optionally you can specify a minimum version of
the module, and the specific version of Perl you're interested in (defaults to
$^V, the running version of Perl).

=item *

L<Module::Load::Conditional> has been upgraded from version 0.54 to 0.58.

C<requires> has been made more robust.  [cpan #83728]

=item *

L<Module::Metadata> has been upgraded from version 1.000014 to 1.000018.

The module's DESCRIPTION has been re-worded regarding safety/security to
satisfy CVE-2013-1437.  Also, versions are now detainted if needed.  [cpan
#88576]

=item *

L<mro> has been upgraded from version 1.13 to 1.14.

This upgrade is part of a larger change to make the array interface 64-bit safe
by using SSize_t instead of I32 for array indices.

=item *

L<Opcode> has been upgraded from version 1.25 to 1.26.

The new kvaslice and kvhslice operators have been added.

=item *

L<parent> has been upgraded from version 0.226 to 0.228.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<Parse::CPAN::Meta> has been upgraded from version 1.4405 to 1.4407.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<Perl::OSType> has been upgraded from version 1.003 to 1.005.

The Unix OSType 'bitrig' has been added.

=item *

L<perlfaq> has been upgraded from version 5.0150043 to 5.0150044.

The use of C<gensym> in a number of examples has been removed, the use of C<&>
in subroutine calls is now clarified and several new questions have been
answered.

=item *

L<Pod::Html> has been upgraded from version 1.20 to 1.21.

This upgrade is part of a larger change to use L<parent> rather than L<base>.

=item *

L<POSIX> has been upgraded from version 1.34 to 1.35.

The list of E* constants exported on Windows has been updated to reflect the
changes made in the assignment of sockets error codes to $! (see
L</Incompatible Changes>).

=item *

L<re> has been upgraded from version 0.25 to 0.26.

This upgrade is part of a larger change to support 64-bit string lengths in the
regular expression engine.

=item *

L<Scalar::Util> has been upgraded from version 1.31 to 1.32.

The documentation of C<blessed> has been improved to mention the fact that
package "0" is defined but false.

=item *

L<Socket> has been upgraded from version 2.011 to 2.012.

Syntax errors when building on the WinCE platform have been fixed.  [cpan
#87389]

=item *

L<Storable> has been upgraded from version 2.46 to 2.47.

This upgrade is part of a larger change to preserve referential identity when
passing C<undef> to a subroutine by using NULL rather than &PL_sv_undef for
non-existent array elements.

=item *

L<Term::ReadLine> has been upgraded from version 1.10 to 1.14.

Term::ReadLine::EditLine support has been added.

=item *

L<Test::Simple> has been patched from version 0.98 to 0.98_06.

A precedence issue has been fixed in the return value of a private subroutine
in L<Test::Builder>.

=item *

L<Time::Piece> has been upgraded from version 1.22 to 1.23.

Day of year parsing (like "%y%j") has been fixed.

=item *

L<Unicode::Collate> has been upgraded from version 0.98 to 0.99.

By default, out-of-range values are replaced with C<U+FFFD> (REPLACEMENT
CHARACTER) when C<UCA_Version> E<gt>= 22, or ignored when C<UCA_Version> E<lt>=
20.  When C<UCA_Version> E<gt>= 22, the weights of out-of-range values can be
overridden.

=item *

L<Unicode::UCD> has been upgraded from version 0.53 to 0.54.

This module now works on EBCDIC platforms.

=item *

L<version> has been upgraded from version 0.9903 to 0.9904.

No changes have been made to the installed code other than the version bump to
keep in sync with the latest CPAN release.

=item *

L<warnings> has been upgraded from version 1.18 to 1.19.

The C<syscalls> warnings category has been added to check for embedded NUL
(C<"\0">) characters in pathnames and string arguments to other system calls.
[perl #117265]

=item *

L<XS::Typemap> has been upgraded from version 0.10 to 0.11.

This upgrade is part of the change to remove the uninitialized warnings
exemption for uninitialized values returned by XSUBs (see the L</Selected Bug
Fixes> section).

=back

=head1 Documentation

=head2 New Documentation

=head3 L<perlrepository>

This document was removed (actually, renamed L<perlgit> and given a major
overhaul) in Perl 5.13.10, causing Perl documentation websites to show the now
out of date version in Perl 5.12 as the latest version.  It has now been
restored in stub form, directing readers to current information.

=head2 Changes to Existing Documentation

=head3 L<perldata>

=over 4

=item *

New sections have been added to document the new index/value array slice and
key/value hash slice syntax.

=back

=head3 L<perldebguts>

=over 4

=item *

The C<&DB::goto> and C<&DB::lsub> debugger subroutines are now documented.
[perl #77680]

=back

=head3 L<perlguts>

=over 4

=item *

Numerous minor changes have been made to reflect changes made to the perl
internals in this release.

=back

=head3 L<perlhack>

=over 4

=item *

The L<SUPER QUICK PATCH GUIDE|perlhack/SUPER QUICK PATCH GUIDE> section has
been updated.

=back

=head3 L<perlsub>

=over 4

=item *

A list of subroutine names used by the perl implementation is now included.
[perl #77680]

=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

=head3 New Errors

=over 4

=item *

L<delete argument is indexE<sol>value array slice, use array slice|perldiag/"delete argument is index/value array slice, use array slice">

(F) You used index/value array slice syntax (C<%array[...]>) as the argument to
C<delete>.  You probably meant C<@array[...]> with an @ symbol instead.

=item *

L<delete argument is keyE<sol>value hash slice, use hash slice|perldiag/"delete argument is key/value hash slice, use hash slice">

(F) You used key/value hash slice syntax (C<%hash{...}>) as the argument to
C<delete>.  You probably meant C<@hash{...}> with an @ symbol instead.

=back

=head3 New Warnings

=over 4

=item *

L<Invalid \0 character in %s for %s: %s\0%s|perldiag/"Invalid \0 character in %s for %s: %s\0%s">

(W syscalls) Embedded \0 characters in pathnames or other system call arguments
produce a warning as of 5.20.  The parts after the \0 were formerly ignored by
system calls.

=item *

L<Possible precedence issue with control flow operator|perldiag/"Possible precedence issue with control flow operator">

(W syntax) There is a possible problem with the mixing of a control flow
operator (e.g. C<return>) and a low-precedence operator like C<or>.  Consider:

    sub { return $a or $b; }

This is parsed as:

    sub { (return $a) or $b; }

Which is effectively just:

    sub { return $a; }

Either use parentheses or the high-precedence variant of the operator.

Note this may be also triggered for constructs like:

    sub { 1 if die; }

=item *

L<Scalar value %%s[%s] better written as $%s[%s]|perldiag/"Scalar value %%s[%s] better written as $%s[%s]">

(W syntax) In scalar context, you've used an array index/value slice (indicated
by %) to select a single element of an array.  Generally it's better to ask for
a scalar value (indicated by $).  The difference is that C<$foo[&bar]> always
behaves like a scalar, both in the value it returns and when evaluating its
argument, while C<%foo[&bar]> provides a list context to its subscript, which
can do weird things if you're expecting only one subscript.  When called in
list context, it also returns the index (what C<&bar> returns) in addition to
the value.

=item *

L<Scalar value %%s{%s} better written as $%s{%s}|perldiag/"Scalar value %%s{%s} better written as $%s{%s}">

(W syntax) In scalar context, you've used a hash key/value slice (indicated by
%) to select a single element of a hash.  Generally it's better to ask for a
scalar value (indicated by $).  The difference is that C<$foo{&bar}> always
behaves like a scalar, both in the value it returns and when evaluating its
argument, while C<@foo{&bar}> and provides a list context to its subscript,
which can do weird things if you're expecting only one subscript.  When called
in list context, it also returns the key in addition to the value.

=item *

L<Use of literal control characters in variable names is deprecated|perldiag/"Use of literal control characters in variable names is deprecated">

(D deprecated) Using literal control characters in the source to refer to the
^FOO variables, like $^X and ${^GLOBAL_PHASE} is now deprecated.  This only
affects code like $\cT, where \cT is a control in the source code: ${"\cT"} and
$^T remain valid.

=back

=head2 Changes to Existing Diagnostics

=over 4

=item *

Warnings and errors from the regexp engine are now UTF-8 clean

=item *

The "Unknown switch condition" error message has some slight changes.  This
error triggers when there is an unknown condition in a C<(?(foo))> conditional.
The error message used to read:

    Unknown switch condition (?(%s in regex;

But what %s could be was mostly up to luck.  For C<(?(foobar))>, you might have
seen "fo" or "f".  For Unicode characters, you would generally get a corrupted
string.  The message has been changed to read:

    Unknown switch condition (?(...)) in regex;

Additionally, the C<'E<lt>-- HERE'> marker in the error will now point to the
correct spot in the regex.

=item *

The "%s "\x%X" does not map to Unicode" warning is now correctly listed as a
severe warning rather than as a fatal error.

=back

=head1 Utility Changes

=head3 L<find2perl>

=over 4

=item *

L<find2perl> now handles C<?> wildcards correctly.  [perl #113054]

=back

=head1 Configuration and Compilation

=over 4

=item *

The F<Makefile.PL> for C<SDBM_File> now generates a better F<Makefile>, which
avoids a race condition during parallel makes, which could cause the build to
fail.  This is the last known parallel make problem (on *nix platforms), and
therefore we believe that a parallel make should now always be error free.

=for comment

Strictly only for a build where build files such as F<Makefile.SH> have not
been updated by C<git> in an already configured and built tree.

=back

=head1 Testing

=over 4

=item *

The test script F<t/bigmem/regexp.t> has been added to test that regular
expression matches on very large strings now succeed as expected.

=item *

A bug that was fixed in Perl 5.15.4 is now tested by the new test script
F<t/io/eintr_print.t>.  [perl #119097]

=item *

The new test scripts F<t/op/kvaslice.t> and F<t/op/kvhslice.t> test the new
index/value array slice and key/value hash slice syntax respectively.

=item *

Various cases of C<die>, C<last>, C<goto> and C<exit> triggering C<DESTROY> are
now tested by the new test script F<t/op/rt119311.t>.

=item *

The new test script F<t/op/waitpid.t> tests the fix for [perl #85228] (see
L</Selected Bug Fixes>).

=item *

The latest copyright years in the top-level F<README> file and the B<perl -v>
output are now tested as matching each other by the new test script
F<t/porting/copyright.t>

=item *

The new test script F<t/win32/signal.t> tests that $! and $^E are now preserved
across signal handlers by the Win32 signal emulation code.

=item *

The test script F<t/x2p/find2perl.t> has been added to test the F<find2perl>
program on platforms where it is practical to do so.

=back

=head1 Platform Support

=head2 New Platforms

=over 4

=item FreeMiNT

Support has been added for FreeMiNT, a free open-source OS for the Atari ST
system and its successors, based on the original MiNT that was officially
adopted by Atari.

=item Bitrig

Compile support has been added for Bitrig, a fork of OpenBSD.

=back

=head2 Discontinued Platforms

Configure hints and conditional code for several very old platforms has been
removed.  We have not received reports for these in many years, typically not
since Perl 5.6.0.

=over 4

=item AT&T 3b1

Configure support for the 3b1, also known as the AT&T Unix PC (and the similar
AT&T 7300), has been removed.

=back

=head2 Platform-Specific Notes

=over 4

=item VMS

The C<PERL_ENV_TABLES> feature to control the population of %ENV at perl
start-up was broken in Perl 5.16.0 but has now been fixed.

=item Win32

C<rename> and C<link> on Win32 now set $! to ENOSPC and EDQUOT when
appropriate.  [perl #119857]

=item WinCE

Perl now builds again on WinCE, following locale-related breakage (WinCE has
non-existent locale support) introduced around 5.19.1.  [perl #119443]

The building of XS modules has largely been restored.  Several still cannot
(yet) be built but it is now possible to build Perl on WinCE with only a couple
of further patches (to L<Socket> and L<ExtUtils::MakeMaker>), hopefully to be
incorporated soon.

=item GNU/Hurd

The BSD compatibility library C<libbsd> is no longer required for builds.

=back

=head1 Internal Changes

=over 4

=item *

The internal representation has changed for the match variables $1, $2 etc.,
$`, $&, $', ${^PREMATCH}, ${^MATCH} and ${^POSTMATCH}.  It uses slightly less
memory, avoids string comparisons and numeric conversions during lookup, and
uses 23 fewer lines of C.  This change should not affect any external code.

=item *

Arrays now use NULL internally to represent unused slots, instead of
&PL_sv_undef.  &PL_sv_undef is no longer treated as a special value, so
av_store(av, 0, &PL_sv_undef) will cause element 0 of that array to hold a
read-only undefined scalar.  C<$array[0] = anything> will croak and
C<\$array[0]> will compare equal to C<\undef>.

=item *

The SV returned by HeSVKEY_force() now correctly reflects the UTF8ness
of the underlying hash key when that key is not stored as a SV.  [perl
#79074]

=item *

Certain rarely used functions and macros available to XS code are now, or are
planned to be, deprecated.  These are:
C<utf8n_to_uvuni> (use C<utf8_to_uvchr_buf> instead),
C<utf8_to_uni_buf> (use C<utf8_to_uvchr_buf> instead),
C<valid_utf8_to_uvuni> (use C<utf8_to_uvchr_buf> instead),
C<uvuni_to_utf8> (use C<uvchr_to_utf8> instead),
C<NATIVE_TO_NEED> (this did not work properly anyway),
and C<ASCII_TO_NEED>  (this did not work properly anyway).

Starting in this release, almost never does application code need to
distinguish between the platform's character set and Latin1, on which the
lowest 256 characters of Unicode are based.

=back

=head1 Selected Bug Fixes

=over 4

=item *

The value of $^E is now saved across signal handlers on Windows.  [perl #85104]

=item *

A lexical filehandle (as in C<open my $fh...>) is usually given a name based on
the current package and the name of the variable, e.g. "main::$fh".  Under
recursion, the filehandle was losing the "$fh" part of the name.  This has been
fixed.

=item *

Perl 5.19.3 accidentally extended the previous bug to all closures, even when
not called recursively, i.e. lexical handles in closure would always be called
"main::" or "MyPackage::" etc.  This has been fixed.

=item *

Uninitialized values returned by XSUBs are no longer exempt from uninitialized
warnings.  [perl #118693]

=item *

C<elsif ("")> no longer erroneously produces a warning about void context.
[perl #118753]

=item *

Passing C<undef> to a subroutine now causes @_ to contain the same read-only
undefined scalar that C<undef> returns.  Furthermore, C<exists $_[0]> will now
return true if C<undef> was the first argument.  [perl #7508, #109726]

=item *

Passing a non-existent array element to a subroutine does not usually
autovivify it unless the subroutine modifies its argument.  This did not work
correctly with negative indices and with non-existent elements within the
array.  The element would be vivified immediately.  The delayed vivification
has been extended to work with those.  [perl #118691]

=item *

Assigning references or globs to the scalar returned by $#foo after the @foo
array has been freed no longer causes assertion failures on debugging builds
and memory leaks on regular builds.

=item *

Perl 5.19.2 threw line numbers off after some cases of line breaks following
keywords, such as

   1 unless
   1;

This has been fixed.  [perl #118931]

=item *

On 64-bit platforms, large ranges like 1..1000000000000 no longer crash, but
eat up all your memory instead.  [perl #119161]

=item *

C<__DATA__> now puts the C<DATA> handle in the right package, even if the
current package has been renamed through glob assignment.

=item *

The string position set by C<pos> could shift if the string changed
representation internally to or from utf8.  This could happen, e.g., with
references to objects with string overloading.

=item *

Taking references to the return values of two C<pos> calls with the same
argument, and then assigning a reference to one and C<undef> to the other,
could result in assertion failures or memory leaks.

=item *

Elements of @- and @+ now update correctly when they refer to non-existent
captures.  Previously, a referenced element (C<$ref = \$-[1]>) could refer to
the wrong match after subsequent matches.

=item *

When C<die>, C<last>, C<next>, C<redo>, C<goto> and C<exit> unwind the scope,
it is possible for C<DESTROY> recursively to call a subroutine or format that
is currently being exited.  It that case, sometimes the lexical variables
inside the sub would start out having values from the outer call, instead of
being undefined as they should.  This has been fixed.  [perl #119311]

=item *

${^MPEN} is no longer treated as a synonym for ${^MATCH}.

=item *

Perl now tries a little harder to return the correct line number in
C<(caller)[2]>.  [perl #115768]

=item *

Line numbers inside multiline quote-like operators are now reported correctly.
[perl #3643]

=item *

C<#line> directives inside code embedded in quote-like operators are now
respected.

=item *

Line numbers are now correct inside the second here-doc when two here-doc
markers occur on the same line.

=item *

Starting with Perl 5.12, line numbers were off by one if the B<-d> switch was
used on the #! line.  Now they are correct.

=item *

Perl 5.19.2 inadvertently stopped some lines of code from being available to
the debugger if C<=E<gt>> occurred at the beginning of a line and the previous
line ended with a keyword.  This is now fixed.

=item *

Perl 5.19.2 allowed the PERL5DB environment variable to contain multiple lines
of code, but those lines were not made available to the debugger.  Now they are
all stuffed into line number 0, accessible via C<$dbline[0]> in the debugger.

=item *

An optimisation in Perl 5.18 made incorrect assumptions causing a bad
interaction with the L<Devel::CallParser> CPAN module.  If the module was
loaded then lexical variables declared in separate statements following a
C<my(...)> list might fail to be cleared on scope exit.

=item *

C<&xsub> and C<goto &xsub> calls now allow the called subroutine to autovivify
elements of @_.

=item *

C<&xsub> and C<goto &xsub> no longer crash if *_ has been undefined and has no
ARRAY entry (i.e. @_ does not exist).

=item *

C<&xsub> and C<goto &xsub> now work with tied @_.

=item *

Overlong identifiers no longer cause a buffer overflow (and a crash).  They
started doing so in Perl 5.18.

=item *

The warning "Scalar value @hash{foo} better written as $hash{foo}" now produces
far fewer false positives.  In particular, C<@hash{+function_returning_a_list}>
and C<@hash{ qw "foo bar baz" }> no longer warn.  The same applies to array
slices.  [perl #28380, #114024]

=item *

C<$! = EINVAL; waitpid(0, WNOHANG);> no longer goes into an internal infinite
loop.  [perl #85228]

=item *

Perl 5.19.3 accidentally caused C<\(1+2)> to return a reference to the same
mutable scalar each time, so that modifications affect future evaluations.
This has been fixed.  [perl #119501]

=item *

A possible segmentation fault in filehandle duplication has been fixed.

=back

=head1 Acknowledgements

XXX Generate this with:

  perl Porting/acknowledgements.pl v5.19.3..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