=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.17.3

=head1 DESCRIPTION

This document describes differences between the 5.17.2 release and the 5.17.3
release.

If you are upgrading from an earlier release such as 5.17.1, first read
L<perl5172delta>, which describes differences between 5.17.1 and 5.17.2.

=head1 Core Enhancements

=head2 Computed Labels

The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
operator, now allow arbitrary expressions to be used to compute labels at run
time.  Previously, any argument that was not a constant was treated as the
empty string.

=head1 Incompatible Changes

=head2 C<$ENV{foo}=undef> deletes value from environ, like C<delete $ENV{foo}>

This facilitates use of C<local()> with C<%ENV> entries.  In previous versions
of Perl, C<undef> was converted to the empty string.

=head2 Defined values stored in environment are forced to byte strings

A value stored in an environment variable has always been stringified.  In this
release, it is converted to be only a byte string.  First, it is forced to be a
only a string.  Then if the string is utf8 and the equivalent of
C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
C<utf8::encode()> is used, and a warning is issued about wide characters
(L</Diagnostics>).

=head2 C<given> now aliases the global C<$_>

Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
global C<$_> an alias for its argument, just like C<foreach>.  However, it
still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
C<foreach>) [perl #114020].

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<B> has been upgraded from version 1.36 to 1.37.  All C<CVf_*> and C<GVf_*>
and more SV-related flag values are now provided as constants in the C<B::>
namespace and available for export.  The default export list has not changed.

=item *

L<B::Concise> has been upgraded from version 0.91 to 0.92.  The C<-nobanner>
option has been fixed, and C<format>s can now be dumped.  When passed a sub
name to dump, it will check also to see whether it is the name of a format.  If
a sub and a format share the same name, it will dump both.

=item *

L<B::Debug> has been upgraded from version 1.17 to 1.18.  This adds support
(experimentally) for C<B::PADLIST>, which will be added in Perl 5.17.4.

=item *

L<B::Deparse> has been upgraded from version 1.15 to 1.16.  It now deparses
loop controls with the correct precedence, and multiple statements in a
C<format> line are also now deparsed correctly.

=item *

L<CGI> has been upgraded from version 3.59 to 3.60.  Unrecognized HTML escape
sequences are now handled better, problematic trailing newlines are no longer
inserted after E<lt>formE<gt> tags by C<startform()> or C<start_form()>, and
bogus "Insecure Dependency" warnings appearing with some versions of perl are
now worked around.

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.05201 to 2.055.  The
misuse of Perl's "magic" API has been fixed.

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.05401 to 2.056.  The
misuse of Perl's "magic" API has been fixed.

=item *

L<Compress::Zlib> has been upgraded from version 2.052 to 2.055. C<compress()>,
C<uncompress()>, C<memGzip()> and C<memGunzip()> have been speeded up by making
parameter validation more efficient.

=item *

L<Data::Dumper> has been upgraded from version 2.135_06 to 2.135_07.  It has
been optimized to only build a seen-scalar hash as necessary, thereby speeding
up serialization drastically.

=item *

L<Devel::Peek> has been upgraded from version 1.08 to 1.09.  The only change
has been to the test script, to account for changes to some flags in perl's
internals.

=item *

L<Encode> has been upgraded from version 2.44 to 2.47.  The Mac alias x-mac-ce
has been added, and various bugs have been fixed in Encode::Unicode,
Encode::UTF7 and Encode::GSM0338.

=item *

L<Module::Build> has been upgraded from version 0.40 to 0.4003.  A minor bug
fix allows markup to be used around the leading "Name" in a POD "abstract"
line, and some documentation improvements have been made.

=item *

L<Module::CoreList> has been upgraded from version 2.69 to 2.71.  Version
information is now stored as a delta, which greatly reduces the size of the
F<CoreList.pm> file.

=item *

L<Module::Load::Conditional> has been upgraded from version 0.50 to 0.54.
Various enhancements include the new use of Module::Metadata.

=item *

L<Module::Metadata> has been upgraded from version 1.000009 to 1.000011.  The
creation of a Module::Metadata object for a typical module file has been sped
up by about 40%, and some spurious warnings about C<$VERSION>s have been
suppressed.

=item *

L<Module::Pluggable> has been upgraded from version 4.0 to 4.3.  Amongst other
changes, triggers are now allowed on events, which gives a powerful way to
modify behaviour.

=item *

L<perlfaq> has been upgraded from version 5.0150040 to 5.0150041.  This
contains a couple of minor corrections and lists one new editor.

=item *

L<Pod::Simple> has been upgraded from version 3.20 to 3.23.  Numerous
improvements have been made, mostly to Pod::Simple::XHTML, which also has a
compatibility change: the C<codes_in_verbatim> option is now disabled by
default.  See F<cpan/Pod-Simple/ChangeLog> for the full details.

=item *

L<re> has been upgraded from version 0.21 to 0.22.  Single character [class]es
like C</[s]/> or C</[s]/i> are now optimized as if they did not have the
brackets, i.e. C</s/> or C</s/i>.

=item *

L<Socket> has been upgraded from version 2.002 to 2.004.  Constants and
functions required for IP multicast source group membership have been added.

=item *

L<Storable> has been upgraded from version 2.37 to 2.38.  It can now freeze and
thaw vstrings correctly.  This causes a slight incompatible change in the
storage format, so the format version has increased to 2.9.

=item *

L<Sys::Syslog> has been upgraded from version 0.29 to 0.31.  This contains
several bug fixes relating to C<getservbyname()>, C<setlogsock()>and log levels
in C<syslog()>, together with fixes for Windows, Haiku-OS and GNU/kFreeBSD.
See F<cpan/Sys-Syslog/Changes> for the full details.

=item *

L<Term::ReadLine> has been upgraded from version 1.09 to 1.10.  This fixes the
use of the B<cpan> and B<cpanp> shells on Windows in the event that the current
drive happens to contain a F<\dev\tty> file.

=item *

L<Text::Tabs> and L<Text::Wrap> have been upgraded from version 2009.0305 to
2012.0818.  Support for Unicode combining characters has been added to them
both.

=item *

L<Time::Local> has been upgraded from version 1.2000 to 1.2300.  Seconds values
greater than 59 but less than 60 no longer cause C<timegm()> and C<timelocal()>
to croak.

=item *

L<Unicode::UCD> has been upgraded from version 0.44 to 0.45.  This has been
modified slightly for reasons of perl internal use only.

=item *

L<Win32> has been upgraded from version 0.44 to 0.45.  New APIs have been added
for getting and setting the current code page.

=item *

L<Win32CORE> has been upgraded from version 0.02 to 0.03.  The use of
PERL_NO_GET_CONTEXT here has resulted in smaller machine code.

=back

=head1 Documentation

=head2 Changes to Existing Documentation

=head3 L<perlfunc>, L<perlop>

=over 4

=item *

Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
had the same precedence as assignment operators, but this was not documented
until now.

=back

=head3 L<perlvar>

=over 4

=item *

A caveat has been added to the documentation for C<$_> warning against the use
of lexical C<$_> [perl #114020].

=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<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">

This message now occurs when a here document label has an initial quotation
mark but the final quotation mark is missing.

This replaces a bogus and misleading error message about not finding the label
itself [perl #114104].

=item *

L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">

This error is thrown when a child pseudo-process in the ithreads implementation
on Windows was not scheduled within the time period allowed and therefore was
not able to initialize properly [perl #88840].

=back

=head3 New Warnings

=over 4

=item *

L<Wide character in setenv|perldiag/"Wide character in %s">

Attempts to put wide characters into environment variables via C<%ENV> now
provoke this warning.

=back

=head1 Configuration and Compilation

=over 4

=item *

The pager detection in F<Configure> has been improved to allow responses which
specify options after the program name, e.g. B</usr/bin/less -R>, if the user
accepts the default value.  This helps B<perldoc> when handling ANSI escapes
[perl #72156].

=back

=head1 Platform Support

=head2 Discontinued Platforms

=over 4

=item UTS Global

Support code relating to UTS global has been removed.  UTS was a mainframe
version of System V created by Amdahl, subsequently sold to UTS Global.  The
port has not been touched since before Perl 5.8.0, and UTS Global is now
defunct.

=back

=head2 Platform-Specific Notes

=over 4

=item Windows

A new makefile option, USE_64_BIT_INT, has been added to the Windows makefiles.
Set this to "define" when building a 32-bit perl if you want it to use 64-bit
integers.

Machine code size reductions, already made to the DLLs of XS modules in Perl
5.17.2, have now been extended to the perl DLL itself.

Building with VC++ 6.0 was inadvertently broken in Perl 5.17.2 but has now been
fixed again.

=item VMS

The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.

=back

=head1 Selected Bug Fixes

=over 4

=item *

C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
(ZERO WIDTH JOINER).  C<\W> no longer matches these.  This change is because
Unicode corrected their definition of what C<\w> should match.

=item *

C<dump LABEL> no longer leaks its label.

=item *

Constant folding no longer changes the behaviour of functions like C<stat()>
and C<truncate()> that can take either filenames or handles.
C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
arbitrary expression), rather than the handle "foo".

=item *

C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
the filehandle has been deleted.  This was broken in Perl 5.16.0.

=item *

Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
longer cause double frees or panic messages.

=item *

C<s///> now turns vstrings into plain strings when performing a substitution,
even if the resulting string is the same (C<s/a/a/>).

=item *

Prototype mismatch warnings no longer erroneously treat constant subs as having
no prototype when they actually have "".

=item *

Constant subroutines and forward declarations no longer prevent prototype
mismatch warnings from omitting the sub name.

=item *

C<undef> on a subroutine now clears call checkers.

=item *

The C<ref> operator started leaking memory on blessed objects in Perl 5.16.0.
This has been fixed [perl #114340].

=item *

C<use> no longer tries to parse its arguments as a statement, making
C<use constant { () };> a syntax error [perl #114222].

=item *

On debugging builds, "uninitialized" warnings inside formats no longer cause
assertion failures.

=item *

On debugging builds, subroutines nested inside formats no longer cause
assertion failures [perl #78550].

=item *

Formats and C<use> statements are now permitted inside formats.

=item *

C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
It was possible for the latter to refuse to close over $x if the variable was
not active; e.g., if it was defined outside a currently-running named
subroutine.

=item *

Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
This also allows "my $x if 0" variables to be seen in the debugger [perl
#114018].

=item *

Formats called recursively no longer stomp on their own lexical variables, but
each recursive call has its own set of lexicals.

=item *

Attempting to free an active format or the handle associated with it no longer
results in a crash.

=item *

Format parsing no longer gets confused by braces, semicolons and low-precedence
operators.  It used to be possible to use braces as format delimiters (instead
of C<=> and C<.>), but only sometimes.  Semicolons and low-precedence operators
in format argument lines no longer confuse the parser into ignoring the line's
return value.  In format argument lines, braces can now be used for anonymous
hashes, instead of being treated always as C<do> blocks.

=item *

Formats can now be nested inside code blocks in regular expressions and other
quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].

=item *

Formats are no longer created after compilation errors.

=item *

Some format syntax errors started causing crashes in Perl 5.17.2, but have now
been fixed.

=item *

Under debugging builds, the B<-DA> command line option started crashing in Perl
5.16.0.  It has been fixed [perl #114368].

=item *

Scope::Escape compatibility, which was broken in Perl 5.17.2, has been restored
[perl #113872].

=item *

A potential deadlock scenario involving the premature termination of a pseudo-
forked child in a Windows build with ithreads enabled has been fixed.  This
resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
#88840].

=item *

The microperl build, broken since Perl 5.15.7, has now been restored.

=item *

The code which generates errors from C<require()> could potentially read one or
two bytes before the start of the filename for filenames less than three bytes
long and ending C</\.p?\z/>.  This has now been fixed.  Note that it could
never have happened with module names given to C<use()> or C<require()> anyway.

=item *

The handling of pathnames of modules given to C<require()> has been made
thread-safe on VMS.

=item *

The C<re_compile()> API function, the entry point for perl's regex compiler,
was accidentally changed in Perl 5.17.1 to operate on the current engine.  This
has now been restored to its former core-engine-specific state [perl #114302].

=item *

Perl 5.17.1 introduced a memory leak into the re-use of run-time regexes where
the pattern hasn't changed (i.e. C</$unchanging/>).  This has now been fixed.

=item *

A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
test suite has been fixed [perl #114242].

=item *

Formats no longer leak.  They started leaking in Perl 5.17.2.

=item *

Pod can now be nested in code inside a quoted construct outside of a string
eval.  This used to work only within string evals [perl #114040].

=back

=head1 Acknowledgements

Perl 5.17.3 represents approximately 4 weeks of development since Perl 5.17.2
and contains approximately 85,000 lines of changes across 470 files from 24
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 5.17.3:

Andy Dougherty, Chip Salzenberg, Chris 'BinGOs' Williams, Craig A. Berry,
Daniel Dragan, Dave Rolsky, David Leadbeater, David Mitchell, Eric Brine,
Father Chrysostomos, Goro Fuji, James E Keenan, Jan Dubois, Joaquin Ferrero,
Karl Williamson, Nicholas Clark, Paul Marquess, Reini Urban, Ricardo Signes,
Robin Barker, Shirakata Kentaro, Steffen Müller, Steve Hay, Tony Cook.

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
