=encoding utf8

=head1 NAME

perl5274delta - what is new for perl v5.27.4

=head1 DESCRIPTION

This document describes differences between the 5.27.3 release and the 5.27.4
release.

If you are upgrading from an earlier release such as 5.27.2, first read
L<perl5273delta>, which describes differences between 5.27.2 and 5.27.3.

=head1 Core Enhancements

=head2 In-place editing is now safer

Previously in-place editing would delete or rename the input file
as soon as you started working on a new file.

Without backups this would result in loss of data if there was an
error, such as a full disk, when writing to the output file.

This has changed so that the input file isn't replaced until the
output file has been completely written and successfully closed.

This works by creating a work file in the same directory, which is
renamed over the input file once the output file is complete.

Incompatibilities:

=over

=item *

Since this renaming needs to only happen once, if you create a thread
or child process, that renaming will only happen in the original
thread or process.

=item *

If you change directories while processing a file, and your operating
system doesn't provide the C<unlinkat()>, C<renameat()> and C<fchmodat()>
functions, the final rename step may fail.

=back

L<[perl #127663]|https://rt.perl.org/Public/Bug/Display.html?id=127663>

=head1 Security

=head2 [CVE-2017-12837] Heap buffer overflow in regular expression compiler

Compiling certain regular expression patterns with the case-insensitive
modifier could cause a heap buffer overflow and crash perl.  This has now been
fixed.
L<[perl #131582]|https://rt.perl.org/Public/Bug/Display.html?id=131582>

=head2 [CVE-2017-12883] Buffer over-read in regular expression parser

For certain types of syntax error in a regular expression pattern, the error
message could either contain the contents of a random, possibly large, chunk of
memory, or could crash perl.  This has now been fixed.
L<[perl #131598]|https://rt.perl.org/Public/Bug/Display.html?id=131598>

=head2 [CVE-2017-12814] C<$ENV{$key}> stack buffer overflow on Windows

A possible stack buffer overflow in the C<%ENV> code on Windows has been fixed
by removing the buffer completely since it was superfluous anyway.
L<[perl #131665]|https://rt.perl.org/Public/Bug/Display.html?id=131665>

=head1 Performance Enhancements

=over 4

=item *

Slightly improved performance when parsing stash names.
L<[perl #129990]|https://rt.perl.org/Public/Bug/Display.html?id=129990>

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<attributes> has been upgraded from version 0.3 to 0.31.

=item *

L<File::Glob> has been upgraded from version 1.29 to 1.30.

=item *

L<I18N::Langinfo> has been upgraded from version 0.13 to 0.14.
This fixes a bug in which the underlying locale was ignored for the
C<RADIXCHAR> (always was returned as a dot, and the C<THOUSEP> (always
empty).  Now the locale-appropriate values are returned.

=item *

L<Module::CoreList> has been upgraded from version 5.20170821 to 5.20170920.

=item *

L<sort> has been upgraded from version 2.02 to 2.03.

=item *

L<Term::ReadLine> has been upgraded from version 1.16 to 1.17.

=item *

L<threads> has been upgraded from version 2.17 to 2.18.

=item *

L<VMS::Stdio> has been upgraded from version 2.41 to 2.42.

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

The C<VMS::stdio> compatibility shim has been removed.

=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 Changes to Existing Diagnostics

=over 4

=item *

A false-positive warning that was issued when using a
numerically-quantified sub-pattern in a recursive regex has been
silenced. L<[perl #131868]|https://rt.perl.org/Public/Bug/Display.html?id=131868>

=back

=head1 Testing

Tests were added and changed to reflect the other additions and changes
in this release.

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item Darwin

Perl now correctly uses reentrant functions, like C<asctime_r>, on
versions of Darwin that have support for them.

=back

=head1 Internal Changes

=over 4

=item *

A new function, L<C<Perl_langinfo()>|perlapi/Perl_langinfo> has been
added.  It is an (almost) drop-in replacement for the system
C<nl_langinfo(3)>, but works on platforms that lack that; as well as
being more thread-safe, and hiding some gotchas with locale handling
from the caller.  Code that uses this, needn't use L<C<localeconv(3)>>
(and be affected by the gotchas) to find the decimal point, thousands
separator, or currency symbol.  See L<perlapi/Perl_langinfo>.

=item *

A new API function L<C<sv_rvunweaken()>|perlapi/sv_rvunweaken> has
been added to complement L<C<sv_rvweaken()>|perlapi/sv_rvweaken>.
The implementation was taken from L<Scalar::Util/unweaken>.

=item *

A new flag, C<SORTf_UNSTABLE>, has been added. This will allow a
future commit to make mergesort unstable when the user specifies ‘no
sort stable’, since it has been decided that mergesort should remain
stable by default.

=back

=head1 Selected Bug Fixes

=over 4

=item *

The internal stack usage checks introduced in 5.27.2 are now also done
by the C<entersub> operator when calling XSUBs.  This means we can
report which XSUB failed to allocate enough stack space.
L<[perl #131975]|https://rt.perl.org/Public/Bug/Display.html?id=131975>

=item *

Parsing a C<sub> definition could cause a use after free if the C<sub>
keyword was followed by whitespace including newlines (and comments.)
L<[perl #131836]|https://rt.perl.org/Public/Bug/Display.html?id=131836>

=item *

The tokenizer now correctly adjusts a parse pointer when skipping
whitespace in a C< ${identifier} > construct.
L<[perl #131949]|https://rt.perl.org/Public/Bug/Display.html?id=131949>

=item *

Accesses to C<${^LAST_FH}> no longer assert after using any of a
variety of I/O operations on a non-glob.
L<[perl #128263]|https://rt.perl.org/Public/Bug/Display.html?id=128263>

=item *

The C<Copy()>, C<Move()>, C<Zero()> macros and their variants now
assert if the pointers supplied are C<NULL>.  ISO C considers
supplying NULL pointers to the functions these macros are built upon
as undefined behaviour even when their count parameters are zero.
Based on these assertions and the original bug report three macro
calls were made conditional.
L<[perl #131746]|https://rt.perl.org/Public/Bug/Display.html?id=131746>
L<[perl #131892]|https://rt.perl.org/Public/Bug/Display.html?id=131892>

=item *

The in-place sort optimisation now correctly strengthens weak
references using the new L<C<sv_rvunweaken()>|perlapi/sv_rvunweaken>
API function.

=item *

Only the C<=> operator is permitted for defining defaults for
parameters in subroutine signatures.  Previously other assignment
operators, e.g. C<+=>, were also permitted.
L<[perl #131777]|https://rt.perl.org/Public/Bug/Display.html?id=131777>

=item *

Package names are now always included in C<:prototype> warnings
L<[perl #131833]|https://rt.perl.org/Public/Bug/Display.html?id=131833>

=item *

Creating a thread with no parameters no longer tries to C<Copy()> a
null pointer. This fixes an assertion failure and allows threaded
builds to work again.

=item *

The C<je_old_stack_hwm> field, previously only found in the C<jmpenv>
structure on debugging builds, has been added to non-debug builds as
well. This fixes an issue with some CPAN modules caused by the size of
this structure varying between debugging and non-debugging builds.
L<[perl #131942]|https://rt.perl.org/Public/Bug/Display.html?id=131942>

=item *

The arguments to the C<ninstr()> macro are now correctly parenthesized.

=item *

A NULL pointer dereference in the C<S_regmatch()> function has been
fixed.
L<[perl #132017]|https://rt.perl.org/Public/Bug/Display.html?id=132017>

=back

=head1 Acknowledgements

Perl 5.27.4 represents approximately 4 weeks of development since Perl 5.27.3
and contains approximately 5,000 lines of changes across 140 files from 18
authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 3,300 lines of changes to 76 .pm, .t, .c and .h files.

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 5.27.4:

Abigail, Chris 'BinGOs' Williams, Dagfinn Ilmari Mannsåker, David Mitchell,
Dominic Hargreaves, Father Chrysostomos, H.Merijn Brand, James E Keenan, Jarkko
Hietaniemi, John SJ Anderson, Karl Williamson, Lukas Mai, Matthew Horsfall,
Neil Bowers, Nicolas R., Steve Hay, Tony Cook, Yves Orton.

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 perl bug database
at L<https://rt.perl.org/> .  There may also be information at
L<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 see
L<perlsec/SECURITY VULNERABILITY CONTACT INFORMATION>
for details of how to report the issue.

=head1 Give Thanks

If you wish to thank the Perl 5 Porters for the work we had done in Perl 5,
you can do so by running the C<perlthanks> program:

    perlthanks

This will send an email to the Perl 5 Porters list with your show of thanks.

=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