=encoding utf8

=head1 NAME

perl5271delta - what is new for perl v5.27.1

=head1 DESCRIPTION

This document describes differences between the 5.27.0 release and the 5.27.1
release.

If you are upgrading from an earlier release such as 5.26.0, first read
L<perl5270delta>, which describes differences between 5.26.0 and 5.27.0.

=head1 Core Enhancements

=head2 L<C<delete>|perlfunc/delete EXPR> on key/value slices

L<C<delete>|perlfunc/delete EXPR> can now be used on key/value slices,
returning the keys along with the deleted values.
L<[perl #131328]|https://rt.perl.org/Ticket/Display.html?id=131328>

=head1 Security

=head2 Default Hash Function Change

Perl 5.27.1 retires various older hash functions which are not viewed as
sufficiently secure for use in Perl. We now support four general purpose
hash functions, Siphash (2-4 and 1-3 variants), and  Zaphod32, and StadtX
hash. In addition we support SBOX32 (a form of tabular hashing) for hashing
short  strings, in conjunction with any of the other hash functions provided.

By default Perl is configured to support SBOX hashing of strings up to 24
characters, in conjunction with StadtX hashing on 64 bit builds, and
Zaphod32 hashing for 32 bit builds.

You may control these settings with the following options to Configure:

    -DPERL_HASH_FUNC_SIPHASH
    -DPERL_HASH_FUNC_SIPHASH13
    -DPERL_HASH_FUNC_STADTX
    -DPERL_HASH_FUNC_ZAPHOD32

To disable SBOX hashing you can use

    -DPERL_HASH_USE_SBOX32_ALSO=0

And to set the maximum length to use SBOX32 hashing on with:

    -DSBOX32_MAX_LEN=16

The maximum length allowed is 256. There probably isn't much point
in setting it higher than the default.

=head1 Incompatible Changes

=head2 Comma-less variable lists in formats are no longer allowed

Omitting the commas between variables passed to formats is no longer
allowed.  This has been deprecated since Perl 5.000.

=head2 The C<:locked> and C<:unique> attributes have been removed

These have been no-ops and deprecated since Perl 5.12 and 5.10,
respectively.

=head2 C<\N{}> with nothing between the braces is now illegal.

This has been deprecated since Perl 5.24.

=head2 Opening the same symbol as both a file and directory handle is no longer allowed

Using C<open()> and C<opendir()> to associate both a filehandle and a dirhandle
to the same symbol (glob or scalar) has been deprecated since Perl 5.10.

=head2 Use of bare C<< << >> to mean C<< <<"" >> is no longer allowed

Use of a bare terminator has been deprecated since Perl 5.000.

=head2 Setting $/ to a reference to a non-positive integer no longer allowed

This used to work like setting it to C<undef>, but has been deprecated
since Perl 5.20.

=head2 Unicode code points with values exceeding C<IV_MAX> are now fatal.

This was deprecated since Perl 5.24.

=head2 C<B::OP::terse> no longer exists.

Use C<B::Concise::b_terse> instead.

=head2 Use of inherited AUTOLOAD for non-methods is no longer allowed.

This was deprecated in Perl 5.004.

=head2 Use of strings with code points over 0xFF is not allowed for
bitwise string operators

Code points over C<0xFF> do not make sense for bitwise operators.

=head2 Setting C<${^ENCODING}> to a defined value is now illegal

This has been deprecated since Perl 5.22 and a no-op since Perl 5.26.

=head2 Backslash no longer escapes colon in PATH for the -S switch

Previously the C<-S> switch incorrectly treated backslash ("\") as an
escape for colon when traversing the C<PATH> environment variable.
[perl #129183]

=head2 the -DH (DEBUG_H) misfeature has been removed

On a perl built with debugging support, the C<H> flag to the C<-D>
debugging option has been removed. This was supposed to dump hash values,
but has been broken for many years.

=head1 Deprecations

=head2 Use of L<C<vec>|perlfunc/vec EXPR,OFFSET,BITS> on strings with code
points above 0xFF is deprecated.

Use of these is nonsensical, as C<vec> is a bit-oriented operation,
which operates on the underlying UTF-8 representation these strings must
be in, and will likely give unexpected results.

=head2 Some uses of unescaped C<"{"> are no longer fatal

Perl 5.26.0 fatalized some uses of an unescaped left brace, but an
exception was made at the last minute, specifically crafted to be a
minimal change to allow GNU Autoconf to work.  This code is heavily
depended upon, and continues to use the deprecated usage.  Its use of an
unescaped left brace is one where we have no intention of repurposing
C<"{"> to be something other than itself.

That exception is now generalized to include various other such cases
where the C<"{"> will not be repurposed.  This is to get real experience
with this more complicated change now, in case we need to issue a dot
release if we find other things like Autoconf that are important to work
around.

Note that these uses continue to raise a deprecation message.

=head1 Performance Enhancements

=over 4

=item *

L<File::Glob> has been modified to remove unnecessary backtracking and
recursion, thanks to Russ Cox. See L<https://research.swtch.com/glob>
for more details.

=item *

The C<ref()> builtin is now much faster in boolean context, since it no
longer bothers to construct a temporary string like C<Foo=ARRAY(0x134af48)>.

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Archive::Tar> has been upgraded from version 2.24 to 2.26.

=item *

L<B::Deparse> has been upgraded from version 1.40 to 1.41. It includes
many bug fixes, and in particular, it now deparses variable attributes
correctly:

    my $x :foo;  # used to deparse as
                 # 'attributes'->import('main', \$x, 'foo'), my $x;

=item *

L<charnames> has been upgraded from version 1.44 to 1.45.

=item *

L<Devel::PPPort> has been upgraded from version 3.35 to 3.36.

=item *

L<DirHandle> has been upgraded from version 1.04 to 1.05.

=item *

L<ExtUtils::Install> has been upgraded from version 2.04 to 2.14.

=item *

L<ExtUtils::MakeMaker> has been upgraded from version 7.24 to 7.30.

=item *

L<File::Path> has been upgraded from version 2.12_01 to 2.14.

=item *

L<Filter::Util::Call> has been upgraded from version 1.55 to 1.57.

=item *

L<GDBM_File> has been upgraded from version 1.15 to 1.16.

=item *

L<Getopt::Long> has been upgraded from version 2.49 to 2.5.

=item *

L<if> has been upgraded from version 0.0606 to 0.0607.

=item *

L<IO::Socket::IP> has been upgraded from version 0.38 to 0.39.

=item *

L<IPC::Cmd> has been upgraded from version 0.96 to 0.98.

=item *

L<JSON::PP> has been upgraded from version 2.27400_02 to 2.94.

=item *

L<Locale::Codes> has been upgraded from version 3.42 to 3.52.

=item *

L<Module::CoreList> has been upgraded from version 5.20170620 to 5.20170621.

=item *

L<mro> has been upgraded from version 1.20 to 1.21.

=item *

L<PerlIO::scalar> has been upgraded from version 0.26 to 0.27.

=item *

L<PerlIO::via> has been upgraded from version 0.16 to 0.17.

=item *

L<Storable> has been upgraded from version 2.62 to 2.63.

=item *

L<Test::Harness> has been upgraded from version 3.38 to 3.39.

=item *

L<threads> has been upgraded from version 2.15 to 2.16.

=item *

L<threads::shared> has been upgraded from version 1.56 to 1.57.

=item *

L<version> has been upgraded from version 0.9917 to 0.9918.

=back

=head1 Testing

Tests were added and changed to reflect the other additions and
changes in this release.  Furthermore, these significant changes were
made:

=over 4

=item *

Testing of the XS-APItest directory is now done in parallel, where
applicable.

=item *

Perl now includes a default F<.travis.yml> file for Travis CI testing
on github mirrors.  [perl #123981]

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item Windows

=over 4

=item *

Support for compiling perl on Windows using Microsoft Visual Studio 2017
(containing Visual C++ 14.1) has been added.

=back

=back

=head1 Internal Changes

=over 4

=item *

The C<PL_statbuf> interpreter variable has been removed.

=item *

The deprecated function C<to_utf8_case()>, accessible from XS code, has
been removed.

=item *

A new function
L<C<is_utf8_invariant_string_loc()>|perlapi/is_utf8_invariant_string_loc>
has been added that is like
L<C<is_utf8_invariant_string()>|perlapi/is_utf8_invariant_string>
but takes an extra pointer parameter into which is stored the location
of the first variant character, if any are found.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Fetching the name of a glob that was previously UTF-8 but wasn't any
longer would return that name flagged as UTF-8.  [perl #131263]

=item *

The perl C<sprintf()> function (via the underlying C function
C<Perl_sv_vcatpvfn_flags()>) has been heavily reworked to fix many minor
bugs, including the integer wrapping of large width and precision
specifiers and potential buffer overruns. It has also been made faster in
many cases.

=item *

Exiting from an C<eval>, whether normally or via an exception, now always
frees temporary values (possibly calling destructors) I<before> setting
C<$@>. For example:

    sub DESTROY { eval { die "died in DESTROY"; } }
    eval { bless []; };
    # $@ used to be equal to "died in DESTROY" here; it's now "".

=back

=head1 Acknowledgements

Perl 5.27.1 represents approximately 3 weeks of development since Perl 5.27.0
and contains approximately 62,000 lines of changes across 510 files from 30
authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 55,000 lines of changes to 380 .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 5.27.1:

Aaron Crane, Abigail, Andy Dougherty, Andy Lester, Aristotle Pagaltzis, Chris
'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Dan Collins,
David Mitchell, Eric Herman, Eugen Konkov, Father Chrysostomos, Graham Knop,
H.Merijn Brand, Jacques Germishuys, James E Keenan, Jerry D. Hedden, John
Peacock, Karl Williamson, Ken Cotterill, Lukas Mai, Matthew Horsfall, Sawyer X,
Steve Hay, Sullivan Beck, Thomas Sibley, Tony Cook, Yves Orton, Zefram.

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
