path: root/pod/perldelta.pod

=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.27.8

=head1 DESCRIPTION

This document describes differences between the 5.27.7 release and the 5.27.8
release.

If you are upgrading from an earlier release such as 5.27.6, first read
L<perl5277delta>, which describes differences between 5.27.6 and 5.27.7.

=head1 Core Enhancements

=head2 Close-on-exec flag set atomically

When opening a file descriptor, perl now generally opens it with its
close-on-exec flag already set, on platforms that support doing so.
This improves thread safety, because it means that an C<exec> initiated
by one thread can no longer cause a file descriptor in the process
of being opened by another thread to be accidentally passed to the
executed program.

Additionally, perl now sets the close-on-exec flag more reliably, whether
it does so atomically or not.  Most file descriptors were getting the
flag set, but some were being missed.

=head2 Mixed Unicode scripts are now detectable

A mixture of scripts, such as Cyrillic and Latin, in a string is often
the sign of a spoofing attack.  A new regular expression construct
now allows for easy detection of these.  For example, you can say

 qr/(?script_run: \d+ \b )/x

And the digits matched will all be from the same set of 10.  You won't
get a look-alike digit from a different script that has a different
value than what it appears to be.

=head2 String- and number-specific bitwise ops are no longer experimental

The new string-specific (C<&. |. ^. ~.>) and number-specific (C<& | ^ ~>)
bitwise operators introduced in Perl 5.22 are no longer experimental.
Because the number-specific ops are spelled the same way as the existing
operators that choose their behaviour based on their operands, these
operators must still be enabled via the "bitwise" feature, in either of
these two ways:

    use feature "bitwise";

    use v5.28; # "bitwise" now included

They are also now enabled by the B<-E> command-line switch.

The "bitwise" feature no longer emits a warning.  Existing code that
disables the "experimental::bitwise" warning category that the feature
previously used will continue to work.

One caveat that module authors ought to be aware of is that the numeric
operators now pass a fifth TRUE argument to overload methods.  Any methods
that check the number of operands may croak if they do not expect so many.
XS authors in particular should be aware that this:

    SV *
    bitop_handler (lobj, robj, swap)

may need to be changed to this:

    SV *
    bitop_handler (lobj, robj, swap, ...)

=head1 Incompatible Changes

=head2 Smartmatch and switch reversion

The changes to the experimental smart match operator (C<~~>) and switch
(C<given>/C<when>) constructs that were made in Perl 5.27.7 have been
reverted due to the extent of the trouble caused to CPAN modules.
It is expected that smartmatch will be changed again in the future,
but preceded by some kind of explicit deprecation.

=head2 Subroutine attribute and signature order

The experimental subroutine signatures feature has been changed so that
subroutine attributes must now come before the signature rather than
after. This is because attributes like C<:lvalue> can affect the
compilation of code within the signature, for example:

    sub f :lvalue ($a = do { $x = "abc"; return substr($x,0,1)}) { ...}

Note that this the second time they have been flipped:

    sub f :lvalue ($a, $b) { 1 }; # 5.20; 5.28 onwards
    sub f ($a, $b) :lvalue { 1 }; # 5.22 - 5.26

=head1 Deprecations

=head2 Use of code points over 0xFF in string bitwise operators

Some uses of these already are illegal after a previous deprecation
cycle.  This deprecates the remaining uses.  See L<perldeprecation>.

=head2 Use of unescaped C<"{"> immediately after a C<"("> in regular
expression patterns

Using unescaped left braces is officially deprecated everywhere, but it
is not enforced in contexts where their use does not interfere with
expected extensions to the language.  A deprecation is added in this
release when the brace appears immediately after an opening parenthesis.
Before this, even if the brace was part of a legal quantifier, it was
not interpreted as such, but as the literal characters, unlike other
quantifiers that follow a C<"("> which are considered errors.  Now,
their use will raise a deprecation message, unless turned off.

=head1 Performance Enhancements

=over 4

=item *

The performance of pattern matching C<[[:ascii:]]> and C<[[:^ascii:]]>
has been improved significantly except on EBCDIC platforms.

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<B> has been upgraded from version 1.73 to 1.74.

=item *

L<B::Deparse> has been upgraded from version 1.46 to 1.47.

=item *

L<Data::Dumper> has been upgraded from version 2.169 to 2.170.

=item *

L<Devel::PPPort> has been upgraded from version 3.37 to 3.38.

=item *

L<Digest::SHA> has been upgraded from version 6.00 to 6.01.

=item *

L<Encode> has been upgraded from version 2.93 to 2.94.

=item *

L<ExtUtils::Miniperl> has been upgraded from version 1.07 to 1.08.

=item *

L<feature> has been upgraded from version 1.50 to 1.51.

=item *

L<File::Spec> has been upgraded from version 3.71 to 3.72.

=item *

L<JSON::PP> has been upgraded from version 2.97000 to 2.97001.

=item *

L<Module::CoreList> has been upgraded from version 5.20171220 to 5.20180120.

=item *

L<Opcode> has been upgraded from version 1.42 to 1.43.

=item *

L<overload> has been upgraded from version 1.29 to 1.30.

=item *

L<Pod::Functions> has been upgraded from version 1.12 to 1.13.

=item *

L<Pod::Html> has been upgraded from version 1.23 to 1.24.

=item *

The podlators bundle has been upgraded from version 4.09 to 4.10.

Man page references and function names now follow the Linux man page
formatting standards, instead of the Solaris standard.

=item *

L<Socket> has been upgraded from version 2.020_04 to 2.027.

=item *

L<Time::HiRes> has been upgraded from version 1.9748 to 1.9752.

=item *

L<Unicode::UCD> has been upgraded from version 0.69 to 0.70.

The function C<num> now accepts an optional parameter to help in
diagnosing error returns.

=item *

L<utf8> has been upgraded from version 1.20 to 1.21.

=item *

L<warnings> has been upgraded from version 1.39 to 1.40.

=item *

L<XSLoader> has been upgraded from version 0.29 to 0.30.

Platforms that use C<mod2fname> to edit the names of loadable
libraries now look for bootstrap (.bs) files under the correct,
non-edited name.

=back

=head1 Documentation

XXX Changes to files in F<pod/> go here.  Consider grouping entries by
file and be sure to link to the appropriate page, e.g. L<perlfunc>.

=head2 Changes to Existing Documentation

We have attempted to update the documentation to reflect the changes
listed in this document.  If you find any we have missed, send email
to L<perlbug@perl.org|mailto:perlbug@perl.org>.

Additionally, the following selected changes have been made:

=head3 L<perlembed>

=over 4

=item *

An example in L<perlembed> used the string value of C<ERRSV> as a
format string when calling croak().  If that string contains format
codes such as C<%s> this could crash the program.

This has been changed to a call to croak_sv().

An alternative could have been to supply a trivial format string:

  croak("%s", SvPV_nolen(ERRSV));

or as a special case for C<ERRSV> simply:

  croak(NULL);

=back

=head3 L<perlfunc>

=over 4

=item *

Improve the documentation of C<each> with a slightly more
explicit description of the sharing of iterator state, and with
caveats regarding the fragility of while-each loops. [perl #132644]

=back

=head3 L<perlfunc>, L<perlop>, L<perlsyn>

=over 4

=item *

Improve the documentation of while condition magic in various
places. [perl #132644]

=back

=head3 L<perlrun>

=over 4

=item *

Clarify the documentation of B<< -m >>. [perl #131518]

=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<Can't "goto" into a binary or list expression|perldiag/"Can't E<quot>gotoE<quot> into a binary or list expression">

Use of C<goto> to jump into the parameter of a binary or list operator has
been prohibited, to prevent crashes and stack corruption.  [perl #130936]

=back

=head2 Changes to Existing Diagnostics

=over 4

=item *

The C<< Unable to flush stdout >> error message was missing a trailing
newline. [debian #875361]

=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 *

Allow override of watchdog timer count in F<re/pat_psycho.t>.

This test can take a long time to run, so there is a timer to keep
this in check (currently, 5 minutes). This commit adds checking
the environment variable C<< PERL_TEST_TIME_OUT_FACTOR >>; if set,
the time out setting is multiplied by its value.

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item Cygwin

A build with the quadmath library can now be done on Cygwin.

=item FreeBSD

FreeBSD's F<< /usr/share/mk/sys.mk >> specifies C<< -O2 >> for
architectures other than arm and mips. By default, compile perl
with the same optimization levels.

=item VMS

Several fix-ups for F<configure.com>, marking function VMS has
(or doesn't have).


=back

=head1 Internal Changes

=over 4

=item *

The format of the non-utf8 transliteration table attached to the C<op_pv>
field of C<OP_TRANS>/C<OP_TRANSR> ops has changed. It's now a
C<struct OPtrans_map>.

=back

=head1 Selected Bug Fixes

=over 4

=item *

The C<printf> format specifier C<%.0f> no longer rounds incorrectly
[perl #47602], and now shows the correct sign for a negative zero.

=item *

Fixed a use after free bug in pp_list introduced in 5.27.1.  [perl #131954]

=item *

Don't stringify numeric first arguments to
C<< system() >> on Windows or VMS. [perl #132633]

=item * 

Fixed an issue where the error C<< Scalar value @arrayname[0] better
written as $arrayname >> would give an error C<< Cannot printf Inf with 'c' >>
when arrayname starts with C<< Inf >>. [perl #132645]

=item *

The Perl implementation of C<< getcwd() >> in C<< Cwd >> in the PathTools
distribution now behaves the same as XS implementation on errors: it
returns an error, and sets C<< $! >>. [perl #132648]

=item *

Fixed argument counting in multiconcat when concatenating adjacent constants.
[perl #132646]

=item *

Vivify array elements when putting them on the stack.
Fixes [perl #8910] (reported in April 2002).

=item *

Fixed parsing of braced subscript after parens. Fixes [perl #8045]
(reported in December 2001).

=item *

C<tr/non_utf8/long_non_utf8/c> could give the wrong results when the
length of the replacement character list was greater than 0x7fff.

=item *

C<tr/non_utf8/non_utf8/cd> failed to add the implied
C<\x{100}-\x{7fffffff}> to the search character list.

=back

=head1 Known Problems

=over 4

=item *

The bugfix for [perl #2754] in Perl 5.27.7 turned out to cause so much
trouble on CPAN [perl #132577] that it is being postponed.  The bug has
been restored, so C<exit(0)> in a C<UNITCHECK> or C<CHECK> block now
once again permits the main program to run, and C<exit(0)> in a C<BEGIN>
block once again permits C<INIT> blocks to run before exiting.  The bug
will be fixed again for Perl 5.30.

=back

=head1 Acknowledgements

Perl 5.27.8 represents approximately 4 weeks of development since Perl
5.27.7 and contains approximately 33,000 lines of changes across 290 files
from 17 authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 25,000 lines of changes to 160 .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 5.27.8:

Abigail, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker,
David Mitchell, Father Chrysostomos, James E Keenan, Karen Etheridge, Karl
Williamson, Niko Tyni, Pali, Peter John Acklam, Scott Lanning, Tomasz
Konojacki, Tom Hukins, Tony Cook, 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