=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.44.0

=head1 DESCRIPTION

This document describes differences between the 5.42.0 release and the 5.44.0
release.

=head1 Core Enhancements

=head2 Reported argument counts in C<method> signatures now account for C<$self>

In previous versions of Perl, the exception message thrown by a C<method>
subroutine with a signature when it does not receive an appropriate number of
arguments to match its declared parameters failed to account for the implied
C<$self> parameter, causing the numbers in the message to be 1 fewer than
intended.

This has now been fixed, so messages report the correct number of arguments
including the object invocant.

=head2 Unicode 17.0 is supported

See L<https://www.unicode.org/versions/Unicode17.0.0/>.

=head2 Named Parameters in Signatures

This adds a major new ability to subroutine signatures, allowing callers
to pass parameters by name/value pairs rather than by position.

    sub f ($x, $y, :$alpha, :$beta = undef) { ... }

    f( 123, 456, alpha => 789 );

Originally specified in
L<PPC0024|https://github.com/Perl/PPCs/blob/main/ppcs/ppc0024-signature-named-parameters.md>.

This feature is currently considered B<experimental>, and is described in
further detail in L<perlsub/Signatures>.

=head2 Multi-variable C<foreach> can now use aliased references

Perl version 5.22 introduced reference aliases, allowing a C<foreach> loop
iteration variable to create new aliases to references. Perl version 5.36
introduced C<foreach> loops with multiple variables, consuming more than one
input list item on each iteration. New in this version, the two features may
now be used together, allowing multiple iteration variables where any of them
are permitted to be reference aliases.

    use v5.44;
    use feature qw( refaliasing declared_refs );

    my %hash = (
        one => [1],
        two => [2, 2],
    );

    foreach my ( $key, \@items ) ( %hash ) {
        say "The $key array contains: @items";
    }

Currently both the C<refaliasing> and C<declared_refs> features remain
B<experimental>.

=head2 New source of entropy for PRNG seeding

Perl now uses the C<getentropy()> system call to fetch random bytes suitable
for seeding the internal PRNG. Previously Perl would read raw bytes from the
F</dev/urandom> device. Perl now seeds itself in this order (and falls through
upon failure):

=over

=item 1.

C<getentropy()> on systems that support this call (Linux, BSD, MacOS)

=item 2.

F</dev/urandom> on systems that have it

=item 3.

Hash of internal state variables: Unix time, process ID, and pointer value

=back

=head2 Enhanced operation of regular expression patterns under /xx

Experimentally, the C</xx> pattern modifier can allow bracketed
character classes (I<e.g.>, C<[a-zA-Z]> to extend across multiple lines
and to contain comments, and to warn you of potential cases where a
portion of a pattern inadvertently has been treated as a comment instead
of what you intended.  This behavior is enabled by S<C<use feature
"enhanced_xx">>.  See L<perlre/E<sol>x and  E<sol>xx>.

=head1 Security

=head2 CVE-2026-8376 - Buffer overflow in Perl_study_chunk

Perl_study_chunk in regcomp_study.c checked the size of the joined substring
buffer in characters rather than bytes. On 32-bit builds, this can lead to
an integer overflow of the size of the buffer leading to out-of-bounds writes.

=head1 Incompatible Changes

=head2 Unicode rules are now fully enforced on identifier and regular expression group names.

Before Unicode, Perl accepted any C<\w> character in an identifier or other
name, except the first character couldn't be a digit.  Later, Unicode
created two properties that described this.  Even later, they found
those properties to be insufficient, and created two new similar
properties.  These are the ones that perl has intended to use since:
C<\p{XID_Start}> and C<\p{XID_Continue}>.  (The C<X> stands for
"eXtended" and indicates these are the more modern versions.)

(And even later, long after Perl identifier rules were formed using
the above properties, Unicode added recommendations to further restrict
legal identifier names.  These were added to counter cases where, for
example, programmers snuck code past reviewers using characters that
look like other ones.  The two properties are C<Identifier_Status> and
C<Identifier_Type>.  See L<https://www.unicode.org/reports/tr39/>.  Perl
currently doesn't do anything with these, except to furnish you the
ability to use them in regular expressions.)

We soon discovered that there were 14 characters that match C<XID_Start>
and C<XID_Continue> that don't also match C<\w>.  To avoid breaking code
that had long relied on C<\w>, we chose to not add those to the list of
acceptable identifier characters.

It turns out that there are about 160 characters that match C<\w> but
not the Unicode C<XID> properties.  Thus they are illegal according to
Unicode.  Those are now explicitly forbidden in both Perl identifiers
and regular expression group names.  Previously, it was likely that
their use in identifiers wouldn't work anyway; they could be accepted
initially as legal, but other code would later reject them, but with a
message that had nothing to do with the underlying problem.  However
group names in regular expression patterns could contain illegal
continuation characters and have a higher probablility of not being
caught.  That is now changed.

Only programs that do L<C<use utf8>|utf8> can be affected, and then only
characters that appear in the 2nd or later positions of the name.  The
characters that an identifier name can begin with are unchanged.

130 of the now unacceptable characters are 5 sets of 26 Latin letters
that are enclosed by some shape, such as CIRCLED LATIN CAPITAL LETTER N.
Another 8 are generic modifiers that add shapes around other characters;
5 are modifiers to Cyrillic numbers; and 16 are Arabic ligatures and
isolated forms.  The other two are GREEK YPOGEGRAMMENI and VERTICAL
TILDE.

=head1 Deprecations

=over 4

=item *

Using C<goto> to jump into the body of a loop or other block construct from
outside is no longer permitted.
[L<GH #23618|https://github.com/Perl/perl5/issues/23618>]

=item *

C<m/...[...].../xx> has new restrictions

Using an unescaped C<#> or literal vertical space is now deprecated in a
regular expression bracketed character class that is compiled with the
C</xx> modifier.  These still work, but deprecation warnings will be
generated unless turned off or the constructs are cured as follows.

=over

=item *

Escape a C<#> by preceding it with a backslash, like in

 m/ [ % \# ( ) ] /xx

=item *

Use constructs like C<\n> instead of literal vertical space.

=back

=back

=head1 Performance Enhancements

=over 4

=item *

Simple (non-overflowing) addition (C<+>), subtraction (C<->) and
multiplication (C<*>) of integers are slightly sped up, as long as
sufficient underlying C compiler support is available.

=back

=over 4

=item *

Populating a hash from a list of key/value pairs, when the keys are constant
string operands known at compile time, is commonly now faster. [L<GH #24228|https://github.com/Perl/perl5/issues/24228>]

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Archive::Tar> has been upgraded from version 3.04 to 3.12.

=item *

L<attributes> has been upgraded from version 0.36 to 0.37.

=item *

L<B> has been upgraded from version 1.89 to 1.92.

=item *

L<B::Concise> has been upgraded from version 1.007 to 1.012.

=item *

L<B::Deparse> has been upgraded from version 1.85 to 1.89.

=item *

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

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.213 to 2.218.

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.213 to 2.222.

=item *

L<Config::Perl::V> has been upgraded from version 0.38 to 0.39.

=item *

L<CPAN::Meta> has been upgraded from version 2.150010 to 2.150013.

=item *

L<CPAN::Meta::Requirements> has been upgraded from version 2.143 to 2.145.

=item *

L<DB_File> has been upgraded from version 1.859 to 1.860.

=item *

L<Encode> has been upgraded from version 3.21 to 3.24.

=item *

L<English> has been upgraded from version 1.11 to 1.12.

=item *

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

=item *

L<experimental> has been upgraded from version 0.035 to 0.036.

=item *

L<ExtUtils::CBuilder> has been upgraded from version 0.280242 to 0.280243.

=item *

L<ExtUtils::MakeMaker> has been upgraded from version 7.76 to 7.78.

=item *

L<ExtUtils::Miniperl> has been upgraded from version 1.14 to 1.15.

=item *

L<ExtUtils::ParseXS> has been upgraded from version 3.57 to 3.63.

=item *

L<ExtUtils::Typemaps> has been upgraded from version 3.57 to 3.63.

=item *

L<feature> has been upgraded from version 1.97 to 2.02.

=item *

L<File::Copy> has been upgraded from version 2.41 to 2.43.

=item *

L<File::Fetch> has been upgraded from version 1.04 to 1.08.

=item *

L<File::Glob> has been upgraded from version 1.42 to 1.44.

=item *

L<File::Spec> has been upgraded from version 3.94 to 3.95.

=item *

L<File::stat> has been upgraded from version 1.14 to 1.15.

=item *

L<File::Temp> has been upgraded from version 0.2311 to 0.2312.

=item *

L<Filter::Simple> has been upgraded from version 0.96 to 0.97.

=item *

L<Filter::Util::Call> has been upgraded from version 1.64 to 1.65.

=item *

L<Getopt::Std> has been upgraded from version 1.14 to 1.15.

=item *

L<HTTP::Tiny> has been upgraded from version 0.090 to 0.096.

=item *

L<IO> has been upgraded from version 1.55 to 1.56.

=item *

L<IO::Compress> has been upgraded from version 2.213 to 2.220.

=item *

L<IO::Socket::IP> has been upgraded from version 0.43 to 0.44.

=item *

L<Math::BigInt> has been upgraded from version 2.005002 to 2.005003.

=item *

L<Module::CoreList> has been upgraded from version 5.20250702 to 5.20260722.

=item *

L<Module::Metadata> has been upgraded from version 1.000038 to 1.000039.

=item *

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

=item *

L<Net::Ping> has been upgraded from version 2.76 to 2.77.

=item *

L<Opcode> has been upgraded from version 1.69 to 1.71.

=item *

L<overloading> has been upgraded from version 0.02 to 0.03.

=item *

L<PerlIO::via> has been upgraded from version 0.19 to 0.21.

=item *

L<Pod::Html> has been upgraded from version 1.35 to 1.36.

=item *

L<Pod::Simple> has been upgraded from version 3.45 to 3.48.

=item *

L<POSIX> has been upgraded from version 2.23 to 2.26.

=item *

L<Scalar::Util> has been upgraded from version 1.68_01 to 1.70.

=item *

L<SelectSaver> has been upgraded from version 1.02 to 1.03.

=item *

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

=item *

L<Socket> has been upgraded from version 2.038 to 2.041.

=item *

L<Storable> has been upgraded from version 3.37 to 3.41.

=item *

L<Term::Table> has been upgraded from version 0.024 to 0.028.

=item *

L<Test::Harness> has been upgraded from version 3.50 to 3.52.

=item *

L<Test::Simple> has been upgraded from version 1.302210 to 1.302219.

=item *

L<Text::Balanced> has been upgraded from version 2.06 to 2.07.

=item *

L<threads> has been upgraded from version 2.43 to 2.45.

=item *

L<threads::shared> has been upgraded from version 1.70 to 1.73.

=item *

L<Time::HiRes> has been upgraded from version 1.9778 to 1.9780.

=item *

L<Time::Piece> has been upgraded from version 1.36 to 1.41.

=item *

L<Unicode::UCD> has been upgraded from version 0.81 to 0.83.

=item *

L<utf8> has been upgraded from version 1.27 to 1.29.

=item *

L<version> has been upgraded from version 0.9933 to 0.9934.

=item *

L<warnings> has been upgraded from version 1.74 to 1.78.

=item *

L<XS::APItest> has been upgraded from version 1.43 to 1.50.

=item *

L<XS::Typemap> has been upgraded from version 0.20 to 0.22.

=back

=head1 Documentation

=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, open an issue
at L<https://github.com/Perl/perl5/issues>.

Additionally, the following selected changes have been made:

=head3 L<perlapi>

=over 4

=item *

Auto-generation of this document now includes the line number of the source
code, as well as its documentation.

=back

=head3 L<perlexperiment>

=over 4

=item *

New entry for "New object system and C<class> syntax".

=item *

L<perlapi> now contains information about how to find what release of
Perl first contained an API element.

=back

=head3 L<perlxs>

=over 4

=item *

The reference manual for writing Perl XS code has been completely rewritten and
modernized.  It is about twice the size of the old file, and promotes more
modern XS syntax, such as ANSI signatures.

=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 *

L<Use of uninitialized value%s|perldiag/"Use of uninitialized value%s">

This warning was issued in the reverse order (right-to-left) when both
operands of a binary operator are uninitialized values.  This is now
fixed to be consistent with evaluation order of operands.

=item *

Certain diagnostics about byte sequences that are supposed to comprise a
UTF-8 encoded character, but that are invalid in some way, now don't
include bytes irrelevant to that determination.  An example is

=over

=item old message

Malformed UTF-8 character: C<\xc1\x27> (any UTF-8 sequence that starts with
C<\xc1> is overlong which can and should be represented with a different,
shorter sequence)

=item new message

Malformed UTF-8 character: C<\xc1> (any UTF-8 sequence that starts with
C<\xc1> is overlong which can and should be represented with a different,
shorter sequence)

=back

In this case the C<\xc1> is all that is needed to make the sequence
invalid.  Whatever comes after it is irrelevant (in this case, C<\x27>),
and including it in the message might lead the reader to think that it
somehow does matter.

=item *

The error C<Unrecognised parameters for "%s" constructor: %s> has been changed
to C<Unrecognized parameters for "%s" constructor: %s>.

=item *

Variables whose name started with C<^_> were incorrectly shown in
diagnostics with a literal C<Ctrl-_> (which is an invisible ASCII
character) in their name.

The names of variables whose names begin with a caret and are longer
than two characters are now wrapped in braces, just as they have to be
in the source code.

Therefore, using an undefined C<${^_FOO}> will now correctly warn with
C<Use of uninitialized value ${^_FOO}>, instead of the earlier C<Use of
uninitialized value $FOO> (with a literal C<Ctrl-_> after the dollar
sign).

[L<GH #24135|https://github.com/Perl/perl5/issues/24135>]

=item *

Calling the C<import> method on a package with no C<import> method now
produces a regular warning rather than a deprecation warning or error.

Since Perl 5.39.1, calling C<import> with arguments on a package without
such a method has triggered a deprecation warning. In Perl 5.43.6, this
deprecation was promoted into an error. This broke a significant amount
of code while providing very little advantage over the warning. This
fatal error has been converted back to a warning, with its deprecation
status removed. There are no longer any plans to make this fatal in the
future. The category for this warning is C<missing_import> and it is
enabled by default.

=back

=head2 New Diagnostics

=head3 New Errors

=over 4

=item *

L<Can't redeclare catch variable as "%s"|perldiag/"Can't redeclare catch variable as "%s"">

(F) A C<my>, C<our> or C<state> keyword was used with the exception variable in
a C<catch> block:

    try { ... }
    catch (my $e) { ... }
    # or catch (our $e) { ... }
    # or catch (state $e) { ... }

This is not valid syntax. C<catch> takes a bare variable name, which is
automatically lexically declared.
[L<GH #23222|https://github.com/Perl/perl5/issues/23222>]

=item *

L<Use of "goto" to jump into a construct is no longer permitted|perldiag/"Use of "goto" to jump into a construct is no longer permitted">

(F) You have used C<goto LABEL;> or C<goto EXPR;> in an attempt to jump into
the body of a loop or other block construct from the outside.  As of Perl 5.44,
this throws an exception.

=item *

L<\x{%X} is a \w char that isn't valid in a name "%s"
|perldiag/\x{%X} is a \w char that isn't valid in a name "%s">

In most cases where this message now appears, an error would have
occurred anyway, but the text would not have been helpful in finding the
problem.

=back

=head3 New Warnings

=over 4

=item *

L<Possible attempt to escape whitespace in qw() list|perldiag/"Possible attempt to escape whitespace in qw() list">

(W qw) qw() lists contain items separated by whitespace; contrary to
what some might expect, backslash characters cannot be used to "protect"
whitespace from being split, but are instead treated as literal data.

Note that this warning is I<only> emitted when the backslash is followed
by actual whitespace (that C<qw> splits on).

=back

=head1 Configuration and Compilation

=over 4

=item *

C23 F<< <stdckdint.h> >> and associated macros are now used if available.

=back

=over 4

=item *

It is now possible to pass to F<Configure> the values dealing with POSIX
locale categories, overriding its automatic calculation of these.  This
enables cross-compilation to work.  The easiest way to do this is to
extract the C program that does the calculation from F<Configure> and
then run it on the target machine, and then pass the values it outputs
to F<Configure> on the other machine.  F<Porting/Glossary> has examples.
[L<GH #22992|https://github.com/Perl/perl5/issues/22992>]

=item *

The C<PERL_CREATE_GVSV> configuration macro has been removed. It was almost
undocumented and it has been disabled by default since Perl 5.10.0. Its purpose
was to force all GVs to initialize their SV slot on creation. [L<GH #24177|https://github.com/Perl/perl5/issues/24177>]

=back

=head1 Testing

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

=over 4

=item *

Karl Williamson gave a talk at TPRC 2025 asking people to contribute
tests to find old issues that are no longer a problem, and todo tests
to reflect reproduction cases for known outstanding bugs.
(L<video link|https://www.youtube.com/watch?v=CwX4Xsf5y5E>)
It gained renewed interest this year,
leading to an uptick in test submissions from new authors,
for which we are extremely grateful.

=item *

When testing embedding, add a sanity check to ensure the C<libperl> we
link against matches the perl we are building.  [L<GH #22125|https://github.com/Perl/perl5/issues/22125>]

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item Windows

=over

=item * Fix builds with C<USE_IMP_SYS> defined but C<USE_ITHREADS> not
defined.

=item * A compilation error in unthreaded builds using MSVC introduced in Perl 5.43.5
has been fixed.  [L<GH #23952|https://github.com/Perl/perl5/issues/23952>]

=back

=item OpenBSD

=over 4

=item * When testing embedding, ensure we link against the correct static
libperl. [L<GH #22125|https://github.com/Perl/perl5/issues/22125>]

=back

=item AIX

=over

=item * Thread-safe locale handling has been turned off on all releases due to
apparent bugs in the underlying operating system support.

=item * The ibm-clang/ibm-clang_r IBM Open XL C/C++ compiler is now supported for AIX
7.2 and 7.3. This is the recommended compiler to use when compiling Perl on
these versions of AIX.

=back

=back

=head1 Internal Changes

=over 4

=item *

The XS parser, L<ExtUtils::ParseXS>, has been further extensively restructured
internally.  Most of these changes shouldn't be visible externally, but might
affect XS code which was using invalid or unsupported syntax.  Several minor
bug-fixes were included.

=item *

Removed the deprecated (since 5.32) functions C<sv_locking()> and
C<sv_unlocking>.

=item *

C<Perl_expected_size> has been added as an experimental stub macro. The
intention is to build on this such that it can be passed a size in bytes,
then returns the interpreter's best informed guess of what actual usable
allocation size would be returned by the malloc implementation in use.

This would help with sizing allocations such that SvLEN is more accurate
and not trying to shrink string buffers to save size when the intended
saving is unrealistic.

=item *

C<SvPV_shrink_to_cur> has been revised to include a byte for copy-on-write
(COW), so that the resulting string could be COWed in the future.

It also now uses C<Perl_expected_size>, compared against the current
buffer size, and does not try to do a reallocation if the requested
memory saving is unrealistic.

=item *

C<sv_vcatpvfn_flags()> now substitutes the Unicode REPLACEMENT CHARACTER
for malformed input.  Previously it used the NUL character.

=item *

For core Perl maintainers, the syntax of F<embed.fnc> has been extended.
Every function, C<foo()>, named in this file has generated for it a
macro named C<PERL_ARGS_ASSERT_FOO>.  The macro expands to C<assert()>
calls that do basic sanity checking for each argument to C<foo()> that
we currently deem as being appropriate to have such checking.  (That
means that many arguments are not checked, and that the generated macro
may currently expand to nothing.)  With this release, you can add
C<assert()> statements yourself to F<embed.fnc> that will be
incorporated into the generated macro, beyond the system-generated ones.
Comments and examples in F<embed.fnc> give details.

=item *

A new function C<valid_utf8_to_uv> has been added.  This is synonymous
with C<valid_utf8_to_uvchr>; its reason for existence is to have
consistent spelling with the names of the other functions that translate
from UTF-8, so you don't have to remember a different spelling.

=item *

L<perlapi/C<newSVsv_flags_NN>> is a new function for creating a new SV
and assigning the value(s) of an existing SV to it.

Historically, C<Perl_newSVsv_flags> and C<Perl_sv_mortalcopy_flags> would
pass a new SV head and the original SV to C<Perl_sv_setsv_flags>. However,
the latter contains many branches of no relevance to a fresh SV, so they
now make use of the new function to streamline the process.

C<Perl_newSVsv_flags> is now essentially a NULL pointer check and wrapper
around the new function, so has been moved into F<sv_inline.h>.

=item *

L<perlapi/C<STATIC_ASSERT_DECL>> and C<STATIC_ASSERT_STMT> are like
C<assert()>, but are evaluated at compile time.  That means their
argument must be a constant expression that can be verified by the
compiler, and so they effectively have no cost, not appearing in the
code that gets executed.  These were added in v5.28, but not until now
have we opened their use up to XS writers.  At the same time, a new
variant has been added, C<STATIC_ASSERT_EXPR> which is suitable for use
in an expression, such as a comma expression in a C macro.

=item *

C<Perl_sv_backoff>, which undoes the C<OOK> string offset mechanism now only moves
the string buffer contents to the start of the buffer if C<SvOK(sv)> is true.
Historically, the buffer contents were always moved, but if the buffer contents
are defunct and no longer required, doing that incurs an unnecessary cost
proportional to the size of the shifted contents.

(The assumption in this change is that C<SvOK(sv)> is a valid indicator of
whether the string buffer contents are "live" or not.)

See [L<GH #23967|https://github.com/Perl/perl5/issues/23967>] for an example of
where such a copy was noticeable.

=item *

Fixed a bug in the L<perlapi/sv_numeq> API where values with numeric
("0+") overloading but not equality or numeric comparison overloading
would always be compared as floating point values.  This could lead to
large integers being reported as equal when they weren't.

=item *

Fixed a bug in L<perlapi/sv_numeq> where the C<SV_SKIP_OVERLOAD> flag
would skip operator overloading, but would still honor numeric ("0+")
overloading.

=item *

Added L<perlapi/sv_numne>, sv_numle, sv_numlt, sv_numge, sv_numgt and
L<perlapi/sv_numcmp> APIs that perform numeric comparison in the same
way perl does, including overloading.  Separate APIs for each
comparison are needed to invoke their corresponding overload when
needed.  Inspired by [L<GH #23918|https://github.com/Perl/perl5/issues/23918>]

This also extends the sv_numeq API to support C<SV_FORCE_OVERLOAD>.

=item *

Added the C<AMGf_force_scalar> flag to the L<perlapi/C<amagic_call>>
API to force scalar context for overload calls.

=item *

Added the C<AMGf_force_overload> flag to the L<perlapi/C<amagic_call>>
API to allow forcing overloading to be honored even in the context of
C<no overloading;>.

=item *

The C<SvFLAGS> bits used by C<SvPCS_IMPORTED()> and C<SvOOK()> have now been
merged into the same position, thus freeing up a flags bit for possible future
purposes. This merge is distinguished by the fact that the C<PCS_IMPORTED>
behaviour is only used on references (when C<SvROK> is true), whereas the
C<OOK> only applies to string buffers (when C<SvROK> is false).

This change shouldn't affect any C<XS> module code that is using the test
macros correctly, though might cause confusion to code that attempts to analyse
C<SvFLAGS> bits directly outside of the helper macros.

=item *

An upper limit has been applied to the multiplier operand of the
repetition operator. Constant folding will not be attempted if the
operand is a numerical constant above C<PERL_FOLD_REPEAT_LIMIT>.
See [L<GH #20586|https://github.com/Perl/perl5/issues/20586>] and [L<GH #23561|https://github.com/Perl/perl5/issues/23561>] for background.

=item *

Dedicated check functions C<Perl_ck_anonhash> and C<Perl_ck_aassign> have been
added and are used to hekify some C<OP_CONST> hash keys at compile time.
[L<GH #24228|https://github.com/Perl/perl5/issues/24228>]

=item *

C<Perl_check_hash_fields_and_hekify>, partly called as a compile-time
optimization, no longer preemptively converts an NV to a HEK if the
compile time and run time locales could differ.
[L<GH #24252|https://github.com/Perl/perl5/issues/24252>]

=item *

C<Perl_check_hash_fields_and_hekify>, partly called as a compile-time
optimization, no longer preemptively converts a UTF-8 string to a HEK
when this will downgrade the string to a single byte representation.

At present, multiple functions inadequately handle the flag used to
denote when a key originally had UTF-8 encoding, making it impossible to
restore the encoding when keys are extracted from a hash (using C<keys>
for example).

Tracking of UTF-8 origins can hopefully be improved in the next development
cycle, allowing for preemptive conversion of all UTF-8 strings once again.
[L<GH #24266|https://github.com/Perl/perl5/issues/24266>]
[L<GH #24287|https://github.com/Perl/perl5/issues/24287>]

=item *

The macro L<perlapi/C<fromCTRL>> has been added to be the inverse of the
existing L<perlapi/C<toCTRL>>.  C<toCTRL('A')> yields 1 (the control
character C<SOH> on all platforms Perl works on); C<fromCTRL(1)>
yields 'A'.

=item *

When a UTF-8 constant string was used as the hash key in an insert
operation, such as C<$hash{'über maus'} = 1;>, and the string could
be converted into a single byte representation, the flag noting the
original encoding (C<HVhek_WASUTF8>) was not always retained.

When this occurred, the relevant scalars returned by C<keys %hash>
would not be in the original, expected UTF-8 encoding.

The original encoding is now captured and propagated.
[L<GH #24266|https://github.com/Perl/perl5/issues/24266>]

=item *

When a constant IV or NV was used as a hash key, such as in
C<< my %hash = ( 42 => 0 ); >>, and was preemptively stringified
into a hash key, the fact that the numerical value came first
was lost. This unintentionally modified deparse output for
such keys.

The numerical values are now carried across, and flags on the
key variable reflect the original data type.

Note: This now preserves the form of constant keys supplied
to tied hashes in list assignments.
[L<GH #24302|https://github.com/Perl/perl5/issues/24302>]

=item *

L<perlapi/defer_error>, formerly known as C<qerror>, and
L<perlapi/op_clear> are now part of the API.

Perl 5.43.2 hid Perl non-API function declarations unless you defined
C<PERL_EXT> or C<PERL_CORE>, so these non-API functions no longer had
visible declarations.

A small number of CPAN modules used these APIs and a stricter GCC 15
started enforcing C99 disallowing implicit function declarations,
producing build failures.

Added qerror() as a deprecated public alias for defer_error() to allow
existing users of that name to build successfully.

[L<GH #23676|https://github.com/Perl/perl5/issues/23676>]

=back

=head1 Selected Bug Fixes

=over 4

=item *

When both operands of arithmetic operators (C<+>, C<->, etc.) are
L<overload>ed objects which have no method for that operator but have
a C<0+> method and the C<fallback> option set to TRUE,
perl will normally call the C<0+> method for the left operand first
and then call one for the right operand, i.e. in the same order
as operand evaluation.
But if C<S<use integer;>> is in effect, the C<0+> methods used to be
called in wrong (reverse) order.

=item *

Certain constructs involving a two-variable C<for> loop would crash the perl
compiler in v5.42.0:

    # Two-variable for loop over a list returned from a method call:
    for my ($x, $y) (Some::Class->foo()) { ... }
    for my ($x, $y) ($object->foo()) { ... }

and

    # Two-variable for loop over a list returned from a call to a
    # lexical(ly imported) subroutine, all inside a lexically scoped
    # or anonymous subroutine:
    my sub foo { ... }
    my $fn = sub {
        for my ($x, $y) (foo()) { ... }
    };

    use builtin qw(indexed);  # lexical import!
    my sub bar {
        for my ($x, $y) (indexed(...)) { ... }
    }

These have been fixed.  [L<GH #23405|https://github.com/Perl/perl5/issues/23405>]

=item *

Several error conditions in the C<pack> and C<unpack> operations were
not detected and now are.

=item * INTERFACE keyword in XS

INTERFACE keyword in XS

Fixed a couple of issues with the INTERFACE keyword in XS.

[L<GH #23640|https://github.com/Perl/perl5/issues/23640>]

=item * C<&CORE::__CLASS__> no longer returns invalid results

C<CORE::__CLASS__> would work as expected when used as a bareword or aliased:

    use feature qw(class);
    class Foo {
        BEGIN { *cls = \&CORE::__CLASS__; }
        method bar() {
            my $class1 = CORE::__CLASS__;  # ok
            my $class2 = cls;              # ok
        }
    }

But when called with an ampersand (C<&CORE::__CLASS__()>) or through a
reference (C<< my $ref = \&CORE::__CLASS__; $ref->() >>), it would return
unrelated strings. These runtime calls have been fixed to throw an error of the
form C<&CORE::__CLASS__ cannot be called directly> instead of silently
returning incorrect results.

[L<GH #23737|https://github.com/Perl/perl5/issues/23737>]

=item * C<parse_subsignature()> can now handle empty subroutine signatures

Previously, calling the C<parse_subsignature()> API function with an empty
signature would cause a "Syntax error" failure, requiring code which calls it
to detect the special case and take appropriate steps.  This is now fixed,
returning the same optree that the parser would yield for a regular empty
signature during normal parse time.

[L<GH #17689|https://github.com/Perl/perl5/issues/17689>]

=item *

The C<-CA> flag (or equivalently, the C<PERL_UNICODE=A> environment setting)
tells perl to treat command-line arguments as UTF-8 strings. (See L<perlrun>
for details.) However, this did not extend to the global variables implicitly
created by the C<-s> option:

 $ perl -CA -s -e 'printf "%vx\n", $_ for $foo, $ARGV[0]' -- -foo=é é
 c3.a9
 e9

Here C<$foo> would end up containing the two-byte UTF-8 representation of
"LATIN SMALL LETTER E WITH ACUTE", but C<$ARGV[0]> would contain a single
codepoint corresponding to U+00E9.

This has been fixed: If C<-CA> is in effect, options parsed by C<-s> are
treated as UTF-8, too. In the example above, C<$foo> and C<$ARGV[0]> now both
contain C<chr(0xE9)>. [L<GH #23377|https://github.com/Perl/perl5/issues/23377>]

=item *

We have long claimed to support identifiers up to about 255 characters
long.  However this was actually true only for identifiers that
consisted of only ASCII characters.  The real upper limit was as few as
64 characters for identifiers written in other languages, for example,
Chinese or Osage.  Now an identifier in any language may contain at
least 255 characters.

=item *

Fixed parsing of array names starting with a digit in double-quotish
context under C<use utf8;>.

=item *

S<C<use 5.42>> now turns on S<C<use source::encoding "ascii">> for the
remainder of the line (besides subsequent lines). [L<GH #23881|https://github.com/Perl/perl5/issues/23881>]

=item *

Since 5.32.0, the second branch of a ternary condition operator wasn't
getting the correct autovivification context applied. For example in
something like

    @{ $cond ? $h{foo} : $h{bar} } = ...;

the first branch would correctly autovivify C<$h{foo}> to an array ref,
but the second branch might incorrectly autovivify C<$h{bar}> to a hash
ref. [L<GH #18669|https://github.com/Perl/perl5/issues/18669>].

=item *

Don't warn about jumping into a construct if we're DIE-ing [L<GH #23922|https://github.com/Perl/perl5/pull/23922>].

=item *

Regexes which include both a sub-pattern (e.g. C<(??{...})> or C<(?&FOO)>) and
a cut (i.e. C<< (?>...) >>) could sometimes cause a premature scope exit in
other code during a match.  For example, in something like
C<(?{ local $x = ... })>, the C<local> might have been unwound before the
pattern has finished matching.
[L<GH #16197|https://github.com/Perl/perl5/issues/16197>]

=item *

C<DB::sub> is not meant to be called for sub calls from the DB package, but
calls to overloaded subs for overloaded values used in the DB package would
result in calls to DB::sub.  Fixed the check for the current package in
amagic_call().  [L<GH #24001|https://github.com/Perl/perl5/issues/24001>].

=item *

Fix parsing of hexadecimal floating-point numbers whose significand
(aka "mantissa") values are too large to fit in UV range.
Such literals (for example, C<0x1234567890.1p+0> for 32-bit IV/UV
platform, or C<0x1234567890_1234567890.1p+0> for 64-bit IV/UV)
used to be parsed incorrectly.

=item *

Perl 5.42.0 does not handle the transition to/from daylight savings time
properly.  The time and/or timezone can be off by an hour in the
intervals surrounding such transitions.  This is a regression from
earlier releases, and is now fixed.  This bug was evident from perl
space in the L<POSIX/strftime> function, and in XS code with any of
L<perlapi/my_strftime>, L<perlapi/sv_strftime_ints>, or
L<perlapi/sv_strftime_tm>.

=item *

sort() optimizes common comparisons from calling the OP tree for a
comparison block into a call to a C function.  The C function used for
overloaded numeric comparisons did not handle the case where there was
no comparison overload but there was a numeric ("0+") overload
correctly, losing precision for large overloaded integer arguments that
are not exactly representable as a Perl floating point value (NV).
[L<GH #23956|https://github.com/Perl/perl5/issues/23956>]

=item *

When a scalar variable used as the target of a filehandle is C<undef>'ed
while being output, garbage bytes would be left in that scalar.
[L<GH #24008|https://github.com/Perl/perl5/issues/24008>]

=over 4

=item *

Additionally, there was a case that would expose garbage bytes in the
target scalar or even trigger a segmentation fault when that scalar is
output on it (as in C<< open $fh, '>', \$str; print $fh $str; >>).
This is also fixed.  [L<GH #24199|https://github.com/Perl/perl5/issues/24199>]

=back

=item *

C<close(STDOUT)> when C<STDOUT> has been opened as a pipe will now
properly wait for the child to exit on Windows.  [L<GH #4106|https://github.com/Perl/perl5/issues/4106>]

=item *

Calling an XSUB via goto in scalar context, where the XSUB didn't return
exactly one value, could result in the return of the wrong number of
items, leading to potential stack corruption. For example:

    sub wrap { goto \&an_xsub_which_returns_no_values }
    $ret = wrap();

[L<GH #24212|https://github.com/Perl/perl5/issues/24212>]

=item *

On debugging perls, instantiating a class with an array field with an empty
initializer list would abort with an error:

    class Foo {
        field @bar = ();
    }
    Foo->new();

Error message: C<< perl: inline.h:194: Perl_av_new_alloc: Assertion `size > 0'
failed. >>

This has been fixed. [L<GH #24246|https://github.com/Perl/perl5/issues/24246>]

=item *

Refassigning to a class field in a method could result in the SV for
that field being released when the method exited.  The next access to
that field could result in a crash or an assertion, or if the freed SV
had been re-used, random data.  Discussed in [L<GH #24187|https://github.com/Perl/perl5/issues/24187>]

=back

=head1 Known Problems

None

=head1 Obituary

"WELL VOLUNTEERED!" echoed across conference rooms and IRC channels. Matt S. Trout's battle
cry that transformed reluctant volunteers into community leaders.

With profound sadness, we announce Matt's passing. Since the early 2000s, Matt
shaped Perl through sheer force of will: IRC operator, PAUSE administrator,
Shadowcat Systems co-founder, architect of DBIx::Class. His opinions came wrapped in
profanity and delivered at maximum volume. He suffered no fools and grew to
sometimes realize he should apologize. Yet this same abrasive exterior
protected fierce dedication to mentoring, developers he harangued into
volunteering now lead the community themselves. Matt's deliberately
mind-bending code pushed Perl forward. Every modern Perl developer touches his
legacy daily.

Well volunteered, Matt. Rest in peace.

=head1 Acknowledgements

Perl 5.44.0 represents approximately 12 months of development since Perl
5.42.0 and contains approximately 270,000 lines of changes across 1,300
files from 71 authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 110,000 lines of changes to 860 .pm, .t, .c and .h files.

Perl continues to flourish into its fourth decade thanks to a vibrant
community of users and developers. The following people are known to have
contributed the improvements that became Perl 5.42.1:

Alexander Karelas, Aristotle Pagaltzis, Arne Johannessen, Bartosz Jarzyna,
Branislav Zahradník, brian d foy, Chad Granum, Chris 'BinGOs' Williams,
Chris Prather, Christian Hansen, Craig A. Berry, Dagfinn Ilmari Mannsåker,
Dan Book, Dan Church, Daniel Dragan, Daniel Laügt, Daniel Tang, Dan Kogai,
Dave Cross, David Mitchell, Dmitrii Kuvaiskii, E. Choroba, Ed J, Elvin
Aslanov, Eric Herman, Eugen Konkov, Graham Knop, Harald Jörg, H.Merijn
Brand, Igor Todorovski, James Cook, James E Keenan, James Raspass, Jörg
Thomas, Karen Etheridge, Karl Williamson, Leon Timmermans, Lukas Mai, Marc
Reisner, Masahiro Iuchi, Matthew Horsfall, Maxim Vuets, Max Maischein,
Nicolas R, Olaf Alders, Paul Evans, Paul Marquess, Peter John Acklam,
Philippe Bruhat (BooK), Ricardo Signes, Richard Leach, Robert Rothenberg,
Ryan Carsten Schmidt, Samuel Smith, Samuel Young, Scott Baker, Sevan
Janiyan, Shirakata Kentaro, Sisyphus, Stan Ulbrych, Stefan Adams, Štěpán
Němec, Steve Hay, TAKAI Kousuke, Thibault Duponchelle, Toby Inkster, Tomasz
Konojacki, Tom Wyant, Tony Cook, Unicode Consortium, Yitzchak
Scott-Thoennes.

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://github.com/Perl/perl5/issues>. There may also be information at
L<https://www.perl.org/>, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at
L<https://github.com/Perl/perl5/issues>. Be sure to trim your bug down to a
tiny but sufficient test case.

If the bug you are reporting has security implications which make it
inappropriate to send to a public issue tracker, 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