[ List each enhancement as a =head2 entry ]
+=head2 Initialisation of aggregate state variables
+
+A persistent lexical array or hash variable can now be initialized,
+by an expression such as C<state @a = qw(x y z)>. Initialization of a
+list of persistent lexical variables is still not possible.
+
+=head2 Full-size inode numbers
+
+On platforms where inode numbers are of a type larger than perl's native
+integer numerical types, L<stat|perlfunc/stat> will preserve the full
+content of large inode numbers by returning them in the form of strings of
+decimal digits. Exact comparison of inode numbers can thus be achieved by
+comparing with C<eq> rather than C<==>. Comparison with C<==>, and other
+numerical operations (which are usually meaningless on inode numbers),
+work as well as they did before, which is to say they fall back to
+floating point, and ultimately operate on a fairly useless rounded inode
+number if the real inode number is too big for the floating point format.
+
=head1 Security
XXX Any security-related notices go here. In particular, any security
[ List each incompatible change as a =head2 entry ]
+=head2 Yada-yada is now strictly a statement
+
+By the time of its initial stable release in Perl 5.12, the C<...>
+(yada-yada) operator was explicitly intended to serve as a statement,
+not an expression. However, the original implementation was confused
+on this point, leading to inconsistent parsing. The operator was
+accidentally accepted in a few situations where it did not serve as a
+complete statement, such as
+
+ ... . "foo";
+ ... if $a < $b;
+
+The parsing has now been made consistent, permitting yada-yada only as
+a statement. Affected code can use C<do{...}> to put a yada-yada into
+an arbitrary expression context.
+
+=head2 Subroutines no longer need typeglobs
+
+Perl 5.22.0 introduced an optimization allowing subroutines to be stored in
+packages as simple sub refs, not requiring a full typeglob (thus
+potentially saving large amounts of memeory). However, the optimization
+was flawed: it only applied to the main package.
+
+This optimization has now been extended to all packages. This may break
+compatibility with introspection code that looks inside stashes and expects
+everything in them to be a typeglob.
+
+When this optimization happens, the typeglob still notionally exists, so
+accessing it will cause the stash entry to be upgraded to a typeglob. The
+optimization does not apply to XSUBs or exported subroutines, and calling a
+method will undo it, since method calls cache things in typeglobs.
+
+[perl #129916] [perl #132252]
+
=head1 Deprecations
XXX Any deprecated features, syntax, modules etc. should be listed here.
=item *
-XXX
+Many string concatenation expressions are now considerably faster, due
+to the introduction internally of a C<multiconcat> opcode which combines
+multiple concatenations, and optionally a C<=> or C<.=>, into a single
+action. For example, apart from retrieving C<$s>, C<$a> and C<$b>, this
+whole expression is now handled as a single op:
+
+ $s .= "a=$a b=$b\n"
+
+As a special case, if the LHS of an assign is a lexical variable or
+C<my $s>, the op itself handles retrieving the lexical variable, which
+is faster.
+
+In general, the more the expression includes a mix of constant strings and
+variable expressions, the longer the expression, and the more it mixes
+together non-utf8 and utf8 strings, the more marked the performance
+improvement. For example on a C<x86_64> system, this code has been
+benchmarked running four times faster:
+
+ my $s;
+ my $a = "ab\x{100}cde";
+ my $b = "fghij";
+ my $c = "\x{101}klmn";
+
+ for my $i (1..10_000_000) {
+ $s = "\x{100}wxyz";
+ $s .= "foo=$a bar=$b baz=$c";
+ }
+
+In addition, C<sprintf> expressions which have a constant format
+containing only C<%s> and C<%%> format elements, and which have a fixed
+number of arguments, are now also optimised into a C<multiconcat> op.
+
+=item *
+
+Subroutines in packages no longer need to be stored in typeglobs, saving
+large amounts of memory. See L</Subroutines no longer need typeglobs>
+under L</Incompatible Changes>, above.
=back
[ Within each section, list entries as an =item entry ]
+=head2 Removal of use vars
+
+=over 4
+
+The usage of "use vars" has been discouraged since the introduction of our in
+Perl 5.6.0. Where possible the usage of this pragma has now been removed from
+the Perl source code.
+
+=back
+
=head2 New Modules and Pragmata
=over 4
=item *
-L<XXX> has been upgraded from version A.xx to B.yy.
+L<Carp> has been upgraded from version 1.43 to 1.44.
+
+If a package on the call stack contains a constant named C<ISA>, Carp no
+longer throws a "Not a GLOB reference" error.
+
+=item *
+
+L<File::Copy> has been upgraded from version 2.32 to 2.33. It will now use
+Time::HiRes utime where available (RT #132401).
+
+=item *
+
+To address a security vulnerability in older versions of the 'zlib' library
+(which is bundled with Compress-Raw-Zlib), L<Compress::Raw::Zlib> has been
+upgraded to CPAN version 2.075.
=back
Additionally, the following selected changes have been made:
-=head3 L<XXX>
+=head3 L<perldiag/Variable length lookbehind not implemented in regex m/%s/>
+
+This now gives more ideas as to workarounds to the issue that was
+introduced in Perl 5.18 (but not documented explicitly in its perldelta)
+for the fact that some Unicode C</i> rules cause a few sequences such as
+
+ (?<!st)
+
+to be considered variable length, and hence disallowed.
=over 4
=item *
+The section on reference counting in L<perlguts> has been heavily revised,
+to describe references in the way a programmer needs to think about them
+rather than in terms of the physical data structures.
+
+=item *
+
+The section "Truth and Falsehood" in L<perlsyn> has been removed from
+that document, where it didn't belong, and merged into the existing
+paragraph on the same topic in L<perldata>.
+
+=item *
+
XXX Description of the change here
=back
=item *
+The diagnostic C<Initialization of state variables in list context
+currently forbidden> has changed to C<Initialization of state variables
+in list currently forbidden>, because list-context initialization of
+single aggregate state variables is now permitted.
+
+=item *
+
XXX Describe change here
=back
=over 4
+=item C89 requirement
+
+Perl has been documented as requiring a C89 compiler to build since October
+1998. A variety of simplifications have now been made to Perl's internals to
+rely on the features specified by the C89 standard. We believe that this
+internal change hasn't altered the set of platforms that Perl builds on, but
+please report a bug if Perl now has new problems building on your platform.
+
=item New probes
=over 2
=item *
-XXX
+A new optimisation phase has been added to the compiler,
+C<optimize_optree()>, which does a top-down scan of a complete optree
+just before the peephole optimiser is run. This phase is not currently
+hookable.
+
+=item *
+
+An C<OP_MULTICONCAT> op has been added. At C<optimize_optree()> time, a
+chain of C<OP_CONCAT> and C<OP_CONST> ops, together optionally with an
+C<OP_STRINGIFY> and/or C<OP_SASSIGN>, are combined into a single
+C<OP_MULTICONCAT> op. The op is of type C<UNOP_AUX>, and the aux array
+contains the argument count, plus a pointer to a constant string and a set
+of segment lengths. For example with
+
+ my $x = "foo=$foo, bar=$bar\n";
+
+the constant string would be C<"foo=, bar=\n"> and the segment lengths
+would be (4,6,1). If the string contains characters such as C<\x80>, whose
+representation changes under utf8, two sets of strings plus lengths are
+precomputed and stored.
+
+=item *
+
+Direct access to L<C<PL_keyword_plugin>|perlapi/PL_keyword_plugin> is not
+safe in the presence of multithreading. A new
+L<C<wrap_keyword_plugin>|perlapi/wrap_keyword_plugin> function has been
+added to allow XS modules to safely define custom keywords even when
+loaded from a thread, analoguous to L<C<PL_check>|perlapi/PL_check> /
+L<C<wrap_op_checker>|perlapi/wrap_op_checker>.
=back
=item *
+C<stat()>, C<lstat()>, and file test operators now fail if given a
+filename containing a nul character, in the same way that C<open()>
+already fails.
+
+=item *
+
+C<stat()>, C<lstat()>, and file test operators now reliably set C<$!> when
+failing due to being applied to a closed or otherwise invalid file handle.
+
+=item *
+
The in-place reverse optimisation now correctly strengthens weak
references using the L<C<sv_rvunweaken()>|perlapi/sv_rvunweaken>
API function.
+=item *
+
+Fixed a read before buffer when parsing a range starting with C<\N{}>
+at the beginning of the character set for the transliteration
+operator. [perl #132245]
+
+=item *
+
+Fixed a leaked SV when parsing an empty C<\N{}> at compile-time.
+[perl #132245]
+
+=item *
+
+Calling C<do $path> on a directory or block device now yields a meaningful
+error code in C<$!>. [perl #125774]
+
+=item *
+
+Lexical sub declarations in C<do> blocks such as C<do { my sub lex; 123 }>
+could corrupt the stack, erasing items already on the stack in the
+enclosing statement. This has been fixed. [perl #132442]
+
=back
=head1 Known Problems
https://perl5.git.perl.org / perl5.git / blobdiff