=item *
-...
+L<DB> has been updated from 1.05 to 1.06 and L<perl5db.pl> from 1.39_10
+to 1.40. The call depth allowed by default in the debugger is now 1000
+rather than 100.
=back
=item *
-XXX
+Perl has a new copy-on-write mechanism that avoids the need to copy the
+internal string buffer when assigning from one scalar to another. This
+makes copying large strings appear much faster. Modifying one of the two
+(or more) strings after an assignment will force a copy internally. This
+makes it unnecessary to pass strings by reference for efficiency.
+
+This feature was already available in 5.18.0, but wasn't enabled by
+default. It is the default now, and so you no longer need build perl with
+the F<Configure> argument:
+
+ -Accflags=PERL_NEW_COPY_ON_WRITE
+
+It can be disabled (for now) in a perl build with:
+
+ -Accflags=PERL_NO_COW
=back
=item *
+B::Deparse has been upgraded from version 1.20 to 1.21.
+
+C<foreach my $lexical> is now deparsed correctly with the B<-p> option.
+[RT #117081]
+
+The B<-l> option no longer puts form feeds in the middle of a line when
+outputting C<map> and C<grep> blocks. [RT #117311]
+
+Elements of C<%#>, such as C<$# {foo}> and C<${#}{foo}> are now deparsed
+correctly. [RT #117531]
+
+=item *
+
+File::Spec has been upgraded from version 3.40 to 3.41.
+
+C<tmpdir> now respects changes to environment variables from which the
+temporary directory is derived. [RT #88940]
+
+=item *
+
Test::Harness has been upgraded from version 3.26 to 3.28
Memory usage is dramatically reduced. t/harness now uses about 10% of the
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.
-=head3 L<XXX>
+=head3 L<perltrap>
=over 4
=item *
-XXX Description of the change here
+There is now a L<JavaScript|perltrap/JavaScript Traps> section.
=back
=item *
-XXX L<message|perldiag/"message">
+L<A sequence of multiple spaces in a charnames alias definition is deprecated|perldiag/"A sequence of multiple spaces in a charnames alias definition is deprecated">
+
+L<Trailing white-space in a charnames alias definition is deprecated|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
+
+These two deprecation warnings involving C<\N{...}> were incorrectly
+implemented. They did not warn by default (now they do) and could not be
+made fatal via C<use warnings FATAL => 'deprecated'> (now they can).
=back
entries for each change
Use L<XXX> with program names to get proper documentation linking. ]
-=head3 L<XXX>
+=head3 F<bisect.pl> enhancements
+
+The git bisection tool F<Porting/bisect.pl> has had many enhancements.
=over 4
=item *
-XXX
+Can optionally run the test case with a timeout.
+
+=item *
+
+Can now run in-place in a clean git checkout.
+
+=item *
+
+Can run the test case under C<valgrind>.
+
+=item *
+
+Can apply user supplied patches and fixes to the source checkout before
+building.
+
+=item *
+
+Now has fixups to enable building several more historical ranges of bleadperl,
+which can be useful for pinpointing the origins of bugs or behaviour changes.
=back
+It is provided as part of the source distribution but not installed because
+it is not self-contained as it relies on being run from within a git
+checkout. Note also that it makes no attempt to fix tests, correct runtime
+bugs or make something useful to install - its purpose is to make minimal
+changes to get any historical revision of interest to build and run as close
+as possible to "as-was", and thereby make C<git bisect> easy to use.
+
=head1 Configuration and Compilation
XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
significant internal changes for future core maintainers should be noted as
well.
-[ List each change as a =item entry ]
-
=over 4
=item *
+Perl's new copy-on-write mechanism (which is now enabled by default),
+allows any C<SvPOK> scalar to be automatically upgraded to a copy-on-write
+scalar when copied. A reference count on the string buffer is stored in
+the string buffer itself.
+
+For example:
+
+ $ perl -MDevel::Peek -e'$a="abc"; $b = $a; Dump $a; Dump $b'
+ SV = PV(0x260cd80) at 0x2620ad8
+ REFCNT = 1
+ FLAGS = (POK,IsCOW,pPOK)
+ PV = 0x2619bc0 "abc"\0
+ CUR = 3
+ LEN = 16
+ COW_REFCNT = 1
+ SV = PV(0x260ce30) at 0x2620b20
+ REFCNT = 1
+ FLAGS = (POK,IsCOW,pPOK)
+ PV = 0x2619bc0 "abc"\0
+ CUR = 3
+ LEN = 16
+ COW_REFCNT = 1
+
+Note that both scalars share the same PV buffer and have a COW_REFCNT
+greater than zero.
+
+This means that XS code which wishes to modify the C<SvPVX()> buffer of an
+SV should call C<SvPV_force()> or similar first, to ensure a valid (and
+unshared) buffer, and to call C<SvSETMAGIC()> afterwards. This in fact has
+always been the case (for example hash keys were already copy-on-write);
+this change just spreads the COW behaviour to a wider variety of SVs.
+
+One important difference is that before 5.18.0, shared hash-key scalars
+used to have the C<SvREADONLY> flag set; this is no longer the case.
+
+This new behaviour can still be disabled by running F<Configure> with
+B<-Accflags=-DPERL_NO_COW>. This option will probably be removed in Perl
+5.22.
+
+=item *
+
+C<PL_sawampersand> is now a constant. The switch this variable provided
+(to enable/disable the pre-match copy depending on whether C<$&> had been
+seen) has been removed and replaced with copy-on-write, eliminating a few
+bugs.
+
+The previous behaviour can still be enabled by running F<Configure> with
+B<-Accflags=-DPERL_SAWAMPERSAND>.
+
+=item *
+
The functions C<my_swap>, C<my_htonl> and C<my_ntohl> have been removed.
It is unclear why these functions were ever marked as I<A>, part of the
API. XS code can't call them directly, as it can't rely on them being
compiled. Unsurprisingly, no code on CPAN references them.
+=item *
+
+The signature of the C<Perl_re_intuit_start()> regex function has changed;
+the function pointer C<intuit> in the regex engine plugin structure
+has also changed accordingly. A new parameter, C<strbeg> has been added;
+this has the same meaning as the same-named parameter in
+C<Perl_regexec_flags>. Previously intuit would try to guess the start of
+the string from the passed SV (if any), and would sometimes get it wrong
+(e.g. with an overloaded SV).
+
=back
=head1 Selected Bug Fixes
on some 32 bit platforms. Notably, this caused the build to fail completely
on sparc GNU/Linux. [RT #118055]
+=item *
+
+The debugger's C<man> command been fixed. It was broken in the v5.18.0
+release. The C<man> command is aliased to the names C<doc> and C<perldoc> -
+all now work again.
+
+=item *
+
+Evaluating large hashes in scalar context is now much faster, as the number
+of used chains in the hash is now cached for larger hashes. Smaller hashes
+continue not to store it and calculate it when needed, as this saves one IV.
+That would be 1 IV overhead for every object built from a hash. [RT #114576]
+
+=item *
+
+Fixed a small number of regexp constructions that could either fail to
+match or crash perl when the string being matched against was
+allocated above the 2GB line on 32-bit systems. [RT #118175]
+
+=item *
+
+Perl v5.16 inadvertently introduced a bug whereby calls to XSUBs that were
+not visible at compile time were treated as lvalues and could be assigned
+to, even when the subroutine was not an lvalue sub. This has been fixed.
+[RT #117947]
+
+=item *
+
+In Perl v5.18.0 dualvars that had an empty string for the string part but a
+non-zero number for the number part starting being treated as true. In
+previous versions they were treated as false, the string representation
+taking precedeence. The old behaviour has been restored. [RT #118159]
+
+=item *
+
+Since Perl v5.12, inlining of constants that override built-in keywords of
+the same name had countermanded C<use subs>, causing subsequent mentions of
+the constant to use the built-in keyword instead. This has been fixed.
+
+=item *
+
+Lexical constants (C<my sub a() { 42 }>) no longer crash when inlined.
+
+=item *
+
+Parameter prototypes attached to lexical subroutines are now respected when
+compiling sub calls without parentheses. Previously, the prototypes were
+honoured only for calls I<with> parentheses. [RT #116735]
+
+=item *
+
+Syntax errors in lexical subroutines in combination with calls to the same
+subroutines no longer cause crashes at compile time.
+
+=item *
+
+The warning produced by C<-l $handle> now applies to IO refs and globs, not
+just to glob refs. That warning is also now UTF8-clean. [RT #117595]
+
+=item *
+
+Various memory leaks involving the parsing of the C<(?[...])> regular
+expression construct have been fixed.
+
+=item *
+
+C<(?[...])> now allows interpolation of precompiled patterns consisting of
+(?[...])> with bracket character classes inside (C<$pat =
+S<qr/(?[ [a] ])/;> S</(?[ $pat ])/>>). Formerly, the brackets would
+confuse the regular expression parser.
+
+=item *
+
+C<delete local $ENV{nonexistent_env_var}> no longer leaks memory.
+
+=item *
+
+C<sort> and C<require> followed by a keyword prefixed with C<CORE::> now
+treat it as a keyword, and not as a subroutine or module name. [RT #24482]
+
+=item *
+
+Through certain conundrums, it is possible to cause the current package to
+be freed. Certain operators (C<bless>, C<reset>, C<open>, C<eval>) could
+not cope and would crash. They have been made more resilient. [RT #117941]
+
+=item *
+
+Aliasing filehandles through glob-to-glob assignment would not update
+internal method caches properly if a package of the same name as the
+filehandle existed, resulting in filehandle method calls going to the
+package instead. This has been fixed.
+
=back
=head1 Known Problems
https://perl5.git.perl.org / perl5.git / blobdiff