5 [ this is a template for a new perldelta file. Any text flagged as XXX needs
6 to be processed before release. ]
8 perldelta - what is new for perl v5.21.6
12 This document describes differences between the 5.21.5 release and the 5.21.6
15 If you are upgrading from an earlier release such as 5.21.4, first read
16 L<perl5215delta>, which describes differences between 5.21.4 and 5.21.5.
20 XXX Any important notices here
22 =head1 Core Enhancements
24 XXX New core language features go here. Summarize user-visible core language
25 enhancements. Particularly prominent performance optimisations could go
26 here, but most should go in the L</Performance Enhancements> section.
28 [ List each enhancement as a =head2 entry ]
30 =head2 List form of pipe open implemented for Win32
32 The list form of pipe:
34 open my $fh, "-|", "program", @arguments;
36 is now implemented on Win32. It has the same limitations as C<system
37 LIST> on Win32, since the Win32 API doesn't accept program arguments
40 =head2 Assignment to list repetition
42 C<(...) x ...> can now be used within a list that is assigned to, as long
43 as the left-hand side is a valid lvalue. This allows C<(undef,undef,$foo)
44 = that_function()> to be written as C<((undef)x2, $foo) = that_function()>.
46 =head2 C<close> now sets C<$!>
48 When an I/O error occurs, the fact that there has been an error is recorded
49 in the handle. C<close> returns false for such a handle. Previously, the
50 value of C<$!> would be untouched by C<close>, so the common convention of
51 writing C<close $fh or die $!> did not work reliably. Now the handle
52 records the value of C<$!>, too, and C<close> restores it.
56 XXX Any security-related notices go here. In particular, any security
57 vulnerabilities closed should be noted here rather than in the
58 L</Selected Bug Fixes> section.
60 [ List each security issue as a =head2 entry ]
62 =head1 Incompatible Changes
64 XXX For a release on a stable branch, this section aspires to be:
66 There are no changes intentionally incompatible with 5.XXX.XXX
67 If any exist, they are bugs, and we request that you submit a
68 report. See L</Reporting Bugs> below.
70 [ List each incompatible change as a =head2 entry ]
74 XXX Any deprecated features, syntax, modules etc. should be listed here.
76 =head2 Module removals
78 XXX Remove this section if inapplicable.
80 The following modules will be removed from the core distribution in a
81 future release, and will at that time need to be installed from CPAN.
82 Distributions on CPAN which require these modules will need to list them as
85 The core versions of these modules will now issue C<"deprecated">-category
86 warnings to alert you to this fact. To silence these deprecation warnings,
87 install the modules in question from CPAN.
89 Note that these are (with rare exceptions) fine modules that you are encouraged
90 to continue to use. Their disinclusion from core primarily hinges on their
91 necessity to bootstrapping a fully functional, CPAN-capable Perl installation,
92 not usually on concerns over their design.
98 XXX Note that deprecated modules should be listed here even if they are listed
99 as an updated module in the L</Modules and Pragmata> section.
103 [ List each other deprecation as a =head2 entry ]
105 =head2 Use of non-graphic characters in single-character variable names
107 The syntax for single-character variable names is more lenient than
108 for longer variable names, allowing the one-character name to be a
109 punctuation character or even invisible (a non-graphic). Perl v5.20
110 deprecated the ASCII-range controls as such a name. Now, all
111 non-graphic characters that formerly were allowed are deprecated.
112 The practical effect of this occurs only when not under C<S<"use
113 utf8">>, and affects just the C1 controls (code points 0x80 through
114 0xFF), NO-BREAK SPACE, and SOFT HYPHEN.
116 =head1 Performance Enhancements
118 XXX Changes which enhance performance without changing behaviour go here.
119 There may well be none in a stable release.
121 [ List each enhancement as a =item entry ]
127 C<(...)x1>, C<("constant")x0> and C<($scalar)x0> are now optimised in list
128 context. If the right-hand argument is a constant 1, the repetition
129 operator disappears. If the right-hand argument is a constant 0, the whole
130 expressions is optimised to the empty list, so long as the left-hand
131 argument is a simple scalar or constant. C<(foo())x0> is not optimised.
135 C<substr> assignment is now optimised into 4-argument C<substr> at the end
136 of a subroutine (or as the argument to C<return>). Previously, this
137 optimisation only happened in void context.
141 Assignment to lexical variables is often optimised away. For instance, in
142 C<$lexical = chr $foo>, the C<chr> operator writes directly to the lexical
143 variable instead of returning a value that gets copied. This optimisation
144 has been extended to C<split>, C<x> and C<vec> on the right-hand side. It
145 has also been made to work with state variable initialization.
149 =head1 Modules and Pragmata
151 XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
152 go here. If Module::CoreList is updated, generate an initial draft of the
153 following sections using F<Porting/corelist-perldelta.pl>. A paragraph summary
154 for important changes should then be added by hand. In an ideal world,
155 dual-life modules would have a F<Changes> file that could be cribbed.
157 [ Within each section, list entries as a =item entry ]
159 =head2 New Modules and Pragmata
169 =head2 Updated Modules and Pragmata
175 L<B::Deparse> has been upgraded from version 1.29 to 1.30.
177 It now deparses C<+sub : attr { ... }> correctly at the start of a
178 statement. Without the initial C<+>, C<sub> would be a statement label.
180 C<BEGIN> blocks are now emitted in the right place most of the time, but
181 the change unfortunately introduced a regression, in that C<BEGIN> blocks
182 occurring just before the end of the enclosing block may appear below it
183 instead. So this change may need to be reverted if it cannot be fixed
184 before Perl 5.22. [perl #77452]
188 L<DynaLoader> has been upgraded from version 1.27 to 1.28.
192 L<IO::Socket> has been upgraded from version 1.37 to 1.38.
194 Document the limitations of the isconnected() method. [perl #123096]
198 =head2 Removed Modules and Pragmata
210 XXX Changes to files in F<pod/> go here. Consider grouping entries by
211 file and be sure to link to the appropriate page, e.g. L<perlfunc>.
213 =head2 New Documentation
215 XXX Changes which create B<new> files in F<pod/> go here.
219 XXX Description of the purpose of the new file here
221 =head2 Changes to Existing Documentation
223 XXX Changes which significantly change existing files in F<pod/> go here.
224 However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
227 =head3 L<perldata/Identifier parsing>
233 The syntax of single-character variable names has been brought
234 up-to-date and more fully explained.
240 The following additions or changes have been made to diagnostic output,
241 including warnings and fatal error messages. For the complete list of
242 diagnostic messages, see L<perldiag>.
244 XXX New or changed warnings emitted by the core's C<C> code go here. Also
245 include any changes in L<perldiag> that reconcile it to the C<C> code.
247 =head2 New Diagnostics
249 XXX Newly added diagnostic messages go under here, separated into New Errors
258 XXX L<message|perldiag/"message">
268 L<Use of literal non-graphic characters in variable names is deprecated|perldiag/"Use of literal non-graphic characters in variable names is deprecated">
272 A new C<locale> warning category has been created, with the following warning
273 messages currently in it:
279 L<Locale '%s' may not work well.%s|perldiag/Locale '%s' may not work well.%s>
283 L<Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".|perldiag/Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".>
289 L<Warning: unable to close filehandle %s properly: %s|perldiag/"Warning: unable to close filehandle %s properly: %s">
293 =head2 Changes to Existing Diagnostics
295 XXX Changes (i.e. rewording) of diagnostic messages go here
301 L<Quantifier unexpected on zero-length expression in regex mE<sol>%sE<sol>|perldiag/"Quantifier unexpected on zero-length expression in regex m/%s/">.
303 This message has had the S<"<-- HERE"> marker removed, as it was always
304 placed at the end of the regular expression, regardless of where the
305 problem actually occurred. [perl #122680]
309 =head1 Utility Changes
311 XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go here.
312 Most of these are built within the directory F<utils>.
314 [ List utility changes as a =head2 entry for each utility and =item
315 entries for each change
316 Use L<XXX> with program names to get proper documentation linking. ]
328 =head1 Configuration and Compilation
330 XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
331 go here. Any other changes to the Perl build process should be listed here.
332 However, any platform-specific changes should be listed in the
333 L</Platform Support> section, instead.
335 [ List changes as a =item entry ].
341 F<Configure> with C<-Dmksymlinks> should now be faster. [perl #122002]
347 XXX Any significant changes to the testing of a freshly built perl should be
348 listed here. Changes which create B<new> files in F<t/> go here as do any
349 large changes to the testing harness (e.g. when parallel testing was added).
350 Changes to existing files in F<t/> aren't worth summarizing, although the bugs
351 that they represent may be covered elsewhere.
353 [ List each test improvement as a =item entry ]
363 =head1 Platform Support
365 XXX Any changes to platform support should be listed in the sections below.
367 [ Within the sections, list each platform as a =item entry with specific
368 changes as paragraphs below it. ]
372 XXX List any platforms that this version of perl compiles on, that previous
373 versions did not. These will either be enabled by new files in the F<hints/>
374 directories, or new subdirectories and F<README> files at the top level of the
379 =item XXX-some-platform
385 =head2 Discontinued Platforms
387 XXX List any platforms that this version of perl no longer compiles on.
391 =item XXX-some-platform
397 =head2 Platform-Specific Notes
399 XXX List any changes for specific platforms. This could include configuration
400 and compilation changes or changes in portability/compatibility. However,
401 changes within modules for platforms should generally be listed in the
402 L</Modules and Pragmata> section.
406 =item XXX-some-platform
418 In the experimental C<:win32> layer, a crash in C<open> was fixed. Also
419 opening C</dev/null>, which works the Win32 Perl's normal C<:unix> layer, was
420 implemented for C<:win32>.
421 L<[perl #122224]|https://rt.perl.org/Ticket/Display.html?id=122224>
425 A new makefile option, C<USE_LONG_DOUBLE>, has been added to the Windows
426 dmake makefile for gcc builds only. Set this to "define" if you want perl to
427 use long doubles to give more accuracy and range for floating point numbers.
431 =head1 Internal Changes
433 XXX Changes which affect the interface available to C<XS> code go here. Other
434 significant internal changes for future core maintainers should be noted as
437 [ List each change as a =item entry ]
443 C<screaminstr> has been removed. Although marked as public API, it is
444 undocumented and has no usage in modern perl versions on CPAN Grep. Calling it
445 has been fatal since 5.17.0.
449 C<newDEFSVOP>, C<block_start>, C<block_end> and C<intro_my> have been added
454 The internal C<convert> function in F<op.c> has been renamed
455 C<op_convert_list> and added to the API.
459 C<sv_magic> no longer forbids "ext" magic on read-only values. After all,
460 perl can't know whether the custom magic will modify the SV or not.
465 =head1 Selected Bug Fixes
467 XXX Important bug fixes in the core language are summarized here. Bug fixes in
468 files in F<ext/> and F<lib/> are best summarized in L</Modules and Pragmata>.
470 [ List each fix as a =item entry ]
476 fchmod() and futimes() now set C<$!> when they fail due to being
477 passed a closed file handle. [perl #122703]
481 Perl now comes with a corrected Unicode 7.0 for the erratum issued on
482 October 21, 2014 (see L<http://www.unicode.org/errata/#current_errata>),
483 dealing with glyph shaping in Arabic.
487 op_free() no longer crashes due to a stack overflow when freeing a
488 deeply recursive op tree. [perl #108276]
492 scalarvoid() would crash due to a stack overflow when processing a
493 deeply recursive op tree. [perl #108276]
497 In Perl 5.20.0, C<$^N> accidentally had the internal UTF8 flag turned off
498 if accessed from a code block within a regular expression, effectively
499 UTF8-encoding the value. This has been fixed. [perl #123135]
503 A failed C<semctl> call no longer overwrites existing items on the stack,
504 causing C<(semctl(-1,0,0,0))[0]> to give an "uninitialized" warning.
508 C<else{foo()}> with no space before C<foo> is now better at assigning the
509 right line number to that statement. [perl #122695]
513 Sometimes the assignment in C<@array = split> gets optimised and C<split>
514 itself writes directly to the array. This caused a bug, preventing this
515 assignment from being used in lvalue context. So
516 C<(@a=split//,"foo")=bar()> was an error. (This bug probably goes back to
517 Perl 3, when the optimisation was added.) This optimisation, and the bug,
518 started to happen in more cases in 5.21.5. It has now been fixed.
523 When argument lists that fail the checks installed by subroutine
524 signatures, the resulting error messages now give the file and line number
525 of the caller, not of the called subroutine. [perl #121374]
529 Flip-flop operators (C<..> and C<...> in scalar context) used to maintain
530 a separate state for each recursion level (the number of times the
531 enclosing sub was called recursively), contrary to the documentation. Now
532 each closure has one internal state for each flip-flop. [perl #122829]
536 C<use>, C<no>, statement labels, special blocks (C<BEGIN>) and pod are now
537 permitted as the first thing in a C<map> or C<grep> block, the block after
538 C<print> or C<say> (or other functions) returning a handle, and within
539 C<${...}>, C<@{...}>, etc. [perl #122782]
543 The repetition operator C<x> now propagates lvalue context to its left-hand
544 argument when used in contexts like C<foreach>. That allows
545 C<for(($#that_array)x2) { ... }> to work as expected if the loop modifies
550 C<(...) x ...> in scalar context used to corrupt the stack if one operand
551 were an object with "x" overloading, causing erratic behaviour.
556 =head1 Known Problems
558 XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
559 tests that had to be C<TODO>ed for the release would be noted here. Unfixed
560 platform specific bugs also go here.
562 [ List each fix as a =item entry ]
568 Starting in 5.21.6, accessing L<perlapi/CvPADLIST> in an XSUB is forbidden.
569 CvPADLIST has be reused for a different internal purpose for XSUBs. Guard all
570 CvPADLIST expressions with C<CvISXSUB()> if your code doesn't already block
571 XSUB CV*s from going through optree CV* expecting code.
575 =head1 Errata From Previous Releases
581 Due to a mistake in the string-copying logic, copying the value of a state
582 variable could instead steal the value and undefine the variable. This
583 bug, introduced in 5.20, would happen mostly for long strings (1250 chars
584 or more), but could happen for any strings under builds with copy-on-write
585 disabled. [perl #123029]
587 This bug was actually fixed in 5.21.5, but it was not until after that
588 release that this bug, and the fact that it had been fixed, were
595 XXX If any significant core contributor has died, we've added a short obituary
598 =head1 Acknowledgements
600 XXX Generate this with:
602 perl Porting/acknowledgements.pl v5.21.5..HEAD
604 =head1 Reporting Bugs
606 If you find what you think is a bug, you might check the articles recently
607 posted to the comp.lang.perl.misc newsgroup and the perl bug database at
608 https://rt.perl.org/ . There may also be information at
609 http://www.perl.org/ , the Perl Home Page.
611 If you believe you have an unreported bug, please run the L<perlbug> program
612 included with your release. Be sure to trim your bug down to a tiny but
613 sufficient test case. Your bug report, along with the output of C<perl -V>,
614 will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
616 If the bug you are reporting has security implications, which make it
617 inappropriate to send to a publicly archived mailing list, then please send it
618 to perl5-security-report@perl.org. This points to a closed subscription
619 unarchived mailing list, which includes all the core committers, who will be
620 able to help assess the impact of issues, figure out a resolution, and help
621 co-ordinate the release of patches to mitigate or fix the problem across all
622 platforms on which Perl is supported. Please only use this address for
623 security issues in the Perl core, not for modules independently distributed on
628 The F<Changes> file for an explanation of how to view exhaustive details on
631 The F<INSTALL> file for how to build Perl.
633 The F<README> file for general stuff.
635 The F<Artistic> and F<Copying> files for copyright information.