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 =head1 Modules and Pragmata
137 XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
138 go here. If Module::CoreList is updated, generate an initial draft of the
139 following sections using F<Porting/corelist-perldelta.pl>. A paragraph summary
140 for important changes should then be added by hand. In an ideal world,
141 dual-life modules would have a F<Changes> file that could be cribbed.
143 [ Within each section, list entries as a =item entry ]
145 =head2 New Modules and Pragmata
155 =head2 Updated Modules and Pragmata
161 L<B::Deparse> has been upgraded from version 1.29 to 1.30.
163 It now deparses C<+sub : attr { ... }> correctly at the start of a
164 statement. Without the initial C<+>, C<sub> would be a statement label.
168 L<DynaLoader> has been upgraded from version 1.27 to 1.28.
172 L<IO::Socket> has been upgraded from version 1.37 to 1.38.
174 Document the limitations of the isconnected() method. [perl #123096]
178 =head2 Removed Modules and Pragmata
190 XXX Changes to files in F<pod/> go here. Consider grouping entries by
191 file and be sure to link to the appropriate page, e.g. L<perlfunc>.
193 =head2 New Documentation
195 XXX Changes which create B<new> files in F<pod/> go here.
199 XXX Description of the purpose of the new file here
201 =head2 Changes to Existing Documentation
203 XXX Changes which significantly change existing files in F<pod/> go here.
204 However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
207 =head3 L<perldata/Identifier parsing>
213 The syntax of single-character variable names has been brought
214 up-to-date and more fully explained.
220 The following additions or changes have been made to diagnostic output,
221 including warnings and fatal error messages. For the complete list of
222 diagnostic messages, see L<perldiag>.
224 XXX New or changed warnings emitted by the core's C<C> code go here. Also
225 include any changes in L<perldiag> that reconcile it to the C<C> code.
227 =head2 New Diagnostics
229 XXX Newly added diagnostic messages go under here, separated into New Errors
238 XXX L<message|perldiag/"message">
248 L<Use of literal non-graphic characters in variable names is deprecated|perldiag/"Use of literal non-graphic characters in variable names is deprecated">
252 A new C<locale> warning category has been created, with the following warning
253 messages currently in it:
259 L<Locale '%s' may not work well.%s|perldiag/Locale '%s' may not work well.%s>
263 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".>
269 L<Warning: unable to close filehandle %s properly: %s|perldiag/"Warning: unable to close filehandle %s properly: %s">
273 =head2 Changes to Existing Diagnostics
275 XXX Changes (i.e. rewording) of diagnostic messages go here
281 L<Quantifier unexpected on zero-length expression in regex m/%s/|perldiag/"Quantifier unexpected on zero-length expression in regex m/%s/">.
283 This message has had the S<"<-- HERE"> marker removed, as it was always
284 placed at the end of the regular expression, regardless of where the
285 problem actually occurred. [perl #122680]
289 =head1 Utility Changes
291 XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go here.
292 Most of these are built within the directory F<utils>.
294 [ List utility changes as a =head2 entry for each utility and =item
295 entries for each change
296 Use L<XXX> with program names to get proper documentation linking. ]
308 =head1 Configuration and Compilation
310 XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
311 go here. Any other changes to the Perl build process should be listed here.
312 However, any platform-specific changes should be listed in the
313 L</Platform Support> section, instead.
315 [ List changes as a =item entry ].
321 F<Configure> with C<-Dmksymlinks> should now be faster. [perl #122002]
327 XXX Any significant changes to the testing of a freshly built perl should be
328 listed here. Changes which create B<new> files in F<t/> go here as do any
329 large changes to the testing harness (e.g. when parallel testing was added).
330 Changes to existing files in F<t/> aren't worth summarizing, although the bugs
331 that they represent may be covered elsewhere.
333 [ List each test improvement as a =item entry ]
343 =head1 Platform Support
345 XXX Any changes to platform support should be listed in the sections below.
347 [ Within the sections, list each platform as a =item entry with specific
348 changes as paragraphs below it. ]
352 XXX List any platforms that this version of perl compiles on, that previous
353 versions did not. These will either be enabled by new files in the F<hints/>
354 directories, or new subdirectories and F<README> files at the top level of the
359 =item XXX-some-platform
365 =head2 Discontinued Platforms
367 XXX List any platforms that this version of perl no longer compiles on.
371 =item XXX-some-platform
377 =head2 Platform-Specific Notes
379 XXX List any changes for specific platforms. This could include configuration
380 and compilation changes or changes in portability/compatibility. However,
381 changes within modules for platforms should generally be listed in the
382 L</Modules and Pragmata> section.
386 =item XXX-some-platform
398 In the experimental C<:win32> layer, a crash in C<open> was fixed. Also
399 opening C</dev/null>, which works the Win32 Perl's normal C<:unix> layer, was
400 implemented for C<:win32>.
401 L<[perl #122224]|https://rt.perl.org/Ticket/Display.html?id=122224>
405 A new makefile option, C<USE_LONG_DOUBLE>, has been added to the Windows
406 dmake makefile for gcc builds only. Set this to "define" if you want perl to
407 use long doubles to give more accuracy and range for floating point numbers.
411 =head1 Internal Changes
413 XXX Changes which affect the interface available to C<XS> code go here. Other
414 significant internal changes for future core maintainers should be noted as
417 [ List each change as a =item entry ]
423 C<screaminstr> has been removed. Although marked as public API, it is
424 undocumented and has no usage in modern perl versions on CPAN Grep. Calling it
425 has been fatal since 5.17.0.
429 C<newDEFSVOP>, C<block_start>, C<block_end> and C<intro_my> have been added
434 The internal C<convert> function in F<op.c> has been renamed
435 C<op_convert_list> and added to the API.
439 C<sv_magic> no longer forbids "ext" magic on read-only values. After all,
440 perl can't know whether the custom magic will modify the SV or not.
445 =head1 Selected Bug Fixes
447 XXX Important bug fixes in the core language are summarized here. Bug fixes in
448 files in F<ext/> and F<lib/> are best summarized in L</Modules and Pragmata>.
450 [ List each fix as a =item entry ]
456 fchmod() and futimes() now set C<$!> when they fail due to being
457 passed a closed file handle. [perl #122703]
461 Perl now comes with a corrected Unicode 7.0 for the erratum issued on
462 October 21, 2014 (see L<http://www.unicode.org/errata/#current_errata>),
463 dealing with glyph shaping in Arabic.
467 op_free() no longer crashes due to a stack overflow when freeing a
468 deeply recursive op tree. [perl #108276]
472 scalarvoid() would crash due to a stack overflow when processing a
473 deeply recursive op tree. [perl #108276]
477 In Perl 5.20.0, C<$^N> accidentally had the internal UTF8 flag turned off
478 if accessed from a code block within a regular expression, effectively
479 UTF8-encoding the value. This has been fixed. [perl #123135]
483 A failed C<semctl> call no longer overwrites existing items on the stack,
484 causing C<(semctl(-1,0,0,0))[0]> to give an "uninitialized" warning.
488 C<else{foo()}> with no space before C<foo> is now better at assigning the
489 right line number to that statement. [perl #122695]
493 Sometimes the assignment in C<@array = split> gets optimised and C<split>
494 itself writes directly to the array. This caused a bug, preventing this
495 assignment from being used in lvalue context. So
496 C<(@a=split//,"foo")=bar()> was an error. (This bug probably goes back to
497 Perl 3, when the optimisation was added.) This optimisation, and the bug,
498 started to happen in more cases in 5.21.5. It has now been fixed.
503 When argument lists that fail the checks installed by subroutine
504 signatures, the resulting error messages now give the file and line number
505 of the caller, not of the called subroutine. [perl #121374]
509 Flip-flop operators (C<..> and C<...> in scalar context) used to maintain
510 a separate state for each recursion level (the number of times the
511 enclosing sub was called recursively), contrary to the documentation. Now
512 each closure has one internal state for each flip-flop. [perl #122829]
516 C<use>, C<no>, statement labels, special blocks (C<BEGIN>) and pod are now
517 permitted as the first thing in a C<map> or C<grep> block, the block after
518 C<print> or C<say> (or other functions) returning a handle, and within
519 C<${...}>, C<@{...}>, etc. [perl #122782]
523 The repetition operator C<x> now propagates lvalue context to its left-hand
524 argument when used in contexts like C<foreach>. That allows
525 C<for(($#that_array)x2) { ... }> to work as expected if the loop modifies
530 =head1 Known Problems
532 XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
533 tests that had to be C<TODO>ed for the release would be noted here. Unfixed
534 platform specific bugs also go here.
536 [ List each fix as a =item entry ]
542 Starting in 5.21.6, accessing L<perlapi/CvPADLIST> in an XSUB is forbidden.
543 CvPADLIST has be reused for a different internal purpose for XSUBs. Guard all
544 CvPADLIST expressions with C<CvISXSUB()> if your code doesn't already block
545 XSUB CV*s from going through optree CV* expecting code.
549 =head1 Errata From Previous Releases
555 Due to a mistake in the string-copying logic, copying the value of a state
556 variable could instead steal the value and undefine the variable. This
557 bug, introduced in 5.20, would happen mostly for long strings (1250 chars
558 or more), but could happen for any strings under builds with copy-on-write
559 disabled. [perl #123029]
561 This bug was actually fixed in 5.21.5, but it was not until after that
562 release that this bug, and the fact that it had been fixed, were
569 XXX If any significant core contributor has died, we've added a short obituary
572 =head1 Acknowledgements
574 XXX Generate this with:
576 perl Porting/acknowledgements.pl v5.21.5..HEAD
578 =head1 Reporting Bugs
580 If you find what you think is a bug, you might check the articles recently
581 posted to the comp.lang.perl.misc newsgroup and the perl bug database at
582 https://rt.perl.org/ . There may also be information at
583 http://www.perl.org/ , the Perl Home Page.
585 If you believe you have an unreported bug, please run the L<perlbug> program
586 included with your release. Be sure to trim your bug down to a tiny but
587 sufficient test case. Your bug report, along with the output of C<perl -V>,
588 will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
590 If the bug you are reporting has security implications, which make it
591 inappropriate to send to a publicly archived mailing list, then please send it
592 to perl5-security-report@perl.org. This points to a closed subscription
593 unarchived mailing list, which includes all the core committers, who will be
594 able to help assess the impact of issues, figure out a resolution, and help
595 co-ordinate the release of patches to mitigate or fix the problem across all
596 platforms on which Perl is supported. Please only use this address for
597 security issues in the Perl core, not for modules independently distributed on
602 The F<Changes> file for an explanation of how to view exhaustive details on
605 The F<INSTALL> file for how to build Perl.
607 The F<README> file for general stuff.
609 The F<Artistic> and F<Copying> files for copyright information.