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]
186 B::Deparse no longer puts erroneous C<local> here and there, such as for
187 C<LIST = tr/a//d>. [perl #119815]
191 L<DynaLoader> has been upgraded from version 1.27 to 1.28.
195 L<IO::Socket> has been upgraded from version 1.37 to 1.38.
197 Document the limitations of the isconnected() method. [perl #123096]
201 =head2 Removed Modules and Pragmata
213 XXX Changes to files in F<pod/> go here. Consider grouping entries by
214 file and be sure to link to the appropriate page, e.g. L<perlfunc>.
216 =head2 New Documentation
218 XXX Changes which create B<new> files in F<pod/> go here.
222 XXX Description of the purpose of the new file here
224 =head2 Changes to Existing Documentation
226 XXX Changes which significantly change existing files in F<pod/> go here.
227 However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
230 =head3 L<perldata/Identifier parsing>
236 The syntax of single-character variable names has been brought
237 up-to-date and more fully explained.
243 The following additions or changes have been made to diagnostic output,
244 including warnings and fatal error messages. For the complete list of
245 diagnostic messages, see L<perldiag>.
247 XXX New or changed warnings emitted by the core's C<C> code go here. Also
248 include any changes in L<perldiag> that reconcile it to the C<C> code.
250 =head2 New Diagnostics
252 XXX Newly added diagnostic messages go under here, separated into New Errors
261 XXX L<message|perldiag/"message">
271 L<Use of literal non-graphic characters in variable names is deprecated|perldiag/"Use of literal non-graphic characters in variable names is deprecated">
275 A new C<locale> warning category has been created, with the following warning
276 messages currently in it:
282 L<Locale '%s' may not work well.%s|perldiag/Locale '%s' may not work well.%s>
286 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".>
292 L<Warning: unable to close filehandle %s properly: %s|perldiag/"Warning: unable to close filehandle %s properly: %s">
296 =head2 Changes to Existing Diagnostics
298 XXX Changes (i.e. rewording) of diagnostic messages go here
304 L<Quantifier unexpected on zero-length expression in regex mE<sol>%sE<sol>|perldiag/"Quantifier unexpected on zero-length expression in regex m/%s/">.
306 This message has had the S<"<-- HERE"> marker removed, as it was always
307 placed at the end of the regular expression, regardless of where the
308 problem actually occurred. [perl #122680]
312 =head1 Utility Changes
314 XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go here.
315 Most of these are built within the directory F<utils>.
317 [ List utility changes as a =head2 entry for each utility and =item
318 entries for each change
319 Use L<XXX> with program names to get proper documentation linking. ]
331 =head1 Configuration and Compilation
333 XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
334 go here. Any other changes to the Perl build process should be listed here.
335 However, any platform-specific changes should be listed in the
336 L</Platform Support> section, instead.
338 [ List changes as a =item entry ].
344 F<Configure> with C<-Dmksymlinks> should now be faster. [perl #122002]
350 XXX Any significant changes to the testing of a freshly built perl should be
351 listed here. Changes which create B<new> files in F<t/> go here as do any
352 large changes to the testing harness (e.g. when parallel testing was added).
353 Changes to existing files in F<t/> aren't worth summarizing, although the bugs
354 that they represent may be covered elsewhere.
356 [ List each test improvement as a =item entry ]
366 =head1 Platform Support
368 XXX Any changes to platform support should be listed in the sections below.
370 [ Within the sections, list each platform as a =item entry with specific
371 changes as paragraphs below it. ]
375 XXX List any platforms that this version of perl compiles on, that previous
376 versions did not. These will either be enabled by new files in the F<hints/>
377 directories, or new subdirectories and F<README> files at the top level of the
382 =item XXX-some-platform
388 =head2 Discontinued Platforms
390 XXX List any platforms that this version of perl no longer compiles on.
394 =item XXX-some-platform
400 =head2 Platform-Specific Notes
402 XXX List any changes for specific platforms. This could include configuration
403 and compilation changes or changes in portability/compatibility. However,
404 changes within modules for platforms should generally be listed in the
405 L</Modules and Pragmata> section.
409 =item XXX-some-platform
421 In the experimental C<:win32> layer, a crash in C<open> was fixed. Also
422 opening C</dev/null>, which works the Win32 Perl's normal C<:unix> layer, was
423 implemented for C<:win32>.
424 L<[perl #122224]|https://rt.perl.org/Ticket/Display.html?id=122224>
428 A new makefile option, C<USE_LONG_DOUBLE>, has been added to the Windows
429 dmake makefile for gcc builds only. Set this to "define" if you want perl to
430 use long doubles to give more accuracy and range for floating point numbers.
434 =head1 Internal Changes
436 XXX Changes which affect the interface available to C<XS> code go here. Other
437 significant internal changes for future core maintainers should be noted as
440 [ List each change as a =item entry ]
446 C<screaminstr> has been removed. Although marked as public API, it is
447 undocumented and has no usage in modern perl versions on CPAN Grep. Calling it
448 has been fatal since 5.17.0.
452 C<newDEFSVOP>, C<block_start>, C<block_end> and C<intro_my> have been added
457 The internal C<convert> function in F<op.c> has been renamed
458 C<op_convert_list> and added to the API.
462 C<sv_magic> no longer forbids "ext" magic on read-only values. After all,
463 perl can't know whether the custom magic will modify the SV or not.
468 =head1 Selected Bug Fixes
470 XXX Important bug fixes in the core language are summarized here. Bug fixes in
471 files in F<ext/> and F<lib/> are best summarized in L</Modules and Pragmata>.
473 [ List each fix as a =item entry ]
479 fchmod() and futimes() now set C<$!> when they fail due to being
480 passed a closed file handle. [perl #122703]
484 Perl now comes with a corrected Unicode 7.0 for the erratum issued on
485 October 21, 2014 (see L<http://www.unicode.org/errata/#current_errata>),
486 dealing with glyph shaping in Arabic.
490 op_free() no longer crashes due to a stack overflow when freeing a
491 deeply recursive op tree. [perl #108276]
495 scalarvoid() would crash due to a stack overflow when processing a
496 deeply recursive op tree. [perl #108276]
500 In Perl 5.20.0, C<$^N> accidentally had the internal UTF8 flag turned off
501 if accessed from a code block within a regular expression, effectively
502 UTF8-encoding the value. This has been fixed. [perl #123135]
506 A failed C<semctl> call no longer overwrites existing items on the stack,
507 causing C<(semctl(-1,0,0,0))[0]> to give an "uninitialized" warning.
511 C<else{foo()}> with no space before C<foo> is now better at assigning the
512 right line number to that statement. [perl #122695]
516 Sometimes the assignment in C<@array = split> gets optimised and C<split>
517 itself writes directly to the array. This caused a bug, preventing this
518 assignment from being used in lvalue context. So
519 C<(@a=split//,"foo")=bar()> was an error. (This bug probably goes back to
520 Perl 3, when the optimisation was added.) This optimisation, and the bug,
521 started to happen in more cases in 5.21.5. It has now been fixed.
526 When argument lists that fail the checks installed by subroutine
527 signatures, the resulting error messages now give the file and line number
528 of the caller, not of the called subroutine. [perl #121374]
532 Flip-flop operators (C<..> and C<...> in scalar context) used to maintain
533 a separate state for each recursion level (the number of times the
534 enclosing sub was called recursively), contrary to the documentation. Now
535 each closure has one internal state for each flip-flop. [perl #122829]
539 C<use>, C<no>, statement labels, special blocks (C<BEGIN>) and pod are now
540 permitted as the first thing in a C<map> or C<grep> block, the block after
541 C<print> or C<say> (or other functions) returning a handle, and within
542 C<${...}>, C<@{...}>, etc. [perl #122782]
546 The repetition operator C<x> now propagates lvalue context to its left-hand
547 argument when used in contexts like C<foreach>. That allows
548 C<for(($#that_array)x2) { ... }> to work as expected if the loop modifies
553 C<(...) x ...> in scalar context used to corrupt the stack if one operand
554 were an object with "x" overloading, causing erratic behaviour.
559 =head1 Known Problems
561 XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
562 tests that had to be C<TODO>ed for the release would be noted here. Unfixed
563 platform specific bugs also go here.
565 [ List each fix as a =item entry ]
571 Starting in 5.21.6, accessing L<perlapi/CvPADLIST> in an XSUB is forbidden.
572 CvPADLIST has be reused for a different internal purpose for XSUBs. Guard all
573 CvPADLIST expressions with C<CvISXSUB()> if your code doesn't already block
574 XSUB CV*s from going through optree CV* expecting code.
578 =head1 Errata From Previous Releases
584 Due to a mistake in the string-copying logic, copying the value of a state
585 variable could instead steal the value and undefine the variable. This
586 bug, introduced in 5.20, would happen mostly for long strings (1250 chars
587 or more), but could happen for any strings under builds with copy-on-write
588 disabled. [perl #123029]
590 This bug was actually fixed in 5.21.5, but it was not until after that
591 release that this bug, and the fact that it had been fixed, were
598 XXX If any significant core contributor has died, we've added a short obituary
601 =head1 Acknowledgements
603 XXX Generate this with:
605 perl Porting/acknowledgements.pl v5.21.5..HEAD
607 =head1 Reporting Bugs
609 If you find what you think is a bug, you might check the articles recently
610 posted to the comp.lang.perl.misc newsgroup and the perl bug database at
611 https://rt.perl.org/ . There may also be information at
612 http://www.perl.org/ , the Perl Home Page.
614 If you believe you have an unreported bug, please run the L<perlbug> program
615 included with your release. Be sure to trim your bug down to a tiny but
616 sufficient test case. Your bug report, along with the output of C<perl -V>,
617 will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
619 If the bug you are reporting has security implications, which make it
620 inappropriate to send to a publicly archived mailing list, then please send it
621 to perl5-security-report@perl.org. This points to a closed subscription
622 unarchived mailing list, which includes all the core committers, who will be
623 able to help assess the impact of issues, figure out a resolution, and help
624 co-ordinate the release of patches to mitigate or fix the problem across all
625 platforms on which Perl is supported. Please only use this address for
626 security issues in the Perl core, not for modules independently distributed on
631 The F<Changes> file for an explanation of how to view exhaustive details on
634 The F<INSTALL> file for how to build Perl.
636 The F<README> file for general stuff.
638 The F<Artistic> and F<Copying> files for copyright information.