[p5sagit/p5-mst-13.2.git] / pod / perl5131delta.pod

=encoding utf8

=head1 NAME

[ this is a template for a new perldelta file. Any text flagged as
XXX needs to be processed before release. ]

perldelta - what is new for perl v5.13.1

=head1 DESCRIPTION

This document describes differences between the 5.13.0 release and
the 5.13.1 release.

If you are upgrading from an earlier release such as 5.10, first read
L<perl5120delta>, which describes differences between 5.10 and
5.12.

=head1 Notice

XXX Any important notices here

=head1 Incompatible Changes

=head2 "C<\cI<X>>"

The backslash-c construct was designed as a way of specifying
non-printable characters, but there were no restrictions (on ASCII
platforms) on what the character following the C<c> could be.  Now, that
character must be one of the ASCII characters.

=head2 localised tied hashes, arrays and scalars are no longed tied

In the following:

    tie @a, ...;
    {
	local @a;
	# here, @a is a now a new, untied array
    }
    # here, @a refers again to the old, tied array

The new local array used to be made tied too, which was fairly pointless,
and has now been fixed. This fix could however potentially cause a change
in behaviour of some code.

=head1 Core Enhancements

XXX New core language features go here. Summarise user-visible core language
enhancements. Particularly prominent performance optimisations could go
here, but most should go in the L</Performance Enhancements> section.

=head2 Exception Handling Reliability

Several changes have been made to the way C<die>, C<warn>, and C<$@>
behave, in order to make them more reliable and consistent.

When an exception is thrown inside an C<eval>, the exception is no
longer at risk of being clobbered by code running during unwinding
(e.g., destructors).  Previously, the exception was written into C<$@>
early in the throwing process, and would be overwritten if C<eval> was
used internally in the destructor for an object that had to be freed
while exiting from the outer C<eval>.  Now the exception is written
into C<$@> last thing before exiting the outer C<eval>, so the code
running immediately thereafter can rely on the value in C<$@> correctly
corresponding to that C<eval>.

Likewise, a C<local $@> inside an C<eval> will no longer clobber any
exception thrown in its scope.  Previously, the restoration of C<$@> upon
unwinding would overwrite any exception being thrown.  Now the exception
gets to the C<eval> anyway.  So C<local $@> is safe inside an C<eval>,
albeit of rather limited use.

Exceptions thrown from object destructors no longer modify the C<$@>
of the surrounding context.  (If the surrounding context was exception
unwinding, this used to be another way to clobber the exception being
thrown.  Due to the above change it no longer has that significance,
but there are other situations where C<$@> is significant.)  Previously
such an exception was sometimes emitted as a warning, and then either
string-appended to the surrounding C<$@> or completely replaced the
surrounding C<$@>, depending on whether that exception and the surrounding
C<$@> were strings or objects.  Now, an exception in this situation is
always emitted as a warning, leaving the surrounding C<$@> untouched.
In addition to object destructors, this also affects any function call
performed by XS code using the C<G_KEEPERR> flag.

C<$@> is also no longer used as an internal temporary variable when
preparing to C<die>.  Previously it was internally necessary to put
any exception object (any non-string exception) into C<$@> first,
before it could be used as an exception.  (The C API still offers the
old option, so an XS module might still clobber C<$@> in the old way.)
This change together with the foregoing means that, in various places,
C<$@> may be observed to contain its previously-assigned value, rather
than having been overwritten by recent exception-related activity.

Warnings for C<warn> can now be objects, in the same way as exceptions
for C<die>.  If an object-based warning gets the default handling,
of writing to standard error, it will of course still be stringified
along the way.  But a C<$SIG{__WARN__}> handler will now receive an
object-based warning as an object, where previously it was passed the
result of stringifying the object.

=head1 New Platforms

XXX List any platforms that this version of perl compiles on, that previous
versions did not. These will either be enabled by new files in the F<hints/>
directories, or new subdirectories and F<README> files at the top level of the
source tree.

=head1 Modules and Pragmata

XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
go here.  If Module::CoreList is updated, generate an initial draft of the
following sections using F<Porting/corelist-perldelta.pl>, which prints stub
entries to STDOUT.  Results can be pasted in place of the '=head2' entries
below.  A paragraph summary for important changes should then be added by hand.
In an ideal world, dual-life modules would have a F<Changes> file that could be
cribbed.

=head2 New Modules and Pragmata

=head2 Pragmata Changes

=head2 Updated Modules

=over

=item Perl 4 C<.pl> libraries

These historical libraries have been minimally modified to avoid using
C<$[>.  This is to prepare them for the deprecation of C<$[>.

=item C<B::Deparse>

A bug has been fixed when deparsing a nextstate op that has both a
change of package (relative to the previous nextstate), or a change of
C<%^H> or other state, and a label.  Previously the label was emitted
first, leading to syntactically invalid output because a label is not
permitted immediately before a package declaration, B<BEGIN> block,
or some other things.  Now the label is emitted last.

=back

=head2 Removed Modules and Pragmata

=head1 Utility Changes

XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go
here. Most of these are built within the directories F<utils> and F<x2p>.

=over 4

=item F<XXX>

XXX

=back

=head1 New Documentation

XXX Changes which create B<new> files in F<pod/> go here.

=over 4

=item L<XXX>

XXX

=back

=head1 Changes to Existing Documentation

XXX Changes which significantly change existing files in F<pod/> go here.
Any changes to F<pod/perldiag.pod> should go in L</New or Changed Diagnostics>.


=head1 Performance Enhancements

XXX Changes which enhance performance without changing behaviour go here. There
may well be none in a stable release.

=over 4

=item *

XXX

=back

=head1 Installation and Configuration Improvements

XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
go here.

=head2 Configuration improvements

XXX

=head2 Compilation improvements

XXX

=head2 Platform Specific Changes

=over 4

=item XXX-some-platform

XXX

=back

=head1 Selected Bug Fixes

XXX Important bug fixes in the core language are summarised here.
Bug fixes in files in F<ext/> and F<lib/> are best summarised in
L</Modules and Pragmata>.

=over 4

=item *

XXX

=back

=head1 New or Changed Diagnostics

XXX New or changed warnings emitted by the core's C<C> code go here.

=over 4

=item C<XXX>

XXX

=back

=head1 Changed Internals

XXX Changes which affect the interface available to C<XS> code go here.

=over 4

=item *

The protocol for unwinding the C stack at the last stage of a C<die>
has changed how it identifies the target stack frame.  This now uses
a separate variable C<PL_restartjmpenv>, where previously it relied on
the C<blk_eval.cur_top_env> pointer in the C<eval> context frame that
has nominally just been discarded.  This change means that code running
during various stages of Perl-level unwinding no longer needs to take
care to avoid destroying the ghost frame.

=item *

XXX

=back

=head1 New Tests

XXX Changes which create B<new> files in F<t/> go here. Changes to
existing files in F<t/> aren't worth summarising, although the bugs that
they represent may be.

=over 4

=item F<XXX>

XXX

=back

=head1 Known Problems

XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
tests that had to be C<TODO>ed for the release would be noted here, unless
they were specific to a particular platform (see below).

This is a list of some significant unfixed bugs, which are regressions
from either 5.XXX.XXX or 5.XXX.XXX.

=over 4

=item *

XXX

=back

=head1 Deprecations

XXX Add any new known deprecations here.

The following items are now deprecated.

=over 4

=item *

XXX

=back

=head1 Platform Specific Notes

XXX Any changes specific to a particular platform. VMS and Win32 are the usual
stars here. It's probably best to group changes under the same section layout
as the main perldelta

=head1 Obituary

XXX If any significant core contributor has died, we've added a short obituary
here.

=head1 Acknowledgements

XXX The list of people to thank goes here.


=head1 Reporting Bugs

If you find what you think is a bug, you might check the articles
recently posted to the comp.lang.perl.misc newsgroup and the perl
bug database at http://rt.perl.org/perlbug/ .  There may also be
information at http://www.perl.org/ , the Perl Home Page.

If you believe you have an unreported bug, please run the B<perlbug>
program included with your release.  Be sure to trim your bug down
to a tiny but sufficient test case.  Your bug report, along with the
output of C<perl -V>, will be sent off to perlbug@perl.org to be
analysed by the Perl porting team.

If the bug you are reporting has security implications, which make it
inappropriate to send to a publicly archived mailing list, then please send
it to perl5-security-report@perl.org. This points to a closed subscription
unarchived mailing list, which includes all the core committers, who be able
to help assess the impact of issues, figure out a resolution, and help
co-ordinate the release of patches to mitigate or fix the problem across all
platforms on which Perl is supported. Please only use this address for
security issues in the Perl core, not for modules independently
distributed on CPAN.

=head1 SEE ALSO

The F<Changes> file for an explanation of how to view exhaustive details
on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut
Commit	Line	Data
d4438f94	1	=encoding utf8
	2
	3	=head1 NAME
	4
	5	[ this is a template for a new perldelta file. Any text flagged as
	6	XXX needs to be processed before release. ]
	7
	8	perldelta - what is new for perl v5.13.1
	9
	10	=head1 DESCRIPTION
	11
	12	This document describes differences between the 5.13.0 release and
	13	the 5.13.1 release.
	14
	15	If you are upgrading from an earlier release such as 5.10, first read
	16	L<perl5120delta>, which describes differences between 5.10 and
	17	5.12.
	18
	19	=head1 Notice
	20
	21	XXX Any important notices here
	22
	23	=head1 Incompatible Changes
	24
df5278db	25	=head2 "C<\cI<X>>"
d4438f94	26
df5278db	27	The backslash-c construct was designed as a way of specifying
	28	non-printable characters, but there were no restrictions (on ASCII
	29	platforms) on what the character following the C<c> could be. Now, that
	30	character must be one of the ASCII characters.
d4438f94	31
72ecaef9	32	=head2 localised tied hashes, arrays and scalars are no longed tied
	33
	34	In the following:
	35
	36	tie @a, ...;
	37	{
	38	local @a;
	39	# here, @a is a now a new, untied array
	40	}
	41	# here, @a refers again to the old, tied array
	42
	43	The new local array used to be made tied too, which was fairly pointless,
	44	and has now been fixed. This fix could however potentially cause a change
	45	in behaviour of some code.
	46
d4438f94	47	=head1 Core Enhancements
	48
	49	XXX New core language features go here. Summarise user-visible core language
	50	enhancements. Particularly prominent performance optimisations could go
	51	here, but most should go in the L</Performance Enhancements> section.
	52
9d5401ce	53	=head2 Exception Handling Reliability
	54
	55	Several changes have been made to the way C<die>, C<warn>, and C<$@>
	56	behave, in order to make them more reliable and consistent.
	57
	58	When an exception is thrown inside an C<eval>, the exception is no
	59	longer at risk of being clobbered by code running during unwinding
	60	(e.g., destructors). Previously, the exception was written into C<$@>
	61	early in the throwing process, and would be overwritten if C<eval> was
	62	used internally in the destructor for an object that had to be freed
	63	while exiting from the outer C<eval>. Now the exception is written
	64	into C<$@> last thing before exiting the outer C<eval>, so the code
	65	running immediately thereafter can rely on the value in C<$@> correctly
	66	corresponding to that C<eval>.
	67
	68	Likewise, a C<local $@> inside an C<eval> will no longer clobber any
	69	exception thrown in its scope. Previously, the restoration of C<$@> upon
	70	unwinding would overwrite any exception being thrown. Now the exception
	71	gets to the C<eval> anyway. So C<local $@> is safe inside an C<eval>,
	72	albeit of rather limited use.
	73
	74	Exceptions thrown from object destructors no longer modify the C<$@>
	75	of the surrounding context. (If the surrounding context was exception
	76	unwinding, this used to be another way to clobber the exception being
	77	thrown. Due to the above change it no longer has that significance,
	78	but there are other situations where C<$@> is significant.) Previously
	79	such an exception was sometimes emitted as a warning, and then either
	80	string-appended to the surrounding C<$@> or completely replaced the
	81	surrounding C<$@>, depending on whether that exception and the surrounding
	82	C<$@> were strings or objects. Now, an exception in this situation is
	83	always emitted as a warning, leaving the surrounding C<$@> untouched.
	84	In addition to object destructors, this also affects any function call
	85	performed by XS code using the C<G_KEEPERR> flag.
	86
	87	C<$@> is also no longer used as an internal temporary variable when
	88	preparing to C<die>. Previously it was internally necessary to put
	89	any exception object (any non-string exception) into C<$@> first,
	90	before it could be used as an exception. (The C API still offers the
	91	old option, so an XS module might still clobber C<$@> in the old way.)
	92	This change together with the foregoing means that, in various places,
	93	C<$@> may be observed to contain its previously-assigned value, rather
	94	than having been overwritten by recent exception-related activity.
	95
	96	Warnings for C<warn> can now be objects, in the same way as exceptions
	97	for C<die>. If an object-based warning gets the default handling,
	98	of writing to standard error, it will of course still be stringified
	99	along the way. But a C<$SIG{__WARN__}> handler will now receive an
	100	object-based warning as an object, where previously it was passed the
	101	result of stringifying the object.
	102
d4438f94	103	=head1 New Platforms
	104
	105	XXX List any platforms that this version of perl compiles on, that previous
	106	versions did not. These will either be enabled by new files in the F<hints/>
	107	directories, or new subdirectories and F<README> files at the top level of the
	108	source tree.
	109
	110	=head1 Modules and Pragmata
	111
	112	XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
	113	go here. If Module::CoreList is updated, generate an initial draft of the
	114	following sections using F<Porting/corelist-perldelta.pl>, which prints stub
	115	entries to STDOUT. Results can be pasted in place of the '=head2' entries
	116	below. A paragraph summary for important changes should then be added by hand.
	117	In an ideal world, dual-life modules would have a F<Changes> file that could be
	118	cribbed.
	119
	120	=head2 New Modules and Pragmata
	121
	122	=head2 Pragmata Changes
	123
	124	=head2 Updated Modules
	125
d6445baf	126	=over
d6445baf	127
f8a182a2	128	=item Perl 4 C<.pl> libraries
	129
	130	These historical libraries have been minimally modified to avoid using
	131	C<$[>. This is to prepare them for the deprecation of C<$[>.
	132
d6445baf	133	=item C<B::Deparse>
	134
	135	A bug has been fixed when deparsing a nextstate op that has both a
	136	change of package (relative to the previous nextstate), or a change of
	137	C<%^H> or other state, and a label. Previously the label was emitted
	138	first, leading to syntactically invalid output because a label is not
	139	permitted immediately before a package declaration, B<BEGIN> block,
	140	or some other things. Now the label is emitted last.
	141
	142	=back
	143
d4438f94	144	=head2 Removed Modules and Pragmata
	145
	146	=head1 Utility Changes
	147
	148	XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go
	149	here. Most of these are built within the directories F<utils> and F<x2p>.
	150
	151	=over 4
	152
	153	=item F<XXX>
	154
	155	XXX
	156
	157	=back
	158
	159	=head1 New Documentation
	160
	161	XXX Changes which create B<new> files in F<pod/> go here.
	162
	163	=over 4
	164
	165	=item L<XXX>
	166
	167	XXX
	168
	169	=back
	170
	171	=head1 Changes to Existing Documentation
	172
	173	XXX Changes which significantly change existing files in F<pod/> go here.
	174	Any changes to F<pod/perldiag.pod> should go in L</New or Changed Diagnostics>.
	175
	176
	177	=head1 Performance Enhancements
	178
	179	XXX Changes which enhance performance without changing behaviour go here. There
	180	may well be none in a stable release.
	181
	182	=over 4
	183
	184	=item *
	185
	186	XXX
	187
	188	=back
	189
	190	=head1 Installation and Configuration Improvements
	191
	192	XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
	193	go here.
	194
	195	=head2 Configuration improvements
	196
	197	XXX
	198
	199	=head2 Compilation improvements
	200
	201	XXX
	202
	203	=head2 Platform Specific Changes
	204
	205	=over 4
	206
	207	=item XXX-some-platform
208
209	XXX
210
211	=back
212
213	=head1 Selected Bug Fixes
214
215	XXX Important bug fixes in the core language are summarised here.
216	Bug fixes in files in F<ext/> and F<lib/> are best summarised in
217	L</Modules and Pragmata>.
218
219	=over 4
220
221	=item *
222
223	XXX
224
225	=back
226
227	=head1 New or Changed Diagnostics
228
229	XXX New or changed warnings emitted by the core's C<C> code go here.
230
231	=over 4
232
233	=item C<XXX>
234
235	XXX
236
237	=back
238
239	=head1 Changed Internals
240
241	XXX Changes which affect the interface available to C<XS> code go here.
242
243	=over 4
244
245	=item *
246
5149cfce	247	The protocol for unwinding the C stack at the last stage of a C<die>
	248	has changed how it identifies the target stack frame. This now uses
	249	a separate variable C<PL_restartjmpenv>, where previously it relied on
	250	the C<blk_eval.cur_top_env> pointer in the C<eval> context frame that
	251	has nominally just been discarded. This change means that code running
	252	during various stages of Perl-level unwinding no longer needs to take
	253	care to avoid destroying the ghost frame.
	254
	255	=item *
	256
d4438f94	257	XXX
	258
	259	=back
	260
	261	=head1 New Tests
	262
	263	XXX Changes which create B<new> files in F<t/> go here. Changes to
	264	existing files in F<t/> aren't worth summarising, although the bugs that
	265	they represent may be.
	266
	267	=over 4
	268
	269	=item F<XXX>
	270
	271	XXX
	272
	273	=back
	274
	275	=head1 Known Problems
	276
	277	XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
	278	tests that had to be C<TODO>ed for the release would be noted here, unless
	279	they were specific to a particular platform (see below).
	280
	281	This is a list of some significant unfixed bugs, which are regressions
	282	from either 5.XXX.XXX or 5.XXX.XXX.
	283
	284	=over 4
	285
	286	=item *
	287
	288	XXX
	289
	290	=back
	291
	292	=head1 Deprecations
	293
	294	XXX Add any new known deprecations here.
	295
	296	The following items are now deprecated.
	297
	298	=over 4
	299
	300	=item *
	301
	302	XXX
	303
	304	=back
	305
	306	=head1 Platform Specific Notes
	307
	308	XXX Any changes specific to a particular platform. VMS and Win32 are the usual
	309	stars here. It's probably best to group changes under the same section layout
	310	as the main perldelta
	311
	312	=head1 Obituary
	313
	314	XXX If any significant core contributor has died, we've added a short obituary
	315	here.
	316
	317	=head1 Acknowledgements
	318
	319	XXX The list of people to thank goes here.
	320
321
322	=head1 Reporting Bugs
323
324	If you find what you think is a bug, you might check the articles
325	recently posted to the comp.lang.perl.misc newsgroup and the perl
326	bug database at http://rt.perl.org/perlbug/ . There may also be
327	information at http://www.perl.org/ , the Perl Home Page.
328
329	If you believe you have an unreported bug, please run the B<perlbug>
330	program included with your release. Be sure to trim your bug down
331	to a tiny but sufficient test case. Your bug report, along with the
332	output of C<perl -V>, will be sent off to perlbug@perl.org to be
333	analysed by the Perl porting team.
334
335	If the bug you are reporting has security implications, which make it
336	inappropriate to send to a publicly archived mailing list, then please send
337	it to perl5-security-report@perl.org. This points to a closed subscription
338	unarchived mailing list, which includes all the core committers, who be able
339	to help assess the impact of issues, figure out a resolution, and help
340	co-ordinate the release of patches to mitigate or fix the problem across all
341	platforms on which Perl is supported. Please only use this address for
342	security issues in the Perl core, not for modules independently
343	distributed on CPAN.
344
345	=head1 SEE ALSO
346
347	The F<Changes> file for an explanation of how to view exhaustive details
348	on what changed.
349
350	The F<INSTALL> file for how to build Perl.
351
352	The F<README> file for general stuff.
353
354	The F<Artistic> and F<Copying> files for copyright information.
355
356	=cut