perldelta up to 8d0b139

[perl5.git] / pod / perldelta.pod

=encoding utf8

=for comment
This has been completed up to 8d0b139, except for
b0f2e9e nwclark     Fix two bugs related to pod files outside of pod/ (important enough?)
43d9ecf jpeacock    Set all version object math ops to noop
f300909 smueller    EU::ParseXS: Silence warning (probably unnecessary)

=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 v5.15.6

=head1 DESCRIPTION

This document describes differences between the 5.15.5 release and
the 5.15.6 release.

If you are upgrading from an earlier release such as 5.15.4, first read
L<perl5155delta>, which describes differences between 5.15.4 and
5.15.5.

=head1 Notice

XXX Any important notices here

=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.

[ List each enhancement as a =head2 entry ]

=head2 C<__SUB__>

The new C<__SUB__> token, available under the "current_sub" feature (see
L<feature>) or C<use v5.15>, returns a reference to the current subroutine,
making it easier to write recursive closures.

=head2 New option for the debugger's B<t> command

The B<t> command in the debugger, which toggles tracing mode, now accepts a
numerical argument that determines how many levels of subroutine calls to
trace.

=head2 Return value of C<tied>

The value returned by C<tied> on a tied variable is now the actual scalar
that holds the object to which the variable is tied.  This allows ties to
be weakened with C<Scalar::Util::weaken(tied $tied_variable)>.

=head2 Lvalue C<scalar>

C<scalar> can now be used as an lvalue.  You might consider this a new
feature (which is why it is listed in this section), but the author of
the change considered it a bug fix, since C<scalar> is only supposed to be
setting scalar context, not changing lvalueness [perl #24346].

=head1 Security

XXX Any security-related notices go here.  In particular, any security
vulnerabilities closed should be noted here rather than in the
L</Selected Bug Fixes> section.

=head2 C<is_utf8_char()>

The XS-callable function C<is_utf8_char()> when presented with malformed
UTF-8 input can read up to 12 bytes beyond the end of the string.  This
cannot be fixed without changing its API.  It is not called from CPAN.
The documentation for it now describes how to use it safely.

=head2 Other C<is_utf8_foo()> functions, as well as C<utf8_to_foo()>, etc.

Most of the other XS-callable functions that take UTF-8 encoded input
implicitly assume that the UTF-8 is valid (not malformed) in regards to
buffer length.  Do not do things such as change a character's case or
see if it is alphanumeric without first being sure that it is valid
UTF-8.  This can be safely done for a whole string by using one of the
functions C<is_utf8_string()>, C<is_utf8_string_loc()>, and
C<is_utf8_string_loclen()>.

=head1 Incompatible Changes

XXX For a release on a stable branch, this section aspires to be:

    There are no changes intentionally incompatible with 5.XXX.XXX
    If any exist, they are bugs and reports are welcome.

[ List each incompatible change as a =head2 entry ]

=head2 C<use I<VERSION>>

As of this release, version declarations like C<use v5.16> now disable all
features before enabling the new feature bundle.  This means that the
following holds true:

    use 5.016;
    # 5.16 features enabled here
    use 5.014;
    # 5.16 features disabled here

C<use v5.12> and higher continue to enable strict, but explicit
C<use strict> and C<no strict> now override the version declaration, even
when they come first:

    no strict;
    use 5.012;
    # no strict here

There is a new ":default" feature bundle, that represents the set of
features enabled before any version declaration or C<use feature> has been
seen.  Version declarations below 5.10 now enable the ":default" feature
set.  This does not actually change the behaviour of C<use v5.8>, because
features added to the ":default" set are those that were traditionally
enabled by default, before they could be turned off.

C<$[> is now disabled under C<use v5.16>.  It is part of the default
feature set and can be turned on or off explicitly
with C<use feature 'array_base'>.

=head2 C<UNIVERSAL::VERSION>

The change to C<UNIVERSAL::VERSION> in 5.15.2 has been reverted.  It now
returns a stringified version object once more.

=head2 C<substr> lvalue revamp

When C<substr> is called in lvalue or potential lvalue context with two or
three arguments, a special lvalue scalar is returned that modifies the
original string (the first argument) when assigned to.

Previously, the offsets (the second and third arguments) passed to
C<substr> would be converted immediately to match the string, negative
offsets being translated to positive and offsets beyond the end of the
string being truncated.

Now, the offsets are recorded without modification in the special lvalue
scalar that is returned, and the original string is not even looked at by
C<substr> itself, but only when the returned lvalue is read or modified.

These changes result in several incompatible changes and bug fixes:

=over

=item *

If the original string changes length after the call to C<substr> but
before assignment to its return value, negative offsets will remember
their position from the end of the string, affecting code like this:

    my $string = "string";
    my $lvalue = \substr $string, -4, 2;
    print $lvalue, "\n"; # prints "ri"
    $string = "bailing twine";
    print $lvalue, "\n"; # prints "wi"; used to print "il"

The same thing happens with an omitted third argument.  The returned lvalue
will always extend to the end of the string, even if the string becomes
longer.

=item *

Tied (and otherwise magical) variables are no longer exempt from the
"Attempt ot use reference as lvalue in substr" warning.

=item *

That warning now occurs when the returned lvalue is assigned to, not when
C<substr> itself is called.  This only makes a difference if the return
value of C<substr> is referenced and assigned to later.

=item *

The order in which "uninitialized" warnings occur for arguments to
C<substr> has changed.

=item *

Passing a substring of a read-only value or a typeglob to a function (potential lvalue context) no longer causes an immediate "Can't coerce" or "Modification of a read-only value" error.  That error only occurs if and
when the value passed is assigned to.

The same thing happens with the "substr outside of string" error.  If the
lvalue is only read, not written to, it is now just a warning, as with
rvalue C<substr>.

=item *

C<substr> assignments no longer call FETCH twice if the first argument is a
tied variable, but just once.

=back

It was impossible to fix all the bugs without an incompatible change, and
the behaviour of negative offsets was never specified, so the change was
deemed acceptable.

=head2 Return value of C<eval>

C<eval> returns C<undef> in scalar context or an empty list in list context
when there is a run-time error.  For syntax errors (when C<eval> is passed
a string), in list context it used to return a list containing a single
undefined element.  Now it returns an empty list in list context for all
errors [perl #80630].

=head2 Anonymous handles

Automatically generated file handles are now named __ANONIO__ when the
variable name cannot be determined, rather than $__ANONIO__.

=head2 Last-accessed filehandle

Perl has an internal variable that stores the last filehandle to be
accessed.  It is used by C<$.> and by C<tell> and C<eof> without arguments.

It used to be possible to set it to a glob copy and then modify that glob
copy to be something other than a glob, and still have it as the
last-accessed filehandle after assigning a glob to it again:

    my $foo = *STDOUT;  # $foo is a glob copy
    <$foo>;             # $foo is now the last-accessed handle
    $foo = 3;           # no longer a glob
    $foo = *STDERR;     # still the last-accessed handle

Now the C<$foo = 3> assignment unset that internal variable, so there is no
last-accessed filehandle, just as if C<< <$foo> >> had never happened.

=head2 XS API tweak

The C<newCONSTSUB_flags> C-level function, added in 5.15.4, now has a
C<len> parameter.

=head1 Deprecations

XXX Any deprecated features, syntax, modules etc. should be listed here.
In particular, deprecated modules should be listed here even if they are
listed as an updated module in the L</Modules and Pragmata> section.

[ List each deprecation as a =head2 entry ]

=head1 Performance Enhancements

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

[ List each enhancement as a =item entry ]

=over 4

=item *

Perl 5.12.0 sped up the destruction of objects whose classes define empty
C<DESTROY> methods (to prevent autoloading), simply by not calling such
empty methods.  This release takes this optimisation a step further, by not
calling any C<DESTROY> method that begins with a C<return> statement.
This can be useful for destructors that are only used for debugging:

    use constant DEBUG => 1;
    sub DESTROY { return unless DEBUG; ... }

Constant-folding will reduce the first statement to C<return;> if DEBUG is
set to 0, triggering this optimisation.

=item *

Assign to a variable that holds a typeglob or copy-on-write scalar is now
much faster.  Previously the typeglob would be stringified or the
copy-on-write scalar would be copied before being clobbered.

=item *

Assignment to C<substr> in void context is now more than twice its
previous speed.  Instead of creating and returning a special lvalue scalar
that is then assigned to, C<substr> modifies the original string itself.

=back

=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.

[ Within each section, list entries as a =item entry ]

=head2 New Modules and Pragmata

=over 4

=item *

XXX

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Archive::Tar> has been upgraded from version 1.80 to version 1.82.

Adjustments to handle files >8gb (>0777777777777 octal) and a feature to
return the MD5SUM of files in the archive.

=item *

L<AutoLoader> has been upgraded from version 5.71 to version 5.72.

=item *

L<B::Debug> has been upgraded from version 1.16 to version 1.17.

=item *

L<B::Deparse> has been upgraded from version 1.09 to version 1.10.

Various constructs that used to be deparsed incorrectly have been fixed:

=over

=item C<sort(foo(bar))>

C<sort foo(bar)>, how it used to deparse, makes foo the sort routine,
rather than a regular function call.

=item Keys and values in C<%^H>

Undefined values in the hint hash were being deparsed as empty strings.
Whenever the hint hash changed, all undefined values, even those
unmodified, were being printed.

Special characters, such as quotation marks, were not being escaped
properly.

Some values used to be omitted if, for instance, a key was the same as a
previous value and vice versa.

=item "method BLOCK" syntax

C<method { $expr }> used to be deparsed as something like
C<< do{ $expr }->method >>, but the latter puts the $expr in scalar
context, whereas the former puts in list context.

=item C<do +{}> and C<do({})>

These are both variants of do-file syntax, but were being deparsed as
do-blocks.

=item Keywords that do not follow the llafr

Keywords like C<return> and C<last> that do not follow the
looks-like-a-function rule are now deparsed correctly with parentheses in
the right place.

Similarly, C<not>, which I<does> follow the llafr, was being deparsed as
though it does not.

=item C<=~>

In various cases, B::Deparse started adding a spurious C<$_ =~> before the
right-hand side in Perl 5.14; e.g., C<< "" =~ <$a> >> would become
C<< "" =~ ($_ =~ <$a>) >>.

=item C<open local *FH>

C<open>, C<pipe> and other functions that autovivify handles used to omit
C<local *> from C<local *FH>.

=item Negated single-letter subroutine calls

Negated subroutine calls like C<- f()> and C<-(f())> were being deparsed
as file test operators.

=item C<&{&}>

C<&{&}> and C<& &>, which are calls to the subroutine named "&", believe it
or not, were being deparsed as C<&&>.

=back

=item *

L<Carp> has been upgraded from version 1.23 to version 1.24.

It now tacks the last-accessed filehandle and line number on to the end of
the error message, just like C<die> [perl #96672].

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.042 to version 2.045.

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.042 to version 2.045.

=item *

L<CPAN::Meta::YAML> has been upgraded from version 0.004 to version 0.005.

=item *

L<CPANPLUS> has been upgraded from version 0.9112 to version 0.9113.

=item *

L<Data::Dumper> has been upgraded from version 2.134 to version 2.135.

The XS implementation has been updated to account for the Unicode symbol
changes in Perl 5.15.4.  It also knows how to output typeglobs with nulls
in their names.

=item *

L<diagnostics> has been upgraded from version 1.25 to version 1.26.

It now understands the "%X" format code, which some error messages started
using in Perl 5.14.0.

=item *

L<Digest::SHA> has been upgraded from version 5.63 to version 5.70.

Added BITS mode to addfile method and shasum which makes partial-byte inputs
now possible via files/STDIN and allows shasum to check all 8074 NIST Msg vectors,
where previously special programming was required to do this.

=item *

L<Exporter> has been upgraded from version 5.65 to version 5.66.

It no longer tries to localise C<$_> unnecessarily.

=item *

L<ExtUtils::ParseXS> has been upgraded from version 3.05 to version 3.07.

=item *

L<IO::Compress::Base> has been upgraded from version 2.042 to version 2.045.

Added zipdetails utility.

=item *

L<Locale::Codes> has been upgraded from version 3.18 to version 3.20.

The code2XXX, XXX2code, all_XXX_codes, and all_XXX_names functions now support retired codes.
All codesets may be specified by a constant or by their name now. Previously,
they were specified only by a constant.
The alias_code function exists for backward compatibility. It has been replaced by rename_country_code.
The alias_code function will be removed sometime after September, 2013.
All work is now done in the central module (Locale::Codes). Previously, some was still done in the
wrapper modules (Locale::Codes::*) but that is gone now.
Added Language Family codes (langfam) as defined in ISO 639-5.

=item *

L<Module::Loaded> has been uprgaded from version 0.06 to version 0.08.

=item *

L<Pod::LaTeX> has been upgraded from version 0.59 to version 0.60.

Added another LaTeX escape: --- => -{}-{}-

Pod::LaTeX doesn't handle -- in PODs specially, passing it directly to
LaTeX, which then proceeds to replace it with a single -. This patch
replaces ----- with -{}-{}-{}-{}-

=item *

L<POSIX> has been upgraded from version 1.26 to version 1.27.

It no longer produces a "Constant subroutine TCSANOW redefined" warning on
Windows.

XXX When did it start producing that warning?  Was it post-5.15.5?  Even if
it was not, adding a note will help whoever compiles perl5160delta.

=item *

L<Socket> has been upgraded from version 1.94_02 to version 1.97.

=item *

L<threads> has been upgraded from version 1.85 to version 1.86.

=item *

L<Unicode::Collate> has been upgraded from version 0.85 to version 0.87.

Tailored compatibility ideographs as well as unified ideographs for
the locales: ja, ko, zh__big5han, zh__gb2312han, zh__pinyin, zh__stroke.

Now Locale/*.pl files are searched in @INC.

=item *

L<UNIVERSAL> has been upgraded from version 1.10 to version 1.11.

Documentation change clarifies return values from UNIVERSAL::VERSION.

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

Changing the case of a UTF-8 encoded string under C<use locale> now
gives better, but still imperfect, results.  Previously, such a string
would entirely lose locale semantics and silently be treated as Unicode.
Now, the code points that are less than 256 are treated with locale
rules, while those above 255 are, of course, treated as Unicode.  See
L<perlfunc/lc> for more details, including the deficiencies of this
scheme.

=back

=head1 Documentation

XXX Changes to files in F<pod/> go here.  Consider grouping entries by
file and be sure to link to the appropriate page, e.g. L<perlfunc>.

=head2 New Documentation

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

=head3 L<XXX>

XXX Description of the purpose of the new file here

=head2 Changes to Existing Documentation

XXX Changes which significantly change existing files in F<pod/> go here.
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.

=head3 L<perlsec/Laundering and Detecting Tainted Data>

=over 4

=item *

The example function for checking for taintedness contained a subtle
error.  C<$@> needs to be localized to prevent its changing this
global's value outside the function.  The preferred method to check for
this, though, remains to use L<Scalar::Util/tainted>.

=back

=head1 Diagnostics

The following additions or changes have been made to diagnostic output,
including warnings and fatal error messages.  For the complete list of
diagnostic messages, see L<perldiag>.

XXX New or changed warnings emitted by the core's C<C> code go here. Also
include any changes in L<perldiag> that reconcile it to the C<C> code.

[ Within each section, list entries as a =item entry that links to perldiag,
  e.g.

  =item *

  L<Invalid version object|perldiag/"Invalid version object">
]

=head2 New Diagnostics

XXX Newly added diagnostic messages go here

=head3 New Errors

=over 4

=item *

XXX L<message|perldiag/"message">

=back

=head3 New Warnings

=over 4

=item *

XXX L<message|perldiag/"message">

=back

=head2 Changes to Existing Diagnostics

XXX Changes (i.e. rewording) of diagnostic messages go here

=over 4

=item *

Redefinition warnings for constant subroutines used to be mandatory, even
occurring under C<no warnings>.  Now they respect the L<warnings> pragma.

=item *

The "Attempt to free non-existent shared string" has had the spelling of
"non-existent" corrected to "nonexistent".  It was already listed with the
correct spelling in L<perldiag>.

=item *

The 'Use of "foo" without parentheses is ambiguous' warning has been
extended to apply also to user-defined subroutines with a (;$) prototype,
and not just to built-in functions.

=item *

The error messages for using C<default> and C<when> outside of a
topicalizer have been standardised to match the messages for C<continue>
and loop controls.  They now read 'Can't "default" outside a topicalizer'
and 'Can't "when" outside a topicalizer'.  They both used to be 'Can't use
when() outside a topicalizer' [perl #91514].

=back

=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>.

[ List utility changes as a =head3 entry for each utility and =item
entries for each change
Use L<XXX> with program names to get proper documentation linking. ]

=head3 L<zipdetails>

=over 4

=item *

L<zipdetails> displays information about the internal record structure of the zip file.
It is not concerned with displaying any details of the compressed data stored in the zip file.

=back

=head1 Configuration and Compilation

XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
go here.  Any other changes to the Perl build process should be listed here.
However, any platform-specific changes should be listed in the
L</Platform Support> section, instead.

[ List changes as a =item entry ].

=over 4

=item *

F<pod/roffitall> is now build by F<pod/buildtoc>, instead of being shipped
with the distribution. Its list of manpages is now generated (and therefore
current). See also RT #103202 for an unresolved related issue.

=item *

Perl 5.15.5 had a bug in its installation script, which did not install
F<unicore/Name.pm>.  This has been corrected [perl #104226].

XXX Is that Perl version correct?  Is the file path correct?

=item *

The -Dusesitecustomize and -Duserelocatableinc options now work together
properly.

=back

=head1 Testing

XXX Any significant changes to the testing of a freshly built perl should be
listed here.  Changes which create B<new> files in F<t/> go here as do any
large changes to the testing harness (e.g. when parallel testing was added).
Changes to existing files in F<t/> aren't worth summarising, although the bugs
that they represent may be covered elsewhere.

[ List each test improvement as a =item entry ]

=over 4

=item *

The F<substr.t> and F<substr_thr.t> scripts for testing C<substr> have been
moved under F<t/op/>, where they were originally.  They had been moved
under F<t/re/> along with the substitution tests when that directory was
created.

=back

=head1 Platform Support

XXX Any changes to platform support should be listed in the sections below.

[ Within the sections, list each platform as a =item entry with specific
changes as paragraphs below it. ]

=head2 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.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Discontinued Platforms

XXX List any platforms that this version of perl no longer compiles on.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Platform-Specific Notes

XXX List any changes for specific platforms. This could include configuration
and compilation changes or changes in portability/compatibility.  However,
changes within modules for platforms should generally be listed in the
L</Modules and Pragmata> section.

=head3 VMS

=over 4

=item *

A link-time error on VMS versions without C<symlink> support was
introduced in 5.15.1, but has now been corrected.

=item *

Explicit support for VMS versions prior to v7.0 and DEC C versions prior
to v6.0 has been removed.

=item *

Since Perl 5.10.1, the home-grown C<stat> wrapper has been unable to
distinguish between a directory name containing an underscore and an
otherwise-identical filename containing a dot in the same position
(e.g., t/test_pl as a directory and t/test.pl as a file). This problem
has been corrected.

=back

=head1 Internal Changes

XXX Changes which affect the interface available to C<XS> code go here.
Other significant internal changes for future core maintainers should
be noted as well.

[ List each change as a =item entry ]

=over 4

=item *

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>.

[ List each fix as a =item entry ]

=over 4

=item *

RT #78266: The regex engine has been leaking memory when accessing
named captures that weren't matched as part of a regex ever since 5.10
when they were introduced, e.g. this would consume over a hundred MB
of memory:

    for (1..10_000_000) {
	if ("foo" =~ /(foo|(?<capture>bar))?/) {
	    my $capture = $+{capture}
	}
    }
    system "ps -o rss $$"'

=item *

A constant subroutine assigned to a glob whose name contains a null will no
longer cause extra globs to pop into existence when the constant is
referenced under its new name.

=item *

C<sort> was not treating C<sub {}> and C<sub {()}> as equivalent when such
a sub was provided as the comparison routine.  It used to croak on
C<sub {()}>.

=item *

Subroutines from the C<autouse> namespace are once more exempt from
redefinition warnings.  This used to work in 5.005, but was broken in 5.6
for most subroutines.  For subs created via XS that redefine subroutines
from the C<autouse> package, this stopped working in 5.10.

=item *

New XSUBs now produce redefinition warnings if they overwrite existing
subs, as they did in 5.8.x.  (The C<autouse> logic was reversed in 5.10-14.
Only subroutines from the C<autouse> namespace would warn when clobbered.)

=item *

Redefinition warnings triggered by the creation of XSUBs now respect
Unicode glob names, instead of using the internal representation.  This was
missed in 5.15.4, partly because this warning was so hard to trigger.  (See
the previous item.)

=item *

C<newCONSTSUB> used to use compile-time warning hints, instead of run-time
hints.  The following code should never produce a redefinition warning, but
it used to, if C<newCONSTSUB> redefine and existing subroutine:

    use warnings;
    BEGIN {
	no warnings;
	some_XS_function_that_calls_new_CONSTSUB();
    }

=item *

Redefinition warnings for constant subroutines are on by default (what are
known as severe warnings in L<perldiag>).  This was only the case when it
was a glob assignment or declaration of a Perl subroutine that caused the
warning.  If the creation of XSUBs triggered the warning, it was not a
default warning.  This has been corrected.

=item *

The internal check to see whether a redefinition warning should occur used
to emit "uninitialized" warnings in cases like this:

    use warnings "uninitialized";
    use constant {u=>undef,v=>undef};
    sub foo(){u} sub foo(){v}

=item *

A bug fix in Perl 5.14 introduced a new bug, causing "uninitialized"
warnings to report the wrong variable if the operator in question has
two operands and one is C<%{...}> or C<@{...}>.  This has been fixed
[perl #103766].

=item *

C<< version->new("version") >> and C<printf "%vd", "version"> no longer
crash [perl #102586].

=item *

C<$tied =~ y/a/b/>, C<chop $tied> and C<chomp $tied> now call FETCH just
once when $tied holds a reference.

=item *

Four-argument C<select> now always calls FETCH on tied arguments.  It used
to skip the call if the tied argument happened to hold C<undef> or a
typeglob.

=item *

Four-argument C<select> no longer produces its "Non-string passed as
bitmask" warning on tied or tainted variables that are strings.

=item *

C<sysread> now always calls FETCH on the buffer passed to it if it is tied.
It used to skip the call if the tied variable happened to hold a typeglob.

=item *

C<< $tied .= <> >> now calls FETCH once on C<$tied>.  It used to call it
multiple times if the last value assigned to or returned from the tied
variable was anything other than a string or typeglob.

=item *

The C<evalbytes> keyword added in 5.15.5 was respecting C<use utf8>
declarations from the outer scope, when it should have been ignoring them.

=item *

C<goto &func> no longers crashes, but produces an error message, when the
unwinding of the current subroutine's scope fires a destructor that
undefines the subroutine being "goneto" [perl #99850].

=item *

Arithmetic assignment (C<$left += $right>) involving overloaded objects that
rely on the 'nomethod' override no longer segfault when the left operand is not
overloaded.

=item *

Assigning C<__PACKAGE__> or any other shared hash key scalar to a stash
element no longer causes a double free.  Regardless of this change, the
results of such assignments are still undefined.

=item *

Creating a C<UNIVERSAL::AUTOLOAD> sub no longer stops C<%+>, C<%-> and
C<%!> from working some of the time [perl #105024].

=item *

Assigning C<__PACKAGE__> or another shared hash key string to a variable no
longer stops that variable from being tied if it happens to be a PVMG or
PVLV internally.

=item *

When presented with malformed UTF-8 input, the XS-callable functions
C<is_utf8_string()>, C<is_utf8_string_loc()>, and
C<is_utf8_string_loclen()> could read beyond the end of the input
string by up to 12 bytes.  This no longer happens.  [perl #32080].
However, currently, C<is_utf8_char()> still has this defect,
see L</is_utf8_char()> above.

=item *

Doing a substitution on a tied variable returning a copy-on-write scalar
used to cause an assertion failure or an "Attempt to free nonexistent
shared string" warning.

=item *

A change in perl 5.15.4 caused C<caller()> to produce malloc errors and a
crash with Perl's own malloc, and possibly with other malloc
implementations, too [perl #104034].

=item *

A bug fix in 5.15.5 could sometimes result in assertion failures under
debugging builds of perl for certain syntax errors in C<eval>, such as
C<eval(q|""!=!~//|);>

=item *

The "c [line num]" debugger command was broken by other debugger changes
release in 5.15.3.  This is now fixed.

=item *

Breakpoints were not properly restored after a debugger restart using the
"R" command.  This was broken in 5.15.3.  This is now fixed.

=item *

The debugger prompt did not display the current line in.  This was broken
in 5.15.3.  This is now fixed.

=item *

Class method calls still suffered from the Unicode bug with Latin-1 package
names.  This was missed in the Unicode package name cleanup in 5.15.4
[perl #105922].

=item *

The debugger no longer tries to do C<local $_> when dumping data
structures.

=item *

Calling C<readline($fh)> where $fh is a glob copy (e.g., after
C<$fh = *STDOUT>), assigning something other than a glob to $fh, and then
freeing $fh (e.g., by leaving the scope where it is defined) no longer
causes the internal variable used by C<$.> (C<PL_last_in_gv>) to point to
a freed scalar, that could be reused for some other glob, causing C<$.> to
use some unrelated filehandle [perl #97988].

=item *

A regression in 5.14 caused these statements not to set the internal
variable that holds the handle used by C<$.>:

    my $fh = *STDOUT;
    tell $fh;
    eof  $fh;
    seek $fh, 0,0;
    tell     *$fh;
    eof      *$fh;
    seek     *$fh, 0,0;
    readline *$fh;

This is now fixed, but C<tell *{ *$fh }> still has the problem, and it is
not clear how to fix it [perl #106536].

=item *

Version comparisons, such as those that happen implicitly with
C<use v5.43>, no longer cause locale settings to change [perl #105784].

=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.

[ List each fix as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Obituary

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

=head1 Acknowledgements

XXX Generate this with:

  perl Porting/acknowledgements.pl v5.15.5..HEAD

=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 L<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 will 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