=head1 This Week on perl5-porters - 25-31 August 2008

"I must admit that I find Perl's Unicode support completely baffling.
I've read the documentation multiple times, and while I can now
predict when it won't work, I still have no idea how to get it to
do what I want. It's kind of frustrating; I don't know if I'm just
dim, or if I'm missing some magic bit of documentation, or if the
support is just really confusing." -- Russ Allbery, shooting fish
in a barrel.

=head1 Topics of Interest

=head2 Profiling parallel tests

On the 17th of August, Nicholas Clark kicked off a thread about
applying Test::Harness's version 3 goodness to the task of running
the core test suite, which offers a satisfying halving of the time
taken.

One thing that surprised him was how much CPU the harness itself
used: if that could be reduced, things would go even faster. Andy
Armstrong thought that O(N²) algorithms might be extracting their
dues from large numbers of test files.

Over the following couple of days, Aristotle Pagaltzis pondered
various strategies for rewriting the hot spots. Steve Hay was
dismayed to discover that no parallelism was available on the Windows
platform, since the technique requires being able perform a C<select>
system call on a file handle, and Windows doesn't like doing things
that way.

  blogged
  http://use.perl.org/~nicholas/journal/37137

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00417.html

=head2 Wrong RE match in 5.10.0

Gisle Aas mentioned that a slightly impaired regular expression used
to dump core on 5.8.8. These days, with an iterative engine under the
hood of 5.10, it no longer dumps core... unfortunately, it returns the
wrong result. Bram was able to simplify the test case to highlight what
was happening.

Abigail showed that the problem was in fact that * (0 or many times) is
implemented as "no more than 32766 times". This is horribly reminiscent
of CP/M, and Dave Mitchell thought that it would be really nice if this
limit could die a quick death. Nicholas Clark was unsure as to how that
could be brought about.

In the meantime, it would be better if hitting this limit caused the
engine to die, rather than merely warn (which you don't even hear about
if warnings are switched off).

  shades of Advice from Klortho, #11912
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00360.html

=head2 C<dprofpp> enhanced

With all the cool kids playing around with C<Devel::NYTProf>, it was good
to see someone lavish some tender loving care on C<Devel::DProf>. Which is
what Daniel Pfeiffer did by adding some new functionality to C<dprofpp>.
No-one picked the patch up.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00379.html

=head2 Regaining 'O's

H.Merijn Brand was saddened by smoke tests failing, simply because a
UTF-8 locale was in use and C<Pod::Man> was getting needlessly
confused and thus marring an otherwise perfect run.

After a moment of confusion, Russ Allbery realised that the problem
probably lay with C<Pod::Simple>, and all that was needed was to add
an C<=encoding> directive to the POD test file. After some Unicode
guidance from Juerd Waalboer, Russ saw the light and prepared a patch
that solved the problems and looked sane at the same time.

Russ was a little scared by what the Correct Use of Unicode entailed
in a program and thought it was incredibly complex. Juerd explained
that there were three main techniques for dealing with Unicode, and
showed where PHP, Perl 5 and Perl 6 fitted in the grand scheme.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00392.html

=head2 Proposed pragma/module C<ensure>

Chris Hall has written a pragmatic module currently named C<ensure> that
attempts to check for undefined subroutine. The denizens
of C<comp.lang.perl.modules> advised him to get in touch with the porters
(on this list) for guidance and feedback on the idea. Unfortunately he
received none.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00415.html

=head2 Moving F<lib/> modules to F<ext/>?

Nicholas Clark explained that he had not got very far in the process
of moving core modules from F</lib> to F</ext>, and noted that it
would probably take off once the move to git was complete.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00449.html

When Jerry D. Hedden pointed out that non-XS modules get built
incorrectly, Nicholas wondered if it were as simple as looking for
XS files in the build directory and in the process discovered
a sub-optimal C<File::Find> construct that had been in the
C<installperl> F<Makefile> target all the way back to change #18.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00451.html

Nicholas went ahead and committed the fix that Jerry wrote to
deal with the above problem, and in doing so, he came to the
conclusion that it would probably fix a bug that no-one had reported
yet.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00483.html

So Jerry fixed it.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00455.html

=head2 C<unless(...)> terser than C<if(!...)>

Nicholas noticed that an C<unless($x)> uses one less op than
C<if(!$x)>, and so he asked whether it was possible to optimise
the latter into the former (or, more precisely, where one would
go about doing it).

Vincent Pit returned a day later with a proof of concept patch
which did just that. As usual with Vincent's patches, after
explaining the difficulty in addressing all that needs to be
taken care of, one is surprised by how little C code is needed
to solve the problem.

Graham Barr warned that overloading can cause C<unless> to
behave in a most curious manner, but Yitzchak Scott-Thoennes
thought that it wouldn't be an issue in practice.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00460.html

=head2 Blead changes to C<ExtUtils::CBuilder>

Ken Williams wondered about the reasoning for a line that played
around with name of the linker and compiler executables used to
compile external C code. Reini Urban explained that Cygwin's
implementation of C<EU::CB> is derived from
C<ExtUtils::CBuilder::Platform::Unix>, and the patch is to undo the
brain damage in the parent.

Ken was not in favour of adding a hack to undo a mistake, and wanted
to fix the problem upstream. Nicholas Clark summarised the problem
nicely, explaining that traditionally on Unix, the same front-end
program can be used for the tasks of compiling and linking. Other
platforms require one to use the linker program directly, and the
perl configuration doesn't really capture this distinction nicely.

So Nicholas wrote a TODO item for it, which you may read about below.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00487.html

=head2 Probably unwanted behaviour of lexical filehandles

Dr. Ruud ran into two types of behaviour when opening a input pipe,
depending on whether a package variable or a lexical variable was
used. Dave Mitchell explained that the results are due to the
fact that package variables aren't cleaned up during global
destruction (unless you ask for it nicely), whereas lexical
variables are always destructed.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00491.html

=head1 TODO of the week

=head2 Split "linker" from "compiler"

Right now, Configure probes for two commands, and sets two variables:

=over 4

=item * C<cc> (in F<cc.U>)

This variable holds the name of a command to execute a C compiler
which can resolve multiple global references that happen to have
the same name.  Usual values are F<cc> and F<gcc>.  Fervent ANSI
compilers may be called F<c89>.  AIX has F<xlc>.

=item * C<ld> (in F<dlsrc.U>)

This variable indicates the program to be used to link libraries
for dynamic loading.  On some systems, it is F<ld>.  On ELF systems,
it should be C<$cc>.  Mostly, we'll try to respect the hint file
setting.

=back

There is an implicit historical assumption from around Perl5.000alpha
something, that C<$cc> is also the correct command for linking
object files together to make an executable. This may be true on
Unix, but it's not true on other platforms, and there are a maze
of work arounds in other places (such as F<Makefile.SH>) to cope
with this.

Ideally, we should create a new variable to hold the name of the
executable linker program, probe for it in F<Configure>, and
centralise all the special case logic there or in hints files.

A small bikeshed issue remains - what to call it, given that C<$ld>
is already taken (arguably for the wrong thing now, but on SunOS
4.1 it is the command for creating dynamically-loadable modules)
and C<$link> could be confused with the Unix command line executable
of the same name, which does something completely different. Andy
Dougherty makes the counter argument "In parrot, I tried to call
the command used to link object files and  libraries into an
executable F<link>, since that's what my vaguely-remembered DOS and
VMS experience suggested. I don't think any real confusion has
ensued, so it's probably a reasonable name for perl5 to use."

"Alas, I've always worried that introducing it would make things
worse, since now the module building utilities would have to look
for C<$Config{link}> and institute a fall-back plan if it weren't
found." Although I can see that as confusing, given that
C<$Config{d_link}> is true when (hard) links are available.

=head1 Patches of Interest

=head2 Safer environment iteration

Milosz Tanski wrote a patch to avoid race conditions when iterating C<%ENV>
in embedded interpreters in multi-threaded applications. Rafaël
Garcia-Suarez applied the patch.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00385.html

=head2 Stop F<lib/ExtUtils/t/Embed.t> from generating F<libperl.a>

Jerry D. Hedden observed that a test file produced a bogus F<libperl.a>
file on Cygwin that would up being installed by accident. So he
patched things to ensure that the test cleans up properly after
itself. Reini Urban wondered how he had not managed to notice this
in the past, and promised to take the code for a spin.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00367.html

=head2 Add open C<|-> and open C<-|> to C<perlopentut>

Shlomi Fish added some documentation for the magic files C<-|> and C<|->
that are used to open input and output pipes. Tom Christiansen wrote a
eloquent response to the question that someone raised regarding singly-
and doubly-quoted strings, arguing convincingly that one should always
use double quoted strings, unless there was a very good reason not to.

One of the most important reasons is merely the visual cue: it's easier
to see a double quote ("), rather than a single quote ('), where certain
fonts may make it very difficult to discriminate between it and a back-tick.

Much discussion followed. No-one commented that at around 1000 lines long,
C<perlopentut> is no longer a tutorial, but more of a Compleat Reference,
and thus probably needs less, rather than more, prose.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00386.html

=head2 Clarify documentation on C<exists> regarding autovivification

Moritz Lenz made a laudable effort at making the documentation clearer by
removing a sentence, rather than adding one. And this was applied.

  seeking clarity, one paragraph at a time
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00436.html

=head2 C<autodie> 1.991 patch

Paul Fenwick announced the latest version of his C<autodie> work. Nicholas
Clark admitted that he was unlikely to review anything major until 5.8.9
goes out the door.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00456.html

=head1 Watching the smoke signals

=head2 Smoke [5.11.0] 34226 FAIL(F) MSWin32 WinXP/.Net SP3 (x86/2 cpu)

Steve Hay's Windows smokes started going bad with a failure in
F<op/local.t>. This highlighted a problem with shell quote characters
and F<test.pl>'s C<runperl> function.  Nicholas Clark was uncertain
as to what it was that caused the failure to arise, but change
#34228 got things back into line again.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00408.html

=head1 New and old bugs from RT

=head2 C<Class::Struct> accessor overrides not called from constructor (#29230)

Renée Bäcker wrote a patch to address the problem which appears to have
fallen through the cracks.

  getting it out
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00489.html

=head2 Repeated spaces on shebang line stops option parsing (#30660)

Renée also noticed that a shebang line containing extra spaces (such as
"-s    -w") will fail to notice the subsequent switches (-w in this case).
After a couple of tweaks from H.Merijn Brand and Nicholas Clark, the code
was adjusted to deal with this problem.

  lost in space
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00391.html

=head2 Loss of stack elements with a do block inside a return (#38809)

Vincent Pit returned to the issue of

  sub foo { do { return do { 1; 2 } }; 3 }

returning C<undef>. He had proposed a patch some time ago, but after studying
the emitted opcodes, came up with an improved patch to address the problem.
And then came back the next day with an improved, improved patch, and some
improved tests to go along with it.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00481.html

=head2 Removing deprecated features for 5.10? (#41480)

Renée noted that Nicholas had noted that using arrays and hashes as
references had been deprecated as far back as 5.8. It so happens
that the warning for undesirable syntax is present in blead (which
will one day become 5.12). The unanswered question is whether or not
removing the code required that deals with it would simplify matters
or not.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00454.html

=head2 Subclassing C<CGI::Pretty> dies in C<new> (#41572)

Renée also had a patch for this. Nicholas forwarded it to Lincoln
Stein, and would fold it back into the core once he got word back
from Lincoln.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00442.html

=head2 Backwards logic in C<perluniintro> (5.10.0) (#58218)

Brad Baxter noted that the documentation that shows how to deal with the
detection of invalid data for a given encoding had its logic backwards.
Dr. Ruud suggested a couple of code variants that were an improvement
on the existing logic, one of which Rafaël Garcia-Suarez applied to
the documentation.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00361.html

=head2 Speed lost on C</^(foo|bar|baz)$/> match (#58280)

Michael G. Schwern, following up on scurrilous Internet rumours,
discovered that captured alternations are in fact slower in 5.10
than they were in 5.8. Steve Peters and Tels confirmed the finding.
No word as to why this is the case.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00362.html

=head2 C<Unicode::UCD::charinfo()> does not work on 21 Han codepoints (#58428)

Karl Williamson discovered Unicode problems that he traced to magic
numbers causing upper bounds to hide more recent Unicode additions.
Renée created a patch to fix the problem. Karl also came back with
a solution that worked with all Unicode database versions from 4.1
and beyond, and imagined that it would work for older versions as
well.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00470.html

=head2 C<Unicode::UCD::casefold()> does not work as documented, nor probably as intended (#58430)

Similarly, Karl found a number of problems relating to the
implementation for Unicode case folding, and saw that it was
such a mess that it couldn't work at all. No-one stepped up
to try and improve matters.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00471.html

=head2 C<perl -d:DProf> handles shift of C<@_> with & function wrong (#58446)

A person, whom some people call Tim, reported that C<Devel::DProf>
failed to deal correctly with @_ being aliased via magic &sub
passing.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00472.html

=head2 Crash on exit with fork done in do FILE on Win32 (#58468)

Alex Davies encountered a problem with a C<do 'file'> after a program
has forked on the Windows platform. No-one reported that they had
confirmed the problem, much less propose a correction, even though
Alex had gone to the trouble of figuring out why perl was crashing
on a null pointer.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00492.html

=head2 Assigning C<*a = \&a> drops a reference (#58480)

Nicholas Clark noted that recent changes that had shifted code around now
caused the assignment of something to one's own typeglob to leak a
reference. He thought he knew how to fix the matter, and called for some
TODO tests, if anyone was in the mood for volunteering.

Zefram thought that the code Nicholas had used to demonstrate the problem
was incorrect.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00494.html

=head2 Perl5 Bug Summary

Someone was very busy this summer.

  261 new + 1028 open = 1289
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00396.html
  http://rt.perl.org/rt3/NoAuth/perl5/Overview.html

=head1 In Brief

Nicholas had been observing an B<occasional assertion failure in
C<S_sv_del_backref>>.  After struggling for a while to reproduce
it at all, Dave Mitchell nailed it with a tweak to a macro in
F<sv.c>.

  safer global destruction
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00378.html

Rick McGee reported running into grief attempting to marry B<5.10
and FreeBSD 7.0>.  Alas, neither Nicholas Clark, nor Scott T.
Hildreth nor Reini Urban were able to reproduce the problem, although
Nicholas suspected it was probably a compiler issue.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00479.html

Jerry D. Hedden announced that the B<TODO related to C<threads::shared>
is done>, and so the item could be removed (if in fact the work he did on
C<threads::shared> was indeed what C<perltodo> was referring to).

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00448.html
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00458.html

Vincent Pit ran into B<a precedence nit in C<Test::Builder>>
(or more specifically C<!$x and $y, 'foo'>) which meant that a
test that should have failed didn't.

  back to the drawing board
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00473.html

=head2 Last week's summary

There wasn't one. I enjoyed a lazy summer doing home renovations,
camping, hiking, swimming, drinking, eating and using computers as
little as possible.

=head2 About this summary

This summary was written by David Landgren.

Weekly summaries are published on F<http://use.perl.org/> and posted
on a mailing list, (subscription: F<perl5-summary-subscribe@perl.org>).
The archive is at F<http://dev.perl.org/perl5/list-summaries/>.
Corrections and comments are welcome.

If you found this summary useful, please consider contributing to
the Perl Foundation or attending a YAPC to help support the development
of Perl.