This Week on perl5-porters - 6-12 January 2008

This Week on perl5-porters - 6-12 January 2008

   "Um, I think you caused me negative work. I rather wanted "dtrace"
   support and it seemed that because of you I didn't have to write it."
   -- Nicholas Clark, on the joys of having other people do your work for
   you.

Topics of Interest

Ever more strict

   In the continuing "strict by default in 5.12" thread, Glenn Linderman
   made a most pertinent remark: Perl 6 has staked the "strict be
   default" claim. Perl 5 may approach the same place, but will have to
   do so more slowly. Not that it shouldn't be done, we need not burden
   ourselves with bad practices forever, but deprecation cycles and
   dealing with dormant CPAN modules and code in the DarkPAN means it
   will take time.

   The other contentious issue (should extra strictures be activated from
   a "feature" pragma) was addressed by Abigail, who put forward the
   argument that "feature" should be considered no more than a message
   from the programmer to the interpreter indicating that constraints
   regarding backwards compatibility are hereby waived.

     advancing, unmasked
     http://xrl.us/bec8z

     the darkpan, defined
     http://xrl.us/bedds

"~~" changing behaviour after using "=="

   brian d foy was puzzled upon learning that smart matching suffered
   from action at a distance, and wondered if it was all documented.
   David Landgren explained that it was a problem due to the "IOK" flag
   being set, which caused the smart matching code to use numishness,
   rather than stringiness as a basis for matching.

   Zefram rightly pointed out that this was exactly the sort of problem
   that prevented Perl from being able to be used in very large projects.
   Nicholas Clark asked himself what would happen if the IOK flag was not
   set during a numish comparison, were the number not truly numeric. And
   so now blead does just that.

     no more action at a distance
     http://xrl.us/bec83

"dtrace" and Perl

   Andy Armstrong added dtrace support to perl to probe subroutine entry
   and exit points and was happy to announce that it incurs no measurable
   performance hit.

   Nicholas Clark made a number of comments regarding the patch: things
   that need to be done and the ways to do it. He went ahead and cleared
   up the nits and applied it all.

     the patch itself
     http://xrl.us/bec85

   The main issue with the patch was dealing with "Configure", partly
   because not many people have strong "Configure"-fu (and H.Merijn Brand
   was busy using his fu to attend to some sorely needed work on it).

   Andy Dougherty helped out with a rough sketch of what needed to be
   done. Bryan Allen of pobox.com generously provided shell access to a
   Solaris box to get the kinks sorted out.

     dtrace sees delight
     http://xrl.us/bec87

   Once that was more or less under control, the next question to ask was
   what probes should we have? The following items were put forward:

   *   Creation and destruction of SVs.

   *   Interpreter set-up and tear down.

   *   Module loading ("use" and "require").

   *   Filesystem access.

   *   opcode arguments

   One of things that needs to be addressed is that in order to trace the
   stack (C's or Perl's, really), a so-called ustack helper is what's
   needed, but these are fiendishly difficult to write. For a start, much
   of dtrace runs in the kernel, not in userland.

   Much of the more esoteric discussion was cross-posted from the
   dtrace-discuss mailing list, where talk of ustacks certainly appeared
   to give them The Fear.

     http://xrl.us/bec89

   In the process of producing "dtrace" support, Andy ran into trouble
   with getting the shellish idiom of if-not-condition-then correct.

   H.Merijn Brand showed one way to do it, Zefram, another.

     http://xrl.us/beda3

grep and smart match should warn in void context

   The discussion continued this week as to whether or not this would be
   a good idea. Michael Schwern started to jot down the history of why
   "map in void context" played such an important part in the history of
   Perl.

     we have a wiki, man
     http://xrl.us/beddu

   Abigail maintained that it would be insane to start warning about a
   construct that has not previously triggered a warning, even if the
   construct was not considered to be a best practice (in which case a
   Perl::Critic policy would be more suitable).

   Zefram put forward a suggestion that was endorsed by Larry Wall.

     should we, should we not
     http://xrl.us/bec9b

"feature.pm" needs some version comparison code somewhere

   Rafaël Garcia-Suarez waved his hands vaguely at the new error that
   comes out of "bleadperl -e 'use 5.10.1'" and hoped something could be
   done about it. Steffen Müller showed how difficult it would be to
   solve the general case.

   The only sane approach is for bleadperl to track feature sets in the
   current maintenance release. No new features could be added to 5.10.x
   after 5.12.0 comes out. Dave Mitchell thought add new features to a
   maintenance track was a bad idea anyway.

     still waiting for patches
     http://xrl.us/bec9d

First pass at META.yml support for the core

   Adam Kennedy took his "YAML::Tiny" module and made it even tinier by
   throwing everything that is not required to parse a META.yml file. He
   named it "Parse::CPAN::Meta" so that it doesn't say "YAML" on the tin.
   The idea being is that it will permit richer semantics in dealing with
   module requirements. This could come in handy for dual-lifed modules
   and modules that depend on external libraries.

   Ævar Arnfjörð Bjarmason found a minor YAML remnant in the test suite.

     ain't what it used to be
     http://xrl.us/bec9f

Segmentation violations with ithreads and regexps

   Nicholas Clark was wondering what change caused a particular language
   construct to go boom! and asked Andreas König to fire up his magic
   binary search patch locator to find the offending change.

   Andreas wasn't around, but Marcus Holland-Moritz was, and in about an
   hour had identified change #30755 as being the culprit. This enabled
   Nicholas to make the required correction.

     homing in
     http://xrl.us/bec9h

   Following that (if it's the same bug we're talking about) Dave
   Mitchell, Yves Orton and he kicked the problem around for a little
   while, and they appeared to arrive at the right solution by the end of
   the week.

     stirring up trouble with re 'eval'
     http://xrl.us/bec9j

"for (2..Inf)"

   Michael G. Schwern had a chance encounter with a C-style "for" loop,
   and realising that the range operation ("..") used a lazy
   implementation, noted that it was a Simple Matter Of Programming to
   get "for my $var (2..Inf)" to Do The Right Thing. So he coded a quick
   and dirty patch (with a test!) to prove that it could be done. Much of
   the discussion that followed, apart from mentioning Ruby and "bc"
   involved what to do when adding 1 to an integer value overflows.

     from her to eternity
     http://xrl.us/bec9m

   Jerry D. Hedden picked up the patch and ran with it, delivering a
   whole pile of code, documentation and tests to implement the whole
   show. Michael made a number of good comments, so Jerry returned to the
   lab and cooked up a fresh patch.

   One sticking point was whether the range should stop or not, when the
   value outgrew the maximum size of an integer. Yves thought that if
   that was a problem, people should really be using "while (1)".

   But even that approach is flawed, since after a few billion or
   quintillion loops any integer-based counter will begin to lose
   precision (after it is upgraded to a float following the overflow an
   integer). And transparently switching over to "Math::BigInt" would be
   Really Hard.

     I do it my way
     http://xrl.us/bec9o

What do we want to see in 5.12?

   A number of porters described the innovations they would like to see
   in perl 5.12, the next major release after 5.10. Nicholas Clark
   commented that a lot of the suggestions had high niftiness values, but
   noted that the difference between suggesting and implementing will
   impose its own natural selection of what gets done.

Deprecated items removed in 5.12

   Firstly, a number of items were marked as deprecated in 5.10 and thus
   may be removed from 5.12. All that could be recalled for the moment
   was the "-P" command-line switch and unnamed "package;" declarations
   (which actually disappeared in 5.10).

     all gone
     http://xrl.us/bec9q

Am I a method call?

   Ricardo Signes wanted support from the language to let him know if the
   routine had been called as a method. Currently, there is no mechanism
   that lets you do this in the general case. One possible approach is to
   do it by extending "caller".

   Given that "caller" already returns an impossible-to-remember list of
   values, Mark Jason Dominus wondered whether the last element should be
   a hashref, or whether an alternate hashified "caller" hashref should
   be made available. This suggestion attracted significant discussion,
   which evolved into calls for having "autobox" brought into core.
   Nicholas Clark warned against making that decision lightly.

     just so long as the hashref is purple
     http://xrl.us/bec9s

Method declaration

   Michael G. Schwern proposed a "method foo" declaration, that would
   work like a "sub foo", except that it fetches the $self object from @_
   for free.

   The open issues are, can you call it as a bare subroutine, what if you
   don't like using the name $self, what about class methods, and should
   $self be removed from @_ or should it remain?

     http://xrl.us/bec9u

     and it's on the wiki
     http://xrl.us/beddw

Lexical named subroutines

   Ricardo also suggested named lexical subroutines, to be used in
   situations such as comparator routines for "sort", while avoiding
   namespace pollution.

   Dave Mitchell pointed out the problems this would have in terms of
   closures. He sketched out two possible implementations and pointed out
   the flaws in both of them.

   Nicholas Clark recalled that Mark Jason Dominus was believed to be in
   the possession of a list of examples of the corner cases that would
   need to be addressed in any such proposal. Dave thought he could come
   up with one of his own at a pinch.

     just a spoonful of sugar
     http://xrl.us/bec9w

Anonymous packages

   Ricardo also mentioned a conversation with Matt Trout concerning the
   issue of creating anonymous packages. Currently it can be hacked
   together using "Package::Generator" or "Class::Mix". In any event,
   more thought needs to go into what the syntax should be.

     heh, inherit from *that*
     http://xrl.us/bec9y

Named parameters

   Michael then kicked off a very large thread by p5p standards,
   proposing real honest-to-goodness named parameters. One point he
   stressed was that what ever solution is implemented, it doesn't have
   to be perfect. We could apply the 80/20 rule and strive for a simple
   solution that is satisfactory 80% of the time.

   Then the difficulties began to surface: should the parameters that are
   named be removed (or not) from @_ (see also: the method declaration
   thread). Should the parameters be aliases (fast, but dangerous) or
   copies (slow and safe, and conforms to the Principle of Least
   Surprise). What happens if not enough parameters are passed. Can we
   have defaults? How does this tie in with prototype specifications?

   One useful item to come out of the discussion was a post from Juerd
   Waalboer who stepped of with a review of subroutine signatures in Perl
   6, and is worth stealing from it for Perl 5. Another point is that,
   one way or another, we'll need better support for aliases in the
   language. Solve that problem, and named parameters are a piece of
   cake.

     http://xrl.us/bec92

     also wikified
     http://xrl.us/beddy

Saner behaviour for "length"

   Aristotle Pagaltzis put forward an elegant suggestion to deal with
   "length(undef)". Rather than issuing a warning, it should quietly
   return "undef". Rafaël Garcia-Suarez liked the idea so much that he
   tried to implement, but was stumped by a number of strange failures in
   the test suite.

   Nicholas Clark picked up where he left off, and discovered that it is
   horrendously hard to get it to work correctly with tied variables.
   After a number of patches, the implementation was satisfactory, and in
   the process, Nicholas uncovered a bug involving (drum roll) UTF-8.

     how long is a string
     http://xrl.us/bec94

Patches of Interest

   Marcus Holland-Moritz's refactoring of PL_opargs generation in
   opcode.pl from last week was applied. As was Jerry Hedden's File::Temp
   cleanup and his "~~" is not a feature documentation tweak. The
   perlcommunity.pod patch from brian d foy was also applied, despite
   being in a yucky diff format. "\X" is equivalent to an atomic group
   made it too.

     see last week for URLs

Change backticks into more readable "qx()"

   Jari Aalto put forward the sensible suggestion of using "qx()" instead
   of backticks (`) since it's to confuse with an apostrophe, and some
   non-English keyboards make it quite difficult to generate.

   Tels fell of his chair since he didn't even know that "qx()" existed,
   but made up for it by spotting an leftover ` in Jari's patch.

     told you they were hard to see
     http://xrl.us/bec96

No more big slowdown in 5.10 @_ parameter passing

   Rick Delaney picked up the gauntlet and delivered a patch to fix the
   issue identified by Dave Mitchell, where the "OPpASSIGN_COMMON" wound
   up being set in error. The amazing part was that Rick didn't even
   believe there was a performance problem, but fixed it anyway. When the
   benchmarks were run, it was clear there was a net gain.

     Dave the M, right as usual
     http://xrl.us/bec98

Getting "Data::Dumper" to dump the new-fangled REGEXPs

   Yves updated "Data::Dumper" to handle blessed regexes in blead, but
   cautioned that the code was probably still too raw for previous
   releases.

     a blessing in disguise
     http://xrl.us/bedaa

   That gave Jerry D. Hedden some grief, until he tracked down the reason
   for the failure.

     that's not supposed to happen
     http://xrl.us/bedac

   Jerry has been building perls for quite a while without including the
   XS component of "re". Yves Orton thought a perl without "re", since it
   was a pragma.

   Jerry revised the patch two more times to get it into shape.

     running light
     http://xrl.us/bedae

   During the discussion, Yves Orton noticed that "regexp_pattern" really
   belonged in universal.c.

   So Jerry made the move, wrote the appropriate changes and their
   attendant tests and this enabled other tests to be moved around and
   simplified some additional housework in "Data::Dumper". All applied by
   Rafaël.

     moving to new digs
     http://xrl.us/bedag

"ARRAY(0x...)" is not very helpful in sprintf.t diagnostics

   Yitzchak Scott-Thoennes noticed that op/sprintf.t could produce
   meaningless messages on failure, and changed this to make it start
   making sense again. Applied by Nicholas Clark.

     http://xrl.us/bedai

Smoke report for 5.11.0 (delivered manually...)

   Steve Hay upgraded his smoking kit to the latest CPAN version, and
   discovered to his dismay that it could no longer mail the smoke
   results. He proffered a patch to get things going again.

     still smoking
     http://xrl.us/bedap

"B::Deparse" fixes for implicit smart matching in "given"/"when"

   Florian Ragwitz thought that the results of deparsing a switch
   statement were suboptimal and offered a patch to make things better.
   Rafaël applied the patch, and added a test too.

     given a patch
     http://xrl.us/bedar

Remove "AutoLoader::can"

   A thread in late November about slowness in "can" for AutoLoader was
   put on hold during the freeze for 5.10.0. Rafaël dug out the final
   patches and applied them. Steffen Müller said he'd push a new version
   out to CPAN.

     picking up where we left off
     http://xrl.us/bedat

Exclude .svn and _darcs from "IPC::SysV"'s Makefile.PL libscan

   Andy Armstrong had been working on "IPC::SysV" and noticed that the
   droppings left over by revision control messed things up and proposed
   a patch to fix things up again.

   A debate followed as to how, when and where to solve the problem and
   at the end of the day, the appropriate repositories received the
   appropriate patches.

     repository droppings
     http://xrl.us/bedav

Move the "reg_stringify" logic to "Perl_sv_2pv_flags"

   Ævar Arnfjörð Bjarmason moved the stringification of regexps into sv.c
   following Nicholas Clark's work of raising regexps into first class
   objects. Ævar explained that this would not break the pluggable
   interface for the regexp engine.

   Nicholas smoothed over some of the rough bits and applied it to blead.

     just another SV
     http://xrl.us/bedax

Porting/manicheck

   Robin Barker noticed that the last patch to manicheck broke its "-x"
   and "-m" command line switches. So he fixed it. Applied by Rafaël.

     switched on
     http://xrl.us/bedaz

tru64: poison stack, write protect string constants

   Jarkko Hietaniemi desired bad code to die a quick death by way of a
   segmentation fault, Steve Peters complied.

     0xfff58005fff58005: segmentation fault *and* NaN
     http://xrl.us/beda5

Watching the smoke signals

Smoke [5.11.0] 32864 FAIL(F) MSWin32 Win2003 SP2 (x86/1 cpu)

   There was a problem with platforms that were able to fork, or merely
   pretend to, or cannot. This was corrected, and Steve Hay recommended
   that for dual-lifed modules that need to test forking, the best
   practices may be found in Test/Simple/t/fork.t and IO/t/io_pipe.t.

     there is no fork
     http://xrl.us/beda7

New and old bugs from RT

forking on Tru64 (alpha-dec-osf) (#3387)

   A bug involving a child reading from a file and looping back to the
   beginning and reading again, and again was posted nearly eight years
   ago (hence the low bug id). The problem was kicked around for a while,
   but no-one was able to figure out what was going wrong.

   And there the bug slumbered from many years, until Franz Fischer
   revived it a few days ago, having run into the same behaviour on
   HP-UX.

     better luck this time
     http://xrl.us/bedbb

     let's do the time warp
     http://rt.perl.org/rt3//Ticket/Display.html?id=3387

Segfault with complicated regex inside "map" (#24898)

   Abigail posted this bug four years ago, and noting that the problem
   was still present, created a TODO test for it.

   Yves Orton wondered if the problem occurred outside of a "map" but
   Abigail listed a number of variations on theme that produced an
   interesting variety of segfaults, valgrind errors or memory
   exhaustion, and some that worked just fine.

     I told you map in void context was evil
     http://xrl.us/bedbd

"CHECK{}", "INIT{}" in sitecustomize.pl (#45627)

   Peter Dintelmann reported a bug that was actually due to a
   misunderstanding of the documentation, so Rafaël tried to improve
   that.

     it's the way it is
     http://xrl.us/bedbh

"pp_ftrread" appears to use the wrong access mode for "-x" (#49003)

   Jason Hord filed a bug last month the behaviour of "-x" when using the
   "filetest" pragma and attached a patch to fix it up. This week, Rafaël
   applied the patch.

     hooray for bug reports with patches
     http://xrl.us/bedbj

"B::Deparse" fails to deparse a reference to an anonymous hash (#49298)

   Rafaël committed a fix that he thought should fix the bug that David
   Leadbeater reported last week.

     anon deparsing is go
     http://xrl.us/bedbm

"Scalar::Util" documentation problem (#49434)

   Ben Okopnik pointed out that the documentation in this module refers
   to a book that never has, and probably never will be published.

     a tad optimistic
     http://xrl.us/bedbo

Attributes and Unknown Error (#49472)

   "mz" reported a significant regression in the clarity of error
   messages between 5.8.8 and 5.10.0 when attributes are involved. No
   takers as yet.

     http://xrl.us/bedbq

Outdated "Test::Harness::Straps" (#49504)

   Imacat from Taiwan, who runs a very tight testing ship, reported that
   the "Test::Harness::Straps" shipped with 5.10.0 is quite far behind
   the current CPAN version. Furthermore, upgrading the module copies it
   to the site directory, hence shadowed by the older core version.
   Michael G. Schwern fixed this.

   Imacat also asked Michael to bundle a Makefile.PL, to enable a vanilla
   5.8.8 distribution (sans "Module::Build" to install THS automatically
   in a CPAN shell.

   Michael was a little more reluctant to take on this additional
   technical debt, but Andreas König thought he had little choice.

     http://xrl.us/bedbs

"state" variable not available (#49522)

   Abigail uncovered a curious omission in the implementation of "state"
   variables, and wrote a TODO test to help with the search for the
   solution.

     here you see it, there you don't
     http://xrl.us/bedbu

"syswrite" layer forgets to encode (#49548)

   Mark Overmeer wrote a small test case showing that "syswrite" failed
   to honour encoding directives.

     http://xrl.us/bedbw

"constant" overloading (#49594)

   Goro Fuji noted that "overload::constant" doesn't work if the constant
   in question contains escaped characters. Michael G. Schwern
   hypothesised that the presence of a backslashed character caused the
   code to run down the wrong path.

     the high road be shorter, but the low road prettier
     http://xrl.us/bedb2

open ':locale' does not work under locale with modifier (#49646 and #49648)

   Mashrab Kuvatov filed a bug regarding problems with locales, UTF-8 and
   Cyrillic. Rafaël trimmed down the test case, saw the problem, but
   wanted to obtain some reference material on how to read encoding
   definitions.

     http://xrl.us/bedb4

Use of uninitialized value in die at /opt/perl/lib/perl5/File/Copy.pm 
line 224. (#49660)

   Marc Lehmann ran into a bug with "File::Copy" but couldn't reproduce
   it (although unfortunately the effect was to remove the file being
   copied).

     ouch
     http://xrl.us/bedb6

Perl5 Bug Summary

   310 new + 1470 open = 1780 (8 created, 4 closed). Robin Barker
   wondered where his #49302 bug went.

     http://xrl.us/bedb8

     overview
     http://rt.perl.org/rt3/NoAuth/perl5/Overview.html

New Core Modules

   Math-Complex 1.43
       Black smoke emerged from 1.42, reasons why "ok($a == $b)" may be
       needed instead of "cmp_ok($a, '==', $b)" were given, long doubles
       were overlooked and so Jarkko Hietaniemi pushed out a new version.

         http://xrl.us/bedca

In Brief

   Andreas König identified the source of H.Merijn Brand's double free
   error in 5.10.0

     it says "rgs@stencil" on the tin
     http://xrl.us/bedcc

   And Moritz Lenz's bugs in extended regexp features were Warnocked.

     perlbug it
     http://xrl.us/bedce

   H.Merijn continued to plough through his "Configure" and metaunits
   work and was happy to report that he was down to a mere 193 warning
   messages.

     a mere SMOP
     http://xrl.us/bedcg

   Jari Aalto wanted an URL for Perl documentation. Two were given.

     a vast program
     http://xrl.us/bedci

   Nicholas Clark was Warnocked over a parallel make bug in "SDBM_File"

     because no-one uses it?
     http://xrl.us/bedck

   Craig Berry noticed that the latest REGEXP patches produced black
   smoke on VMS. Robin Barker and Nicholas Clark vied to produce the best
   patch to resolve the problem and at the end of the day VMS and Craig
   were happy again.

     http://xrl.us/bedcn

   Yves Orton complained that development version numbers, warnings, XS
   and MakeMaker don't mix. The concensus is that using underscore in a
   version number to signify the beta release of a module to PAUSE blows
   chunks, and a much better idea would be to have something in META.yml.

     a call for metadata
     http://xrl.us/bedcp

   Nicholas welcomed Marcus Holland-Moritz's correction of an 8 year old
   bug, and wondered how much perl 4 code still remained in the code
   base, as this could lead to the possibility of correcting an 18 year
   old bug.

   Andy Dougherty thought that much of doio.c dated back to Perl 4 and
   significant parts of sv.c could be traced all the way back to Perl 1.

     layer upon layer upon layer
     http://xrl.us/bedcr

   Coverity was a great help to the development of perl 5.10, helping pin
   down a number of questionable C practices. Andy Lester asked for
   volunteers to say good things about the product.

     scratch my back
     http://xrl.us/bedct

   Max "Corion" Maischein made perl build again on Win32 when the path
   contains whitespace.

     under program files
     http://xrl.us/bedcv

   Patrick Rutkowski ran into a problem with "typedef" definitions in XS
   code written in C++. Jan Dubois had already dealt with the problem in
   the past and show Patrick what to do.

     http://xrl.us/bedcx

   Ask Bjørn Hansen encountered some weird behaviour when @INC contained
   "./" (that is, with a trailing slash). Andy Armstrong noted that the
   perl in question was from a Red Hat distribution, and wondered if one
   of their own patches was interfering with normal @INC behaviour.

     http://xrl.us/bedcz

   The latest version of the smoking harness for the perl core fell
   apart, and some fixes were made. Further improvements may be
   necessary.

     sync early, sync often
     http://xrl.us/bedc3

   Gerard Goossen released kurila 1.7, an experimental fork of the perl
   codebase, the aim of which is wto see what would happen if one were to
   free one's self completely of any notions of backwards compatibility.

     where does a kurila sit?
     http://xrl.us/bedc5

   Rick Delaney's patch from last week to allow the clearing of @ISA from
   XS was applied.

     assign with impunity
     http://xrl.us/bedc7

   Robin Barker had some more consting goodness applied to POSIX.xs

     strtoul() and helper
     http://xrl.us/bedc9

   as well as "Compress::Raw::Zlib" and "Filter::Util::Call" from a short
   time back.

     http://xrl.us/beddb

   Nicholas Clark's change to assert that these are the regexps you were
   looking for came to grief on Jerry D. Hedden's machine. A revised
   patch appears to have fixed the problem.

     http://xrl.us/beddd

About this summary

   This summary was written by David Landgren.

     last week's
     http://xrl.us/beddf

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