This Week on perl5-porters (9-15 October 2006)

This Week on perl5-porters - 9-15 October 2006

   "May I remind everybody my personal opinion, which is that I see
   little to null utility to style patches to C or perl code, but that
   they clobber version control history, waste my time, and that in most
   I cases will not apply them." -- Rafaël Garcia-Suarez, current
   pumpking, on why people should not fiddle with the bloody whitespace.

Topics of Interest

Coding styles and ancient perls

   Last week, Dr. Ruud and Yves Orton worked on bringing "makepatch" up
   to speed on the Windows platform. For some reason it sparked a long
   discussion about the merits of writing code compatible with ancient
   versions of Perl and $_ topicalisation.

     http://xrl.us/sm5z

5.8.8+ invalid "free()" in "Perl_do_exec3"

   Alexey Tourbin spotted a problem with the current 5.8 snapshot that
   doesn't show up in the 5.8.8 release. Dave Mitchell thanked him for
   picking it up, and fixed it.

   Alexey went on to mention that he runs a git repository that tracks
   the 5.8 and 5.9 sources, and lamented that he could not quite figure
   out to which change corresponded the 5.9.0 release.

     ah say git down
     http://xrl.us/sm52

Resolving downstream breakages from version.pm changes

   Adam Kennedy uses "only.pm" to lock down the versions of modules used
   in the code he delivers to clients, and noticed that "only" doesn't
   work correctly with changes that have taken place since in "version",
   and development on "only" appears to have dragged to a halt.

   John Peacock took a look at "only"'s code, saw what was wrong with it,
   and at the same time asked Adam wither "version::Limit" might do the
   trick instead.

     http://xrl.us/sm53

g++ compile and make test 100%

   After weeks of patching and tweaking the source, Jarkko Hietaniemi
   announced that he had succeeded in performing a C++ compilation of the
   perl source, and a completely successful test suite run. Rafaël
   Garcia-Suarez noted that "NDBM_File" still had trouble. Jarkko didn't
   notice that because it wasn't configured to be built on his platform.
   Robin Barker provided a patch to fix it up.

   Paul Marquess, Steve Peters and Jesse Vincent reported successes with
   other C++ compilers and platforms. H.Merijn Brand found a problem on
   Suse Linux, as did Dominic Dunlop on Mac OS/X.

     http://xrl.us/sm54

     Robin's patches
     http://xrl.us/sm55
     http://xrl.us/sm56
     http://xrl.us/sm57

The curious case of the last close parenthesis

   Yves Orton surfaced briefly to discuss some oddities he had found in
   the regular expression concerning how opening and closing capturing
   parentheses are managed. An optimisation in the engine consists of
   throwing the regop codes that denote the parentheses, and tracks them
   itself... but doesn't track them all that well.

   Over time, this has manifested itself through a variety of bugs, all
   of which have been solved in ad hoc ways, as no one really understood
   the big picture.

   Yves thinks that his hypothesis is right, and wanted to know what Dave
   Mitchell thought of it. Ilya Zakharevich remembered that Yves's two
   variables, "PL_reglastparen" and "PL_reglastcloseparen" were once upon
   a time a single variable, but were split into two, probably when
   non-capturing parentheses were introduced. As such, it's quite
   possible that the code was not correctly updated in all the required
   places. In a patch elsewhere this week, Yves dropped some comment
   markers here and there, where he thought the variables should be
   updated.

     http://xrl.us/sm58

Will the real "Perl_reg_named_buff_sv" please stand up?

   Craig A. Berry was having trouble building the "re" extension on VMS,
   since the VMS linker didn't like the fact that the
   "Perl_reg_named_buff_sv" symbol was defined twice, in two different
   object files.

   Yves explained that one was derived from the other, in order to
   generate the debugging version. His linker, being slightly more lax,
   did not complain about this issue, and fixed it up in a subsequent
   patch.

     http://xrl.us/sm59

Status of Perl 5.10 TODO list

   Yves then looked at the TODO list for 5.10 and counted four issues
   outstanding. He wanted to know that their status was, and what needs
   to be done. Rafaël said three of them were issues he planned to deal
   with, and one was less important (lexical encoding pragmas). He also
   mentioned that aliases were probably important enough to be taken on
   board, as were "UNITCHECK" blocks.

   Juerd was very keen to see work done on the "encoding" pragma. He as
   released a work-around "encoding::split" to get things to work to his
   satisfaction, but would like to see the functionality appear in the
   core.

   Adriano Ferreira reminded the porters of bug #38945, which notes that
   "Configure" is not "x.10" version aware. Andreas König mentioned that
   DBI doesn't compile on "blead" (and someone needs to open a ticket on
   that).

     http://xrl.us/sm6a

   Philip M. Gollucci, almost left behind, pointed out that there was an
   icky attribute/printf problem that needed to be sorted out as well.

     http://xrl.us/sm6b

"SVpvs" vs "SVpvn"

   Jim Cromie was looking through the source when he noticed that there
   were a number of places where the "newSVpvn" call could be more
   profitably replaced by a "newSVpvs", the reason being that this
   removes the need to keep hard-coded lengths of strings lying around
   (as this can allow bit-rot to creep in).

   Nicholas Clark went ahead and made the change. Aaron Sherman pointed
   out that the hard-coded length might be a slightly sick way of taking
   a substring of a constant, such as

     SV *s = newSVpvn("pear",3);

   Nicholas had already looked for such cases in the code, and the only
   occurrences he found were deliberate tests.

   Vadim Konovalov wondered whether the real reason that hard-coded
   lengths were used was to avoid possibly costly length computations.
   Jim Cromie believed that this was not a problem, since the constructs
   tended to be evaluated when the C source is compiled, and boil down to
   a constant in the resulting object code.

     http://xrl.us/sm6c

New version diagnostic breaks a bunch of modules

   Michael G. Schwern wished to register his disgruntledness at the fact
   that a diagnostic change caused a number of his modules
   ("Exporter::Lite", "UNIVERSAL::exports" and "UNIVERSAL::require" for
   starters), and wondered how many other modules were in the same boat.

   John Peacock was loathe to give up the more informative new error
   message. He could get close to matching the old message if certain
   conditions were met, but not completely. Michael remarked that
   future-proofing the checking of perl error messages is hard.

     Never mind localisation
     http://xrl.us/sm6d

Off by one in the trie code?

   Nicholas Clark wrote a psychotic regular expression to provoke a leak
   that was picked up by valgrind, and he wondered if there was an
   off-by-one error. Yves promised to have a look at it later.

     http://xrl.us/sm6e

Patches of Interest

What Jarkko Hietaniemi did this week

   Jarkko tweaked some of Yves's code to get it to compile cleanly with
   the more fussy compilers that he has at his disposal.

     Do not cross the initialisation boundary, do not collect $200
     http://xrl.us/sm6f

   Jarkko transformed "Digest::SHA" from K&R C to ANSI, and described the
   delicate footwork required to ensure that "blead" and CPAN play nicely
   together.

   Mark Shelor, "Digest::SHA"'s author, thanked Jarkko for the patch, and
   planned to integrate it for the upcoming 5.44 release, so with luck no
   one will have to take extra care for very long.

     http://xrl.us/sm6g

   Jarkko performed similar tweaks for Encode.xs, with a eye on C++.

     http://xrl.us/sm6h
     http://xrl.us/sm6i

   He then gave a few hints to Linux and Solaris to tell C++ how to deal
   with "dlerror", noting that if a third platform needs this trickery
   then it will be time to push it off into "Configure".

     http://xrl.us/sm6j

   Moving on through the modules, he then performed a classy act on
   "ExtUtils::ParseXS".

     http://xrl.us/sm6k

   And then ANSIfied the "Text::Soundex" module.

     A530 T500 A521 T000 T232 M340
     http://xrl.us/sm6m

   And an "EXTERN_C" wrapper for something in "re.pm"

     http://xrl.us/sm6n

What Yves Orton did to the regular expression engine this week

   Yves Orton, the unstoppable feature-adder to the regular expression
   engine, added named recursion this week, whereby "<(?&NAME)>" recurses
   to the capture buffer defined by "(?<NAME>...)".

     No, my brane hurts
     http://xrl.us/sm6o

   He landed another patch to fix bugs, test code and add more
   functionality to deal with conditionals in regular expressions.

     http://xrl.us/sm6p

   He then added even more documentation, of note is an update to
   perlreguts.

     http://xrl.us/sm6q

   And last but not least, Yves announced that he had added possessive
   quantifiers to the engine. He also put floated the idea of removing
   the dire warnings about the experimental status of the existing
   extensions, since they have been around for a long time and have been
   well documented and well explored by large numbers of people.

     http://xrl.us/sm6r

   Sadahiro-san delivered a patch to remove "leaveit" from
   toke.c:scan_const, which deals with escaped characters in patterns.
   There were a number of short-comings with the current code, not to
   mention breakage. Now it's better.

     http://xrl.us/sm6s

New and old bugs from RT

"sprintf" width+precision fails on wide chars (#40473)

   Anatoly Vorobey found a bug in the way "sprintf" handles UTF-8
   characters and supplied a patch against "blead" to correct it. Applied
   by Rafaël.

     Why aren't all bug reports like this?
     http://xrl.us/sm6t

Regular expression recursion (#40495)

   Matthias Urlichs demonstrated a bug in the regular expression engine.
   It failed with "x{2}" but went away when replaced by "xx". Dave
   Mitchell explained that sometimes the optimiser fails to recognise
   such transforms. In any event, with the latest work to the engine in
   "blead", the offending pattern works just fine.

     Even if it does consume quite a bit of memory
     http://xrl.us/sm6u

"Can't locate Foo/Bar.pm" isn't a helpful message (#40516)

   Tina thought that this message exposed too much of how things are
   implemented, and a beginner might not necessarily realise that there
   was a problem loading the "Foo::Bar" module. She thought that adding a
   "perhaps Foo::Bar is not installed" to the end of the message would
   help improve matters.

   Juerd wondered whether this would encourage newbies to hunt down the
   Foo/Bar.pm file and dump it in an @INC directory. People already tend
   to do this, which leads to problems when modules have XS components
   and the result is traffic on mailing lists and other fora.

     http://xrl.us/sm6v

Perl5 Bug Summary

     1525, bugometric pressure steady
     http://xrl.us/sm6w

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

New Core Modules

   *   "version" 0.67_03 from John Peacock,

         http://xrl.us/sm6x

   *   "ExtUtils::MakeMaker" 6.31 from Michael G. Schwern,

         http://xrl.us/sm6y

   *   "CPANPLUS" 0.076 (although not part of core) from Jos I. Boumans,

         http://xrl.us/sm6z

   *   and "XSLoader" 0.07 from Sébastien Aperghis-Tramoni.

         http://xrl.us/sm62

In Brief

   Tels made a few suggestions about the code in "makepatch" that
   received a work-over last week.

     http://xrl.us/sm63

   Dave Nicol suggested that the source code be formatted according to a
   fixed set of rules.

     http://xrl.us/sm64

   Johan Vromans looked at "Carp::Clan" and thought that its
   functionality was so useful that it should be subsumed into the core
   "Carp" module, arguing that it is better to extend an existing module
   than to introduce a new one that duplicates a lot of the functionality
   of the previous one.

     http://xrl.us/sm65

   Gabor Szabo asked about running "Devel::Cover" on core modules in
   blead and Paul Johnson set him straight.

     http://xrl.us/sm66

   Andreas König found that "change #28976 breaks YAML", but Rafaël was
   unable to reproduce the problem. Andreas later discovered that #28997
   resolved the problem in any event.

     http://xrl.us/sm67

   Similarly, David Landgren compiled Template Toolkit on a recent build
   of "blead" (change #28998) and watched in blow up. Rafaël noted that
   the code in "Template.xs" relied on a macro producing a parenthesised
   result, which was used directly in a C "switch" statement, and at some
   point the "blead" version of the macro lost the parenthesis wrapper.
   So "Template.xs" needs to add in the parentheses itself.

     relying on the core to do it for you
     http://xrl.us/sm68

   Jerry D. Hedden raised "threads" to version 1.44, and
   "threads::shared" to version 1.04.

     http://xrl.us/sm69
     http://xrl.us/sm7a

   Juerd Waalboer wondered if he had hit a "B::Deparse" bug, since a
   nested hashref/listref structure deparses into a different structure
   that in turn deparses to something else...

     ... and so on to viscosity
     http://xrl.us/sm7b

   Yves shed some light on why he chose "\k<...>" over C<\k{...}> for
   named captures in regular expressions.

     Because
     http://xrl.us/sm7c

   Jos I. Boumans proposed adding "Log::Message" and
   "Log::Message::Simple" to the core.

     http://xrl.us/sm7d

   Mark J. Reed sought more information on the way "File::Find" orders
   directories and files, since he could not see a way to process
   directories first and then files.

     lots of "HACK:" comments
     http://xrl.us/sm7e

   Jim Cromie wanted to know how does "Configure -O" work.

     delete config.sh and Policy.sh beforehand
     http://xrl.us/sm7f

   Leopold Tötsch was encountering some ambiguous behaviour with
   "sprintf" and wondered who was right. Sadahiro Tomoyuki straightened
   it out with a sharp patch to the right.

     http://xrl.us/sm7g

About this summary

   This summary was written by David Landgren.

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