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All the Perl that's Practical to Extract and Report

This Week on perl5-porters - 15-21 September 2008

posted by grinder on 2008.10.20 15:27   Printer-friendly

This Week on perl5-porters - 15-21 September 2008

This is sort of like one of those useless Windows alert boxes that pop up to tell you something perfectly normal has happened and you should do nothing. "A USB device was safely removed!" Yes, thank you, I just removed it. It's this sort of hand-wringing user interface design ("but the user might not have expected that USB device to be removed, they should be told so they can maybe, possibly do something!") that I'd like Perl to avoid. -- Michael G. Schwern, wanting numeric upgrades to JFDI.

(Please take note of the date. I'm posting the backlog of summaries after having encountered problems trying to post them last month).

Topics of Interest

Y2038 branch

Michael G. Schwern's work (in a git branch) on Y2038+ dates continued apace, with H.Merijn Brand adding some configuration hooks for minimum and maximum date values, and discussions of how to set up tests to check for sane values in the year 803619167319 or so, especially if daylight savings is still in place.

  fresh dates
  http://xrl.us/oscvv 

Blead on OpenSUSE 11.0/64

H.Merijn Brand reported that the only failure on this platform for 5.8.9-to-be was one test in CGI. On the other hand, ODBM_File was collapsing in a heap on blead, but H.Merijn was puzzled as to why, since he was using the same configuration settings, and there has been no changes under ext/ODBM_File between 5.8.x and blead.

Andy Dougherty thought that 5.8.x's Configure was missing ODBM_File altogether, but blead's was a little more aggressive and found a header that led it to conclude it could try and build the extension, and this revealed that SUSE's dbm compatibility is not up to par.

  not ODBC
  http://xrl.us/oscvx 

autodie behaviour with flock()

Paul Fenwick asked what autodie should do in the light of blocking and non-blocking file lock acquisitions, reasoning that calling flock() in blocking mode means "I need this lock", whereas calling it in non-blocking mode is a question: "Can I get this lock right now?". From this, he could come up with sensible behaviour for autodie.

The main sticking point was the possibility that a flock call returns the EWOULDBLOCK error, which is not really an error, or at least, not something worth dying for.

There was a long discussion about exceptions, errors and opportunistic code, but the main point to take home is when Zefram pointed out that if autodie's behaviour for flock is unsuitable, one is always free to use a no autodie 'flock' to switch it off and handle it manually.


  blocked on flock
  http://xrl.us/oscvz 

One may assume that Paul had been pulling his hair out over the issue and that the documentation wasn't much help. So he improved documentation for flock() in perlfunc.pod and tidied up the code examples for by using lexical filehandles rather than globs, checking for errors, and using constants rather than magic numbers.

  aiding the cargo cult
  http://xrl.us/oscv3 

Is the prototype for CORE::truncate wrong?

Paul then looked at truncate in trying to figure out how to override it for autodie. His version could not take a typeglob as a parameter, as the parser thought it was a bareword, due to truncate's prototype.

He missed the fact that truncate can also work with the name of a file, not just a file handle, which is why the prototype had to fudge matters slightly.

This reminded Jan Dubois of a subtlety he encountered with unlink a while ago: unlink() will remove the file named by $_, but unlink(()) does nothing. The reason for this oddity is to prevent unlink(@stuff) from unlinking whatever $_ points to, should @stuff happen to be empty.

Jan gave up trying to implement the same semantics in pure Perl, instead concluding that there are some core functions that are impossible to duplicate. And perl 5.10's _ prototype doesn't help either, given that it imposes scalar context.

Rafaël wondered what would happen (what would break) if he tweaked opcode.pl to change the prototype to something more suitable for Paul's need. Paul wondered too.

  trunk call
  http://xrl.us/oscv5 

Practical considerations in changing the integer upgrade path?

Michael G. Schwern asked for people's considered opinions on how painful it would really be to change the integer upgrade path from signed -> unsigned -> double -> Inf to signed -> long long (or whatever) -> arbitrary precision.

Specifically, he wondered how one creates a new SV type, what impact would this have on the code base, and whether it would break XS code.

Yuval Kogman answered all three questions quite clearly. And there ended the thread.

  and python does it right
  http://xrl.us/oscv7 

Change 30638 introduces regression

Following on from a change for bug #59168 reported by Father Chrysostomos and an error in the test suite for XML::LibXML::Simple, Nicholas Clark backed the regressing change out and added some tests to identify the problem so that that future attempts don't cause the same breakage. Dave Mitchell said he had a cold, and was thus unlikely to look at things for a while.

  get well soon
  http://xrl.us/oscv9 

$* is no longer supported

Rory Kingan was worried about some code that crawled out of the woodwork complaining about $* no longer implemented in 5.10. Aristotle Pagaltzis looked at the regular expressions Rory posted and concluded that it was just cargo cult code that could be safely deleted.


  night of the living regexp
  http://xrl.us/oscwb 

Milestone: metaconfig now under GIT

H.Merijn Brand thanked Sam Vilain and Abhijit Menon-Sen for helping him get metaconfig hosted entirely in git (at http://perl5.git.perl.org/), and declared its Perforce branches officially closed.

  it's dead, jim
  http://xrl.us/oscwd 

Syntax incompatibility (5.8.8 vs 5.10)

Edward Peschko wrote about a problem with Readonly::XS that was complaining about a use of Carp::croak. This can be traced to a decision taken over three years ago to remove the loading of Carp from warnings.

Since the author of the module sees no reason to release a new version of the module just to fix this problem, it is unlikely that it will be fixed in the near future. Certainly there is no desire to put Carp back into warnings, and Perl::Critic::StricterSubs can be used by authors to find such problems (where client code loads module X, which in turn loads module Y, and then the client code calls routines in Y without having loaded it explicitly).

  EWONTFIX
  http://xrl.us/oscwf 


TODO of the week

Here's a simple task that requires no C knowledge.

Fix tainting bugs

Fix the bugs revealed by running the test suite with the -t switch (via make test.taintwarn).

(In fact, you don't even have to fix all of them, or most of them. Just updating perltodo.pod (patches welcome!) with the list of problematic files would be a start).


Patches of Interest

icc wants -fPIC on x86_64

Vincent Pit offered a patch to get Intel's icc compiling XS modules correctly. Apparently this went nowhere.

  http://xrl.us/oscwh 

Pod/Text.pm Can't call method pod2text without a package or object reference

Jari Aalto uncovered a problem in 5.10 with an undefined file descriptor in Pod::Text. He supplied a patch for it, which appears to be stuck in limbo.

  http://xrl.us/oscwj 

Don't reuse temp files in tests

Jerry D. Hedden found some more tests that had problems with names of temporary file names being reused, so he changed them to use genuine temporary file names. Jan Dubois pointed out that this was likely to be a win for Windows systems that have on-access virus scanning, which can interfere with files that are rapidly deleted and recreated.

  do not use a random method to generate random filenames
  http://xrl.us/oscwm 

Show using waitpid in IPC::Open[23] SYNOPSIS

brian d foy noted that the documentation recommends using waitpid to clean up, but the supplied examples don't. So he amended them to provide baseline best practices for people to use.

  do as i say not as i do
  http://xrl.us/oscwo 


New and old bugs from RT

Volunteer for fixing the "Unicode" bug (#58182)

Back in August, when I was on my summ(?:ary|er) break, Karl Williamson filed a bug report relating to the inconsistent handling of 8-bit characters in strings during case mapping when no locale has been specified.

For instance, uc("\x{e0}") returns itself (à, or lowercase a grave) rather than À (uppercase A grave). And this, regardless of whether there are any multi-byte characters.

As a consequence, "\x{e0}" =~ /\x{c0}/i fails to match. Moritz Lenz explained that this was a known bug but unfortunately was not fixable because too much code relies on the current behaviour (which Karl summarises quite nicely in the original bug report). Moritz showed how one could make things work, at the expense of a little make-work code involving utf8::upgrade.

Juerd Waalboer mentioned that it is fixable and scheduled for implementation in perl 5.12, and that such backwards compatibility issues have been noted in perl510delta.

Dave Mitchell sketched out how one might go about producing an implementation for this, which would involve breaking out the semantically overloaded SVf_UTF8 flag from SvFLAGS and hanging it out in an auxilliary structure, which could be used to store additional bits of information such as character set, encoding, locales, UTF-8 caches and more, since there's no space for such extravagances in a standard SV.

Juerd and Glenn Linderman weren't sure it this would end up being a win. Glenn in particular thought that locale and encoding metadata should probably be associated with file handles and the like.

  prologue
  http://xrl.us/oscwq 

Fast-forward to this week, when Karl reported back to the list, explaining that he'd implemented the change in behaviour in a copy of 5.10 source that seemed to do the trick, and asked the list where to go from here. In a nutshell, his patch extends ASCII semantics to the characters in the 128..255 Latin1 characters.

Glenn Linderman explained that Karl should use a pragma to introduce this new change for code that wants to use it.

Rafaël amended this suggestion by saying that the Unicode situation as it stands at the moment is such a mess that no pragma would be required for 5.12: it would just Do The Right Thing and backwards compatibility be damned. If the change was back-ported to the 5.10 track, then a pragma would be required in order to switch to the new behaviour.

Andreas König pointed out that Karl should base his patches on blead, rather than 5.10. Rafaël said that starting a branch from git://perl5.git.perl.org/perl.git would be as good a place as any from which to start.

Juerd thought that Karl should have no qualms about breaking code with his changes, since a certain amount of reverse breakage would may occur, whereby existing buggy code suddenly begins to work correctly...

  famous last words "I just have to fix this bug"
  http://xrl.us/oscws 

Building Perl 5.10.0 in AIX 5.3 using -Duseshrplib option gives ERROR: Undefined symbol: boot_DynaLoader (#58858)

Tippa found a problem that (s)he was able to fix by a minor tweak to Makefile.SH and so filed a bug report. Jan Dubois repackaged the fix as a patch to makedef.pl. H.Merijn Brand confirmed the problem and the fix, and committed it as change #34379.

  AIX en provence
  http://xrl.us/oscwu 

3-arg re-open drops IO layers (#58920)

Frank Meisschaert discovered that if STDOUT is redirected to a UTF-8 file using the 3-argument form of open, the UTF-8 layer does not get set. The work-around is to close STDOUT explicitly beforehand.

Michael G. Schwern confirmed that the problem exists from 5.8.8 to 5.10.0 to blead on OS/X .

  not a team (p)layer
  http://xrl.us/oscww 

grep unpack a/(a) loops and eats all memory (#58942)

Ambrus Zsbán discovered a nifty way to have perl eat all available memory. Nicholas Clark reported that the problem had already been identified and fixed in blead. The correction will be backported to 5.10.1 and 5.8.9, which Nicholas said should be out within a month.

  that's not a feature!
  http://xrl.us/oscwy 

Typo in CGI(3perl) man page (#59132)

Reuben Thomas identified two typos (in bug reports #59128 and #59130) which were either already fixed in blead, or fixed thanks to his report. Reuben found another typo in CGI, for which Renée Bäcker produced a small patch, although this will have to be pushed upstream to Lincoln Stein, CGI's maintainer.

  meanwhile back at the CSHL
  http://xrl.us/oscw2 

He also found a typo in File::stat (filed in bug #59134).

  the proof is in the reading
  http://xrl.us/oscw4 

Perl5 Bug Summary

Heading north. 268 new + 1032 open = 1300 (+6 -2)


  http://xrl.us/oscw6
  http://rt.perl.org/rt3/NoAuth/perl5/Overview.html 


New Core Modules

constant 1.16

Sébastien Aperghis-Tramoni uploaded what is essentially a documentation fix. Applied to blead by H.Merijn Brand.

  http://xrl.us/oscw8 
podlators 2.1.4

Russ Allbery fixed up the test suite to skip Unicode tests below 5.8, since Pod::Simple doesn't support UTF-8 encoding with those versions, and rearranged things to deal with Red Hat ispell idiosyncracies.

  http://xrl.us/oscxa 

This followed 2.1.3, which was Russ's first attempt at addressing error handling (emitting to STDERR instead of creating a POD ERRORS section), along with the errors that H.Merijn brought up recently, where an otherwise flawless smoke run was choking on UTF-8 locales.

  http://xrl.us/oscxc 

In Brief

Gábor Szabó chose Debug::Client as the name for his client for the built-in debugger.

  now available on CPAN
  http://xrl.us/oscxe 

Alexandr Ciornii set up dual life for Text::ParseWords . The previous module on CPAN is 9.5 years old.

  now available on CPAN
  http://xrl.us/oscxg 

Paul Marquess was worried about the complexities and potential for breakage if he created a composite distribution that contains all his Compress::Zlib / IO::Compress::Gzip / IO::Compress::Bzip2 goodness. Fortunately the solution is simple and robust.

  now available on CPAN
  http://xrl.us/oscxk 

Michael G. Schwern reported on Method::Signatures and the \@foo prototype, and how nice it all was.


  now available on CPAN
  http://xrl.us/oscxn 

Last week's summary

  http://xrl.us/oru8q 

About this summary

This summary was written by David Landgren.

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

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