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 "[EMAIL PROTECTED]" 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
Weekly summaries are published on http://use.perl.org/ and posted on a
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