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1=head1 NAME
2
3perltodo - Perl TO-DO List
4
5=head1 DESCRIPTION
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7This is a list of wishes for Perl. The tasks we think are smaller or easier
8are listed first. Anyone is welcome to work on any of these, but it's a good
9idea to first contact I<perl5-porters@perl.org> to avoid duplication of
10effort. By all means contact a pumpking privately first if you prefer.
e50bb9a1 11
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12Whilst patches to make the list shorter are most welcome, ideas to add to
13the list are also encouraged. Check the perl5-porters archives for past
14ideas, and any discussion about them. One set of archives may be found at:
e50bb9a1 15
0bdfc961 16 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
938c8732 17
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18What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
19not, but if your patch is incorporated, then we'll add your name to the
20F<AUTHORS> file, which ships in the official distribution. How many other
21programming languages offer you 1 line of immortality?
938c8732 22
0bdfc961 23=head1 Tasks that only need Perl knowledge
e50bb9a1 24
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25=head2 Remove duplication of test setup.
26
27Schwern notes, that there's duplication of code - lots and lots of tests have
28some variation on the big block of C<$Is_Foo> checks. We can safely put this
29into a file, change it to build an C<%Is> hash and require it. Maybe just put
30it into F<test.pl>. Throw in the handy tainting subroutines.
31
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32=head2 merge common code in installperl and installman
33
34There are some common subroutines and a common C<BEGIN> block in F<installperl>
35and F<installman>. These should probably be merged. It would also be good to
36check for duplication in all the utility scripts supplied in the source
37tarball. It might be good to move them all to a subdirectory, but this would
38require careful checking to find all places that call them, and change those
39correctly.
40
0bdfc961 41=head2 common test code for timed bail out
e50bb9a1 42
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43Write portable self destruct code for tests to stop them burning CPU in
44infinite loops. This needs to avoid using alarm, as some of the tests are
45testing alarm/sleep or timers.
e50bb9a1 46
87a942b1 47=head2 POD -E<gt> HTML conversion in the core still sucks
e50bb9a1 48
938c8732 49Which is crazy given just how simple POD purports to be, and how simple HTML
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50can be. It's not actually I<as> simple as it sounds, particularly with the
51flexibility POD allows for C<=item>, but it would be good to improve the
52visual appeal of the HTML generated, and to avoid it having any validation
53errors. See also L</make HTML install work>, as the layout of installation tree
54is needed to improve the cross-linking.
938c8732 55
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56The addition of C<Pod::Simple> and its related modules may make this task
57easier to complete.
58
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59=head2 merge checkpods and podchecker
60
61F<pod/checkpods.PL> (and C<make check> in the F<pod/> subdirectory)
62implements a very basic check for pod files, but the errors it discovers
63aren't found by podchecker. Add this check to podchecker, get rid of
64checkpods and have C<make check> use podchecker.
65
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66=head2 perlmodlib.PL rewrite
67
68Currently perlmodlib.PL needs to be run from a source directory where perl
69has been built, or some modules won't be found, and others will be
70skipped. Make it run from a clean perl source tree (so it's reproducible).
71
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72=head2 Parallel testing
73
b2e2905c 74(This probably impacts much more than the core: also the Test::Harness
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75and TAP::* modules on CPAN.)
76
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77The core regression test suite is getting ever more comprehensive, which has
78the side effect that it takes longer to run. This isn't so good. Investigate
79whether it would be feasible to give the harness script the B<option> of
80running sets of tests in parallel. This would be useful for tests in
81F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
82
83Questions to answer
84
85=over 4
86
87=item 1
88
89How does screen layout work when you're running more than one test?
90
91=item 2
92
93How does the caller of test specify how many tests to run in parallel?
94
95=item 3
96
97How do setup/teardown tests identify themselves?
98
99=back
100
101Pugs already does parallel testing - can their approach be re-used?
102
0bdfc961 103=head2 Make Schwern poorer
e50bb9a1 104
613bd4f7 105We should have tests for everything. When all the core's modules are tested,
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106Schwern has promised to donate to $500 to TPF. We may need volunteers to
107hold him upside down and shake vigorously in order to actually extract the
108cash.
3958b146 109
0bdfc961 110=head2 Improve the coverage of the core tests
e50bb9a1 111
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112Use Devel::Cover to ascertain the core modules's test coverage, then add
113tests that are currently missing.
30222c0f 114
0bdfc961 115=head2 test B
e50bb9a1 116
0bdfc961 117A full test suite for the B module would be nice.
e50bb9a1 118
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119=head2 Deparse inlined constants
120
121Code such as this
122
123 use constant PI => 4;
124 warn PI
125
126will currently deparse as
127
128 use constant ('PI', 4);
129 warn 4;
130
131because the tokenizer inlines the value of the constant subroutine C<PI>.
132This allows various compile time optimisations, such as constant folding
133and dead code elimination. Where these haven't happened (such as the example
134above) it ought be possible to make B::Deparse work out the name of the
135original constant, because just enough information survives in the symbol
136table to do this. Specifically, the same scalar is used for the constant in
137the optree as is used for the constant subroutine, so by iterating over all
138symbol tables and generating a mapping of SV address to constant name, it
139would be possible to provide B::Deparse with this functionality.
140
0bdfc961 141=head2 A decent benchmark
e50bb9a1 142
617eabfa 143C<perlbench> seems impervious to any recent changes made to the perl core. It
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144would be useful to have a reasonable general benchmarking suite that roughly
145represented what current perl programs do, and measurably reported whether
146tweaks to the core improve, degrade or don't really affect performance, to
147guide people attempting to optimise the guts of perl. Gisle would welcome
148new tests for perlbench.
6168cf99 149
0bdfc961 150=head2 fix tainting bugs
6168cf99 151
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152Fix the bugs revealed by running the test suite with the C<-t> switch (via
153C<make test.taintwarn>).
e50bb9a1 154
0bdfc961 155=head2 Dual life everything
e50bb9a1 156
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157As part of the "dists" plan, anything that doesn't belong in the smallest perl
158distribution needs to be dual lifed. Anything else can be too. Figure out what
159changes would be needed to package that module and its tests up for CPAN, and
160do so. Test it with older perl releases, and fix the problems you find.
e50bb9a1 161
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162To make a minimal perl distribution, it's useful to look at
163F<t/lib/commonsense.t>.
164
0bdfc961 165=head2 Improving C<threads::shared>
722d2a37 166
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167Investigate whether C<threads::shared> could share aggregates properly with
168only Perl level changes to shared.pm
722d2a37 169
0bdfc961 170=head2 POSIX memory footprint
e50bb9a1 171
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172Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
173various times worked to cut it down. There is probably still fat to cut out -
174for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 175
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176=head2 embed.pl/makedef.pl
177
178There is a script F<embed.pl> that generates several header files to prefix
179all of Perl's symbols in a consistent way, to provide some semblance of
180namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
907b3e23 181in F<interpvar.h>. Quite a few of the functions and variables
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182are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
183doesn't understand the C macros, so the rules about which symbols are present
184when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
185It would be good to teach C<embed.pl> to understand the conditional
186compilation, and hence remove the duplication, and the mistakes it has caused.
e50bb9a1 187
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188=head2 use strict; and AutoLoad
189
190Currently if you write
191
192 package Whack;
193 use AutoLoader 'AUTOLOAD';
194 use strict;
195 1;
196 __END__
197 sub bloop {
198 print join (' ', No, strict, here), "!\n";
199 }
200
201then C<use strict;> isn't in force within the autoloaded subroutines. It would
202be more consistent (and less surprising) to arrange for all lexical pragmas
203in force at the __END__ block to be in force within each autoloaded subroutine.
204
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205There's a similar problem with SelfLoader.
206
0bdfc961 207=head1 Tasks that need a little sysadmin-type knowledge
e50bb9a1 208
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209Or if you prefer, tasks that you would learn from, and broaden your skills
210base...
e50bb9a1 211
cd793d32 212=head2 make HTML install work
e50bb9a1 213
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214There is an C<installhtml> target in the Makefile. It's marked as
215"experimental". It would be good to get this tested, make it work reliably, and
216remove the "experimental" tag. This would include
217
218=over 4
219
220=item 1
221
222Checking that cross linking between various parts of the documentation works.
223In particular that links work between the modules (files with POD in F<lib/>)
224and the core documentation (files in F<pod/>)
225
226=item 2
227
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228Work out how to split C<perlfunc> into chunks, preferably one per function
229group, preferably with general case code that could be used elsewhere.
230Challenges here are correctly identifying the groups of functions that go
231together, and making the right named external cross-links point to the right
232page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
233C<endservent>, two or more C<=items> giving the different parameter lists, such
234as
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235
236 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
adebf063 237 =item substr EXPR,OFFSET,LENGTH
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238 =item substr EXPR,OFFSET
239
240and different parameter lists having different meanings. (eg C<select>)
241
242=back
3a89a73c 243
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244=head2 compressed man pages
245
246Be able to install them. This would probably need a configure test to see how
247the system does compressed man pages (same directory/different directory?
248same filename/different filename), as well as tweaking the F<installman> script
249to compress as necessary.
250
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251=head2 Add a code coverage target to the Makefile
252
253Make it easy for anyone to run Devel::Cover on the core's tests. The steps
254to do this manually are roughly
255
256=over 4
257
258=item *
259
260do a normal C<Configure>, but include Devel::Cover as a module to install
261(see F<INSTALL> for how to do this)
262
263=item *
264
265 make perl
266
267=item *
268
269 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
270
271=item *
272
273Process the resulting Devel::Cover database
274
275=back
276
277This just give you the coverage of the F<.pm>s. To also get the C level
278coverage you need to
279
280=over 4
281
282=item *
283
284Additionally tell C<Configure> to use the appropriate C compiler flags for
285C<gcov>
286
287=item *
288
289 make perl.gcov
290
291(instead of C<make perl>)
292
293=item *
294
295After running the tests run C<gcov> to generate all the F<.gcov> files.
296(Including down in the subdirectories of F<ext/>
297
298=item *
299
300(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
301to get their stats into the cover_db directory.
302
303=item *
304
305Then process the Devel::Cover database
306
307=back
308
309It would be good to add a single switch to C<Configure> to specify that you
310wanted to perform perl level coverage, and another to specify C level
311coverage, and have C<Configure> and the F<Makefile> do all the right things
312automatically.
313
02f21748 314=head2 Make Config.pm cope with differences between built and installed perl
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315
316Quite often vendors ship a perl binary compiled with their (pay-for)
317compilers. People install a free compiler, such as gcc. To work out how to
318build extensions, Perl interrogates C<%Config>, so in this situation
319C<%Config> describes compilers that aren't there, and extension building
320fails. This forces people into choosing between re-compiling perl themselves
321using the compiler they have, or only using modules that the vendor ships.
322
323It would be good to find a way teach C<Config.pm> about the installation setup,
324possibly involving probing at install time or later, so that the C<%Config> in
325a binary distribution better describes the installed machine, when the
326installed machine differs from the build machine in some significant way.
327
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328=head2 linker specification files
329
330Some platforms mandate that you provide a list of a shared library's external
331symbols to the linker, so the core already has the infrastructure in place to
332do this for generating shared perl libraries. My understanding is that the
333GNU toolchain can accept an optional linker specification file, and restrict
334visibility just to symbols declared in that file. It would be good to extend
335F<makedef.pl> to support this format, and to provide a means within
336C<Configure> to enable it. This would allow Unix users to test that the
337export list is correct, and to build a perl that does not pollute the global
338namespace with private symbols.
339
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340=head2 Cross-compile support
341
342Currently C<Configure> understands C<-Dusecrosscompile> option. This option
343arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
344assumed then to be copied to TARGET machine and used as a replacement of full
345C<perl> executable.
346
d1307786 347This could be done little differently. Namely C<miniperl> should be built for
a229ae3b 348HOST and then full C<perl> with extensions should be compiled for TARGET.
d1307786 349This, however, might require extra trickery for %Config: we have one config
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350first for HOST and then another for TARGET. Tools like MakeMaker will be
351mightily confused. Having around two different types of executables and
352libraries (HOST and TARGET) makes life interesting for Makefiles and
353shell (and Perl) scripts. There is $Config{run}, normally empty, which
354can be used as an execution wrapper. Also note that in some
355cross-compilation/execution environments the HOST and the TARGET do
356not see the same filesystem(s), the $Config{run} may need to do some
357file/directory copying back and forth.
0bdfc961 358
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359=head2 roffitall
360
361Make F<pod/roffitall> be updated by F<pod/buildtoc>.
362
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363=head1 Tasks that need a little C knowledge
364
365These tasks would need a little C knowledge, but don't need any specific
366background or experience with XS, or how the Perl interpreter works
367
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368=head2 Weed out needless PERL_UNUSED_ARG
369
370The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
371unused arguments. Often the arguments can't be removed, as there is an
372external constraint that determines the prototype of the function, so this
373approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
374could be removed. Specifically
375
376=over 4
377
378=item *
379
380The prototypes of (nearly all) static functions can be changed
381
382=item *
383
384Unused arguments generated by short cut macros are wasteful - the short cut
385macro used can be changed.
386
387=back
388
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389=head2 Modernize the order of directories in @INC
390
391The way @INC is laid out by default, one cannot upgrade core (dual-life)
392modules without overwriting files. This causes problems for binary
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393package builders. One possible proposal is laid out in this
394message:
395L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
fbf638cb 396
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397=head2 -Duse32bit*
398
399Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
400On these systems, it might be the default compilation mode, and there
401is currently no guarantee that passing no use64bitall option to the
402Configure process will build a 32bit perl. Implementing -Duse32bit*
403options would be nice for perl 5.12.
404
0bdfc961 405=head2 Make it clear from -v if this is the exact official release
89007cb3 406
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407Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
408usually defines one local patch, of the form "MAINT12345" or "RC1". The output
409of perl -v doesn't report that a perl isn't an official release, and this
89007cb3 410information can get lost in bugs reports. Because of this, the minor version
fa11829f 411isn't bumped up until RC time, to minimise the possibility of versions of perl
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412escaping that believe themselves to be newer than they actually are.
413
414It would be useful to find an elegant way to have the "this is an interim
415maintenance release" or "this is a release candidate" in the terse -v output,
416and have it so that it's easy for the pumpking to remove this just as the
417release tarball is rolled up. This way the version pulled out of rsync would
418always say "I'm a development release" and it would be safe to bump the
419reported minor version as soon as a release ships, which would aid perl
420developers.
421
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422This task is really about thinking of an elegant way to arrange the C source
423such that it's trivial for the Pumpking to flag "this is an official release"
424when making a tarball, yet leave the default source saying "I'm not the
425official release".
426
fee0a0f7 427=head2 Profile Perl - am I hot or not?
62403a3c 428
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429The Perl source code is stable enough that it makes sense to profile it,
430identify and optimise the hotspots. It would be good to measure the
431performance of the Perl interpreter using free tools such as cachegrind,
432gprof, and dtrace, and work to reduce the bottlenecks they reveal.
433
434As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
435the ops that are most commonly used. The idea is that by grouping them, their
436object code will be adjacent in the executable, so they have a greater chance
437of already being in the CPU cache (or swapped in) due to being near another op
438already in use.
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439
440Except that it's not clear if these really are the most commonly used ops. So
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441as part of exercising your skills with coverage and profiling tools you might
442want to determine what ops I<really> are the most commonly used. And in turn
443suggest evictions and promotions to achieve a better F<pp_hot.c>.
62403a3c 444
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445=head2 Allocate OPs from arenas
446
447Currently all new OP structures are individually malloc()ed and free()d.
448All C<malloc> implementations have space overheads, and are now as fast as
449custom allocates so it would both use less memory and less CPU to allocate
450the various OP structures from arenas. The SV arena code can probably be
451re-used for this.
452
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453Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
454Perl_Slab_alloc() to pack optrees into a contiguous block, which is
455probably superior to the use of OP arenas, esp. from a cache locality
456standpoint. See L<Profile Perl - am I hot or not?>.
457
a229ae3b 458=head2 Improve win32/wince.c
0bdfc961 459
a229ae3b 460Currently, numerous functions look virtually, if not completely,
02f21748 461identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
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462be good.
463
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464=head2 Use secure CRT functions when building with VC8 on Win32
465
466Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
467that they were "unsafe" and introduced differently named secure versions of
468them as replacements, e.g. instead of writing
469
470 FILE* f = fopen(__FILE__, "r");
471
472one should now write
473
474 FILE* f;
475 errno_t err = fopen_s(&f, __FILE__, "r");
476
477Currently, the warnings about these deprecations have been disabled by adding
478-D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
479warning suppressant and actually make use of the new secure CRT functions.
480
481There is also a similar issue with POSIX CRT function names like fileno having
482been deprecated in favour of ISO C++ conformant names like _fileno. These
26a6faa8 483warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
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484might be nice to do as Microsoft suggest here too, although, unlike the secure
485functions issue, there is presumably little or no benefit in this case.
486
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487=head2 Fix POSIX::access() and chdir() on Win32
488
489These functions currently take no account of DACLs and therefore do not behave
490correctly in situations where access is restricted by DACLs (as opposed to the
491read-only attribute).
492
493Furthermore, POSIX::access() behaves differently for directories having the
494read-only attribute set depending on what CRT library is being used. For
495example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
496such directories are not writable, whereas in fact all directories are writable
497unless access is denied by DACLs. (In the case of directories, the read-only
498attribute actually only means that the directory cannot be deleted.) This CRT
499bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
500not actually be writable if access is indeed denied by DACLs).
501
502For the chdir() issue, see ActiveState bug #74552:
503http://bugs.activestate.com/show_bug.cgi?id=74552
504
505Therefore, DACLs should be checked both for consistency across CRTs and for
506the correct answer.
507
508(Note that perl's -w operator should not be modified to check DACLs. It has
509been written so that it reflects the state of the read-only attribute, even
510for directories (whatever CRT is being used), for symmetry with chmod().)
511
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512=head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
513
514Maybe create a utility that checks after each libperl.a creation that
515none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
516ever creep back to libperl.a.
517
518 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
519
520Note, of course, that this will only tell whether B<your> platform
521is using those naughty interfaces.
522
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523=head2 -D_FORTIFY_SOURCE=2, -fstack-protector
524
525Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
526(4.1 onwards?) supports C<-fstack-protector>, both of which give
527protection against various kinds of buffer overflow problems.
528These should probably be used for compiling Perl whenever available,
529Configure and/or hints files should be adjusted to probe for the
530availability of these features and enable them as appropriate.
16815324 531
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532=head2 Arenas for GPs? For MAGIC?
533
534C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
535It might be a speed or memory saving to change to using arenas. Or it might
536not. It would need some suitable benchmarking first. In particular, C<GP>s
537can probably be changed with minimal compatibility impact (probably nothing
538outside of the core, or even outside of F<gv.c> allocates them), but they
539probably aren't allocated/deallocated often enough for a speed saving. Whereas
540C<MAGIC> is allocated/deallocated more often, but in turn, is also something
541more externally visible, so changing the rules here may bite external code.
542
543
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544=head1 Tasks that need a knowledge of XS
545
546These tasks would need C knowledge, and roughly the level of knowledge of
547the perl API that comes from writing modules that use XS to interface to
548C.
549
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550=head2 autovivification
551
552Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
553
554This task is incremental - even a little bit of work on it will help.
555
556=head2 Unicode in Filenames
557
558chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
559opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
560system, truncate, unlink, utime, -X. All these could potentially accept
561Unicode filenames either as input or output (and in the case of system
562and qx Unicode in general, as input or output to/from the shell).
563Whether a filesystem - an operating system pair understands Unicode in
564filenames varies.
565
566Known combinations that have some level of understanding include
567Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
568OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
569create Unicode filenames, what forms of Unicode are accepted and used
570(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
571and so on, varies. Finding the right level of interfacing to Perl
572requires some thought. Remember that an OS does not implicate a
573filesystem.
574
575(The Windows -C command flag "wide API support" has been at least
576temporarily retired in 5.8.1, and the -C has been repurposed, see
577L<perlrun>.)
578
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579Most probably the right way to do this would be this:
580L</"Virtualize operating system access">.
581
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582=head2 Unicode in %ENV
583
584Currently the %ENV entries are always byte strings.
87a942b1 585See L</"Virtualize operating system access">.
6d71adcd 586
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587=head2 Unicode and glob()
588
589Currently glob patterns and filenames returned from File::Glob::glob()
87a942b1 590are always byte strings. See L</"Virtualize operating system access">.
1f2e7916 591
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592=head2 Unicode and lc/uc operators
593
594Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
595what the internal encoding of their argument is. That should not be the
596case. Maybe add a pragma to switch behaviour.
597
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598=head2 use less 'memory'
599
600Investigate trade offs to switch out perl's choices on memory usage.
601Particularly perl should be able to give memory back.
602
603This task is incremental - even a little bit of work on it will help.
604
605=head2 Re-implement C<:unique> in a way that is actually thread-safe
606
607The old implementation made bad assumptions on several levels. A good 90%
608solution might be just to make C<:unique> work to share the string buffer
609of SvPVs. That way large constant strings can be shared between ithreads,
610such as the configuration information in F<Config>.
611
612=head2 Make tainting consistent
613
614Tainting would be easier to use if it didn't take documented shortcuts and
615allow taint to "leak" everywhere within an expression.
616
617=head2 readpipe(LIST)
618
619system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
620running a shell. readpipe() (the function behind qx//) could be similarly
621extended.
622
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623=head2 Audit the code for destruction ordering assumptions
624
625Change 25773 notes
626
627 /* Need to check SvMAGICAL, as during global destruction it may be that
628 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
629 is now part of the linked list of SV heads, rather than pointing to
630 the original body. */
631 /* FIXME - audit the code for other bugs like this one. */
632
633adding the C<SvMAGICAL> check to
634
635 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
636 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
637
638Go through the core and look for similar assumptions that SVs have particular
639types, as all bets are off during global destruction.
640
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641=head2 Extend PerlIO and PerlIO::Scalar
642
643PerlIO::Scalar doesn't know how to truncate(). Implementing this
644would require extending the PerlIO vtable.
645
646Similarly the PerlIO vtable doesn't know about formats (write()), or
647about stat(), or chmod()/chown(), utime(), or flock().
648
649(For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
650would mean.)
651
652PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
653opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
654readlink().
655
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656See also L</"Virtualize operating system access">.
657
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658=head2 -C on the #! line
659
660It should be possible to make -C work correctly if found on the #! line,
661given that all perl command line options are strict ASCII, and -C changes
662only the interpretation of non-ASCII characters, and not for the script file
663handle. To make it work needs some investigation of the ordering of function
664calls during startup, and (by implication) a bit of tweaking of that order.
665
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666=head2 Propagate const outwards from Perl_moreswitches()
667
668Change 32057 changed the parameter and return value of C<Perl_moreswitches()>
669from <char *> to <const char *>. It should now be possible to propagate
670const-correctness outwards to C<S_parse_body()>, C<Perl_moreswitches()>
671and C<Perl_yylex()>.
672
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673=head2 Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload()
674
675A comment in C<S_method_common> notes
676
677 /* This code tries to figure out just what went wrong with
678 gv_fetchmethod. It therefore needs to duplicate a lot of
679 the internals of that function. We can't move it inside
680 Perl_gv_fetchmethod_autoload(), however, since that would
681 cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we
682 don't want that.
683 */
684
685If C<Perl_gv_fetchmethod_autoload> gets rewritten to take (more) flag bits,
686then it ought to be possible to move the logic from C<S_method_common> to
687the "right" place. When making this change it would probably be good to also
688pass in at least the method name length, if not also pre-computed hash values
689when known. (I'm contemplating a plan to pre-compute hash values for common
690fixed strings such as C<ISA> and pass them in to functions.)
691
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692=head2 Organize error messages
693
694Perl's diagnostics (error messages, see L<perldiag>) could use
a8d0aeb9 695reorganizing and formalizing so that each error message has its
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696stable-for-all-eternity unique id, categorized by severity, type, and
697subsystem. (The error messages would be listed in a datafile outside
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698of the Perl source code, and the source code would only refer to the
699messages by the id.) This clean-up and regularizing should apply
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700for all croak() messages.
701
702This would enable all sorts of things: easier translation/localization
703of the messages (though please do keep in mind the caveats of
704L<Locale::Maketext> about too straightforward approaches to
705translation), filtering by severity, and instead of grepping for a
706particular error message one could look for a stable error id. (Of
707course, changing the error messages by default would break all the
708existing software depending on some particular error message...)
709
710This kind of functionality is known as I<message catalogs>. Look for
711inspiration for example in the catgets() system, possibly even use it
712if available-- but B<only> if available, all platforms will B<not>
de96509d 713have catgets().
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714
715For the really pure at heart, consider extending this item to cover
716also the warning messages (see L<perllexwarn>, C<warnings.pl>).
3236f110 717
0bdfc961 718=head1 Tasks that need a knowledge of the interpreter
3298bd4d 719
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720These tasks would need C knowledge, and knowledge of how the interpreter works,
721or a willingness to learn.
3298bd4d 722
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723=head2 lexicals used only once
724
725This warns:
726
727 $ perl -we '$pie = 42'
728 Name "main::pie" used only once: possible typo at -e line 1.
729
730This does not:
731
732 $ perl -we 'my $pie = 42'
733
734Logically all lexicals used only once should warn, if the user asks for
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SP
735warnings. An unworked RT ticket (#5087) has been open for almost seven
736years for this discrepancy.
718140ec 737
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RGS
738=head2 UTF-8 revamp
739
740The handling of Unicode is unclean in many places. For example, the regexp
741engine matches in Unicode semantics whenever the string or the pattern is
742flagged as UTF-8, but that should not be dependent on an internal storage
743detail of the string. Likewise, case folding behaviour is dependent on the
744UTF8 internal flag being on or off.
745
746=head2 Properly Unicode safe tokeniser and pads.
747
748The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
749variable names are stored in stashes as raw bytes, without the utf-8 flag
750set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
751tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
752source filters. All this could be fixed.
753
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754=head2 state variable initialization in list context
755
756Currently this is illegal:
757
758 state ($a, $b) = foo();
759
a2874905 760In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
a8d0aeb9 761semantics, which is tricky to implement in Perl 5 as currently they produce
a2874905 762the same opcode trees. The Perl 6 design is firm, so it would be good to
a8d0aeb9 763implement the necessary code in Perl 5. There are comments in
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764C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
765constructions involving state variables.
636e63cb 766
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767=head2 Implement $value ~~ 0 .. $range
768
769It would be nice to extend the syntax of the C<~~> operator to also
770understand numeric (and maybe alphanumeric) ranges.
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RGS
771
772=head2 A does() built-in
773
774Like ref(), only useful. It would call the C<DOES> method on objects; it
775would also tell whether something can be dereferenced as an
776array/hash/etc., or used as a regexp, etc.
777L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
778
779=head2 Tied filehandles and write() don't mix
780
781There is no method on tied filehandles to allow them to be called back by
782formats.
4fedb12c 783
d10fc472 784=head2 Attach/detach debugger from running program
1626a787 785
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786The old perltodo notes "With C<gdb>, you can attach the debugger to a running
787program if you pass the process ID. It would be good to do this with the Perl
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788debugger on a running Perl program, although I'm not sure how it would be
789done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
1626a787 790
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791=head2 Optimize away empty destructors
792
793Defining an empty DESTROY method might be useful (notably in
794AUTOLOAD-enabled classes), but it's still a bit expensive to call. That
795could probably be optimized.
796
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797=head2 LVALUE functions for lists
798
799The old perltodo notes that lvalue functions don't work for list or hash
800slices. This would be good to fix.
801
802=head2 LVALUE functions in the debugger
803
804The old perltodo notes that lvalue functions don't work in the debugger. This
805would be good to fix.
806
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807=head2 regexp optimiser optional
808
809The regexp optimiser is not optional. It should configurable to be, to allow
810its performance to be measured, and its bugs to be easily demonstrated.
811
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812=head2 delete &function
813
814Allow to delete functions. One can already undef them, but they're still
815in the stash.
816
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817=head2 C</w> regex modifier
818
819That flag would enable to match whole words, and also to interpolate
820arrays as alternations. With it, C</P/w> would be roughly equivalent to:
821
822 do { local $"='|'; /\b(?:P)\b/ }
823
824See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
825for the discussion.
826
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827=head2 optional optimizer
828
829Make the peephole optimizer optional. Currently it performs two tasks as
830it walks the optree - genuine peephole optimisations, and necessary fixups of
831ops. It would be good to find an efficient way to switch out the
832optimisations whilst keeping the fixups.
833
834=head2 You WANT *how* many
835
836Currently contexts are void, scalar and list. split has a special mechanism in
837place to pass in the number of return values wanted. It would be useful to
838have a general mechanism for this, backwards compatible and little speed hit.
839This would allow proposals such as short circuiting sort to be implemented
840as a module on CPAN.
841
842=head2 lexical aliases
843
844Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
845
846=head2 entersub XS vs Perl
847
848At the moment pp_entersub is huge, and has code to deal with entering both
849perl and XS subroutines. Subroutine implementations rarely change between
850perl and XS at run time, so investigate using 2 ops to enter subs (one for
851XS, one for perl) and swap between if a sub is redefined.
2810d901 852
de535794 853=head2 Self-ties
2810d901 854
de535794 855Self-ties are currently illegal because they caused too many segfaults. Maybe
a8d0aeb9 856the causes of these could be tracked down and self-ties on all types
de535794 857reinstated.
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858
859=head2 Optimize away @_
860
861The old perltodo notes "Look at the "reification" code in C<av.c>".
862
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863=head2 The yada yada yada operators
864
865Perl 6's Synopsis 3 says:
866
867I<The ... operator is the "yada, yada, yada" list operator, which is used as
868the body in function prototypes. It complains bitterly (by calling fail)
869if it is ever executed. Variant ??? calls warn, and !!! calls die.>
870
871Those would be nice to add to Perl 5. That could be done without new ops.
872
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873=head2 Virtualize operating system access
874
875Implement a set of "vtables" that virtualizes operating system access
876(open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
877least these interfaces should take SVs as "name" arguments instead of
878bare char pointers; probably the most flexible and extensible way
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879would be for the Perl-facing interfaces to accept HVs. The system
880needs to be per-operating-system and per-file-system
881hookable/filterable, preferably both from XS and Perl level
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882(L<perlport/"Files and Filesystems"> is good reading at this point,
883in fact, all of L<perlport> is.)
884
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885This has actually already been implemented (but only for Win32),
886take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
887variants go through a set of "vtables" for operating system access,
888non-Win32 systems currently go straight for the POSIX/UNIX-style
889system/library call. Similar system as for Win32 should be
890implemented for all platforms. The existing Win32 implementation
891probably does not need to survive alongside this proposed new
892implementation, the approaches could be merged.
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893
894What would this give us? One often-asked-for feature this would
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895enable is using Unicode for filenames, and other "names" like %ENV,
896usernames, hostnames, and so forth.
897(See L<perlunicode/"When Unicode Does Not Happen">.)
898
899But this kind of virtualization would also allow for things like
900virtual filesystems, virtual networks, and "sandboxes" (though as long
901as dynamic loading of random object code is allowed, not very safe
902sandboxes since external code of course know not of Perl's vtables).
903An example of a smaller "sandbox" is that this feature can be used to
904implement per-thread working directories: Win32 already does this.
905
906See also L</"Extend PerlIO and PerlIO::Scalar">.
87a942b1 907
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908=head2 Investigate PADTMP hash pessimisation
909
910The peephole optimier converts constants used for hash key lookups to shared
911hash key scalars. Under ithreads, something is undoing this work. See
912See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html
913
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914=head1 Big projects
915
916Tasks that will get your name mentioned in the description of the "Highlights
87a942b1 917of 5.12"
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918
919=head2 make ithreads more robust
920
4e577f8b 921Generally make ithreads more robust. See also L</iCOW>
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922
923This task is incremental - even a little bit of work on it will help, and
924will be greatly appreciated.
925
6c047da7
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926One bit would be to write the missing code in sv.c:Perl_dirp_dup.
927
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RGS
928Fix Perl_sv_dup, et al so that threads can return objects.
929
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930=head2 iCOW
931
932Sarathy and Arthur have a proposal for an improved Copy On Write which
933specifically will be able to COW new ithreads. If this can be implemented
934it would be a good thing.
935
936=head2 (?{...}) closures in regexps
937
938Fix (or rewrite) the implementation of the C</(?{...})/> closures.
939
940=head2 A re-entrant regexp engine
941
942This will allow the use of a regex from inside (?{ }), (??{ }) and
943(?(?{ })|) constructs.
6bda09f9 944
6bda09f9
YO
945=head2 Add class set operations to regexp engine
946
947Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
948
949demerphq has this on his todo list, but right at the bottom.