X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperltodo.pod;h=a16cf0d604adff14905f09dfc0f43ed39d2aacd2;hb=c1c4ae3a961df5aa9544fb76ce5c1d031b6f0dd5;hp=0c85ceb1ce0e5033d1aa4ac4238b3e7c5f9ca8af;hpb=de5357942a5c1ad0c651e7d2ce26b08c92cd7a61;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perltodo.pod b/pod/perltodo.pod index 0c85ceb..a16cf0d 100644 --- a/pod/perltodo.pod +++ b/pod/perltodo.pod @@ -4,10 +4,14 @@ perltodo - Perl TO-DO List =head1 DESCRIPTION -This is a list of wishes for Perl. The tasks we think are smaller or easier -are listed first. Anyone is welcome to work on any of these, but it's a good -idea to first contact I to avoid duplication of -effort. By all means contact a pumpking privately first if you prefer. +This is a list of wishes for Perl. The most up to date version of this file +is at http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod + +The tasks we think are smaller or easier are listed first. Anyone is welcome +to work on any of these, but it's a good idea to first contact +I to avoid duplication of effort, and to learn from +any previous attempts. By all means contact a pumpking privately first if you +prefer. Whilst patches to make the list shorter are most welcome, ideas to add to the list are also encouraged. Check the perl5-porters archives for past @@ -22,83 +26,89 @@ programming languages offer you 1 line of immortality? =head1 Tasks that only need Perl knowledge -=head2 Remove duplication of test setup. +=head2 Improve Porting/cmpVERSION.pl to work from git tags -Schwern notes, that there's duplication of code - lots and lots of tests have -some variation on the big block of C<$Is_Foo> checks. We can safely put this -into a file, change it to build an C<%Is> hash and require it. Maybe just put -it into F. Throw in the handy tainting subroutines. +See F for a bit more detail. -=head2 merge common code in installperl and installman +=head2 Migrate t/ from custom TAP generation -There are some common subroutines and a common C block in F -and F. These should probably be merged. It would also be good to -check for duplication in all the utility scripts supplied in the source -tarball. It might be good to move them all to a subdirectory, but this would -require careful checking to find all places that call them, and change those -correctly. +Many tests below F still generate TAP by "hand", rather than using library +functions. As explained in L, tests in F are +written in a particular way to test that more complex constructions actually +work before using them routinely. Hence they don't use C, but +instead there is an intentionally simpler library, F. However, +quite a few tests in F have not been refactored to use it. Refactoring +any of these tests, one at a time, is a useful thing TODO. -=head2 common test code for timed bail out +The subdirectories F, F and F, that contain the most +basic tests, should be excluded from this task. -Write portable self destruct code for tests to stop them burning CPU in -infinite loops. This needs to avoid using alarm, as some of the tests are -testing alarm/sleep or timers. +=head2 Test that regen.pl was run -=head2 POD -E HTML conversion in the core still sucks +There are various generated files shipped with the perl distribution, for +things like header files generate from data. The generation scripts are +written in perl, and all can be run by F. However, because they're +written in perl, we can't run them before we've built perl. We can't run them +as part of the F, because changing files underneath F confuses +it completely, and we don't want to run them automatically anyway, as they +change files shipped by the distribution, something we seek not do to. -Which is crazy given just how simple POD purports to be, and how simple HTML -can be. It's not actually I simple as it sounds, particularly with the -flexibility POD allows for C<=item>, but it would be good to improve the -visual appeal of the HTML generated, and to avoid it having any validation -errors. See also L, as the layout of installation tree -is needed to improve the cross-linking. +If someone changes the data, but forgets to re-run F then the +generated files are out of sync. It would be good to have a test in +F that checks that the generated files are in sync, and fails +otherwise, to alert someone before they make a poor commit. I suspect that this +would require adapting the scripts run from F to have dry-run +options, and invoking them with these, or by refactoring them into a library +that does the generation, which can be called by the scripts, and by the test. -The addition of C and its related modules may make this task -easier to complete. +=head2 Automate perldelta generation -=head2 merge checkpods and podchecker +The perldelta file accompanying each release summaries the major changes. +It's mostly manually generated currently, but some of that could be +automated with a bit of perl, specifically the generation of -F (and C in the F subdirectory) -implements a very basic check for pod files, but the errors it discovers -aren't found by podchecker. Add this check to podchecker, get rid of -checkpods and have C use podchecker. +=over -=head2 perlmodlib.PL rewrite +=item Modules and Pragmata -Currently perlmodlib.PL needs to be run from a source directory where perl -has been built, or some modules won't be found, and others will be -skipped. Make it run from a clean perl source tree (so it's reproducible). +=item New Documentation -=head2 Parallel testing +=item New Tests -(This probably impacts much more than the core: also the Test::Harness -and TAP::* modules on CPAN.) +=back -The core regression test suite is getting ever more comprehensive, which has -the side effect that it takes longer to run. This isn't so good. Investigate -whether it would be feasible to give the harness script the B, as the layout of installation tree +is needed to improve the cross-linking. -=item 2 +The addition of C and its related modules may make this task +easier to complete. -How does the caller of test specify how many tests to run in parallel? +=head2 Make ExtUtils::ParseXS use strict; -=item 3 +F contains this line -How do setup/teardown tests identify themselves? + # use strict; # One of these days... -=back +Simply uncomment it, and fix all the resulting issues :-) -Pugs already does parallel testing - can their approach be re-used? +The more practical approach, to break the task down into manageable chunks, is +to work your way though the code from bottom to top, or if necessary adding +extra C<{ ... }> blocks, and turning on strict within them. =head2 Make Schwern poorer @@ -109,35 +119,13 @@ cash. =head2 Improve the coverage of the core tests -Use Devel::Cover to ascertain the core modules's test coverage, then add +Use Devel::Cover to ascertain the core modules' test coverage, then add tests that are currently missing. =head2 test B A full test suite for the B module would be nice. -=head2 Deparse inlined constants - -Code such as this - - use constant PI => 4; - warn PI - -will currently deparse as - - use constant ('PI', 4); - warn 4; - -because the tokenizer inlines the value of the constant subroutine C. -This allows various compile time optimisations, such as constant folding -and dead code elimination. Where these haven't happened (such as the example -above) it ought be possible to make B::Deparse work out the name of the -original constant, because just enough information survives in the symbol -table to do this. Specifically, the same scalar is used for the constant in -the optree as is used for the constant subroutine, so by iterating over all -symbol tables and generating a mapping of SV address to constant name, it -would be possible to provide B::Deparse with this functionality. - =head2 A decent benchmark C seems impervious to any recent changes made to the perl core. It @@ -162,10 +150,13 @@ do so. Test it with older perl releases, and fix the problems you find. To make a minimal perl distribution, it's useful to look at F. -=head2 Improving C +=head2 Move dual-life pod/*.PL into ext -Investigate whether C could share aggregates properly with -only Perl level changes to shared.pm +Nearly all the dual-life modules have been moved to F. However, we +still need to move F into their respective directories +in F. They're referenced by (at least) C in F +and C in F and F, and listed +explicitly in F, F and F =head2 POSIX memory footprint @@ -204,6 +195,18 @@ in force at the __END__ block to be in force within each autoloaded subroutine. There's a similar problem with SelfLoader. +=head2 profile installman + +The F script is slow. All it is doing text processing, which we're +told is something Perl is good at. So it would be nice to know what it is doing +that is taking so much CPU, and where possible address it. + +=head2 enable lexical enabling/disabling of inidvidual warnings + +Currently, warnings can only be enabled or disabled by category. There +are times when it would be useful to quash a single warning, not a +whole category. + =head1 Tasks that need a little sysadmin-type knowledge Or if you prefer, tasks that you would learn from, and broaden your skills @@ -360,15 +363,102 @@ file/directory copying back and forth. Make F be updated by F. +=head2 Split "linker" from "compiler" + +Right now, Configure probes for two commands, and sets two variables: + +=over 4 + +=item * C (in F) + +This variable holds the name of a command to execute a C compiler which +can resolve multiple global references that happen to have the same +name. Usual values are F and F. +Fervent ANSI compilers may be called F. AIX has F. + +=item * C (in F) + +This variable indicates the program to be used to link +libraries for dynamic loading. On some systems, it is F. +On ELF systems, it should be C<$cc>. Mostly, we'll try to respect +the hint file setting. + +=back + +There is an implicit historical assumption from around Perl5.000alpha +something, that C<$cc> is also the correct command for linking object files +together to make an executable. This may be true on Unix, but it's not true +on other platforms, and there are a maze of work arounds in other places (such +as F) to cope with this. + +Ideally, we should create a new variable to hold the name of the executable +linker program, probe for it in F, and centralise all the special +case logic there or in hints files. + +A small bikeshed issue remains - what to call it, given that C<$ld> is already +taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command +for creating dynamically-loadable modules) and C<$link> could be confused with +the Unix command line executable of the same name, which does something +completely different. Andy Dougherty makes the counter argument "In parrot, I +tried to call the command used to link object files and libraries into an +executable F, since that's what my vaguely-remembered DOS and VMS +experience suggested. I don't think any real confusion has ensued, so it's +probably a reasonable name for perl5 to use." + +"Alas, I've always worried that introducing it would make things worse, +since now the module building utilities would have to look for +C<$Config{link}> and institute a fall-back plan if it weren't found." +Although I can see that as confusing, given that C<$Config{d_link}> is true +when (hard) links are available. + +=head2 Configure Windows using PowerShell + +Currently, Windows uses hard-coded config files based to build the +config.h for compiling Perl. Makefiles are also hard-coded and need to be +hand edited prior to building Perl. While this makes it easy to create a perl.exe +that works across multiple Windows versions, being able to accurately +configure a perl.exe for a specific Windows versions and VS C++ would be +a nice enhancement. With PowerShell available on Windows XP and up, this +may now be possible. Step 1 might be to investigate whether this is possible +and use this to clean up our current makefile situation. Step 2 would be to +see if there would be a way to use our existing metaconfig units to configure a +Windows Perl or whether we go in a separate direction and make it so. Of +course, we all know what step 3 is. + +=head2 decouple -g and -DDEBUGGING + +Currently F automatically adds C<-DDEBUGGING> to the C compiler +flags if it spots C<-g> in the optimiser flags. The pre-processor directive +C enables F's command line C<-D> options, but in the process +makes F slower. It would be good to disentangle this logic, so that +C-level debugging with C<-g> and Perl level debugging with C<-D> can easily +be enabled independently. + =head1 Tasks that need a little C knowledge These tasks would need a little C knowledge, but don't need any specific background or experience with XS, or how the Perl interpreter works -=head2 Exterminate PL_na! +=head2 Weed out needless PERL_UNUSED_ARG + +The C code uses the macro C to stop compilers warning about +unused arguments. Often the arguments can't be removed, as there is an +external constraint that determines the prototype of the function, so this +approach is valid. However, there are some cases where C +could be removed. Specifically -C festers still in the darkest corners of various typemap files. -It needs to be exterminated, replaced by a local variable of type C. +=over 4 + +=item * + +The prototypes of (nearly all) static functions can be changed + +=item * + +Unused arguments generated by short cut macros are wasteful - the short cut +macro used can be changed. + +=back =head2 Modernize the order of directories in @INC @@ -386,28 +476,6 @@ is currently no guarantee that passing no use64bitall option to the Configure process will build a 32bit perl. Implementing -Duse32bit* options would be nice for perl 5.12. -=head2 Make it clear from -v if this is the exact official release - -Currently perl from C/C ships with a F file that -usually defines one local patch, of the form "MAINT12345" or "RC1". The output -of perl -v doesn't report that a perl isn't an official release, and this -information can get lost in bugs reports. Because of this, the minor version -isn't bumped up until RC time, to minimise the possibility of versions of perl -escaping that believe themselves to be newer than they actually are. - -It would be useful to find an elegant way to have the "this is an interim -maintenance release" or "this is a release candidate" in the terse -v output, -and have it so that it's easy for the pumpking to remove this just as the -release tarball is rolled up. This way the version pulled out of rsync would -always say "I'm a development release" and it would be safe to bump the -reported minor version as soon as a release ships, which would aid perl -developers. - -This task is really about thinking of an elegant way to arrange the C source -such that it's trivial for the Pumpking to flag "this is an official release" -when making a tarball, yet leave the default source saying "I'm not the -official release". - =head2 Profile Perl - am I hot or not? The Perl source code is stable enough that it makes sense to profile it, @@ -426,6 +494,8 @@ as part of exercising your skills with coverage and profiling tools you might want to determine what ops I are the most commonly used. And in turn suggest evictions and promotions to achieve a better F. +One piece of Perl code that might make a good testbed is F. + =head2 Allocate OPs from arenas Currently all new OP structures are individually malloc()ed and free()d. @@ -468,6 +538,31 @@ warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It might be nice to do as Microsoft suggest here too, although, unlike the secure functions issue, there is presumably little or no benefit in this case. +=head2 Fix POSIX::access() and chdir() on Win32 + +These functions currently take no account of DACLs and therefore do not behave +correctly in situations where access is restricted by DACLs (as opposed to the +read-only attribute). + +Furthermore, POSIX::access() behaves differently for directories having the +read-only attribute set depending on what CRT library is being used. For +example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that +such directories are not writable, whereas in fact all directories are writable +unless access is denied by DACLs. (In the case of directories, the read-only +attribute actually only means that the directory cannot be deleted.) This CRT +bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still +not actually be writable if access is indeed denied by DACLs). + +For the chdir() issue, see ActiveState bug #74552: +http://bugs.activestate.com/show_bug.cgi?id=74552 + +Therefore, DACLs should be checked both for consistency across CRTs and for +the correct answer. + +(Note that perl's -w operator should not be modified to check DACLs. It has +been written so that it reflects the state of the read-only attribute, even +for directories (whatever CRT is being used), for symmetry with chmod().) + =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf() Maybe create a utility that checks after each libperl.a creation that @@ -488,12 +583,202 @@ These should probably be used for compiling Perl whenever available, Configure and/or hints files should be adjusted to probe for the availability of these features and enable them as appropriate. +=head2 Arenas for GPs? For MAGIC? + +C and C are both currently allocated by C. +It might be a speed or memory saving to change to using arenas. Or it might +not. It would need some suitable benchmarking first. In particular, Cs +can probably be changed with minimal compatibility impact (probably nothing +outside of the core, or even outside of F allocates them), but they +probably aren't allocated/deallocated often enough for a speed saving. Whereas +C is allocated/deallocated more often, but in turn, is also something +more externally visible, so changing the rules here may bite external code. + +=head2 Shared arenas + +Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and +PVHV, and PVCV and PVFM. It should be possible to allocate and return same +sized bodies from the same actual arena, rather than maintaining one arena for +each. This could save 4-6K per thread, of memory no longer tied up in the +not-yet-allocated part of an arena. + + =head1 Tasks that need a knowledge of XS These tasks would need C knowledge, and roughly the level of knowledge of the perl API that comes from writing modules that use XS to interface to C. +=head2 Write an XS cookbook + +Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that +demonstrate common tasks and good practices. (Some of these might be +extracted from perlguts.) The target audience should be XS novices, who need +more examples than perlguts but something less overwhelming than perlapi. +Recipes should provide "one pretty good way to do it" instead of TIMTOWTDI. + +Rather than focusing on interfacing Perl to C libraries, such a cookbook +should probably focus on how to optimize Perl routines by re-writing them +in XS. This will likely be more motivating to those who mostly work in +Perl but are looking to take the next step into XS. + +Deconstructing and explaining some simpler XS modules could be one way to +bootstrap a cookbook. (List::Util? Class::XSAccessor? Tree::Ternary_XS?) +Another option could be deconstructing the implementation of some simpler +functions in op.c. + +=head2 Allow XSUBs to inline themselves as OPs + +For a simple XSUB, often the subroutine dispatch takes more time than the +XSUB itself. The tokeniser already has the ability to inline constant +subroutines - it would be good to provide a way to inline other subroutines. + +Specifically, simplest approach looks to be to allow an XSUB to provide an +alternative implementation of itself as a custom OP. A new flag bit in +C would signal to the peephole optimiser to take an optree +such as this: + + b <@> leave[1 ref] vKP/REFC ->(end) + 1 <0> enter ->2 + 2 <;> nextstate(main 1 -e:1) v:{ ->3 + a <2> sassign vKS/2 ->b + 8 <1> entersub[t2] sKS/TARG,1 ->9 + - <1> ex-list sK ->8 + 3 <0> pushmark s ->4 + 4 <$> const(IV 1) sM ->5 + 6 <1> rv2av[t1] lKM/1 ->7 + 5 <$> gv(*a) s ->6 + - <1> ex-rv2cv sK ->- + 7 <$> gv(*x) s/EARLYCV ->8 + - <1> ex-rv2sv sKRM*/1 ->a + 9 <$> gvsv(*b) s ->a + +perform the symbol table lookup of C and C, locate the +pointer to the custom OP that provides the direct implementation, and re- +write the optree something like: + + b <@> leave[1 ref] vKP/REFC ->(end) + 1 <0> enter ->2 + 2 <;> nextstate(main 1 -e:1) v:{ ->3 + a <2> sassign vKS/2 ->b + 7 <1> custom_x -> 8 + - <1> ex-list sK ->7 + 3 <0> pushmark s ->4 + 4 <$> const(IV 1) sM ->5 + 6 <1> rv2av[t1] lKM/1 ->7 + 5 <$> gv(*a) s ->6 + - <1> ex-rv2cv sK ->- + - <$> ex-gv(*x) s/EARLYCV ->7 + - <1> ex-rv2sv sKRM*/1 ->a + 8 <$> gvsv(*b) s ->a + +I the C OP has been nulled and spliced out of the execution +path, and the C OP has been replaced by the custom op. + +This approach should provide a measurable speed up to simple XSUBs inside +tight loops. Initially one would have to write the OP alternative +implementation by hand, but it's likely that this should be reasonably +straightforward for the type of XSUB that would benefit the most. Longer +term, once the run-time implementation is proven, it should be possible to +progressively update ExtUtils::ParseXS to generate OP implementations for +some XSUBs. + +=head2 Remove the use of SVs as temporaries in dump.c + +F contains debugging routines to dump out the contains of perl data +structures, such as Cs, Cs and Cs. Currently, the dumping code +B Cs for its temporary buffers, which was a logical initial +implementation choice, as they provide ready made memory handling. + +However, they also lead to a lot of confusion when it happens that what you're +trying to debug is seen by the code in F, correctly or incorrectly, as +a temporary scalar it can use for a temporary buffer. It's also not possible +to dump scalars before the interpreter is properly set up, such as during +ithreads cloning. It would be good to progressively replace the use of scalars +as string accumulation buffers with something much simpler, directly allocated +by C. The F code is (or should be) only producing 7 bit +US-ASCII, so output character sets are not an issue. + +Producing and proving an internal simple buffer allocation would make it easier +to re-write the internals of the PerlIO subsystem to avoid using Cs for +B buffers, use of which can cause problems similar to those of F, +at similar times. + +=head2 safely supporting POSIX SA_SIGINFO + +Some years ago Jarkko supplied patches to provide support for the POSIX +SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler. + +Unfortunately, it only works with "unsafe" signals, because under safe +signals, by the time Perl gets to run the signal handler, the extra +information has been lost. Moreover, it's not easy to store it somewhere, +as you can't call mutexs, or do anything else fancy, from inside a signal +handler. + +So it strikes me that we could provide safe SA_SIGINFO support + +=over 4 + +=item 1 + +Provide global variables for two file descriptors + +=item 2 + +When the first request is made via C for C, create a +pipe, store the reader in one, the writer in the other + +=item 3 + +In the "safe" signal handler (C/C), if +the C pointer non-C, and the writer file handle is open, + +=over 8 + +=item 1 + +serialise signal number, C (or at least the parts we care +about) into a small auto char buff + +=item 2 + +C that (non-blocking) to the writer fd + +=over 12 + +=item 1 + +if it writes 100%, flag the signal in a counter of "signals on the pipe" akin +to the current per-signal-number counts + +=item 2 + +if it writes 0%, assume the pipe is full. Flag the data as lost? + +=item 3 + +if it writes partially, croak a panic, as your OS is broken. + +=back + +=back + +=item 4 + +in the regular C processing, if there are "signals on +the pipe", read the data out, deserialise, build the Perl structures on +the stack (code in C, the "unsafe" handler), and call as +usual. + +=back + +I think that this gets us decent C support, without the current risk +of running Perl code inside the signal handler context. (With all the dangers +of things like C corruption that that currently offers us) + +For more information see the thread starting with this message: +http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html + =head2 autovivification Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; @@ -536,12 +821,6 @@ See L. Currently glob patterns and filenames returned from File::Glob::glob() are always byte strings. See L. -=head2 Unicode and lc/uc operators - -Some built-in operators (C, C, etc.) behave differently, based on -what the internal encoding of their argument is. That should not be the -case. Maybe add a pragma to switch behaviour. - =head2 use less 'memory' Investigate trade offs to switch out perl's choices on memory usage. @@ -610,32 +889,6 @@ only the interpretation of non-ASCII characters, and not for the script file handle. To make it work needs some investigation of the ordering of function calls during startup, and (by implication) a bit of tweaking of that order. -=head2 Propagate const outwards from Perl_moreswitches() - -Change 32057 changed the parameter and return value of C -from to . It should now be possible to propagate -const-correctness outwards to C, C -and C. - -=head2 Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload() - -A comment in C notes - - /* This code tries to figure out just what went wrong with - gv_fetchmethod. It therefore needs to duplicate a lot of - the internals of that function. We can't move it inside - Perl_gv_fetchmethod_autoload(), however, since that would - cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we - don't want that. - */ - -If C gets rewritten to take (more) flag bits, -then it ought to be possible to move the logic from C to -the "right" place. When making this change it would probably be good to also -pass in at least the method name length, if not also pre-computed hash values -when known. (I'm contemplating a plan to pre-compute hash values for common -fixed strings such as C and pass them in to functions.) - =head2 Organize error messages Perl's diagnostics (error messages, see L) could use @@ -667,6 +920,76 @@ also the warning messages (see L, C). These tasks would need C knowledge, and knowledge of how the interpreter works, or a willingness to learn. +=head2 forbid labels with keyword names + +Currently C "computes" the label value: + + $ perl -e 'goto print' + Can't find label 1 at -e line 1. + +It is controversial if the right way to avoid the confusion is to forbid +labels with keyword names, or if it would be better to always treat +bareword expressions after a "goto" as a label and never as a keyword. + +=head2 truncate() prototype + +The prototype of truncate() is currently C<$$>. It should probably +be C<*$> instead. (This is changed in F) + +=head2 decapsulation of smart match argument + +Currently C<$foo ~~ $object> will die with the message "Smart matching a +non-overloaded object breaks encapsulation". It would be nice to allow +to bypass this by using explictly the syntax C<$foo ~~ %$object> or +C<$foo ~~ @$object>. + +=head2 error reporting of [$a ; $b] + +Using C<;> inside brackets is a syntax error, and we don't propose to change +that by giving it any meaning. However, it's not reported very helpfully: + + $ perl -e '$a = [$b; $c];' + syntax error at -e line 1, near "$b;" + syntax error at -e line 1, near "$c]" + Execution of -e aborted due to compilation errors. + +It should be possible to hook into the tokeniser or the lexer, so that when a +C<;> is parsed where it is not legal as a statement terminator (ie inside +C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like +I<';' isn't legal inside an expression - if you need multiple statements use a +do {...} block>. See the thread starting at +http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html + +=head2 lexicals used only once + +This warns: + + $ perl -we '$pie = 42' + Name "main::pie" used only once: possible typo at -e line 1. + +This does not: + + $ perl -we 'my $pie = 42' + +Logically all lexicals used only once should warn, if the user asks for +warnings. An unworked RT ticket (#5087) has been open for almost seven +years for this discrepancy. + +=head2 UTF-8 revamp + +The handling of Unicode is unclean in many places. For example, the regexp +engine matches in Unicode semantics whenever the string or the pattern is +flagged as UTF-8, but that should not be dependent on an internal storage +detail of the string. + +=head2 Properly Unicode safe tokeniser and pads. + +The tokeniser isn't actually very UTF-8 clean. C is a hack - +variable names are stored in stashes as raw bytes, without the utf-8 flag +set. The pad API only takes a C pointer, so that's all bytes too. The +tokeniser ignores the UTF-8-ness of C, or any SVs returned from +source filters. All this could be fixed. + =head2 state variable initialization in list context Currently this is illegal: @@ -697,6 +1020,15 @@ L There is no method on tied filehandles to allow them to be called back by formats. +=head2 Propagate compilation hints to the debugger + +Currently a debugger started with -dE on the command-line doesn't see the +features enabled by -E. More generally hints (C<$^H> and C<%^H>) aren't +propagated to the debugger. Probably it would be a good thing to propagate +hints from the innermost non-C scope: this would make code eval'ed +in the debugger see the features (and strictures, etc.) currently in +scope. + =head2 Attach/detach debugger from running program The old perltodo notes "With C, you can attach the debugger to a running @@ -704,22 +1036,11 @@ program if you pass the process ID. It would be good to do this with the Perl debugger on a running Perl program, although I'm not sure how it would be done." ssh and screen do this with named pipes in /tmp. Maybe we can too. -=head2 Optimize away empty destructors - -Defining an empty DESTROY method might be useful (notably in -AUTOLOAD-enabled classes), but it's still a bit expensive to call. That -could probably be optimized. - =head2 LVALUE functions for lists The old perltodo notes that lvalue functions don't work for list or hash slices. This would be good to fix. -=head2 LVALUE functions in the debugger - -The old perltodo notes that lvalue functions don't work in the debugger. This -would be good to fix. - =head2 regexp optimiser optional The regexp optimiser is not optional. It should configurable to be, to allow @@ -776,24 +1097,6 @@ reinstated. The old perltodo notes "Look at the "reification" code in C". -=head2 Properly Unicode safe tokeniser and pads. - -The tokeniser isn't actually very UTF-8 clean. C is a hack - -variable names are stored in stashes as raw bytes, without the utf-8 flag -set. The pad API only takes a C pointer, so that's all bytes too. The -tokeniser ignores the UTF-8-ness of C, or any SVs returned from -source filters. All this could be fixed. - -=head2 The yada yada yada operators - -Perl 6's Synopsis 3 says: - -I - -Those would be nice to add to Perl 5. That could be done without new ops. - =head2 Virtualize operating system access Implement a set of "vtables" that virtualizes operating system access @@ -809,7 +1112,7 @@ in fact, all of L is.) This has actually already been implemented (but only for Win32), take a look at F and F. While all Win32 variants go through a set of "vtables" for operating system access, -non-Win32 systems currently go straight for the POSIX/UNIX-style +non-Win32 systems currently go straight for the POSIX/Unix-style system/library call. Similar system as for Win32 should be implemented for all platforms. The existing Win32 implementation probably does not need to survive alongside this proposed new @@ -831,10 +1134,120 @@ See also L. =head2 Investigate PADTMP hash pessimisation -The peephole optimier converts constants used for hash key lookups to shared -hash key scalars. Under ithreads, something is undoing this work. See +The peephole optimiser converts constants used for hash key lookups to shared +hash key scalars. Under ithreads, something is undoing this work. See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html +=head2 Store the current pad in the OP slab allocator + +=for clarification +I hope that I got that "current pad" part correct + +Currently we leak ops in various cases of parse failure. I suggested that we +could solve this by always using the op slab allocator, and walking it to +free ops. Dave comments that as some ops are already freed during optree +creation one would have to mark which ops are freed, and not double free them +when walking the slab. He notes that one problem with this is that for some ops +you have to know which pad was current at the time of allocation, which does +change. I suggested storing a pointer to the current pad in the memory allocated +for the slab, and swapping to a new slab each time the pad changes. Dave thinks +that this would work. + +=head2 repack the optree + +Repacking the optree after execution order is determined could allow +removal of NULL ops, and optimal ordering of OPs with respect to cache-line +filling. The slab allocator could be reused for this purpose. I think that +the best way to do this is to make it an optional step just before the +completed optree is attached to anything else, and to use the slab allocator +unchanged, so that freeing ops is identical whether or not this step runs. +Note that the slab allocator allocates ops downwards in memory, so one would +have to actually "allocate" the ops in reverse-execution order to get them +contiguous in memory in execution order. + +See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html + +Note that running this copy, and then freeing all the old location ops would +cause their slabs to be freed, which would eliminate possible memory wastage if +the previous suggestion is implemented, and we swap slabs more frequently. + +=head2 eliminate incorrect line numbers in warnings + +This code + + use warnings; + my $undef; + + if ($undef == 3) { + } elsif ($undef == 0) { + } + +used to produce this output: + + Use of uninitialized value in numeric eq (==) at wrong.pl line 4. + Use of uninitialized value in numeric eq (==) at wrong.pl line 4. + +where the line of the second warning was misreported - it should be line 5. +Rafael fixed this - the problem arose because there was no nextstate OP +between the execution of the C and the C, hence C still +reports that the currently executing line is line 4. The solution was to inject +a nextstate OPs for each C, although it turned out that the nextstate +OP needed to be a nulled OP, rather than a live nextstate OP, else other line +numbers became misreported. (Jenga!) + +The problem is more general than C (although the C case is the +most common and the most confusing). Ideally this code + + use warnings; + my $undef; + + my $a = $undef + 1; + my $b + = $undef + + 1; + +would produce this output + + Use of uninitialized value $undef in addition (+) at wrong.pl line 4. + Use of uninitialized value $undef in addition (+) at wrong.pl line 7. + +(rather than lines 4 and 5), but this would seem to require every OP to carry +(at least) line number information. + +What might work is to have an optional line number in memory just before the +BASEOP structure, with a flag bit in the op to say whether it's present. +Initially during compile every OP would carry its line number. Then add a late +pass to the optimiser (potentially combined with L) which +looks at the two ops on every edge of the graph of the execution path. If +the line number changes, flags the destination OP with this information. +Once all paths are traced, replace every op with the flag with a +nextstate-light op (that just updates C), which in turn then passes +control on to the true op. All ops would then be replaced by variants that +do not store the line number. (Which, logically, why it would work best in +conjunction with L, as that is already copying/reallocating +all the OPs) + +(Although I should note that we're not certain that doing this for the general +case is worth it) + +=head2 optimize tail-calls + +Tail-calls present an opportunity for broadly applicable optimization; +anywhere that C<< return foo(...) >> is called, the outer return can +be replaced by a goto, and foo will return directly to the outer +caller, saving (conservatively) 25% of perl's call&return cost, which +is relatively higher than in C. The scheme language is known to do +this heavily. B::Concise provides good insight into where this +optimization is possible, ie anywhere entersub,leavesub op-sequence +occurs. + + perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)' + +Bottom line on this is probably a new pp_tailcall function which +combines the code in pp_entersub, pp_leavesub. This should probably +be done 1st in XS, and using B::Generate to patch the new OP into the +optrees. + =head1 Big projects Tasks that will get your name mentioned in the description of the "Highlights @@ -871,3 +1284,24 @@ This will allow the use of a regex from inside (?{ }), (??{ }) and Apparently these are quite useful. Anyway, Jeffery Friedl wants them. demerphq has this on his todo list, but right at the bottom. + + +=head1 Tasks for microperl + + +[ Each and every one of these may be obsolete, but they were listed + in the old Todo.micro file] + + +=head2 make creating uconfig.sh automatic + +=head2 make creating Makefile.micro automatic + +=head2 do away with fork/exec/wait? + +(system, popen should be enough?) + +=head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime: + +(uConfigure? :-) native datatype widths and endianness come to mind +