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diff --git a/Master/tlpkg/tlperl/lib/pods/perltodo.pod b/Master/tlpkg/tlperl/lib/pods/perltodo.pod new file mode 100755 index 00000000000..7e7a3526742 --- /dev/null +++ b/Master/tlpkg/tlperl/lib/pods/perltodo.pod @@ -0,0 +1,1229 @@ +=head1 NAME + +perltodo - Perl TO-DO List + +=head1 DESCRIPTION + +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<perl5-porters@perl.org> 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 +ideas, and any discussion about them. One set of archives may be found at: + + http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ + +What can we offer you in return? Fame, fortune, and everlasting glory? Maybe +not, but if your patch is incorporated, then we'll add your name to the +F<AUTHORS> file, which ships in the official distribution. How many other +programming languages offer you 1 line of immortality? + +=head1 Tasks that only need Perl knowledge + +=head2 Remove macperl references from tests + +MacPerl is gone. The tests don't need to be there. + +=head2 Remove duplication of test setup. + +Schwern notes, that there's duplication of code - lots and lots of tests have +some variation on the big block of C<$Is_Foo> checks. We can safely put this +into a file, change it to build an C<%Is> hash and require it. Maybe just put +it into F<test.pl>. Throw in the handy tainting subroutines. + +=head2 POD -E<gt> HTML conversion in the core still sucks + +Which is crazy given just how simple POD purports to be, and how simple HTML +can be. It's not actually I<as> simple as it sounds, particularly with the +flexibility POD allows for C<=item>, but it would be good to improve the +visual appeal of the HTML generated, and to avoid it having any validation +errors. See also L</make HTML install work>, as the layout of installation tree +is needed to improve the cross-linking. + +The addition of C<Pod::Simple> and its related modules may make this task +easier to complete. + +=head2 Make ExtUtils::ParseXS use strict; + +F<lib/ExtUtils/ParseXS.pm> contains this line + + # use strict; # One of these days... + +Simply uncomment it, and fix all the resulting issues :-) + +The more practical approach, to break the task down into manageable chunks, is +to work your way though the code from bottom to top, or if necessary adding +extra C<{ ... }> blocks, and turning on strict within them. + +=head2 Parallel testing + +(This probably impacts much more than the core: also the Test::Harness +and TAP::* modules on CPAN.) + +All of the tests in F<t/> can now be run in parallel, if C<$ENV{TEST_JOBS}> +is set. However, tests within each directory in F<ext> and F<lib> are still +run in series, with directories run in parallel. This is an adequate +heuristic, but it might be possible to relax it further, and get more +throughput. Specifically, it would be good to audit all of F<lib/*.t>, and +make them use C<File::Temp>. + +=head2 Make Schwern poorer + +We should have tests for everything. When all the core's modules are tested, +Schwern has promised to donate to $500 to TPF. We may need volunteers to +hold him upside down and shake vigorously in order to actually extract the +cash. + +=head2 Improve the coverage of the core tests + +Use Devel::Cover to ascertain the core modules's test coverage, then add +tests that are currently missing. + +=head2 test B + +A full test suite for the B module would be nice. + +=head2 A decent benchmark + +C<perlbench> seems impervious to any recent changes made to the perl core. It +would be useful to have a reasonable general benchmarking suite that roughly +represented what current perl programs do, and measurably reported whether +tweaks to the core improve, degrade or don't really affect performance, to +guide people attempting to optimise the guts of perl. Gisle would welcome +new tests for perlbench. + +=head2 fix tainting bugs + +Fix the bugs revealed by running the test suite with the C<-t> switch (via +C<make test.taintwarn>). + +=head2 Dual life everything + +As part of the "dists" plan, anything that doesn't belong in the smallest perl +distribution needs to be dual lifed. Anything else can be too. Figure out what +changes would be needed to package that module and its tests up for CPAN, and +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<t/lib/commonsense.t>. + +=head2 Bundle dual life modules in ext/ + +For maintenance (and branch merging) reasons, it would be useful to move +some architecture-independent dual-life modules from lib/ to ext/, if this +has no negative impact on the build of perl itself. + +=head2 POSIX memory footprint + +Ilya observed that use POSIX; eats memory like there's no tomorrow, and at +various times worked to cut it down. There is probably still fat to cut out - +for example POSIX passes Exporter some very memory hungry data structures. + +=head2 embed.pl/makedef.pl + +There is a script F<embed.pl> that generates several header files to prefix +all of Perl's symbols in a consistent way, to provide some semblance of +namespace support in C<C>. Functions are declared in F<embed.fnc>, variables +in F<interpvar.h>. Quite a few of the functions and variables +are conditionally declared there, using C<#ifdef>. However, F<embed.pl> +doesn't understand the C macros, so the rules about which symbols are present +when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay. +It would be good to teach C<embed.pl> to understand the conditional +compilation, and hence remove the duplication, and the mistakes it has caused. + +=head2 use strict; and AutoLoad + +Currently if you write + + package Whack; + use AutoLoader 'AUTOLOAD'; + use strict; + 1; + __END__ + sub bloop { + print join (' ', No, strict, here), "!\n"; + } + +then C<use strict;> isn't in force within the autoloaded subroutines. It would +be more consistent (and less surprising) to arrange for all lexical pragmas +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<installman> 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. + + +=head1 Tasks that need a little sysadmin-type knowledge + +Or if you prefer, tasks that you would learn from, and broaden your skills +base... + +=head2 make HTML install work + +There is an C<installhtml> target in the Makefile. It's marked as +"experimental". It would be good to get this tested, make it work reliably, and +remove the "experimental" tag. This would include + +=over 4 + +=item 1 + +Checking that cross linking between various parts of the documentation works. +In particular that links work between the modules (files with POD in F<lib/>) +and the core documentation (files in F<pod/>) + +=item 2 + +Work out how to split C<perlfunc> into chunks, preferably one per function +group, preferably with general case code that could be used elsewhere. +Challenges here are correctly identifying the groups of functions that go +together, and making the right named external cross-links point to the right +page. Things to be aware of are C<-X>, groups such as C<getpwnam> to +C<endservent>, two or more C<=items> giving the different parameter lists, such +as + + =item substr EXPR,OFFSET,LENGTH,REPLACEMENT + =item substr EXPR,OFFSET,LENGTH + =item substr EXPR,OFFSET + +and different parameter lists having different meanings. (eg C<select>) + +=back + +=head2 compressed man pages + +Be able to install them. This would probably need a configure test to see how +the system does compressed man pages (same directory/different directory? +same filename/different filename), as well as tweaking the F<installman> script +to compress as necessary. + +=head2 Add a code coverage target to the Makefile + +Make it easy for anyone to run Devel::Cover on the core's tests. The steps +to do this manually are roughly + +=over 4 + +=item * + +do a normal C<Configure>, but include Devel::Cover as a module to install +(see F<INSTALL> for how to do this) + +=item * + + make perl + +=item * + + cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness + +=item * + +Process the resulting Devel::Cover database + +=back + +This just give you the coverage of the F<.pm>s. To also get the C level +coverage you need to + +=over 4 + +=item * + +Additionally tell C<Configure> to use the appropriate C compiler flags for +C<gcov> + +=item * + + make perl.gcov + +(instead of C<make perl>) + +=item * + +After running the tests run C<gcov> to generate all the F<.gcov> files. +(Including down in the subdirectories of F<ext/> + +=item * + +(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files +to get their stats into the cover_db directory. + +=item * + +Then process the Devel::Cover database + +=back + +It would be good to add a single switch to C<Configure> to specify that you +wanted to perform perl level coverage, and another to specify C level +coverage, and have C<Configure> and the F<Makefile> do all the right things +automatically. + +=head2 Make Config.pm cope with differences between built and installed perl + +Quite often vendors ship a perl binary compiled with their (pay-for) +compilers. People install a free compiler, such as gcc. To work out how to +build extensions, Perl interrogates C<%Config>, so in this situation +C<%Config> describes compilers that aren't there, and extension building +fails. This forces people into choosing between re-compiling perl themselves +using the compiler they have, or only using modules that the vendor ships. + +It would be good to find a way teach C<Config.pm> about the installation setup, +possibly involving probing at install time or later, so that the C<%Config> in +a binary distribution better describes the installed machine, when the +installed machine differs from the build machine in some significant way. + +=head2 linker specification files + +Some platforms mandate that you provide a list of a shared library's external +symbols to the linker, so the core already has the infrastructure in place to +do this for generating shared perl libraries. My understanding is that the +GNU toolchain can accept an optional linker specification file, and restrict +visibility just to symbols declared in that file. It would be good to extend +F<makedef.pl> to support this format, and to provide a means within +C<Configure> to enable it. This would allow Unix users to test that the +export list is correct, and to build a perl that does not pollute the global +namespace with private symbols. + +=head2 Cross-compile support + +Currently C<Configure> understands C<-Dusecrosscompile> option. This option +arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is +assumed then to be copied to TARGET machine and used as a replacement of full +C<perl> executable. + +This could be done little differently. Namely C<miniperl> should be built for +HOST and then full C<perl> with extensions should be compiled for TARGET. +This, however, might require extra trickery for %Config: we have one config +first for HOST and then another for TARGET. Tools like MakeMaker will be +mightily confused. Having around two different types of executables and +libraries (HOST and TARGET) makes life interesting for Makefiles and +shell (and Perl) scripts. There is $Config{run}, normally empty, which +can be used as an execution wrapper. Also note that in some +cross-compilation/execution environments the HOST and the TARGET do +not see the same filesystem(s), the $Config{run} may need to do some +file/directory copying back and forth. + +=head2 roffitall + +Make F<pod/roffitall> be updated by F<pod/buildtoc>. + +=head2 Split "linker" from "compiler" + +Right now, Configure probes for two commands, and sets two variables: + +=over 4 + +=item * C<cc> (in F<cc.U>) + +This variable holds the name of a command to execute a C compiler which +can resolve multiple global references that happen to have the same +name. Usual values are F<cc> and F<gcc>. +Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>. + +=item * C<ld> (in F<dlsrc.U>) + +This variable indicates the program to be used to link +libraries for dynamic loading. On some systems, it is F<ld>. +On ELF systems, it should be C<$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<$cc> is also the correct command for linking object files +together to make an executable. This may be true on Unix, but it's not true +on other platforms, and there are a maze of work arounds in other places (such +as F<Makefile.SH>) to cope with this. + +Ideally, we should create a new variable to hold the name of the executable +linker program, probe for it in F<Configure>, and centralise all the special +case logic there or in hints files. + +A small bikeshed issue remains - what to call it, given that C<$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<$link> could be confused with +the Unix command line executable of the same name, which does something +completely different. Andy Dougherty makes the counter argument "In parrot, I +tried to call the command used to link object files and libraries into an +executable F<link>, since that's what my vaguely-remembered DOS and VMS +experience suggested. I don't think any real confusion has ensued, so it's +probably a reasonable name for perl5 to use." + +"Alas, I've always worried that introducing it would make things worse, +since now the module building utilities would have to look for +C<$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<Configure> automatically adds C<-DDEBUGGING> to the C compiler +flags if it spots C<-g> in the optimiser flags. The pre-processor directive +C<DEBUGGING> enables F<perl>'s command line <-D> options, but in the process +makes F<perl> 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 Weed out needless PERL_UNUSED_ARG + +The C code uses the macro C<PERL_UNUSED_ARG> 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<PERL_UNUSED_ARG> +could be removed. Specifically + +=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 + +The way @INC is laid out by default, one cannot upgrade core (dual-life) +modules without overwriting files. This causes problems for binary +package builders. One possible proposal is laid out in this +message: +L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>. + +=head2 -Duse32bit* + +Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall. +On these systems, it might be the default compilation mode, and there +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 Profile Perl - am I hot or not? + +The Perl source code is stable enough that it makes sense to profile it, +identify and optimise the hotspots. It would be good to measure the +performance of the Perl interpreter using free tools such as cachegrind, +gprof, and dtrace, and work to reduce the bottlenecks they reveal. + +As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops, +the ops that are most commonly used. The idea is that by grouping them, their +object code will be adjacent in the executable, so they have a greater chance +of already being in the CPU cache (or swapped in) due to being near another op +already in use. + +Except that it's not clear if these really are the most commonly used ops. So +as part of exercising your skills with coverage and profiling tools you might +want to determine what ops I<really> are the most commonly used. And in turn +suggest evictions and promotions to achieve a better F<pp_hot.c>. + +One piece of Perl code that might make a good testbed is F<installman>. + +=head2 Allocate OPs from arenas + +Currently all new OP structures are individually malloc()ed and free()d. +All C<malloc> implementations have space overheads, and are now as fast as +custom allocates so it would both use less memory and less CPU to allocate +the various OP structures from arenas. The SV arena code can probably be +re-used for this. + +Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use +Perl_Slab_alloc() to pack optrees into a contiguous block, which is +probably superior to the use of OP arenas, esp. from a cache locality +standpoint. See L<Profile Perl - am I hot or not?>. + +=head2 Improve win32/wince.c + +Currently, numerous functions look virtually, if not completely, +identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't +be good. + +=head2 Use secure CRT functions when building with VC8 on Win32 + +Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis +that they were "unsafe" and introduced differently named secure versions of +them as replacements, e.g. instead of writing + + FILE* f = fopen(__FILE__, "r"); + +one should now write + + FILE* f; + errno_t err = fopen_s(&f, __FILE__, "r"); + +Currently, the warnings about these deprecations have been disabled by adding +-D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that +warning suppressant and actually make use of the new secure CRT functions. + +There is also a similar issue with POSIX CRT function names like fileno having +been deprecated in favour of ISO C++ conformant names like _fileno. These +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 +none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets()) +ever creep back to libperl.a. + + nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/' + +Note, of course, that this will only tell whether B<your> platform +is using those naughty interfaces. + +=head2 -D_FORTIFY_SOURCE=2, -fstack-protector + +Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc +(4.1 onwards?) supports C<-fstack-protector>, both of which give +protection against various kinds of buffer overflow problems. +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<struct gp> and C<struct magic> are both currently allocated by C<malloc>. +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, C<GP>s +can probably be changed with minimal compatibility impact (probably nothing +outside of the core, or even outside of F<gv.c> allocates them), but they +probably aren't allocated/deallocated often enough for a speed saving. Whereas +C<MAGIC> 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 Remove the use of SVs as temporaries in dump.c + +F<dump.c> contains debugging routines to dump out the contains of perl data +structures, such as C<SV>s, C<AV>s and C<HV>s. Currently, the dumping code +B<uses> C<SV>s 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<dump.c>, 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<malloc>. The F<dump.c> 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 C<SV>s for +B<its> buffers, use of which can cause problems similar to those of F<dump.c>, +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<sigaction> for C<SA_SIGINFO>, create a +pipe, store the reader in one, the writer in the other + +=item 3 + +In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if +the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open, + +=over 8 + +=item 1 + +serialise signal number, C<struct siginfo_t> (or at least the parts we care +about) into a small auto char buff + +=item 2 + +C<write()> 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<PERL_ASYNC_CHECK()> processing, if there are "signals on +the pipe", read the data out, deserialise, build the Perl structures on +the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as +usual. + +=back + +I think that this gets us decent C<SA_SIGINFO> support, without the current risk +of running Perl code inside the signal handler context. (With all the dangers +of things like C<malloc> 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; + +This task is incremental - even a little bit of work on it will help. + +=head2 Unicode in Filenames + +chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, +opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen, +system, truncate, unlink, utime, -X. All these could potentially accept +Unicode filenames either as input or output (and in the case of system +and qx Unicode in general, as input or output to/from the shell). +Whether a filesystem - an operating system pair understands Unicode in +filenames varies. + +Known combinations that have some level of understanding include +Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac +OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to +create Unicode filenames, what forms of Unicode are accepted and used +(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, +and so on, varies. Finding the right level of interfacing to Perl +requires some thought. Remember that an OS does not implicate a +filesystem. + +(The Windows -C command flag "wide API support" has been at least +temporarily retired in 5.8.1, and the -C has been repurposed, see +L<perlrun>.) + +Most probably the right way to do this would be this: +L</"Virtualize operating system access">. + +=head2 Unicode in %ENV + +Currently the %ENV entries are always byte strings. +See L</"Virtualize operating system access">. + +=head2 Unicode and glob() + +Currently glob patterns and filenames returned from File::Glob::glob() +are always byte strings. See L</"Virtualize operating system access">. + +=head2 Unicode and lc/uc operators + +Some built-in operators (C<lc>, C<uc>, 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. +Particularly perl should be able to give memory back. + +This task is incremental - even a little bit of work on it will help. + +=head2 Re-implement C<:unique> in a way that is actually thread-safe + +The old implementation made bad assumptions on several levels. A good 90% +solution might be just to make C<:unique> work to share the string buffer +of SvPVs. That way large constant strings can be shared between ithreads, +such as the configuration information in F<Config>. + +=head2 Make tainting consistent + +Tainting would be easier to use if it didn't take documented shortcuts and +allow taint to "leak" everywhere within an expression. + +=head2 readpipe(LIST) + +system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid +running a shell. readpipe() (the function behind qx//) could be similarly +extended. + +=head2 Audit the code for destruction ordering assumptions + +Change 25773 notes + + /* Need to check SvMAGICAL, as during global destruction it may be that + AvARYLEN(av) has been freed before av, and hence the SvANY() pointer + is now part of the linked list of SV heads, rather than pointing to + the original body. */ + /* FIXME - audit the code for other bugs like this one. */ + +adding the C<SvMAGICAL> check to + + if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) { + MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen); + +Go through the core and look for similar assumptions that SVs have particular +types, as all bets are off during global destruction. + +=head2 Extend PerlIO and PerlIO::Scalar + +PerlIO::Scalar doesn't know how to truncate(). Implementing this +would require extending the PerlIO vtable. + +Similarly the PerlIO vtable doesn't know about formats (write()), or +about stat(), or chmod()/chown(), utime(), or flock(). + +(For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership +would mean.) + +PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), +opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(), +readlink(). + +See also L</"Virtualize operating system access">. + +=head2 -C on the #! line + +It should be possible to make -C work correctly if found on the #! line, +given that all perl command line options are strict ASCII, and -C changes +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 Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload() + +A comment in C<S_method_common> 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<Perl_gv_fetchmethod_autoload> gets rewritten to take (more) flag bits, +then it ought to be possible to move the logic from C<S_method_common> 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<ISA> and pass them in to functions.) + +=head2 Organize error messages + +Perl's diagnostics (error messages, see L<perldiag>) could use +reorganizing and formalizing so that each error message has its +stable-for-all-eternity unique id, categorized by severity, type, and +subsystem. (The error messages would be listed in a datafile outside +of the Perl source code, and the source code would only refer to the +messages by the id.) This clean-up and regularizing should apply +for all croak() messages. + +This would enable all sorts of things: easier translation/localization +of the messages (though please do keep in mind the caveats of +L<Locale::Maketext> about too straightforward approaches to +translation), filtering by severity, and instead of grepping for a +particular error message one could look for a stable error id. (Of +course, changing the error messages by default would break all the +existing software depending on some particular error message...) + +This kind of functionality is known as I<message catalogs>. Look for +inspiration for example in the catgets() system, possibly even use it +if available-- but B<only> if available, all platforms will B<not> +have catgets(). + +For the really pure at heart, consider extending this item to cover +also the warning messages (see L<perllexwarn>, C<warnings.pl>). + +=head1 Tasks that need a knowledge of the interpreter + +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<goto keyword> "computes" the label value: + + $ perl -e 'goto print' + Can't find label 1 at -e line 1. + +It would be nice to forbid labels with keyword names, to avoid confusion. + +=head2 truncate() prototype + +The prototype of truncate() is currently C<$$>. It should probably +be C<*$> instead. (This is changed in F<opcode.pl>) + +=head2 decapsulation of smart match argument + +Currently C<$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 $pie = 42' + +Logically all lexicals used only once should warn, if the user asks for +warnings. An unworked RT ticket (#5087) has been open for almost seven +years for this discrepancy. + +=head2 UTF-8 revamp + +The handling of Unicode is unclean in many places. For example, the regexp +engine matches in Unicode semantics whenever the string or the pattern is +flagged as UTF-8, but that should not be dependent on an internal storage +detail of the string. Likewise, case folding behaviour is dependent on the +UTF8 internal flag being on or off. + +=head2 Properly Unicode safe tokeniser and pads. + +The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack - +variable names are stored in stashes as raw bytes, without the utf-8 flag +set. The pad API only takes a C<char *> pointer, so that's all bytes too. The +tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from +source filters. All this could be fixed. + +=head2 state variable initialization in list context + +Currently this is illegal: + + state ($a, $b) = foo(); + +In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different +semantics, which is tricky to implement in Perl 5 as currently they produce +the same opcode trees. The Perl 6 design is firm, so it would be good to +implement the necessary code in Perl 5. There are comments in +C<Perl_newASSIGNOP()> that show the code paths taken by various assignment +constructions involving state variables. + +=head2 Implement $value ~~ 0 .. $range + +It would be nice to extend the syntax of the C<~~> operator to also +understand numeric (and maybe alphanumeric) ranges. + +=head2 A does() built-in + +Like ref(), only useful. It would call the C<DOES> method on objects; it +would also tell whether something can be dereferenced as an +array/hash/etc., or used as a regexp, etc. +L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html> + +=head2 Tied filehandles and write() don't mix + +There is no method on tied filehandles to allow them to be called back by +formats. + +=head2 Propagate compilation hints to the debugger + +Currently a debugger started with -dE on the command-line doesn't see the +features enabled by -E. More generally hints (C<$^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<DB::> 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<gdb>, you can attach the debugger to a running +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 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 regexp optimiser optional + +The regexp optimiser is not optional. It should configurable to be, to allow +its performance to be measured, and its bugs to be easily demonstrated. + +=head2 delete &function + +Allow to delete functions. One can already undef them, but they're still +in the stash. + +=head2 C</w> regex modifier + +That flag would enable to match whole words, and also to interpolate +arrays as alternations. With it, C</P/w> would be roughly equivalent to: + + do { local $"='|'; /\b(?:P)\b/ } + +See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> +for the discussion. + +=head2 optional optimizer + +Make the peephole optimizer optional. Currently it performs two tasks as +it walks the optree - genuine peephole optimisations, and necessary fixups of +ops. It would be good to find an efficient way to switch out the +optimisations whilst keeping the fixups. + +=head2 You WANT *how* many + +Currently contexts are void, scalar and list. split has a special mechanism in +place to pass in the number of return values wanted. It would be useful to +have a general mechanism for this, backwards compatible and little speed hit. +This would allow proposals such as short circuiting sort to be implemented +as a module on CPAN. + +=head2 lexical aliases + +Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>. + +=head2 entersub XS vs Perl + +At the moment pp_entersub is huge, and has code to deal with entering both +perl and XS subroutines. Subroutine implementations rarely change between +perl and XS at run time, so investigate using 2 ops to enter subs (one for +XS, one for perl) and swap between if a sub is redefined. + +=head2 Self-ties + +Self-ties are currently illegal because they caused too many segfaults. Maybe +the causes of these could be tracked down and self-ties on all types +reinstated. + +=head2 Optimize away @_ + +The old perltodo notes "Look at the "reification" code in C<av.c>". + +=head2 The yada yada yada operators + +Perl 6's Synopsis 3 says: + +I<The ... operator is the "yada, yada, yada" list operator, which is used as +the body in function prototypes. It complains bitterly (by calling fail) +if it is ever executed. Variant ??? calls warn, and !!! calls die.> + +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 +(open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very +least these interfaces should take SVs as "name" arguments instead of +bare char pointers; probably the most flexible and extensible way +would be for the Perl-facing interfaces to accept HVs. The system +needs to be per-operating-system and per-file-system +hookable/filterable, preferably both from XS and Perl level +(L<perlport/"Files and Filesystems"> is good reading at this point, +in fact, all of L<perlport> is.) + +This has actually already been implemented (but only for Win32), +take a look at F<iperlsys.h> and F<win32/perlhost.h>. 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 +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 +implementation, the approaches could be merged. + +What would this give us? One often-asked-for feature this would +enable is using Unicode for filenames, and other "names" like %ENV, +usernames, hostnames, and so forth. +(See L<perlunicode/"When Unicode Does Not Happen">.) + +But this kind of virtualization would also allow for things like +virtual filesystems, virtual networks, and "sandboxes" (though as long +as dynamic loading of random object code is allowed, not very safe +sandboxes since external code of course know not of Perl's vtables). +An example of a smaller "sandbox" is that this feature can be used to +implement per-thread working directories: Win32 already does this. + +See also L</"Extend PerlIO and PerlIO::Scalar">. + +=head2 Investigate PADTMP hash pessimisation + +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<if> and the C<elsif>, hence C<PL_curcop> still +reports that the currently executing line is line 4. The solution was to inject +a nextstate OPs for each C<elsif>, 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<elsif> (although the C<elsif> 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</repack the optree>) 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<PL_curcop>), 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</repack the optree>, 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. + +=head2 C<\N> + +It should be possible to add a C<\N> regex assertion, meaning "every +character except C<\n>° independently of the context. That would +of course imply that C<\N> couldn't be followed by an opening C<{>. + +=head1 Big projects + +Tasks that will get your name mentioned in the description of the "Highlights +of 5.12" + +=head2 make ithreads more robust + +Generally make ithreads more robust. See also L</iCOW> + +This task is incremental - even a little bit of work on it will help, and +will be greatly appreciated. + +One bit would be to write the missing code in sv.c:Perl_dirp_dup. + +Fix Perl_sv_dup, et al so that threads can return objects. + +=head2 iCOW + +Sarathy and Arthur have a proposal for an improved Copy On Write which +specifically will be able to COW new ithreads. If this can be implemented +it would be a good thing. + +=head2 (?{...}) closures in regexps + +Fix (or rewrite) the implementation of the C</(?{...})/> closures. + +=head2 A re-entrant regexp engine + +This will allow the use of a regex from inside (?{ }), (??{ }) and +(?(?{ })|) constructs. + +=head2 Add class set operations to regexp engine + +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 + |