This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
Multiple commits in 1 attachment in Patch Guide
[perl5.git] / pod / perlhack.pod
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04c692a8 1=encoding utf8
35c336e6 2
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3=for comment
4Consistent formatting of this file is achieved with:
5 perl ./Porting/podtidy pod/perlhack.pod
35c336e6 6
04c692a8 7=head1 NAME
35c336e6 8
04c692a8 9perlhack - How to hack on Perl
35c336e6 10
04c692a8 11=head1 DESCRIPTION
35c336e6 12
531e2078 13This document explains how Perl development works. It includes details
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14about the Perl 5 Porters email list, the Perl repository, the Perlbug
15bug tracker, patch guidelines, and commentary on Perl development
16philosophy.
f7e1e956 17
04c692a8 18=head1 SUPER QUICK PATCH GUIDE
f7e1e956 19
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20If you just want to submit a single small patch like a pod fix, a test
21for a bug, comment fixes, etc., it's easy! Here's how:
f7e1e956 22
04c692a8 23=over 4
e018f8be 24
04c692a8 25=item * Check out the source repository
e018f8be 26
531e2078 27The perl source is in a git repository. You can clone the repository
04c692a8 28with the following command:
e018f8be 29
04c692a8 30 % git clone git://perl5.git.perl.org/perl.git perl
e018f8be 31
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32=item * Ensure you're following the latest advice
33
34In case the advice in this guide has been updated recently, read the
35latest version directly from the perl source:
36
37 % perldoc pod/perlhack.pod
38
04c692a8 39=item * Make your change
e018f8be 40
04c692a8 41Hack, hack, hack.
7205a85d 42
04c692a8 43=item * Test your change
e018f8be 44
04c692a8 45You can run all the tests with the following commands:
b26492ee 46
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47 % ./Configure -des -Dusedevel
48 % make test
7205a85d 49
04c692a8 50Keep hacking until the tests pass.
b26492ee 51
04c692a8 52=item * Commit your change
e018f8be 53
b6538e4f 54Committing your work will save the change I<on your local system>:
7205a85d 55
04c692a8 56 % git commit -a -m 'Commit message goes here'
e018f8be 57
04c692a8 58Make sure the commit message describes your change in a single
531e2078 59sentence. For example, "Fixed spelling errors in perlhack.pod".
e018f8be 60
04c692a8 61=item * Send your change to perlbug
7a834142 62
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63The next step is to submit your patch to the Perl core ticket system
64via email.
7a834142 65
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66If your changes are in a single git commit, run the following commands
67to write the file as a MIME attachment and send it with a meaningful
5c70016e 68subject:
e018f8be 69
7eac65da 70 % git format-patch -1 --attach
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71 % ./perl -Ilib utils/perlbug -s "[PATCH] $(
72 git log -1 --oneline HEAD)" -f 0001-*.patch
e018f8be 73
04c692a8 74The perlbug program will ask you a few questions about your email
531e2078 75address and the patch you're submitting. Once you've answered them it
84b19098 76will submit your patch via email.
e018f8be 77
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78If your changes are in multiple commits, generate a patch file
79containing them all, and attach that:
2d1c9392 80
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81 % git format-patch origin/blead --attach --stdout > patches
82 % ./perl -Ilib utils/perlbug -f patches
2d1c9392 83
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84When prompted, pick a subject that summarizes your changes overall and
85has "[PATCH]" at the beginning.
2d1c9392 86
04c692a8 87=item * Thank you
e018f8be 88
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89The porters appreciate the time you spent helping to make Perl better.
90Thank you!
e018f8be 91
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92=item * Next time
93
94The next time you wish to make a patch, you need to start from the
95latest perl in a pristine state. Check you don't have any local changes
96or added files in your perl check-out which you wish to keep, then run
97these commands:
98
99 % git pull
100 % git reset --hard origin/blead
101 % git clean -dxf
102
cce04beb 103=back
e018f8be 104
04c692a8 105=head1 BUG REPORTING
cc0710ff 106
9e6670f3 107If you want to report a bug in Perl, you must use the F<perlbug>
531e2078 108command line tool. This tool will ensure that your bug report includes
9e6670f3 109all the relevant system and configuration information.
7205a85d 110
04c692a8 111To browse existing Perl bugs and patches, you can use the web interface
a8d15a22 112at L<http://rt.perl.org/>.
244d9cb7 113
04c692a8 114Please check the archive of the perl5-porters list (see below) and/or
531e2078 115the bug tracking system before submitting a bug report. Often, you'll
04c692a8 116find that the bug has been reported already.
244d9cb7 117
04c692a8 118You can log in to the bug tracking system and comment on existing bug
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119reports. If you have additional information regarding an existing bug,
120please add it. This will help the porters fix the bug.
7205a85d 121
04c692a8 122=head1 PERL 5 PORTERS
7205a85d 123
04c692a8 124The perl5-porters (p5p) mailing list is where the Perl standard
531e2078 125distribution is maintained and developed. The people who maintain Perl
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126are also referred to as the "Perl 5 Porters", "p5p" or just the
127"porters".
a75f557c 128
04c692a8 129A searchable archive of the list is available at
531e2078 130L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/>. There is
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131also another archive at
132L<http://archive.develooper.com/perl5-porters@perl.org/>.
7205a85d 133
04c692a8 134=head2 perl-changes mailing list
7205a85d 135
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136The perl5-changes mailing list receives a copy of each patch that gets
137submitted to the maintenance and development branches of the perl
531e2078 138repository. See L<http://lists.perl.org/list/perl5-changes.html> for
04c692a8 139subscription and archive information.
244d9cb7 140
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141=head2 #p5p on IRC
142
143Many porters are also active on the L<irc://irc.perl.org/#p5p> channel.
144Feel free to join the channel and ask questions about hacking on the
145Perl core.
146
04c692a8 147=head1 GETTING THE PERL SOURCE
244d9cb7 148
04c692a8 149All of Perl's source code is kept centrally in a Git repository at
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150I<perl5.git.perl.org>. The repository contains many Perl revisions
151from Perl 1 onwards and all the revisions from Perforce, the previous
04c692a8 152version control system.
244d9cb7 153
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154For much more detail on using git with the Perl repository, please see
155L<perlgit>.
244d9cb7 156
04c692a8 157=head2 Read access via Git
244d9cb7 158
531e2078 159You will need a copy of Git for your computer. You can fetch a copy of
04c692a8 160the repository using the git protocol:
244d9cb7 161
04c692a8 162 % git clone git://perl5.git.perl.org/perl.git perl
244d9cb7 163
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164This clones the repository and makes a local copy in the F<perl>
165directory.
7205a85d 166
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167If you cannot use the git protocol for firewall reasons, you can also
168clone via http, though this is much slower:
7205a85d 169
04c692a8 170 % git clone http://perl5.git.perl.org/perl.git perl
7205a85d 171
04c692a8 172=head2 Read access via the web
7205a85d 173
531e2078 174You may access the repository over the web. This allows you to browse
04c692a8 175the tree, see recent commits, subscribe to RSS feeds for the changes,
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176search for particular commits and more. You may access it at
177L<http://perl5.git.perl.org/perl.git>. A mirror of the repository is
a8d15a22 178found at L<http://github.com/mirrors/perl>.
7205a85d 179
04c692a8 180=head2 Read access via rsync
7205a85d 181
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182You can also choose to use rsync to get a copy of the current source
183tree for the bleadperl branch and all maintenance branches:
7205a85d 184
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185 % rsync -avz rsync://perl5.git.perl.org/perl-current .
186 % rsync -avz rsync://perl5.git.perl.org/perl-5.12.x .
187 % rsync -avz rsync://perl5.git.perl.org/perl-5.10.x .
188 % rsync -avz rsync://perl5.git.perl.org/perl-5.8.x .
189 % rsync -avz rsync://perl5.git.perl.org/perl-5.6.x .
190 % rsync -avz rsync://perl5.git.perl.org/perl-5.005xx .
7205a85d 191
a8d15a22 192(Add the C<--delete> option to remove leftover files.)
7205a85d 193
04c692a8 194To get a full list of the available sync points:
7205a85d 195
7eac65da 196 % rsync perl5.git.perl.org::
7205a85d 197
04c692a8 198=head2 Write access via git
7205a85d 199
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200If you have a commit bit, please see L<perlgit> for more details on
201using git.
7205a85d 202
04c692a8 203=head1 PATCHING PERL
7205a85d 204
04c692a8 205If you're planning to do more extensive work than a single small fix,
531e2078 206we encourage you to read the documentation below. This will help you
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207focus your work and make your patches easier to incorporate into the
208Perl source.
244d9cb7 209
04c692a8 210=head2 Submitting patches
244d9cb7 211
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212If you have a small patch to submit, please submit it via perlbug. You
213can also send email directly to perlbug@perl.org. Please note that
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214messages sent to perlbug may be held in a moderation queue, so you
215won't receive a response immediately.
244d9cb7 216
04c692a8 217You'll know your submission has been processed when you receive an
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218email from our ticket tracking system. This email will give you a
219ticket number. Once your patch has made it to the ticket tracking
04c692a8 220system, it will also be sent to the perl5-porters@perl.org list.
244d9cb7 221
531e2078 222Patches are reviewed and discussed on the p5p list. Simple,
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223uncontroversial patches will usually be applied without any discussion.
224When the patch is applied, the ticket will be updated and you will
531e2078 225receive email. In addition, an email will be sent to the p5p list.
244d9cb7 226
531e2078 227In other cases, the patch will need more work or discussion. That will
04c692a8 228happen on the p5p list.
244d9cb7 229
04c692a8 230You are encouraged to participate in the discussion and advocate for
531e2078 231your patch. Sometimes your patch may get lost in the shuffle. It's
04c692a8 232appropriate to send a reminder email to p5p if no action has been taken
531e2078 233in a month. Please remember that the Perl 5 developers are all
04c692a8 234volunteers, and be polite.
244d9cb7 235
04c692a8 236Changes are always applied directly to the main development branch,
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237called "blead". Some patches may be backported to a maintenance
238branch. If you think your patch is appropriate for the maintenance
239branch, please explain why when you submit it.
244d9cb7 240
04c692a8 241=head2 Getting your patch accepted
244d9cb7 242
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243If you are submitting a code patch there are several things that you
244can do to help the Perl 5 Porters accept your patch.
244d9cb7 245
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246=head3 Patch style
247
248If you used git to check out the Perl source, then using C<git
531e2078 249format-patch> will produce a patch in a style suitable for Perl. The
a126fb62 250C<format-patch> command produces one patch file for each commit you
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251made. If you prefer to send a single patch for all commits, you can
252use C<git diff>.
a126fb62 253
9d440a18 254 % git checkout blead
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255 % git pull
256 % git diff blead my-branch-name
257
258This produces a patch based on the difference between blead and your
531e2078 259current branch. It's important to make sure that blead is up to date
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260before producing the diff, that's why we call C<git pull> first.
261
531e2078 262We strongly recommend that you use git if possible. It will make your
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263life easier, and ours as well.
264
265However, if you're not using git, you can still produce a suitable
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266patch. You'll need a pristine copy of the Perl source to diff against.
267The porters prefer unified diffs. Using GNU C<diff>, you can produce a
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268diff like this:
269
270 % diff -Npurd perl.pristine perl.mine
271
272Make sure that you C<make realclean> in your copy of Perl to remove any
273build artifacts, or you may get a confusing result.
274
04c692a8 275=head3 Commit message
244d9cb7 276
04c692a8 277As you craft each patch you intend to submit to the Perl core, it's
531e2078 278important to write a good commit message. This is especially important
04c692a8 279if your submission will consist of a series of commits.
244d9cb7 280
04c692a8 281The first line of the commit message should be a short description
531e2078 282without a period. It should be no longer than the subject line of an
a8d15a22 283email, 50 characters being a good rule of thumb.
f7e1e956 284
a8d15a22 285A lot of Git tools (Gitweb, GitHub, git log --pretty=oneline, ...) will
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286only display the first line (cut off at 50 characters) when presenting
287commit summaries.
7cd58830 288
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289The commit message should include a description of the problem that the
290patch corrects or new functionality that the patch adds.
7cd58830 291
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292As a general rule of thumb, your commit message should help a
293programmer who knows the Perl core quickly understand what you were
294trying to do, how you were trying to do it, and why the change matters
295to Perl.
7cd58830 296
04c692a8 297=over 4
7cd58830 298
04c692a8 299=item * Why
7cd58830 300
04c692a8 301Your commit message should describe why the change you are making is
531e2078 302important. When someone looks at your change in six months or six
04c692a8 303years, your intent should be clear.
7cd58830 304
04c692a8 305If you're deprecating a feature with the intent of later simplifying
531e2078 306another bit of code, say so. If you're fixing a performance problem or
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307adding a new feature to support some other bit of the core, mention
308that.
7cd58830 309
04c692a8 310=item * What
7cd58830 311
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312Your commit message should describe what part of the Perl core you're
313changing and what you expect your patch to do.
7cd58830 314
04c692a8 315=item * How
7cd58830 316
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317While it's not necessary for documentation changes, new tests or
318trivial patches, it's often worth explaining how your change works.
319Even if it's clear to you today, it may not be clear to a porter next
320month or next year.
d7889f52 321
04c692a8 322=back
d7889f52 323
04c692a8 324A commit message isn't intended to take the place of comments in your
531e2078 325code. Commit messages should describe the change you made, while code
04c692a8 326comments should describe the current state of the code.
d7889f52 327
04c692a8 328If you've just implemented a new feature, complete with doc, tests and
531e2078 329well-commented code, a brief commit message will often suffice. If,
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330however, you've just changed a single character deep in the parser or
331lexer, you might need to write a small novel to ensure that future
332readers understand what you did and why you did it.
d7889f52 333
04c692a8 334=head3 Comments, Comments, Comments
d7889f52 335
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336Be sure to adequately comment your code. While commenting every line
337is unnecessary, anything that takes advantage of side effects of
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338operators, that creates changes that will be felt outside of the
339function being patched, or that others may find confusing should be
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340documented. If you are going to err, it is better to err on the side
341of adding too many comments than too few.
d7889f52 342
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343The best comments explain I<why> the code does what it does, not I<what
344it does>.
d7889f52 345
04c692a8 346=head3 Style
d7889f52 347
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348In general, please follow the particular style of the code you are
349patching.
d7889f52 350
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351In particular, follow these general guidelines for patching Perl
352sources:
cce04beb 353
04c692a8 354=over 4
d7889f52
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355
356=item *
357
04c692a8 3588-wide tabs (no exceptions!)
d7889f52
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359
360=item *
361
04c692a8 3624-wide indents for code, 2-wide indents for nested CPP #defines
ee9468a2 363
cce04beb 364=item *
ee9468a2 365
04c692a8 366Try hard not to exceed 79-columns
bc028b6b 367
ee9468a2
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368=item *
369
04c692a8 370ANSI C prototypes
d7889f52
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371
372=item *
373
04c692a8 374Uncuddled elses and "K&R" style for indenting control constructs
0bec6c03 375
04c692a8 376=item *
d7889f52 377
04c692a8 378No C++ style (//) comments
d7889f52
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379
380=item *
381
04c692a8 382Mark places that need to be revisited with XXX (and revisit often!)
27565cb6
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383
384=item *
385
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386Opening brace lines up with "if" when conditional spans multiple lines;
387should be at end-of-line otherwise
27565cb6 388
04c692a8 389=item *
27565cb6 390
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391In function definitions, name starts in column 0 (return value is on
392previous line)
27565cb6 393
04c692a8 394=item *
27565cb6 395
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396Single space after keywords that are followed by parens, no space
397between function name and following paren
606fd33d 398
27565cb6
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399=item *
400
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401Avoid assignments in conditionals, but if they're unavoidable, use
402extra paren, e.g. "if (a && (b = c)) ..."
27565cb6
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403
404=item *
405
04c692a8 406"return foo;" rather than "return(foo);"
27565cb6
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407
408=item *
409
04c692a8 410"if (!foo) ..." rather than "if (foo == FALSE) ..." etc.
606fd33d 411
a8bd0d47
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412=item *
413
414Do not declare variables using "register". It may be counterproductive
415with modern compilers, and is deprecated in C++, under which the Perl
416source is regularly compiled.
417
5b48d9bb
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418=item *
419
420In-line functions that are in headers that are accessible to XS code
421need to be able to compile without warnings with commonly used extra
422compilation flags, such as gcc's C<-Wswitch-default> which warns
423whenever a switch statement does not have a "default" case. The use of
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424these extra flags is to catch potential problems in legal C code, and
425is often used by Perl aggregators, such as Linux distributors.
5b48d9bb 426
606fd33d 427=back
27565cb6 428
04c692a8 429=head3 Test suite
d7889f52 430
a8d15a22 431If your patch changes code (rather than just changing documentation),
04c692a8 432you should also include one or more test cases which illustrate the bug
531e2078 433you're fixing or validate the new functionality you're adding. In
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434general, you should update an existing test file rather than create a
435new one.
2bbc8d55 436
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437Your test suite additions should generally follow these guidelines
438(courtesy of Gurusamy Sarathy <gsar@activestate.com>):
2bbc8d55 439
04c692a8 440=over 4
0bec6c03 441
04c692a8 442=item *
0bec6c03 443
531e2078 444Know what you're testing. Read the docs, and the source.
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445
446=item *
447
04c692a8 448Tend to fail, not succeed.
0bec6c03 449
04c692a8 450=item *
0bec6c03 451
04c692a8 452Interpret results strictly.
27565cb6 453
04c692a8 454=item *
27565cb6 455
04c692a8 456Use unrelated features (this will flush out bizarre interactions).
27565cb6 457
04c692a8 458=item *
27565cb6 459
04c692a8 460Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
27565cb6 461
04c692a8 462=item *
d7889f52 463
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464Avoid using hardcoded test numbers whenever possible (the EXPECTED/GOT
465found in t/op/tie.t is much more maintainable, and gives better failure
466reports).
d7889f52 467
04c692a8 468=item *
d7889f52 469
04c692a8 470Give meaningful error messages when a test fails.
d7889f52 471
04c692a8 472=item *
d7889f52 473
531e2078 474Avoid using qx// and system() unless you are testing for them. If you
04c692a8 475do use them, make sure that you cover _all_ perl platforms.
d7889f52 476
04c692a8 477=item *
0bec6c03 478
04c692a8 479Unlink any temporary files you create.
63796a85 480
04c692a8 481=item *
0bec6c03 482
04c692a8 483Promote unforeseen warnings to errors with $SIG{__WARN__}.
0bec6c03 484
04c692a8 485=item *
0bec6c03 486
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487Be sure to use the libraries and modules shipped with the version being
488tested, not those that were already installed.
d7889f52 489
04c692a8 490=item *
d7889f52 491
04c692a8 492Add comments to the code explaining what you are testing for.
d7889f52 493
04c692a8 494=item *
d7889f52 495
531e2078 496Make updating the '1..42' string unnecessary. Or make sure that you
04c692a8 497update it.
d7889f52 498
04c692a8 499=item *
d7889f52 500
04c692a8 501Test _all_ behaviors of a given operator, library, or function.
d7889f52 502
04c692a8 503Test all optional arguments.
d7889f52 504
04c692a8 505Test return values in various contexts (boolean, scalar, list, lvalue).
d7889f52 506
04c692a8 507Use both global and lexical variables.
d7889f52 508
04c692a8 509Don't forget the exceptional, pathological cases.
0bec6c03 510
cce04beb 511=back
0bec6c03 512
04c692a8 513=head2 Patching a core module
ee9468a2 514
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515This works just like patching anything else, with one extra
516consideration.
63796a85 517
a8d15a22 518Modules in the F<cpan/> directory of the source tree are maintained
531e2078 519outside of the Perl core. When the author updates the module, the
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520updates are simply copied into the core. See that module's
521documentation or its listing on L<http://search.cpan.org/> for more
522information on reporting bugs and submitting patches.
523
524In most cases, patches to modules in F<cpan/> should be sent upstream
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525and should not be applied to the Perl core individually. If a patch to
526a file in F<cpan/> absolutely cannot wait for the fix to be made
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527upstream, released to CPAN and copied to blead, you must add (or
528update) a C<CUSTOMIZED> entry in the F<"Porting/Maintainers.pl"> file
529to flag that a local modification has been made. See
530F<"Porting/Maintainers.pl"> for more details.
63796a85 531
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532In contrast, modules in the F<dist/> directory are maintained in the
533core.
63796a85 534
04c692a8 535=head2 Updating perldelta
63796a85 536
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537For changes significant enough to warrant a F<pod/perldelta.pod> entry,
538the porters will greatly appreciate it if you submit a delta entry
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539along with your actual change. Significant changes include, but are
540not limited to:
63796a85 541
04c692a8 542=over 4
63796a85 543
04c692a8 544=item *
63796a85 545
04c692a8 546Adding, deprecating, or removing core features
ee9468a2 547
04c692a8 548=item *
ee9468a2 549
04c692a8 550Adding, deprecating, removing, or upgrading core or dual-life modules
ee9468a2 551
04c692a8 552=item *
ee9468a2 553
04c692a8 554Adding new core tests
ee9468a2 555
04c692a8 556=item *
ee9468a2 557
04c692a8 558Fixing security issues and user-visible bugs in the core
cce04beb 559
04c692a8 560=item *
ad7244db 561
04c692a8 562Changes that might break existing code, either on the perl or C level
ad7244db
JH
563
564=item *
565
04c692a8 566Significant performance improvements
ad7244db
JH
567
568=item *
569
04c692a8
DR
570Adding, removing, or significantly changing documentation in the
571F<pod/> directory
ad7244db 572
cce04beb 573=item *
ad7244db 574
04c692a8 575Important platform-specific changes
d7889f52 576
cce04beb
DG
577=back
578
04c692a8 579Please make sure you add the perldelta entry to the right section
531e2078 580within F<pod/perldelta.pod>. More information on how to write good
04c692a8
DR
581perldelta entries is available in the C<Style> section of
582F<Porting/how_to_write_a_perldelta.pod>.
d7889f52 583
04c692a8 584=head2 What makes for a good patch?
d7889f52 585
531e2078 586New features and extensions to the language can be contentious. There
04c692a8
DR
587is no specific set of criteria which determine what features get added,
588but here are some questions to consider when developing a patch:
d7889f52 589
04c692a8 590=head3 Does the concept match the general goals of Perl?
d7889f52 591
04c692a8 592Our goals include, but are not limited to:
d7889f52 593
04c692a8 594=over 4
d7889f52 595
04c692a8 596=item 1.
d7889f52 597
04c692a8 598Keep it fast, simple, and useful.
cce04beb 599
04c692a8 600=item 2.
cce04beb 601
04c692a8 602Keep features/concepts as orthogonal as possible.
902b9dbf 603
04c692a8 604=item 3.
902b9dbf 605
04c692a8 606No arbitrary limits (platforms, data sizes, cultures).
a958818a 607
04c692a8 608=item 4.
ac036724 609
04c692a8 610Keep it open and exciting to use/patch/advocate Perl everywhere.
a958818a 611
04c692a8 612=item 5.
a958818a 613
04c692a8 614Either assimilate new technologies, or build bridges to them.
a958818a 615
04c692a8 616=back
a958818a 617
04c692a8 618=head3 Where is the implementation?
a958818a 619
531e2078 620All the talk in the world is useless without an implementation. In
04c692a8 621almost every case, the person or people who argue for a new feature
531e2078 622will be expected to be the ones who implement it. Porters capable of
04c692a8
DR
623coding new features have their own agendas, and are not available to
624implement your (possibly good) idea.
a1b65709 625
04c692a8 626=head3 Backwards compatibility
37c0adeb 627
531e2078 628It's a cardinal sin to break existing Perl programs. New warnings can
04c692a8 629be contentious--some say that a program that emits warnings is not
531e2078 630broken, while others say it is. Adding keywords has the potential to
04c692a8
DR
631break programs, changing the meaning of existing token sequences or
632functions might break programs.
f50e5b73 633
04c692a8
DR
634The Perl 5 core includes mechanisms to help porters make backwards
635incompatible changes more compatible such as the L<feature> and
531e2078 636L<deprecate> modules. Please use them when appropriate.
902b9dbf 637
04c692a8 638=head3 Could it be a module instead?
902b9dbf 639
04c692a8 640Perl 5 has extension mechanisms, modules and XS, specifically to avoid
531e2078 641the need to keep changing the Perl interpreter. You can write modules
04c692a8
DR
642that export functions, you can give those functions prototypes so they
643can be called like built-in functions, you can even write XS code to
644mess with the runtime data structures of the Perl interpreter if you
645want to implement really complicated things.
902b9dbf 646
04c692a8
DR
647Whenever possible, new features should be prototyped in a CPAN module
648before they will be considered for the core.
902b9dbf 649
04c692a8 650=head3 Is the feature generic enough?
902b9dbf 651
04c692a8
DR
652Is this something that only the submitter wants added to the language,
653or is it broadly useful? Sometimes, instead of adding a feature with a
654tight focus, the porters might decide to wait until someone implements
655the more generalized feature.
902b9dbf 656
04c692a8 657=head3 Does it potentially introduce new bugs?
902b9dbf 658
04c692a8
DR
659Radical rewrites of large chunks of the Perl interpreter have the
660potential to introduce new bugs.
902b9dbf 661
04c692a8 662=head3 How big is it?
902b9dbf 663
531e2078 664The smaller and more localized the change, the better. Similarly, a
04c692a8 665series of small patches is greatly preferred over a single large patch.
902b9dbf 666
04c692a8 667=head3 Does it preclude other desirable features?
902b9dbf 668
04c692a8 669A patch is likely to be rejected if it closes off future avenues of
531e2078 670development. For instance, a patch that placed a true and final
04c692a8
DR
671interpretation on prototypes is likely to be rejected because there are
672still options for the future of prototypes that haven't been addressed.
902b9dbf 673
04c692a8 674=head3 Is the implementation robust?
902b9dbf 675
04c692a8 676Good patches (tight code, complete, correct) stand more chance of going
531e2078 677in. Sloppy or incorrect patches might be placed on the back burner
04c692a8
DR
678until the pumpking has time to fix, or might be discarded altogether
679without further notice.
902b9dbf 680
04c692a8 681=head3 Is the implementation generic enough to be portable?
902b9dbf 682
531e2078 683The worst patches make use of system-specific features. It's highly
04c692a8
DR
684unlikely that non-portable additions to the Perl language will be
685accepted.
902b9dbf 686
04c692a8 687=head3 Is the implementation tested?
902b9dbf 688
04c692a8
DR
689Patches which change behaviour (fixing bugs or introducing new
690features) must include regression tests to verify that everything works
691as expected.
902b9dbf 692
04c692a8
DR
693Without tests provided by the original author, how can anyone else
694changing perl in the future be sure that they haven't unwittingly
695broken the behaviour the patch implements? And without tests, how can
696the patch's author be confident that his/her hard work put into the
697patch won't be accidentally thrown away by someone in the future?
902b9dbf 698
04c692a8 699=head3 Is there enough documentation?
902b9dbf 700
04c692a8 701Patches without documentation are probably ill-thought out or
531e2078 702incomplete. No features can be added or changed without documentation,
04c692a8
DR
703so submitting a patch for the appropriate pod docs as well as the
704source code is important.
902b9dbf 705
04c692a8 706=head3 Is there another way to do it?
902b9dbf 707
04c692a8 708Larry said "Although the Perl Slogan is I<There's More Than One Way to
531e2078 709Do It>, I hesitate to make 10 ways to do something". This is a tricky
04c692a8
DR
710heuristic to navigate, though--one man's essential addition is another
711man's pointless cruft.
902b9dbf 712
04c692a8 713=head3 Does it create too much work?
902b9dbf 714
04c692a8
DR
715Work for the pumpking, work for Perl programmers, work for module
716authors, ... Perl is supposed to be easy.
902b9dbf 717
04c692a8 718=head3 Patches speak louder than words
902b9dbf 719
531e2078 720Working code is always preferred to pie-in-the-sky ideas. A patch to
04c692a8
DR
721add a feature stands a much higher chance of making it to the language
722than does a random feature request, no matter how fervently argued the
a44b8c28
S
723request might be. This ties into "Will it be useful?", as the fact
724that someone took the time to make the patch demonstrates a strong
725desire for the feature.
c406981e 726
04c692a8 727=head1 TESTING
c406981e 728
04c692a8
DR
729The core uses the same testing style as the rest of Perl, a simple
730"ok/not ok" run through Test::Harness, but there are a few special
731considerations.
c406981e 732
531e2078 733There are three ways to write a test in the core: L<Test::More>,
a44b8c28
S
734F<t/test.pl> and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">.
735The decision of which to use depends on what part of the test suite
736you're working on. This is a measure to prevent a high-level failure
737(such as Config.pm breaking) from causing basic functionality tests to
738fail.
c406981e 739
04c692a8
DR
740The F<t/test.pl> library provides some of the features of
741L<Test::More>, but avoids loading most modules and uses as few core
742features as possible.
902b9dbf 743
9e6670f3
DR
744If you write your own test, use the L<Test Anything
745Protocol|http://testanything.org>.
902b9dbf
MLF
746
747=over 4
748
bb52f720 749=item * F<t/base>, F<t/comp> and F<t/opbasic>
902b9dbf 750
04c692a8 751Since we don't know if require works, or even subroutines, use ad hoc
531e2078 752tests for these three. Step carefully to avoid using the feature being
a44b8c28
S
753tested. Tests in F<t/opbasic>, for instance, have been placed there
754rather than in F<t/op> because they test functionality which
755F<t/test.pl> presumes has already been demonstrated to work.
902b9dbf 756
a8d15a22 757=item * F<t/cmd>, F<t/run>, F<t/io> and F<t/op>
902b9dbf 758
04c692a8
DR
759Now that basic require() and subroutines are tested, you can use the
760F<t/test.pl> library.
902b9dbf 761
a8d15a22 762You can also use certain libraries like Config conditionally, but be
04c692a8 763sure to skip the test gracefully if it's not there.
902b9dbf 764
04c692a8 765=item * Everything else
902b9dbf 766
04c692a8 767Now that the core of Perl is tested, L<Test::More> can and should be
531e2078 768used. You can also use the full suite of core modules in the tests.
902b9dbf
MLF
769
770=back
771
a8d15a22 772When you say "make test", Perl uses the F<t/TEST> program to run the
a44b8c28
S
773test suite (except under Win32 where it uses F<t/harness> instead).
774All tests are run from the F<t/> directory, B<not> the directory which
775contains the test. This causes some problems with the tests in
776F<lib/>, so here's some opportunity for some patching.
902b9dbf 777
531e2078 778You must be triply conscious of cross-platform concerns. This usually
04c692a8
DR
779boils down to using L<File::Spec> and avoiding things like C<fork()>
780and C<system()> unless absolutely necessary.
7a834142 781
04c692a8 782=head2 Special C<make test> targets
07aa3531 783
04c692a8 784There are various special make targets that can be used to test Perl
531e2078
FC
785slightly differently than the standard "test" target. Not all them are
786expected to give a 100% success rate. Many of them have several
04c692a8
DR
787aliases, and many of them are not available on certain operating
788systems.
07aa3531 789
04c692a8 790=over 4
d44161bf 791
04c692a8 792=item * test_porting
7a834142 793
04c692a8
DR
794This runs some basic sanity tests on the source tree and helps catch
795basic errors before you submit a patch.
7a834142 796
04c692a8 797=item * minitest
51a35ef1 798
04c692a8
DR
799Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>,
800F<t/op>, F<t/uni> and F<t/mro> tests.
51a35ef1 801
499cea6b 802=item * test.valgrind check.valgrind
51a35ef1 803
04c692a8 804(Only in Linux) Run all the tests using the memory leak + naughty
531e2078 805memory access tool "valgrind". The log files will be named
04c692a8 806F<testname.valgrind>.
83f0ef60 807
04c692a8 808=item * test_harness
83f0ef60 809
04c692a8 810Run the test suite with the F<t/harness> controlling program, instead
531e2078 811of F<t/TEST>. F<t/harness> is more sophisticated, and uses the
04c692a8 812L<Test::Harness> module, thus using this test target supposes that perl
531e2078 813mostly works. The main advantage for our purposes is that it prints a
a44b8c28
S
814detailed summary of failed tests at the end. Also, unlike F<t/TEST>,
815it doesn't redirect stderr to stdout.
83f0ef60 816
04c692a8
DR
817Note that under Win32 F<t/harness> is always used instead of F<t/TEST>,
818so there is no special "test_harness" target.
83f0ef60 819
04c692a8
DR
820Under Win32's "test" target you may use the TEST_SWITCHES and
821TEST_FILES environment variables to control the behaviour of
531e2078 822F<t/harness>. This means you can say
83f0ef60 823
04c692a8
DR
824 nmake test TEST_FILES="op/*.t"
825 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t"
83f0ef60 826
78087e0a
R
827=item * test-notty test_notty
828
829Sets PERL_SKIP_TTY_TEST to true before running normal test.
830
83f0ef60
JH
831=back
832
04c692a8 833=head2 Parallel tests
83f0ef60 834
04c692a8 835The core distribution can now run its regression tests in parallel on
531e2078 836Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS>
04c692a8 837in your environment to the number of tests to run in parallel, and run
531e2078 838C<make test_harness>. On a Bourne-like shell, this can be done as
07aa3531 839
04c692a8 840 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
07aa3531 841
04c692a8
DR
842An environment variable is used, rather than parallel make itself,
843because L<TAP::Harness> needs to be able to schedule individual
844non-conflicting test scripts itself, and there is no standard interface
845to C<make> utilities to interact with their job schedulers.
51a35ef1 846
9e6670f3 847Note that currently some test scripts may fail when run in parallel
a44b8c28
S
848(most notably F<ext/IO/t/io_dir.t>). If necessary, run just the
849failing scripts again sequentially and see if the failures go away.
51a35ef1 850
04c692a8 851=head2 Running tests by hand
51a35ef1 852
9e6670f3
DR
853You can run part of the test suite by hand by using one of the
854following commands from the F<t/> directory:
51a35ef1 855
04c692a8 856 ./perl -I../lib TEST list-of-.t-files
51a35ef1 857
04c692a8 858or
51a35ef1 859
04c692a8 860 ./perl -I../lib harness list-of-.t-files
51a35ef1 861
a8d15a22 862(If you don't specify test scripts, the whole test suite will be run.)
51a35ef1 863
04c692a8 864=head2 Using F<t/harness> for testing
51a35ef1 865
9e6670f3 866If you use C<harness> for testing, you have several command line
531e2078 867options available to you. The arguments are as follows, and are in the
9e6670f3 868order that they must appear if used together.
51a35ef1 869
04c692a8
DR
870 harness -v -torture -re=pattern LIST OF FILES TO TEST
871 harness -v -torture -re LIST OF PATTERNS TO MATCH
07aa3531 872
a8d15a22 873If C<LIST OF FILES TO TEST> is omitted, the file list is obtained from
531e2078 874the manifest. The file list may include shell wildcards which will be
04c692a8 875expanded out.
07aa3531 876
04c692a8 877=over 4
4ae3d70a 878
04c692a8 879=item * -v
4ae3d70a 880
04c692a8
DR
881Run the tests under verbose mode so you can see what tests were run,
882and debug output.
51a35ef1 883
04c692a8 884=item * -torture
4ae3d70a 885
04c692a8 886Run the torture tests as well as the normal set.
4ae3d70a 887
04c692a8 888=item * -re=PATTERN
6c41479b 889
a44b8c28
S
890Filter the file list so that all the test files run match PATTERN.
891Note that this form is distinct from the B<-re LIST OF PATTERNS> form
892below in that it allows the file list to be provided as well.
6c41479b 893
04c692a8 894=item * -re LIST OF PATTERNS
6c41479b 895
04c692a8 896Filter the file list so that all the test files run match
531e2078 897/(LIST|OF|PATTERNS)/. Note that with this form the patterns are joined
04c692a8
DR
898by '|' and you cannot supply a list of files, instead the test files
899are obtained from the MANIFEST.
6c41479b 900
04c692a8 901=back
6c41479b 902
04c692a8 903You can run an individual test by a command similar to
6c41479b 904
a8d15a22 905 ./perl -I../lib path/to/foo.t
6c41479b 906
04c692a8
DR
907except that the harnesses set up some environment variables that may
908affect the execution of the test:
6c41479b
JH
909
910=over 4
911
04c692a8 912=item * PERL_CORE=1
6c41479b 913
a8d15a22 914indicates that we're running this test as part of the perl core test
531e2078 915suite. This is useful for modules that have a dual life on CPAN.
6c41479b 916
04c692a8 917=item * PERL_DESTRUCT_LEVEL=2
6c41479b 918
04c692a8 919is set to 2 if it isn't set already (see
a8d15a22 920L<perlhacktips/PERL_DESTRUCT_LEVEL>).
6c41479b 921
04c692a8 922=item * PERL
6c41479b 923
04c692a8
DR
924(used only by F<t/TEST>) if set, overrides the path to the perl
925executable that should be used to run the tests (the default being
926F<./perl>).
6c41479b 927
04c692a8 928=item * PERL_SKIP_TTY_TEST
6c41479b 929
a44b8c28
S
930if set, tells to skip the tests that need a terminal. It's actually
931set automatically by the Makefile, but can also be forced artificially
932by running 'make test_notty'.
6c41479b 933
04c692a8 934=back
6c41479b 935
04c692a8 936=head3 Other environment variables that may influence tests
6c41479b 937
04c692a8 938=over 4
6c41479b 939
04c692a8 940=item * PERL_TEST_Net_Ping
6c41479b 941
04c692a8 942Setting this variable runs all the Net::Ping modules tests, otherwise
531e2078 943some tests that interact with the outside world are skipped. See
04c692a8 944L<perl58delta>.
6c41479b 945
04c692a8 946=item * PERL_TEST_NOVREXX
cce04beb 947
04c692a8 948Setting this variable skips the vrexx.t tests for OS2::REXX.
cce04beb 949
04c692a8 950=item * PERL_TEST_NUMCONVERTS
cce04beb 951
04c692a8 952This sets a variable in op/numconvert.t.
cce04beb 953
ff5db609
TC
954=item * PERL_TEST_MEMORY
955
956Setting this variable includes the tests in F<t/bigmem/>. This should
a44b8c28
S
957be set to the number of gigabytes of memory available for testing, eg.
958C<PERL_TEST_MEMORY=4> indicates that tests that require 4GiB of
ff5db609
TC
959available memory can be run safely.
960
04c692a8 961=back
cce04beb 962
04c692a8
DR
963See also the documentation for the Test and Test::Harness modules, for
964more environment variables that affect testing.
cce04beb 965
04c692a8 966=head1 MORE READING FOR GUTS HACKERS
cce04beb 967
04c692a8 968To hack on the Perl guts, you'll need to read the following things:
cce04beb 969
04c692a8 970=over 4
cce04beb 971
04c692a8 972=item * L<perlsource>
b8ddf6b3 973
531e2078 974An overview of the Perl source tree. This will help you find the files
04c692a8 975you're looking for.
b8ddf6b3 976
04c692a8 977=item * L<perlinterp>
b8ddf6b3 978
04c692a8
DR
979An overview of the Perl interpreter source code and some details on how
980Perl does what it does.
b8ddf6b3 981
04c692a8 982=item * L<perlhacktut>
b8ddf6b3 983
04c692a8 984This document walks through the creation of a small patch to Perl's C
531e2078 985code. If you're just getting started with Perl core hacking, this will
04c692a8 986help you understand how it works.
b8ddf6b3 987
04c692a8 988=item * L<perlhacktips>
b8ddf6b3 989
531e2078 990More details on hacking the Perl core. This document focuses on lower
04c692a8
DR
991level details such as how to write tests, compilation issues,
992portability, debugging, etc.
b8ddf6b3 993
04c692a8 994If you plan on doing serious C hacking, make sure to read this.
b8ddf6b3 995
04c692a8 996=item * L<perlguts>
b8ddf6b3 997
04c692a8 998This is of paramount importance, since it's the documentation of what
531e2078 999goes where in the Perl source. Read it over a couple of times and it
04c692a8
DR
1000might start to make sense - don't worry if it doesn't yet, because the
1001best way to study it is to read it in conjunction with poking at Perl
1002source, and we'll do that later on.
b8ddf6b3 1003
04c692a8
DR
1004Gisle Aas's "illustrated perlguts", also known as I<illguts>, has very
1005helpful pictures:
9965345d 1006
04c692a8 1007L<http://search.cpan.org/dist/illguts/>
9965345d 1008
04c692a8 1009=item * L<perlxstut> and L<perlxs>
f1fac472 1010
04c692a8
DR
1011A working knowledge of XSUB programming is incredibly useful for core
1012hacking; XSUBs use techniques drawn from the PP code, the portion of
531e2078 1013the guts that actually executes a Perl program. It's a lot gentler to
04c692a8
DR
1014learn those techniques from simple examples and explanation than from
1015the core itself.
f1fac472 1016
04c692a8 1017=item * L<perlapi>
f1fac472 1018
04c692a8
DR
1019The documentation for the Perl API explains what some of the internal
1020functions do, as well as the many macros used in the source.
f1fac472 1021
04c692a8 1022=item * F<Porting/pumpkin.pod>
f1fac472 1023
04c692a8
DR
1024This is a collection of words of wisdom for a Perl porter; some of it
1025is only useful to the pumpkin holder, but most of it applies to anyone
1026wanting to go about Perl development.
f1fac472 1027
04c692a8 1028=back
f1fac472 1029
04c692a8 1030=head1 CPAN TESTERS AND PERL SMOKERS
f1fac472 1031
04c692a8
DR
1032The CPAN testers ( http://testers.cpan.org/ ) are a group of volunteers
1033who test CPAN modules on a variety of platforms.
b8ddf6b3 1034
a8d15a22 1035Perl Smokers ( http://www.nntp.perl.org/group/perl.daily-build/ and
04c692a8
DR
1036http://www.nntp.perl.org/group/perl.daily-build.reports/ )
1037automatically test Perl source releases on platforms with various
1038configurations.
f1fac472 1039
531e2078 1040Both efforts welcome volunteers. In order to get involved in smoke
04c692a8 1041testing of the perl itself visit
531e2078 1042L<http://search.cpan.org/dist/Test-Smoke/>. In order to start smoke
04c692a8
DR
1043testing CPAN modules visit
1044L<http://search.cpan.org/dist/CPANPLUS-YACSmoke/> or
1045L<http://search.cpan.org/dist/minismokebox/> or
1046L<http://search.cpan.org/dist/CPAN-Reporter/>.
f1fac472 1047
04c692a8 1048=head1 WHAT NEXT?
a422fd2d 1049
04c692a8
DR
1050If you've read all the documentation in the document and the ones
1051listed above, you're more than ready to hack on Perl.
a422fd2d 1052
04c692a8 1053Here's some more recommendations
a422fd2d 1054
04c692a8 1055=over 4
a422fd2d
SC
1056
1057=item *
1058
1059Subscribe to perl5-porters, follow the patches and try and understand
1060them; don't be afraid to ask if there's a portion you're not clear on -
1061who knows, you may unearth a bug in the patch...
1062
1063=item *
1064
04c692a8 1065Do read the README associated with your operating system, e.g.
531e2078 1066README.aix on the IBM AIX OS. Don't hesitate to supply patches to that
04c692a8 1067README if you find anything missing or changed over a new OS release.
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1068
1069=item *
1070
a422fd2d 1071Find an area of Perl that seems interesting to you, and see if you can
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S
1072work out how it works. Scan through the source, and step over it in
1073the debugger. Play, poke, investigate, fiddle! You'll probably get to
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1074understand not just your chosen area but a much wider range of
1075F<perl>'s activity as well, and probably sooner than you'd think.
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1076
1077=back
1078
04c692a8 1079=head2 "The Road goes ever on and on, down from the door where it began."
a422fd2d 1080
04c692a8 1081If you can do these things, you've started on the long road to Perl
531e2078 1082porting. Thanks for wanting to help make Perl better - and happy
04c692a8 1083hacking!
a422fd2d 1084
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1085=head2 Metaphoric Quotations
1086
1087If you recognized the quote about the Road above, you're in luck.
1088
04c692a8 1089Most software projects begin each file with a literal description of
531e2078 1090each file's purpose. Perl instead begins each with a literary allusion
04c692a8 1091to that file's purpose.
4ac71550 1092
04c692a8 1093Like chapters in many books, all top-level Perl source files (along
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1094with a few others here and there) begin with an epigrammatic
1095inscription that alludes, indirectly and metaphorically, to the
1096material you're about to read.
4ac71550 1097
a8d15a22 1098Quotations are taken from writings of J.R.R. Tolkien pertaining to his
531e2078 1099Legendarium, almost always from I<The Lord of the Rings>. Chapters and
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1100page numbers are given using the following editions:
1101
1102=over 4
1103
04c692a8 1104=item *
4ac71550 1105
531e2078 1106I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary
04c692a8
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1107edition of 2007 was used, published in the UK by Harper Collins
1108Publishers and in the US by the Houghton Mifflin Company.
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1109
1110=item *
1111
531e2078 1112I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover,
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111350th-anniversary edition of 2004 was used, published in the UK by
1114Harper Collins Publishers and in the US by the Houghton Mifflin
1115Company.
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1116
1117=item *
1118
04c692a8
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1119I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously
1120by his son and literary executor, C.J.R. Tolkien, being the 3rd of the
531e2078 112112 volumes in Christopher's mammoth I<History of Middle Earth>. Page
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1122numbers derive from the hardcover edition, first published in 1983 by
1123George Allen & Unwin; no page numbers changed for the special 3-volume
1124omnibus edition of 2002 or the various trade-paper editions, all again
1125now by Harper Collins or Houghton Mifflin.
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1126
1127=back
1128
04c692a8
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1129Other JRRT books fair game for quotes would thus include I<The
1130Adventures of Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>,
1131and I<The Tale of the Children of Hurin>, all but the first
531e2078 1132posthumously assembled by CJRT. But I<The Lord of the Rings> itself is
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1133perfectly fine and probably best to quote from, provided you can find a
1134suitable quote there.
4ac71550 1135
04c692a8
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1136So if you were to supply a new, complete, top-level source file to add
1137to Perl, you should conform to this peculiar practice by yourself
1138selecting an appropriate quotation from Tolkien, retaining the original
1139spelling and punctuation and using the same format the rest of the
531e2078 1140quotes are in. Indirect and oblique is just fine; remember, it's a
04c692a8 1141metaphor, so being meta is, after all, what it's for.
4ac71550 1142
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1143=head1 AUTHOR
1144
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1145This document was originally written by Nathan Torkington, and is
1146maintained by the perl5-porters mailing list.
b16c2e4a 1147