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9b657a62 PF |
1 | package autodie::hints; |
2 | ||
3 | use strict; | |
4 | use warnings; | |
5 | ||
eb8d423f PF |
6 | use constant PERL58 => ( $] < 5.009 ); |
7 | ||
8 | our $VERSION = '2.03'; | |
9b657a62 PF |
9 | |
10 | =head1 NAME | |
11 | ||
12 | autodie::hints - Provide hints about user subroutines to autodie | |
13 | ||
14 | =head1 SYNOPSIS | |
15 | ||
16 | package Your::Module; | |
17 | ||
18 | our %DOES = ( 'autodie::hints::provider' => 1 ); | |
19 | ||
20 | sub AUTODIE_HINTS { | |
21 | return { | |
22 | foo => { scalar => HINTS, list => SOME_HINTS }, | |
23 | bar => { scalar => HINTS, list => MORE_HINTS }, | |
24 | } | |
25 | } | |
26 | ||
27 | # Later, in your main program... | |
28 | ||
29 | use Your::Module qw(foo bar); | |
30 | use autodie qw(:default foo bar); | |
31 | ||
32 | foo(); # succeeds or dies based on scalar hints | |
33 | ||
34 | # Alternatively, hints can be set on subroutines we've | |
35 | # imported. | |
36 | ||
37 | use autodie::hints; | |
38 | use Some::Module qw(think_positive); | |
39 | ||
40 | BEGIN { | |
41 | autodie::hints->set_hints_for( | |
42 | \&think_positive, | |
43 | { | |
44 | fail => sub { $_[0] <= 0 } | |
45 | } | |
46 | ) | |
47 | } | |
48 | use autodie qw(think_positive); | |
49 | ||
50 | think_positive(...); # Returns positive or dies. | |
51 | ||
52 | ||
53 | =head1 DESCRIPTION | |
54 | ||
55 | =head2 Introduction | |
56 | ||
57 | The L<autodie> pragma is very smart when it comes to working with | |
58 | Perl's built-in functions. The behaviour for these functions are | |
59 | fixed, and C<autodie> knows exactly how they try to signal failure. | |
60 | ||
61 | But what about user-defined subroutines from modules? If you use | |
62 | C<autodie> on a user-defined subroutine then it assumes the following | |
63 | behaviour to demonstrate failure: | |
64 | ||
65 | =over | |
66 | ||
67 | =item * | |
68 | ||
69 | A false value, in scalar context | |
70 | ||
71 | =item * | |
72 | ||
73 | An empty list, in list context | |
74 | ||
75 | =item * | |
76 | ||
77 | A list containing a single undef, in list context | |
78 | ||
79 | =back | |
80 | ||
81 | All other return values (including the list of the single zero, and the | |
82 | list containing a single empty string) are considered successful. However, | |
83 | real-world code isn't always that easy. Perhaps the code you're working | |
eb8d423f | 84 | with returns a string containing the word "FAIL" upon failure, or a |
9b657a62 PF |
85 | two element list containing C<(undef, "human error message")>. To make |
86 | autodie work with these sorts of subroutines, we have | |
87 | the I<hinting interface>. | |
88 | ||
89 | The hinting interface allows I<hints> to be provided to C<autodie> | |
90 | on how it should detect failure from user-defined subroutines. While | |
91 | these I<can> be provided by the end-user of C<autodie>, they are ideally | |
92 | written into the module itself, or into a helper module or sub-class | |
93 | of C<autodie> itself. | |
94 | ||
95 | =head2 What are hints? | |
96 | ||
97 | A I<hint> is a subroutine or value that is checked against the | |
98 | return value of an autodying subroutine. If the match returns true, | |
eb8d423f | 99 | C<autodie> considers the subroutine to have failed. |
9b657a62 PF |
100 | |
101 | If the hint provided is a subroutine, then C<autodie> will pass | |
102 | the complete return value to that subroutine. If the hint is | |
103 | any other value, then C<autodie> will smart-match against the | |
eb8d423f | 104 | value provided. In Perl 5.8.x there is no smart-match operator, and as such |
9b657a62 PF |
105 | only subroutine hints are supported in these versions. |
106 | ||
eb8d423f | 107 | Hints can be provided for both scalar and list contexts. Note |
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108 | that an autodying subroutine will never see a void context, as |
109 | C<autodie> always needs to capture the return value for examination. | |
110 | Autodying subroutines called in void context act as if they're called | |
111 | in a scalar context, but their return value is discarded after it | |
112 | has been checked. | |
113 | ||
114 | =head2 Example hints | |
115 | ||
116 | Hints may consist of scalars, array references, regular expressions and | |
117 | subroutine references. You can specify different hints for how | |
118 | failure should be identified in scalar and list contexts. | |
119 | ||
120 | These examples apply for use in the C<AUTODIE_HINTS> subroutine and when | |
121 | calling C<autodie::hints->set_hints_for()>. | |
122 | ||
123 | The most common context-specific hints are: | |
124 | ||
125 | # Scalar failures always return undef: | |
126 | { scalar => undef } | |
127 | ||
128 | # Scalar failures return any false value [default expectation]: | |
129 | { scalar => sub { ! $_[0] } } | |
130 | ||
131 | # Scalar failures always return zero explicitly: | |
132 | { scalar => '0' } | |
133 | ||
eb8d423f | 134 | # List failures always return an empty list: |
9b657a62 PF |
135 | { list => [] } |
136 | ||
137 | # List failures return () or (undef) [default expectation]: | |
138 | { list => sub { ! @_ || @_ == 1 && !defined $_[0] } } | |
139 | ||
140 | # List failures return () or a single false value: | |
141 | { list => sub { ! @_ || @_ == 1 && !$_[0] } } | |
142 | ||
143 | # List failures return (undef, "some string") | |
144 | { list => sub { @_ == 2 && !defined $_[0] } } | |
145 | ||
146 | # Unsuccessful foo() returns 'FAIL' or '_FAIL' in scalar context, | |
147 | # returns (-1) in list context... | |
148 | autodie::hints->set_hints_for( | |
149 | \&foo, | |
150 | { | |
151 | scalar => qr/^ _? FAIL $/xms, | |
152 | list => [-1], | |
153 | } | |
154 | ); | |
155 | ||
156 | # Unsuccessful foo() returns 0 in all contexts... | |
157 | autodie::hints->set_hints_for( | |
158 | \&foo, | |
159 | { | |
160 | scalar => 0, | |
161 | list => [0], | |
162 | } | |
eb8d423f | 163 | ); |
9b657a62 PF |
164 | |
165 | This "in all contexts" construction is very common, and can be | |
166 | abbreviated, using the 'fail' key. This sets both the C<scalar> | |
167 | and C<list> hints to the same value: | |
168 | ||
169 | # Unsuccessful foo() returns 0 in all contexts... | |
170 | autodie::hints->set_hints_for( | |
171 | \&foo, | |
172 | { | |
173 | fail => sub { @_ == 1 and defined $_[0] and $_[0] == 0 } | |
174 | } | |
175 | ); | |
176 | ||
177 | # Unsuccessful think_positive() returns negative number on failure... | |
178 | autodie::hints->set_hints_for( | |
179 | \&think_positive, | |
180 | { | |
181 | fail => sub { $_[0] < 0 } | |
182 | } | |
183 | ); | |
184 | ||
185 | # Unsuccessful my_system() returns non-zero on failure... | |
186 | autodie::hints->set_hints_for( | |
187 | \&my_system, | |
188 | { | |
189 | fail => sub { $_[0] != 0 } | |
190 | } | |
191 | ); | |
192 | ||
193 | =head1 Manually setting hints from within your program | |
194 | ||
195 | If you are using a module which returns something special on failure, then | |
196 | you can manually create hints for each of the desired subroutines. Once | |
197 | the hints are specified, they are available for all files and modules loaded | |
198 | thereafter, thus you can move this work into a module and it will still | |
199 | work. | |
200 | ||
201 | use Some::Module qw(foo bar); | |
202 | use autodie::hints; | |
203 | ||
204 | autodie::hints->set_hints_for( | |
205 | \&foo, | |
206 | { | |
207 | scalar => SCALAR_HINT, | |
208 | list => LIST_HINT, | |
209 | } | |
210 | ); | |
211 | autodie::hints->set_hints_for( | |
212 | \&bar, | |
213 | { fail => SOME_HINT, } | |
214 | ); | |
215 | ||
216 | It is possible to pass either a subroutine reference (recommended) or a fully | |
217 | qualified subroutine name as the first argument. This means you can set hints | |
218 | on modules that I<might> get loaded: | |
219 | ||
220 | use autodie::hints; | |
221 | autodie::hints->set_hints_for( | |
222 | 'Some::Module:bar', { fail => SCALAR_HINT, } | |
223 | ); | |
224 | ||
225 | This technique is most useful when you have a project that uses a | |
226 | lot of third-party modules. You can define all your possible hints | |
227 | in one-place. This can even be in a sub-class of autodie. For | |
228 | example: | |
229 | ||
230 | package my::autodie; | |
231 | ||
232 | use parent qw(autodie); | |
233 | use autodie::hints; | |
234 | ||
235 | autodie::hints->set_hints_for(...); | |
236 | ||
237 | 1; | |
238 | ||
239 | You can now C<use my::autodie>, which will work just like the standard | |
240 | C<autodie>, but is now aware of any hints that you've set. | |
241 | ||
242 | =head1 Adding hints to your module | |
243 | ||
244 | C<autodie> provides a passive interface to allow you to declare hints for | |
245 | your module. These hints will be found and used by C<autodie> if it | |
246 | is loaded, but otherwise have no effect (or dependencies) without autodie. | |
247 | To set these, your module needs to declare that it I<does> the | |
248 | C<autodie::hints::provider> role. This can be done by writing your | |
249 | own C<DOES> method, using a system such as C<Class::DOES> to handle | |
250 | the heavy-lifting for you, or declaring a C<%DOES> package variable | |
251 | with a C<autodie::hints::provider> key and a corresponding true value. | |
252 | ||
253 | Note that checking for a C<%DOES> hash is an C<autodie>-only | |
254 | short-cut. Other modules do not use this mechanism for checking | |
255 | roles, although you can use the C<Class::DOES> module from the | |
256 | CPAN to allow it. | |
257 | ||
258 | In addition, you must define a C<AUTODIE_HINTS> subroutine that returns | |
259 | a hash-reference containing the hints for your subroutines: | |
260 | ||
eb8d423f | 261 | package Your::Module; |
9b657a62 PF |
262 | |
263 | # We can use the Class::DOES from the CPAN to declare adherence | |
264 | # to a role. | |
265 | ||
266 | use Class::DOES 'autodie::hints::provider' => 1; | |
267 | ||
268 | # Alternatively, we can declare the role in %DOES. Note that | |
269 | # this is an autodie specific optimisation, although Class::DOES | |
270 | # can be used to promote this to a true role declaration. | |
271 | ||
272 | our %DOES = ( 'autodie::hints::provider' => 1 ); | |
273 | ||
274 | # Finally, we must define the hints themselves. | |
275 | ||
276 | sub AUTODIE_HINTS { | |
277 | return { | |
278 | foo => { scalar => HINTS, list => SOME_HINTS }, | |
279 | bar => { scalar => HINTS, list => MORE_HINTS }, | |
280 | baz => { fail => HINTS }, | |
281 | } | |
282 | } | |
283 | ||
284 | This allows your code to set hints without relying on C<autodie> and | |
285 | C<autodie::hints> being loaded, or even installed. In this way your | |
286 | code can do the right thing when C<autodie> is installed, but does not | |
287 | need to depend upon it to function. | |
288 | ||
289 | =head1 Insisting on hints | |
290 | ||
291 | When a user-defined subroutine is wrapped by C<autodie>, it will | |
292 | use hints if they are available, and otherwise reverts to the | |
293 | I<default behaviour> described in the introduction of this document. | |
294 | This can be problematic if we expect a hint to exist, but (for | |
295 | whatever reason) it has not been loaded. | |
296 | ||
297 | We can ask autodie to I<insist> that a hint be used by prefixing | |
298 | an exclamation mark to the start of the subroutine name. A lone | |
299 | exclamation mark indicates that I<all> subroutines after it must | |
300 | have hints declared. | |
301 | ||
302 | # foo() and bar() must have their hints defined | |
303 | use autodie qw( !foo !bar baz ); | |
304 | ||
305 | # Everything must have hints (recommended). | |
306 | use autodie qw( ! foo bar baz ); | |
307 | ||
308 | # bar() and baz() must have their hints defined | |
309 | use autodie qw( foo ! bar baz ); | |
310 | ||
311 | # Enable autodie for all of Perl's supported built-ins, | |
312 | # as well as for foo(), bar() and baz(). Everything must | |
313 | # have hints. | |
314 | use autodie qw( ! :all foo bar baz ); | |
315 | ||
316 | If hints are not available for the specified subroutines, this will cause a | |
317 | compile-time error. Insisting on hints for Perl's built-in functions | |
318 | (eg, C<open> and C<close>) is always successful. | |
319 | ||
320 | Insisting on hints is I<strongly> recommended. | |
321 | ||
322 | =cut | |
323 | ||
324 | # TODO: implement regular expression hints | |
325 | ||
326 | use constant UNDEF_ONLY => sub { not defined $_[0] }; | |
327 | use constant EMPTY_OR_UNDEF => sub { | |
328 | ! @_ or | |
329 | @_==1 && !defined $_[0] | |
330 | }; | |
331 | ||
332 | use constant EMPTY_ONLY => sub { @_ == 0 }; | |
333 | use constant EMPTY_OR_FALSE => sub { | |
334 | ! @_ or | |
335 | @_==1 && !$_[0] | |
336 | }; | |
337 | ||
eb8d423f PF |
338 | use constant SINGLE_TRUE => sub { @_ == 1 and not $_[0] }; |
339 | ||
9b657a62 PF |
340 | use constant DEFAULT_HINTS => { |
341 | scalar => UNDEF_ONLY, | |
342 | list => EMPTY_OR_UNDEF, | |
343 | }; | |
344 | ||
eb8d423f | 345 | |
9b657a62 PF |
346 | use constant HINTS_PROVIDER => 'autodie::hints::provider'; |
347 | ||
348 | use base qw(Exporter); | |
349 | ||
350 | our $DEBUG = 0; | |
351 | ||
352 | # Only ( undef ) is a strange but possible situation for very | |
353 | # badly written code. It's not supported yet. | |
354 | ||
9b657a62 | 355 | my %Hints = ( |
eb8d423f PF |
356 | 'File::Copy::copy' => { scalar => SINGLE_TRUE, list => SINGLE_TRUE }, |
357 | 'File::Copy::move' => { scalar => SINGLE_TRUE, list => SINGLE_TRUE }, | |
358 | 'File::Copy::cp' => { scalar => SINGLE_TRUE, list => SINGLE_TRUE }, | |
359 | 'File::Copy::mv' => { scalar => SINGLE_TRUE, list => SINGLE_TRUE }, | |
9b657a62 PF |
360 | ); |
361 | ||
362 | # Start by using Sub::Identify if it exists on this system. | |
363 | ||
364 | eval { require Sub::Identify; Sub::Identify->import('get_code_info'); }; | |
365 | ||
366 | # If it doesn't exist, we'll define our own. This code is directly | |
367 | # taken from Rafael Garcia's Sub::Identify 0.04, used under the same | |
368 | # license as Perl itself. | |
369 | ||
370 | if ($@) { | |
371 | require B; | |
372 | ||
373 | no warnings 'once'; | |
374 | ||
375 | *get_code_info = sub ($) { | |
376 | ||
377 | my ($coderef) = @_; | |
378 | ref $coderef or return; | |
379 | my $cv = B::svref_2object($coderef); | |
380 | $cv->isa('B::CV') or return; | |
381 | # bail out if GV is undefined | |
382 | $cv->GV->isa('B::SPECIAL') and return; | |
383 | ||
384 | return ($cv->GV->STASH->NAME, $cv->GV->NAME); | |
385 | }; | |
386 | ||
387 | } | |
388 | ||
389 | sub sub_fullname { | |
390 | return join( '::', get_code_info( $_[1] ) ); | |
391 | } | |
392 | ||
393 | my %Hints_loaded = (); | |
394 | ||
395 | sub load_hints { | |
396 | my ($class, $sub) = @_; | |
397 | ||
398 | my ($package) = ( $sub =~ /(.*)::/ ); | |
399 | ||
400 | if (not defined $package) { | |
401 | require Carp; | |
402 | Carp::croak( | |
403 | "Internal error in autodie::hints::load_hints - no package found. | |
404 | "); | |
405 | } | |
406 | ||
407 | # Do nothing if we've already tried to load hints for | |
408 | # this package. | |
409 | return if $Hints_loaded{$package}++; | |
410 | ||
411 | my $hints_available = 0; | |
412 | ||
413 | { | |
414 | no strict 'refs'; ## no critic | |
415 | ||
416 | if ($package->can('DOES') and $package->DOES(HINTS_PROVIDER) ) { | |
417 | $hints_available = 1; | |
418 | } | |
eb8d423f PF |
419 | elsif ( PERL58 and $package->isa(HINTS_PROVIDER) ) { |
420 | $hints_available = 1; | |
421 | } | |
9b657a62 PF |
422 | elsif ( ${"${package}::DOES"}{HINTS_PROVIDER.""} ) { |
423 | $hints_available = 1; | |
424 | } | |
425 | } | |
426 | ||
427 | return if not $hints_available; | |
428 | ||
429 | my %package_hints = %{ $package->AUTODIE_HINTS }; | |
430 | ||
431 | foreach my $sub (keys %package_hints) { | |
432 | ||
433 | my $hint = $package_hints{$sub}; | |
434 | ||
435 | # Ensure we have a package name. | |
436 | $sub = "${package}::$sub" if $sub !~ /::/; | |
437 | ||
438 | # TODO - Currently we don't check for conflicts, should we? | |
439 | $Hints{$sub} = $hint; | |
440 | ||
441 | $class->normalise_hints(\%Hints, $sub); | |
442 | } | |
443 | ||
444 | return; | |
445 | ||
446 | } | |
447 | ||
448 | sub normalise_hints { | |
449 | my ($class, $hints, $sub) = @_; | |
450 | ||
451 | if ( exists $hints->{$sub}->{fail} ) { | |
452 | ||
453 | if ( exists $hints->{$sub}->{scalar} or | |
454 | exists $hints->{$sub}->{list} | |
455 | ) { | |
456 | # TODO: Turn into a proper diagnostic. | |
457 | require Carp; | |
458 | local $Carp::CarpLevel = 1; | |
459 | Carp::croak("fail hints cannot be provided with either scalar or list hints for $sub"); | |
460 | } | |
461 | ||
462 | # Set our scalar and list hints. | |
463 | ||
464 | $hints->{$sub}->{scalar} = | |
465 | $hints->{$sub}->{list} = delete $hints->{$sub}->{fail}; | |
466 | ||
467 | return; | |
468 | ||
469 | } | |
470 | ||
471 | # Check to make sure all our hints exist. | |
472 | ||
473 | foreach my $hint (qw(scalar list)) { | |
474 | if ( not exists $hints->{$sub}->{$hint} ) { | |
475 | # TODO: Turn into a proper diagnostic. | |
476 | require Carp; | |
477 | local $Carp::CarpLevel = 1; | |
478 | Carp::croak("$hint hint missing for $sub"); | |
479 | } | |
480 | } | |
481 | ||
482 | return; | |
483 | } | |
484 | ||
485 | sub get_hints_for { | |
486 | my ($class, $sub) = @_; | |
487 | ||
488 | my $subname = $class->sub_fullname( $sub ); | |
489 | ||
490 | # If we have hints loaded for a sub, then return them. | |
491 | ||
492 | if ( exists $Hints{ $subname } ) { | |
493 | return $Hints{ $subname }; | |
494 | } | |
495 | ||
496 | # If not, we try to load them... | |
497 | ||
498 | $class->load_hints( $subname ); | |
499 | ||
500 | # ...and try again! | |
501 | ||
502 | if ( exists $Hints{ $subname } ) { | |
503 | return $Hints{ $subname }; | |
504 | } | |
505 | ||
506 | # It's the caller's responsibility to use defaults if desired. | |
507 | # This allows on autodie to insist on hints if needed. | |
508 | ||
509 | return; | |
510 | ||
511 | } | |
512 | ||
513 | sub set_hints_for { | |
514 | my ($class, $sub, $hints) = @_; | |
515 | ||
516 | if (ref $sub) { | |
517 | $sub = $class->sub_fullname( $sub ); | |
518 | ||
519 | require Carp; | |
520 | ||
521 | $sub or Carp::croak("Attempts to set_hints_for unidentifiable subroutine"); | |
522 | } | |
523 | ||
524 | if ($DEBUG) { | |
525 | warn "autodie::hints: Setting $sub to hints: $hints\n"; | |
526 | } | |
527 | ||
528 | $Hints{ $sub } = $hints; | |
529 | ||
530 | $class->normalise_hints(\%Hints, $sub); | |
531 | ||
532 | return; | |
533 | } | |
534 | ||
535 | 1; | |
536 | ||
537 | __END__ | |
538 | ||
539 | ||
540 | =head1 Diagnostics | |
541 | ||
542 | =over 4 | |
543 | ||
544 | =item Attempts to set_hints_for unidentifiable subroutine | |
545 | ||
546 | You've called C<< autodie::hints->set_hints_for() >> using a subroutine | |
547 | reference, but that reference could not be resolved back to a | |
548 | subroutine name. It may be an anonymous subroutine (which can't | |
549 | be made autodying), or may lack a name for other reasons. | |
550 | ||
551 | If you receive this error with a subroutine that has a real name, | |
552 | then you may have found a bug in autodie. See L<autodie/BUGS> | |
553 | for how to report this. | |
554 | ||
555 | =item fail hints cannot be provided with either scalar or list hints for %s | |
556 | ||
557 | When defining hints, you can either supply both C<list> and | |
558 | C<scalar> keywords, I<or> you can provide a single C<fail> keyword. | |
559 | You can't mix and match them. | |
560 | ||
561 | =item %s hint missing for %s | |
562 | ||
563 | You've provided either a C<scalar> hint without supplying | |
564 | a C<list> hint, or vice-versa. You I<must> supply both C<scalar> | |
565 | and C<list> hints, I<or> a single C<fail> hint. | |
566 | ||
567 | =back | |
568 | ||
569 | =head1 ACKNOWLEDGEMENTS | |
570 | ||
571 | =over | |
572 | ||
573 | =item * | |
574 | ||
575 | Dr Damian Conway for suggesting the hinting interface and providing the | |
576 | example usage. | |
577 | ||
578 | =item * | |
579 | ||
580 | Jacinta Richardson for translating much of my ideas into this | |
581 | documentation. | |
582 | ||
583 | =back | |
584 | ||
585 | =head1 AUTHOR | |
586 | ||
587 | Copyright 2009, Paul Fenwick E<lt>pjf@perltraining.com.auE<gt> | |
588 | ||
589 | =head1 LICENSE | |
590 | ||
591 | This module is free software. You may distribute it under the | |
592 | same terms as Perl itself. | |
593 | ||
594 | =head1 SEE ALSO | |
595 | ||
596 | L<autodie>, L<Class::DOES> | |
597 | ||
598 | =cut |