Profile of Module/Runtime.pm

Filename	/usr/share/perl5/Module/Runtime.pm
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1			=head1 NAME
2
3			Module::Runtime - runtime module handling
4
5			=head1 SYNOPSIS
6
7			use Module::Runtime qw(
8			$module_name_rx is_module_name check_module_name
9			module_notional_filename require_module
10			);
11
12			if($module_name =~ /\A$module_name_rx\z/o) { ...
13			if(is_module_name($module_name)) { ...
14			check_module_name($module_name);
15
16			$notional_filename = module_notional_filename($module_name);
17			require_module($module_name);
18
19			use Module::Runtime qw(use_module use_package_optimistically);
20
21			$bi = use_module("Math::BigInt", 1.31)->new("1_234");
22			$widget = use_package_optimistically("Local::Widget")->new;
23
24			use Module::Runtime qw(
25			$top_module_spec_rx $sub_module_spec_rx
26			is_module_spec check_module_spec
27			compose_module_name
28			);
29
30			if($spec =~ /\A$top_module_spec_rx\z/o) { ...
31			if($spec =~ /\A$sub_module_spec_rx\z/o) { ...
32			if(is_module_spec("Standard::Prefix", $spec)) { ...
33			check_module_spec("Standard::Prefix", $spec);
34
35			$module_name =
36			compose_module_name("Standard::Prefix", $spec);
37
38			=head1 DESCRIPTION
39
40			The functions exported by this module deal with runtime handling of
41			Perl modules, which are normally handled at compile time. This module
42			avoids using any other modules, so that it can be used in low-level
43			infrastructure.
44
45			The parts of this module that work with module names apply the same syntax
46			that is used for barewords in Perl source. In principle this syntax
47			can vary between versions of Perl, and this module applies the syntax of
48			the Perl on which it is running. In practice the usable syntax hasn't
49			changed yet. There's some intent for Unicode module names to be supported
50			in the future, but this hasn't yet amounted to any consistent facility.
51
52			The functions of this module whose purpose is to load modules include
53			workarounds for three old Perl core bugs regarding C<require>. These
54			workarounds are applied on any Perl version where the bugs exist, except
55			for a case where one of the bugs cannot be adequately worked around in
56			pure Perl.
57
58			=head2 Module name syntax
59
60			The usable module name syntax has not changed from Perl 5.000 up to
61			Perl 5.19.8. The syntax is composed entirely of ASCII characters.
62			From Perl 5.6 onwards there has been some attempt to allow the use of
63			non-ASCII Unicode characters in Perl source, but it was fundamentally
64			broken (like the entirety of Perl 5.6's Unicode handling) and remained
65			pretty much entirely unusable until it got some attention in the Perl
66			5.15 series. Although Unicode is now consistently accepted by the
67			parser in some places, it remains broken for module names. Furthermore,
68			there has not yet been any work on how to map Unicode module names into
69			filenames, so in that respect also Unicode module names are unusable.
70
71			The module name syntax is, precisely: the string must consist of one or
72			more segments separated by C<::>; each segment must consist of one or more
73			identifier characters (ASCII alphanumerics plus "_"); the first character
74			of the string must not be a digit. Thus "C<IO::File>", "C<warnings>",
75			and "C<foo::123::x_0>" are all valid module names, whereas "C<IO::>"
76			and "C<1foo::bar>" are not. C<'> separators are not permitted by this
77			module, though they remain usable in Perl source, being translated to
78			C<::> in the parser.
79
80			=head2 Core bugs worked around
81
82			The first bug worked around is core bug [perl #68590], which causes
83			lexical state in one file to leak into another that is C<require>d/C<use>d
84			from it. This bug is present from Perl 5.6 up to Perl 5.10, and is
85			fixed in Perl 5.11.0. From Perl 5.9.4 up to Perl 5.10.0 no satisfactory
86			workaround is possible in pure Perl. The workaround means that modules
87			loaded via this module don't suffer this pollution of their lexical
88			state. Modules loaded in other ways, or via this module on the Perl
89			versions where the pure Perl workaround is impossible, remain vulnerable.
90			The module L<Lexical::SealRequireHints> provides a complete workaround
91			for this bug.
92
93			The second bug worked around causes some kinds of failure in module
94			loading, principally compilation errors in the loaded module, to be
95			recorded in C<%INC> as if they were successful, so later attempts to load
96			the same module immediately indicate success. This bug is present up
97			to Perl 5.8.9, and is fixed in Perl 5.9.0. The workaround means that a
98			compilation error in a module loaded via this module won't be cached as
99			a success. Modules loaded in other ways remain liable to produce bogus
100			C<%INC> entries, and if a bogus entry exists then it will mislead this
101			module if it is used to re-attempt loading.
102
103			The third bug worked around causes the wrong context to be seen at
104			file scope of a loaded module, if C<require> is invoked in a location
105			that inherits context from a higher scope. This bug is present up to
106			Perl 5.11.2, and is fixed in Perl 5.11.3. The workaround means that
107			a module loaded via this module will always see the correct context.
108			Modules loaded in other ways remain vulnerable.
109
110			=cut
111
112			package Module::Runtime;
113
114			# Don't "use 5.006" here, because Perl 5.15.6 will load feature.pm if
115			# the version check is done that way.
116			BEGIN { require 5.006; }
117			# Don't "use warnings" here, to avoid dependencies. Do standardise the
118			# warning status by lexical override; unfortunately the only safe bitset
119			# to build in is the empty set, equivalent to "no warnings".
120			BEGIN { ${^WARNING_BITS} = ""; }
121			# Don't "use strict" here, to avoid dependencies.
122
123			our $VERSION = "0.014";
124
125			# Don't use Exporter here, to avoid dependencies.
126			our @EXPORT_OK = qw(
127			$module_name_rx is_module_name is_valid_module_name check_module_name
128			module_notional_filename require_module
129			use_module use_package_optimistically
130			$top_module_spec_rx $sub_module_spec_rx
131			is_module_spec is_valid_module_spec check_module_spec
132			compose_module_name
133			);
134			my %export_ok = map { ($_ => undef) } @EXPORT_OK;
135			sub import {
136			my $me = shift;
137			my $callpkg = caller(0);
138			my $errs = "";
139			foreach(@_) {
140			if(exists $export_ok{$_}) {
141			# We would need to do "no strict 'refs'" here
142			# if we had enabled strict at file scope.
143			if(/\A\$(.*)\z/s) {
144			*{$callpkg."::".$1} = \$$1;
145			} else {
146			*{$callpkg."::".$_} = \&$_;
147			}
148			} else {
149			$errs .= "\"$_\" is not exported by the $me module\n";
150			}
151			}
152			if($errs ne "") {
153			die "${errs}Can't continue after import errors ".
154			"at @{[(caller(0))[1]]} line @{[(caller(0))[2]]}.\n";
155			}
156			}
157
158			# Logic duplicated from Params::Classify. Duplicating it here avoids
159			# an extensive and potentially circular dependency graph.
160			sub _is_string($) {
161			my($arg) = @_;
162			return defined($arg) && ref(\$arg) eq "SCALAR";
163			}
164
165			=head1 REGULAR EXPRESSIONS
166
167			These regular expressions do not include any anchors, so to check
168			whether an entire string matches a syntax item you must supply the
169			anchors yourself.
170
171			=over
172
173			=item $module_name_rx
174
175			Matches a valid Perl module name in bareword syntax.
176
177			=cut
178
179			our $module_name_rx = qr/[A-Z_a-z][0-9A-Z_a-z](?:::[0-9A-Z_a-z]+)/;
180
181			=item $top_module_spec_rx
182
183			Matches a module specification for use with L</compose_module_name>,
184			where no prefix is being used.
185
186			=cut
187
188			my $qual_module_spec_rx =
189			qr#(?:/\|::)[A-Z_a-z][0-9A-Z_a-z](?:(?:/\|::)[0-9A-Z_a-z]+)#;
190
191			my $unqual_top_module_spec_rx =
192			qr#[A-Z_a-z][0-9A-Z_a-z](?:(?:/\|::)[0-9A-Z_a-z]+)#;
193
194			our $top_module_spec_rx = qr/$qual_module_spec_rx\|$unqual_top_module_spec_rx/o;
195
196			=item $sub_module_spec_rx
197
198			Matches a module specification for use with L</compose_module_name>,
199			where a prefix is being used.
200
201			=cut
202
203			my $unqual_sub_module_spec_rx = qr#[0-9A-Z_a-z]+(?:(?:/\|::)[0-9A-Z_a-z]+)*#;
204
205			our $sub_module_spec_rx = qr/$qual_module_spec_rx\|$unqual_sub_module_spec_rx/o;
206
207			=back
208
209			=head1 FUNCTIONS
210
211			=head2 Basic module handling
212
213			=over
214
215			=item is_module_name(ARG)
216
217			Returns a truth value indicating whether I<ARG> is a plain string
218			satisfying Perl module name syntax as described for L</$module_name_rx>.
219
220			=cut
221
222			sub is_module_name($) { _is_string($_[0]) && $_[0] =~ /\A$module_name_rx\z/o }
223
224			=item is_valid_module_name(ARG)
225
226			Deprecated alias for L</is_module_name>.
227
228			=cut
229
230			*is_valid_module_name = \&is_module_name;
231
232			=item check_module_name(ARG)
233
234			Check whether I<ARG> is a plain string
235			satisfying Perl module name syntax as described for L</$module_name_rx>.
236			Return normally if it is, or C<die> if it is not.
237
238			=cut
239
240			sub check_module_name($) {
241			unless(&is_module_name) {
242			die +(_is_string($_[0]) ? "`$_[0]'" : "argument").
243			" is not a module name\n";
244			}
245			}
246
247			=item module_notional_filename(NAME)
248
249			Generates a notional relative filename for a module, which is used in
250			some Perl core interfaces.
251			The I<NAME> is a string, which should be a valid module name (one or
252			more C<::>-separated segments). If it is not a valid name, the function
253			C<die>s.
254
255			The notional filename for the named module is generated and returned.
256			This filename is always in Unix style, with C</> directory separators
257			and a C<.pm> suffix. This kind of filename can be used as an argument to
258			C<require>, and is the key that appears in C<%INC> to identify a module,
259			regardless of actual local filename syntax.
260
261			=cut
262
263			sub module_notional_filename($) {
264			&check_module_name;
265			my($name) = @_;
266			$name =~ s!::!/!g;
267			return $name.".pm";
268			}
269
270			=item require_module(NAME)
271
272			This is essentially the bareword form of C<require>, in runtime form.
273			The I<NAME> is a string, which should be a valid module name (one or
274			more C<::>-separated segments). If it is not a valid name, the function
275			C<die>s.
276
277			The module specified by I<NAME> is loaded, if it hasn't been already,
278			in the manner of the bareword form of C<require>. That means that a
279			search through C<@INC> is performed, and a byte-compiled form of the
280			module will be used if available.
281
282			The return value is as for C<require>. That is, it is the value returned
283			by the module itself if the module is loaded anew, or C<1> if the module
284			was already loaded.
285
286			=cut
287
288			# Don't "use constant" here, to avoid dependencies.
289			BEGIN {
290			*_WORK_AROUND_HINT_LEAKAGE =
291			"$]" < 5.011 && !("$]" >= 5.009004 && "$]" < 5.010001)
292			? sub(){1} : sub(){0};
293			*_WORK_AROUND_BROKEN_MODULE_STATE = "$]" < 5.009 ? sub(){1} : sub(){0};
294			}
295
296			BEGIN { if(_WORK_AROUND_BROKEN_MODULE_STATE) { eval q{
297			sub Module::Runtime::__GUARD__::DESTROY {
298			delete $INC{$_[0]->[0]} if @{$_[0]};
299			}
300			1;
301			}; die $@ if $@ ne ""; } }
302
303			sub require_module($) {
304			# Localise %^H to work around [perl #68590], where the bug exists
305			# and this is a satisfactory workaround. The bug consists of
306			# %^H state leaking into each required module, polluting the
307			# module's lexical state.
308			local %^H if _WORK_AROUND_HINT_LEAKAGE;
309			if(_WORK_AROUND_BROKEN_MODULE_STATE) {
310			my $notional_filename = &module_notional_filename;
311			my $guard = bless([ $notional_filename ],
312			"Module::Runtime::__GUARD__");
313			my $result = CORE::require($notional_filename);
314			pop @$guard;
315			return $result;
316			} else {
317	1	10µs	return scalar(CORE::require(&module_notional_filename));
318			}
319			}
320
321			=back
322
323			=head2 Structured module use
324
325			=over
326
327			=item use_module(NAME[, VERSION])
328
329			This is essentially C<use> in runtime form, but without the importing
330			feature (which is fundamentally a compile-time thing). The I<NAME> is
331			handled just like in C<require_module> above: it must be a module name,
332			and the named module is loaded as if by the bareword form of C<require>.
333
334			If a I<VERSION> is specified, the C<VERSION> method of the loaded module is
335			called with the specified I<VERSION> as an argument. This normally serves to
336			ensure that the version loaded is at least the version required. This is
337			the same functionality provided by the I<VERSION> parameter of C<use>.
338
339			On success, the name of the module is returned. This is unlike
340			L</require_module>, and is done so that the entire call to L</use_module>
341			can be used as a class name to call a constructor, as in the example in
342			the synopsis.
343
344			=cut
345
346			sub use_module($;$) {
347			my($name, $version) = @_;
348			require_module($name);
349			$name->VERSION($version) if @_ >= 2;
350			return $name;
351			}
352
353			=item use_package_optimistically(NAME[, VERSION])
354
355			This is an analogue of L</use_module> for the situation where there is
356			uncertainty as to whether a package/class is defined in its own module
357			or by some other means. It attempts to arrange for the named package to
358			be available, either by loading a module or by doing nothing and hoping.
359
360			An attempt is made to load the named module (as if by the bareword form
361			of C<require>). If the module cannot be found then it is assumed that
362			the package was actually already loaded by other means, and no error
363			is signalled. That's the optimistic bit.
364
365			This is mostly the same operation that is performed by the L<base> pragma
366			to ensure that the specified base classes are available. The behaviour
367			of L<base> was simplified in version 2.18, and later improved in version
368			2.20, and on both occasions this function changed to match.
369
370			If a I<VERSION> is specified, the C<VERSION> method of the loaded package is
371			called with the specified I<VERSION> as an argument. This normally serves
372			to ensure that the version loaded is at least the version required.
373			On success, the name of the package is returned. These aspects of the
374			function work just like L</use_module>.
375
376			=cut
377
378			sub use_package_optimistically($;$) {
379			my($name, $version) = @_;
380			my $fn = module_notional_filename($name);
381			eval { local $SIG{__DIE__}; require_module($name); };
382			die $@ if $@ ne "" &&
383			($@ !~ /\ACan't locate \Q$fn\E .+ at \Q@{[__FILE__]}\E line/s \|\|
384			$@ =~ /^Compilation\ failed\ in\ require
385			\ at\ \Q@{[__FILE__]}\E\ line/xm);
386			$name->VERSION($version) if @_ >= 2;
387			return $name;
388			}
389
390			=back
391
392			=head2 Module name composition
393
394			=over
395
396			=item is_module_spec(PREFIX, SPEC)
397
398			Returns a truth value indicating
399			whether I<SPEC> is valid input for L</compose_module_name>.
400			See below for what that entails. Whether a I<PREFIX> is supplied affects
401			the validity of I<SPEC>, but the exact value of the prefix is unimportant,
402			so this function treats I<PREFIX> as a truth value.
403
404			=cut
405
406			sub is_module_spec($$) {
407			my($prefix, $spec) = @_;
408			return _is_string($spec) &&
409			$spec =~ ($prefix ? qr/\A$sub_module_spec_rx\z/o :
410			qr/\A$top_module_spec_rx\z/o);
411			}
412
413			=item is_valid_module_spec(PREFIX, SPEC)
414
415			Deprecated alias for L</is_module_spec>.
416
417			=cut
418
419			*is_valid_module_spec = \&is_module_spec;
420
421			=item check_module_spec(PREFIX, SPEC)
422
423			Check whether I<SPEC> is valid input for L</compose_module_name>.
424			Return normally if it is, or C<die> if it is not.
425
426			=cut
427
428			sub check_module_spec($$) {
429			unless(&is_module_spec) {
430			die +(_is_string($_[1]) ? "`$_[1]'" : "argument").
431			" is not a module specification\n";
432			}
433			}
434
435			=item compose_module_name(PREFIX, SPEC)
436
437			This function is intended to make it more convenient for a user to specify
438			a Perl module name at runtime. Users have greater need for abbreviations
439			and context-sensitivity than programmers, and Perl module names get a
440			little unwieldy. I<SPEC> is what the user specifies, and this function
441			translates it into a module name in standard form, which it returns.
442
443			I<SPEC> has syntax approximately that of a standard module name: it
444			should consist of one or more name segments, each of which consists
445			of one or more identifier characters. However, C</> is permitted as a
446			separator, in addition to the standard C<::>. The two separators are
447			entirely interchangeable.
448
449			Additionally, if I<PREFIX> is not C<undef> then it must be a module
450			name in standard form, and it is prefixed to the user-specified name.
451			The user can inhibit the prefix addition by starting I<SPEC> with a
452			separator (either C</> or C<::>).
453
454			=cut
455
456			sub compose_module_name($$) {
457			my($prefix, $spec) = @_;
458			check_module_name($prefix) if defined $prefix;
459			&check_module_spec;
460			if($spec =~ s#\A(?:/\|::)##) {
461			# OK
462			} else {
463			$spec = $prefix."::".$spec if defined $prefix;
464			}
465			$spec =~ s#/#::#g;
466			return $spec;
467			}
468
469			=back
470
471			=head1 BUGS
472
473			On Perl versions 5.7.2 to 5.8.8, if C<require> is overridden by the
474			C<CORE::GLOBAL> mechanism, it is likely to break the heuristics used by
475			L</use_package_optimistically>, making it signal an error for a missing
476			module rather than assume that it was already loaded. From Perl 5.8.9
477			onwards, and on 5.7.1 and earlier, this module can avoid being confused
478			by such an override. On the affected versions, a C<require> override
479			might be installed by L<Lexical::SealRequireHints>, if something requires
480			its bugfix but for some reason its XS implementation isn't available.
481
482			=head1 SEE ALSO
483
484			L<Lexical::SealRequireHints>,
485			L<base>,
486			L<perlfunc/require>,
487			L<perlfunc/use>
488
489			=head1 AUTHOR
490
491			Andrew Main (Zefram) <zefram@fysh.org>
492
493			=head1 COPYRIGHT
494
495			Copyright (C) 2004, 2006, 2007, 2009, 2010, 2011, 2012, 2014
496			Andrew Main (Zefram) <zefram@fysh.org>
497
498			=head1 LICENSE
499
500			This module is free software; you can redistribute it and/or modify it
501			under the same terms as Perl itself.
502
503			=cut
504
505			1;