| Module::Runtime - runtime module handling |
Module::Runtime - runtime module handling
use Module::Runtime qw(
$module_name_rx is_module_name check_module_name
module_notional_filename require_module);
if($module_name =~ /\A$module_name_rx\z/o) { ...
if(is_module_name($module_name)) { ...
check_module_name($module_name);
$notional_filename = module_notional_filename($module_name);
require_module($module_name);
use Module::Runtime qw(use_module use_package_optimistically);
$bi = use_module("Math::BigInt", 1.31)->new("1_234");
$widget = use_package_optimistically("Local::Widget")->new;
use Module::Runtime qw(
$top_module_spec_rx $sub_module_spec_rx
is_module_spec check_module_spec
compose_module_name);
if($spec =~ /\A$top_module_spec_rx\z/o) { ...
if($spec =~ /\A$sub_module_spec_rx\z/o) { ...
if(is_module_spec("Standard::Prefix", $spec)) { ...
check_module_spec("Standard::Prefix", $spec);
$module_name = compose_module_name("Standard::Prefix", $spec);
The functions exported by this module deal with runtime handling of Perl modules, which are normally handled at compile time. This module avoids using any other modules, so that it can be used in low-level infrastructure.
The parts of this module that work with module names apply the same syntax that is used for barewords in Perl source. In principle this syntax can vary between versions of Perl, and this module applies the syntax of the Perl on which it is running. In practice the usable syntax hasn't changed yet. There's some intent for Unicode module names to be supported in the future, but this hasn't yet amounted to any consistent facility.
The functions of this module whose purpose is to load modules include
workarounds for three old Perl core bugs regarding require. These
workarounds are applied on any Perl version where the bugs exist, except
for a case where one of the bugs cannot be adequately worked around in
pure Perl.
The usable module name syntax has not changed from Perl 5.000 up to Perl 5.19.8. The syntax is composed entirely of ASCII characters. From Perl 5.6 onwards there has been some attempt to allow the use of non-ASCII Unicode characters in Perl source, but it was fundamentally broken (like the entirety of Perl 5.6's Unicode handling) and remained pretty much entirely unusable until it got some attention in the Perl 5.15 series. Although Unicode is now consistently accepted by the parser in some places, it remains broken for module names. Furthermore, there has not yet been any work on how to map Unicode module names into filenames, so in that respect also Unicode module names are unusable.
The module name syntax is, precisely: the string must consist of one or
more segments separated by ::; each segment must consist of one or more
identifier characters (ASCII alphanumerics plus ``_''); the first character
of the string must not be a digit. Thus ``IO::File'', ``warnings'',
and ``foo::123::x_0'' are all valid module names, whereas ``IO::''
and ``1foo::bar'' are not. ' separators are not permitted by this
module, though they remain usable in Perl source, being translated to
:: in the parser.
The first bug worked around is core bug [perl #68590], which causes
lexical state in one file to leak into another that is required/used
from it. This bug is present from Perl 5.6 up to Perl 5.10, and is
fixed in Perl 5.11.0. From Perl 5.9.4 up to Perl 5.10.0 no satisfactory
workaround is possible in pure Perl. The workaround means that modules
loaded via this module don't suffer this pollution of their lexical
state. Modules loaded in other ways, or via this module on the Perl
versions where the pure Perl workaround is impossible, remain vulnerable.
The module the Lexical::SealRequireHints manpage provides a complete workaround
for this bug.
The second bug worked around causes some kinds of failure in module
loading, principally compilation errors in the loaded module, to be
recorded in %INC as if they were successful, so later attempts to load
the same module immediately indicate success. This bug is present up
to Perl 5.8.9, and is fixed in Perl 5.9.0. The workaround means that a
compilation error in a module loaded via this module won't be cached as
a success. Modules loaded in other ways remain liable to produce bogus
%INC entries, and if a bogus entry exists then it will mislead this
module if it is used to re-attempt loading.
The third bug worked around causes the wrong context to be seen at
file scope of a loaded module, if require is invoked in a location
that inherits context from a higher scope. This bug is present up to
Perl 5.11.2, and is fixed in Perl 5.11.3. The workaround means that
a module loaded via this module will always see the correct context.
Modules loaded in other ways remain vulnerable.
These regular expressions do not include any anchors, so to check whether an entire string matches a syntax item you must supply the anchors yourself.
is_module_name(ARG)is_valid_module_name(ARG)check_module_name(ARG)die if it is not.
module_notional_filename(NAME)::-separated segments). If it is not a valid name, the function
dies.
The notional filename for the named module is generated and returned.
This filename is always in Unix style, with / directory separators
and a .pm suffix. This kind of filename can be used as an argument to
require, and is the key that appears in %INC to identify a module,
regardless of actual local filename syntax.
require_module(NAME)require, in runtime form.
The NAME is a string, which should be a valid module name (one or
more ::-separated segments). If it is not a valid name, the function
dies.
The module specified by NAME is loaded, if it hasn't been already,
in the manner of the bareword form of require. That means that a
search through @INC is performed, and a byte-compiled form of the
module will be used if available.
The return value is as for require. That is, it is the value returned
by the module itself if the module is loaded anew, or 1 if the module
was already loaded.
use in runtime form, but without the importing
feature (which is fundamentally a compile-time thing). The NAME is
handled just like in require_module above: it must be a module name,
and the named module is loaded as if by the bareword form of require.
If a VERSION is specified, the VERSION method of the loaded module is
called with the specified VERSION as an argument. This normally serves to
ensure that the version loaded is at least the version required. This is
the same functionality provided by the VERSION parameter of use.
On success, the name of the module is returned. This is unlike require_module, and is done so that the entire call to use_module can be used as a class name to call a constructor, as in the example in the synopsis.
An attempt is made to load the named module (as if by the bareword form
of require). If the module cannot be found then it is assumed that
the package was actually already loaded by other means, and no error
is signalled. That's the optimistic bit.
Warning: this optional module loading is liable to cause unreliable
behaviour, including security problems. It interacts especially badly
with having . in @INC, which was the default state of affairs in
Perls prior to 5.25.11. If a package is actually defined by some means
other than a module, then applying this function to it causes a spurious
attempt to load a module that is expected to be non-existent. If a
module actually exists under that name then it will be unintentionally
loaded. If . is in @INC and this code is ever run with the current
directory being one writable by a malicious user (such as /tmp), then
the malicious user can easily cause the victim to run arbitrary code, by
creating a module file under the predictable spuriously-loaded name in the
writable directory. Generally, optional module loading should be avoided.
This is mostly the same operation that is performed by the the base manpage pragma to ensure that the specified base classes are available. The behaviour of the base manpage was simplified in version 2.18, and later improved in version 2.20, and on both occasions this function changed to match.
If a VERSION is specified, the VERSION method of the loaded package is
called with the specified VERSION as an argument. This normally serves
to ensure that the version loaded is at least the version required.
On success, the name of the package is returned. These aspects of the
function work just like use_module.
die if it is not.
SPEC has syntax approximately that of a standard module name: it
should consist of one or more name segments, each of which consists
of one or more identifier characters. However, / is permitted as a
separator, in addition to the standard ::. The two separators are
entirely interchangeable.
Additionally, if PREFIX is not undef then it must be a module
name in standard form, and it is prefixed to the user-specified name.
The user can inhibit the prefix addition by starting SPEC with a
separator (either / or ::).
On Perl versions 5.7.2 to 5.8.8, if require is overridden by the
CORE::GLOBAL mechanism, it is likely to break the heuristics used by
use_package_optimistically, making it signal an error for a missing
module rather than assume that it was already loaded. From Perl 5.8.9
onwards, and on 5.7.1 and earlier, this module can avoid being confused
by such an override. On the affected versions, a require override
might be installed by the Lexical::SealRequireHints manpage, if something requires
its bugfix but for some reason its XS implementation isn't available.
the Lexical::SealRequireHints manpage, the base manpage, require in the perlfunc manpage, use in the perlfunc manpage
Andrew Main (Zefram) <zefram@fysh.org>
Copyright (C) 2004, 2006, 2007, 2009, 2010, 2011, 2012, 2014, 2017 Andrew Main (Zefram) <zefram@fysh.org>
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| Module::Runtime - runtime module handling |