Devel::Hide(3) User Contributed Perl Documentation Devel::Hide(3)
NAME
Devel::Hide - Forces the unavailability of specified Perl modules (for
testing)
SYNOPSIS
# hide modules globally, across the entire process
use Devel::Hide qw(Module/ToHide.pm);
require Module::ToHide; # fails
use Devel::Hide qw(Test::Pod Test::Pod::Coverage);
require Test::More; # ok
use Test::Pod 1.18; # fails
# hide modules lexically
{
use Devel::Hide qw(-lexically Foo::Bar);
# this will fail to load
eval 'use Foo::Bar';
}
# but this will load
use Foo::Bar;
Other common usage patterns:
$ perl -MDevel::Hide=Module::ToHide Makefile.PL
$ perl -MDevel::Hide=Module::ToHide,Test::Pod Makefile.PL
$ PERL5OPT=-MDevel::Hide
$ DEVEL_HIDE_PM='Module::ToHide Test::Pod'
$ export PERL5OPT DEVEL_HIDE_PM
$ perl Makefile.PL
COMPATIBILITY
global hiding
At some point global hiding may go away and only lexical hiding be
supported. At that point support for perl versions below 5.10 will
be dropped. There will be at least a two year deprecation cycle
before that happens.
You are strongly encouraged to only use lexical hiding and to
update existing code.
perl 5.6
Support will be dropped at some point after 2022-01-01 with no
further warning. This is because bugs in older perls prevent some
code improvements. See commit dd27e50 in the repository if you care
to know what those are.
DESCRIPTION
Given a list of Perl modules/filenames, this module makes "require" and
"use" statements fail (no matter the specified files/modules are
installed or not).
They die with a message like:
Can't locate Module/ToHide.pm in @INC (hidden)
The original intent of this module is to allow Perl developers to test
for alternative behavior when some modules are not available. In a Perl
installation, where many modules are already installed, there is a
chance to screw things up because you take for granted things that may
not be there in other machines.
For example, to test if your distribution does the right thing when a
module is missing, you can do
perl -MDevel::Hide=Test::Pod Makefile.PL
forcing "Test::Pod" to not be found (whether it is installed or not).
Another use case is to force a module which can choose between two
requisites to use the one which is not the default. For example,
"XML::Simple" needs a parser module and may use "XML::Parser" or
"XML::SAX" (preferring the latter). If you have both of them
installed, it will always try "XML::SAX". But you can say:
perl -MDevel::Hide=XML::SAX script_which_uses_xml_simple.pl
NOTE. This module does not use Carp. As said before, denial dies.
This module is pretty trivial. It uses a code reference in @INC to get
rid of specific modules during require - denying they can be
successfully loaded and stopping the search before they have a chance
to be found.
There are three alternative ways to include modules in the hidden list:
import()
this is probably the most commonly used method, called
automagically when you do this:
use Devel::Hide qw(Foo Bar::Baz);
or
perl -MDevel::Hide=...
setting @Devel::Hide::HIDDEN
environment variable DEVEL_HIDE_PM
both of these two only support 'global' hiding, whereas "import()"
supports lexical hiding as well.
Optionally, you can provide some arguments *before* the list of
modules:
-from:children
propagate the list of hidden modules to your process' child
processes. This works by populating "PERL5OPT", and is incompatible
with Taint mode, as explained in perlrun. Of course, this is
unnecessary if your child processes are just forks of the current
one.
-lexically
This is only available on perl 5.10.0 and later. It is a fatal
error to try to use it on an older perl.
Everything following this will only have effect until the end of
the current scope. Yes, that includes "-quiet".
-quiet
suppresses diagnostic output. You will still get told about errors.
This is passed to child processes if -from:children is in effect.
CAVEATS
There is some interaction between "lib" and this module
use Devel::Hide qw(Module/ToHide.pm);
use lib qw(my_lib);
In this case, 'my_lib' enters the include path before the Devel::Hide
hook and if Module/ToHide.pm is found in 'my_lib', it succeeds. More
generally, any code that adds anything to the front of the @INC list
after Devel::Hide is loaded will have this effect.
Also for modules that were loaded before Devel::Hide, "require" and
"use" succeeds.
Since 0.0005, Devel::Hide warns about modules already loaded.
$ perl -MDevel::Hide=Devel::Hide -e ''
Devel::Hide: Too late to hide Devel/Hide.pm
EXPORTS
Nothing is exported.
ENVIRONMENT VARIABLES
DEVEL_HIDE_PM - if defined, the list of modules is added
to the list of hidden modules
DEVEL_HIDE_VERBOSE - on by default. If off, suppresses
the initial message which shows the list of hidden modules
in effect
PERL5OPT - used if you specify '-from:children'
SEE ALSO
"perldoc -f require"
Test::Without::Module(3)
BUGS
bug "-from:children" and "-lexically" don't like each other. Anything
hidden lexically may be hidden from all child processes without
regard for scope. Don't use them together.
Please report any other bugs you find via CPAN RT
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Devel-Hide>.
AUTHORS
Adriano R. Ferreira, <ferreira@cpan.org>
with contributions from David Cantrell <dcantrell@cpan.org>
COPYRIGHT AND LICENSE
Copyright (C) 2005-2007, 2018 by Adriano R. Ferreira
Some parts copyright (C) 2020 by David Cantrell
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.34.1 2021-09-28 Devel::Hide(3)
devel-hide 0.1.500 - Generated Tue Aug 20 11:21:03 CDT 2024