NAME
    Require::HookChain - Chainable require hook

VERSION
    This document describes version 0.013 of Require::HookChain (from Perl
    distribution Require-HookChain), released on 2023-04-22.

SYNOPSIS
    Say you want to create a require hook to prepend some code to the module
    source code that is loaded. In your hook source, in
    Require/HookChain/munge/prepend.pm:

     package Require::HookChain::munge::prepend;

     sub new {
         my ($class, $preamble) = @_;
         bless { preamble => $preamble }, $class;
     }

     sub Require::HookChain::munge::prepend::INC {
         my ($self, $r) = @_;

         # safety, in case we are not called by Require::HookChain
         return () unless ref $r;

         my $src = $r->src;
         return unless defined $src;
         $src = "$self->{preamble};\n$src";
         $r->src($src);
     }

     1;

    In a code to use this hook:

     use Require::HookChain 'munge::prepend' => 'use strict';
     use Foo::Bar; # Foo/Bar.pm will be loaded with added 'use strict;' at the start

    Install another hook, but put it at the end of @INC instead of at the
    beginning:

     use Require::HookChain -end => 1, append => 'some code';

DESCRIPTION
    This module lets you create chainable require hooks. As one already
    understands, Perl lets you put a coderef or object in @INC. In the case
    of object, its "INC" method will be called by Perl:

     package My::INCHandler;
     sub new { ... }
     sub My::INCHandler::INC {
         my ($self, $filename) = @_;
         ...
     }

    The method is passed itself then filename (which is what is passed to
    "require()") and is expected to return nothing or a list of up to four
    values: a scalar reference containing source code, filehandle, reference
    to subroutine, optional state for subroutine (more information can be
    read from the perlfunc manpage). As soon as the first hook in @INC
    returns non-empty value then the search for source code is stopped.

    With "Require::HookChain", you can put multiple hooks in @INC that all
    get executed. When "use"'d, "Require::HookChain" will install its own
    hook at the beginning of @INC which will search for source code in @INC
    as well as execute "INC" method of all the other hooks which are
    instances of "Require::HookChain::*" class. Instead of filename, the
    method is passed a "Require::HookChain::r" object ($r). The method can
    do things on $r, for example retrieve source code via "$r->src" or
    modify source code via "$r->src($new_content)". After the method
    returns, the next "Require::HookChain::*" hook is executed, and so on.
    The final source code will be retrieved from "$r->src" and returned for
    Perl.

    This lets one chainable hook munge the result of the previous chainable
    hook.

    To create your own chainable require hook, see example in "SYNOPSIS".
    First you create a module under the "Require::HookChain::*" namespace,
    then create a constructor as well as "INC" handler.

  Import options
    Options must be specified at the beginning, before specifying

    *   -end

        Bool. If set to true, then hooks will be put at the end of @INC
        instead of at the beginning (after Require::HookChain's own hook).
        Regardless, Require::HookChain's own hook will be put at the
        beginning to allow executing all the other hooks.

    *   -debug

        Bool. If set to true, then debug messages will be printed to stderr.

  Subnamespace organization
    *   Require::HookChain::debug::

        Hooks that do debugging-related stuffs. See also: "log::"
        subnamespace, "timestamp::" subnamespace.

    *   Require::HookChain::filter::

        Hooks that filter module loading due to some criteria. These hooks
        can fail a module being loaded even though the source is available,
        if the additional criteria are not met.

    *   Require::HookChain::log::

        Hooks that add logging to module loading process. See also:
        "debug::" subnamespace.

    *   Require::HookChain::munge::

        Hooks that modify source code.

    *   Require::HookChain::source::

        Hooks that allow loading module source from alternative sources.

    *   Require::HookChain::test::

        Testing-related, particularly testing the Require::HookCHain hook
        module itself.

    *   Require::HookChain::timestamp::

        Hooks that add timestamps during module loading process.

Require::HookChain::r OBJECT
  Methods
   filename
    Usage:

     my $filename = $r->filename;

   src
    Usage:

     my $src = $r->src;
     $r->src($new_src);

    Get or set source code content. Will return undef if source code has not
    been found or set.

FAQ
  Loading a hook does nothing!
    Make sure you use a hook this way:

     use Require::HookChain 'hookname'; # correct

    instead of:

     use Require::HookChain::hookname; # INCORRECT

HOMEPAGE
    Please visit the project's homepage at
    <https://metacpan.org/release/Require-HookChain>.

SOURCE
    Source repository is at
    <https://github.com/perlancar/perl-Require-HookChain>.

SEE ALSO
    RHC for convenience of using on the command-line or one-liners.

AUTHOR
    perlancar <perlancar@cpan.org>

CONTRIBUTING
    To contribute, you can send patches by email/via RT, or send pull
    requests on GitHub.

    Most of the time, you don't need to build the distribution yourself. You
    can simply modify the code, then test via:

     % prove -l

    If you want to build the distribution (e.g. to try to install it locally
    on your system), you can install Dist::Zilla,
    Dist::Zilla::PluginBundle::Author::PERLANCAR,
    Pod::Weaver::PluginBundle::Author::PERLANCAR, and sometimes one or two
    other Dist::Zilla- and/or Pod::Weaver plugins. Any additional steps
    required beyond that are considered a bug and can be reported to me.

COPYRIGHT AND LICENSE
    This software is copyright (c) 2023, 2022, 2020, 2017 by perlancar
    <perlancar@cpan.org>.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

BUGS
    Please report any bugs or feature requests on the bugtracker website
    <https://rt.cpan.org/Public/Dist/Display.html?Name=Require-HookChain>

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.

