NAME

App::perlimports - Make implicit imports explicit

VERSION

version 0.000006

SYNOPSIS

Update a file in place. (Make sure you can revert the file if you need to.)

    perlimports --filename test-data/foo.pl --inplace-edit

If some of your imported modules are in local directories, you can give some hints as to where to find them:

    perlimports --filename test-data/foo.pl --inplace-edit --libs t/lib,/some/dir/lib

Redirect output to a new file:

    perlimports --filename test-data/foo.pl > foo.new.pl

COMMAND LINE INTERFACE

See perlimports for more complete documentation of the command line interface.

ANNOTATIONS/IGNORING MODULES

Aside from the documented command line switches for ignoring modules, you can add annotations in your code.

    use Encode; ## no perlimports

The above will tell perlimports not to attempt a tidy of this line.

    ## no perlimports
    use Encode;
    use Cpanel::JSON::XS;
    ## use perlimports

    use POSIX ();

The above will tell perlimports not to tidy the two modules contained inside of the annotations.

Please note that since perlimports needs to know as much as possible about what's going on in a file, the annotations don't prevent modules from being loaded. It's only a directive to leave the lines in the file unchanged after processing.

VIM

If you're a vim user, you can pipe your import statements to perlimports directly.

    :vnoremap <silent> im :!perlimports --read-stdin --filename '%:p'<CR>

The above statement will allow you to visually select one or more lines of code and have them updated in place by perlimports. Once you have selected the code enter im to have your imports (re)formatted.

MOTIVATION

Many Perl modules helpfully export functions and variables by default. These provide handy shortcuts when you're writing a quick or small script, but they can quickly become a maintenance burden as code grows organically. When code increases in complexity, it leads to greater costs in terms of development time. Conversely, reducing code complexity can speed up development. This tool aims to reduce complexity to further this goal.

While importing symbols by default or using export tags provides a convenient shorthand for getting work done, this shorthand requires the developer to retain knowledge of these defaults and tags in order to understand the code. perlimports aims to allow you to develop your code as you see fit, while still giving you a viable option of tidying your imports automatically. In much the same way as you might use perltidy to format your code, you can now automate the process of making your imports easier to understand. Let's look at some examples.

Where is this function defined?

You may come across some code like this:

    use strict;
    use warnings;

    use HTTP::Request::Common;
    use LWP::UserAgent;

    my $ua = LWP::UserAgent->new;
    my $req = $ua->request( GET 'https://metacpan.org/' );
    print $req->content;

Where does GET come from? If you're not familiar with HTTP::Request::Common, you may not realize that the statement use HTTP::Request::Common has implicitly imported the functions GET, HEAD, PUT, PATCH, POST and OPTIONS into to this block of code.

What would happen if we used perlimports to import all needed functions explicitly? It might look something like this:

    use strict;
    use warnings;

    use HTTP::Request::Common qw( GET );
    use LWP::UserAgent ();

    my $ua = LWP::UserAgent->new;
    my $req = $ua->request( GET 'https://metacpan.org/' );
    print $req->content;

The code above makes it immediately obvious where GET originates, which in turn makes it easier for us to look up its documentation. It has the added bonus of also not importing HEAD, PUT or any of the other functions which HTTP::Request::Common exports by default. So, those functions cannot unwittingly be used later in the code. This makes for more understandable code for present day you, future you and any others tasked with reading your code at some future point.

Keep in mind that this simple act can save much time for developers who are not intimately familiar with Perl and the default exports of many CPAN modules.

Are we even using all of these imports?

Imagine the following import statement

    use HTTP::Status qw(
        is_cacheable_by_default
        is_client_error
        is_error
        is_info
        is_redirect
        is_server_error
        is_success
        status_message
    );

followed by 3,000 lines of code. How do you know if all of these functions are actually being used? Were they ever used? You can grep all of these function names manually or you can remove them by trial and error to see what breaks. This is a doable solution, but it does not scale well to scripts and modules with many imports or to large code bases with many imports. Having an unmaintained list of imports is preferable to implicit imports, but it would be helpful to automate maintaining this list.

perlimports can, in many situations, clean up your import statements and automate this maintenance burden away. This makes it easier for you to write clean code, which is easier to understand.

Are we even using all of these modules?

In cases where code is implicitly importing from modules or where explicit imports are not being curated, it can be hard to discover which modules are no longer being used in a script, module or even a code base. Removing unused modules from code can lead to gains in performance and decrease in consumption of resources. Removing entire modules from your code base can decrease the number of dependencies which you need to manage and decrease friction in your your deployment process.

perlimports does not remove unused modules for you, but using it to actively tidy your imports can make this manual process much easier to manage.

Enforcing a consistent style

Having a messy list of module imports makes your code harder to read. Imagine this:

    use Cpanel::JSON::XS;
    use Database::Migrator::Types qw( HashRef ArrayRef Object Str Bool Maybe CodeRef FileHandle RegexpRef );
    use List::AllUtils qw( uniq any );
    use LWP::UserAgent    q{};
    use Try::Tiny qw/ catch     try /;
    use WWW::Mechanize  q<>;

perlimports turns the above list into:

    use Cpanel::JSON::XS ();
    use Database::Migrator::Types qw(
        ArrayRef
        Bool
        CodeRef
        FileHandle
        HashRef
        Maybe
        Object
        RegexpRef
        Str
    );
    use List::AllUtils qw( any uniq );
    use LWP::UserAgent ();
    use Try::Tiny qw( catch try);
    use WWW::Mechanize ();

Where possible, perlimports will enforce a consistent style of parentheses and will also sort your imports and break up long lines. As mentioned above, if some imports are no longer in use, perlimports will helpfully remove these for you.

Import tags

Import tags may obscure where symbols are coming from. While import tags provide a useful shorthand, they can contribute to code complexity by obscuring the origin of imported symbols. Consider:

    use HTTP::Status qw(:constants :is status_message);

The above line imports the status_message() function as well *some other things* via :constants and :is. What exactly are these things? We'll need to read the documentation to know for sure.

perlimports can audit your code and expand the line above to list the symbols which you are actually importing. So, the line above might now look something like:

    use HTTP::Status qw(
        HTTP_ACCEPTED
        HTTP_BAD_REQUEST
        HTTP_CONTINUE
        HTTP_I_AM_A_TEAPOT
        HTTP_MOVED_PERMANENTLY
        HTTP_NO_CODE
        HTTP_NOT_FOUND
        HTTP_OK
        HTTP_PAYLOAD_TOO_LARGE
        HTTP_PERMANENT_REDIRECT
        HTTP_RANGE_NOT_SATISFIABLE
        HTTP_REQUEST_ENTITY_TOO_LARGE
        HTTP_REQUEST_RANGE_NOT_SATISFIABLE
        HTTP_REQUEST_URI_TOO_LARGE
        HTTP_TOO_EARLY
        HTTP_UNORDERED_COLLECTION
        HTTP_URI_TOO_LONG
        is_cacheable_by_default
        is_client_error
        is_error
        is_info
        is_redirect
        is_server_error
        is_success
        status_message
    );

This is more verbose, but grepping your code will now reveal to you where something like is_cacheable_by_default gets defined. You have increased the lines of code, but you have also reduced complexity.

DESCRIPTION

This distribution provides the perlimports binary, which aims to automate the cleanup and maintenance of Perl import statements.

CAVEATS

There are lots of shenanigans that Perl modules can get up to. This code will not find exports for all of those cases, but it should only attempt to rewrite imports which it knows how to handle. Please file a bug report in all other cases.

SEE ALSO

Perl::Critic::Policy::TooMuchCode::ProhibitUnusedImport, Perl::Critic::Policy::TooMuchCode::ProhibitUnusedInclude and Perl::Critic::Policy::TooMuchCode::ProhibitUnusedConstant

AUTHOR

Olaf Alders <olaf@wundercounter.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2020 by Olaf Alders.

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