Mix Unused

Mix compiler tracer for detecting unused public functions.

Installation

def deps do
  [
    {:mix_unused, "~> 0.3.0"}
  ]
end

The docs can be found at https://hexdocs.pm/mix_unused.

Usage

After installation you need to add :unused as a compiler to the list of Mix compilers:

defmodule MySystem.MixProject do
  use Mix.Project

  def project do
    [
      compilers: [:unused] ++ Mix.compilers(),
      # In case of Phoenix projects you need to add it to the list
      # compilers: [:unused, :phoenix, :gettext] ++ Mix.compilers()
      # ...
      #
      # If you want to only run it in the dev environment you could do
      # it by using `compilers: compilers(Mix.env()) ++ Mix.compilers()`
      # instead and then returning the right compilers per environment.
    ]
  end

  # ...
end

Then you just need to run mix compile or mix compile --force as usual and unused hints will be added to the end of the output.

Cleaning your project

The tool keeps track of the calls traced during the compilation. The first time make sure that there is no compiled code:

mix clean

Doing so all the application code is recompiled and the calls are traced properly.

It is recommended to also perform a clean in the CI when the build does not start from a fresh project, for instance:

mix do clean, compile --all-warnings --warnings-as-errors

Please make sure you don't improperly override the clean task with an alias:

def project do
  [
    # ⋯
    aliases: [
      # don't do this:
      clean: "deps.unlock --unused",

      # do this:
      clean: ["clean", "deps.unlock --unused"],
    ],
    # ⋯
  ]
end

Warning

This isn't perfect solution and this will not find dynamic calls in form of:

apply(mod, func, args)

So this mean that, for example, if you have custom child_spec/1 definition then mix unused can return such function as unused even when you are using that indirectly in your supervisor.

This issue can be mitigated using the Unreachable check, explained below.

Configuration

You can configure the tool using the unused options in the project configuration. The following is the default configuration.

def project do
  [
    # ⋯
    unused: [
      checks: [
        # find public functions that could be private
        MixUnused.Analyzers.Private,
        # find unused public functions
        MixUnused.Analyzers.Unused,
        # find functions called only recursively
        MixUnused.Analyzers.RecursiveOnly
      ],
      ignore: [],
      limit: nil,
      paths: nil,
      severity: :hint
    ],
    # ⋯
  ]
end

It supports the following options:

• checks: list of analyzer modules to use.

  In alternative to the default set, you can use the MixUnused.Analyzers.Unreachable check (see the specific guide).

• ignore: list of ignored functions, example:

  [
    {:_, ~r/^__.+__\??$/, :_},
    {~r/^MyAppWeb\..*Controller/, :_, 2},
    {MyApp.Test, :foo, 1..2}
  ]

  See the Mix.Tasks.Compile.Unused task for further details.

• limit: max number of results to report (available also as the command option --limit).

• paths: report only functions defined in such paths.

  Useful to restrict the reported functions only to the functions defined in specific paths (i.e. set paths: ["lib"] to ignore functions defined in the tests folder).

• severity: severity of the reported messages. Allowed levels are :hint, :information, :warning, and :error.

Copyright and License

Copyright © 2021 by Łukasz Niemier

This work is free. You can redistribute it and/or modify it under the terms of the MIT License. See the LICENSE file for more details.