unused/README.md

# Unused [![Build Status](https://travis-ci.org/joshuaclayton/unused.svg?branch=master)](https://travis-ci.org/joshuaclayton/unused)

A command line tool to identify unused code.

# NOTICE: As of May 27, 2020, this version of Unused has been deprecated

Unused has been rewritten and now lives at https://github.com/unused-code/unused

Issues, updates, and all future work will occur there.

![Image of Unused Output](http://i.giphy.com/3o7qDT1I4OfQxnJTvW.gif)

## "What kinds of projects can I used it on?"

Anything.

Yes, literally anything.

It's probably best if you have a file generated from `ctags` it can read from
(it looks in `.git`, `tmp`, and the root directory for a `tags` file), but if
you have another way to pipe a bunch of
methods/functions/classes/modules/whatever in, that works too.

Right now, there are some special cases built in for Rails and Phoenix apps
(specifically, assumptions about what's fine to only have one reference to,
e.g. Controllers in Rails and Views in Phoenix), but it'll work on Rubygems,
Elixir packages, or anything else.

That said, **be confident the code you're removing won't break your program**.
Especially with projects built in Ruby, Elixir, or JavaScript, there are ways
to dynamically trigger or define behavior that may be surprising. A test suite
can help here, but still cannot determine every possible execution path.

## Installing and Updating

### Homebrew (Recommended)

You can install [my formulae] via [Homebrew] with `brew tap`:

```sh
brew tap joshuaclayton/formulae
```

Next, run:

```sh
brew install unused
```

[my formulae]: https://github.com/joshuaclayton/homebrew-formulae
[Homebrew]: http://brew.sh/

This will install `unused` and its corresponding dependencies.

To update, run:

```sh
brew update
brew upgrade unused
```

Alternatively, you can install with [Stack] or by hand. Because it needs to compile, installation times may vary, but it's often several minutes.

### Stack

If you already have [Stack] installed, ensure you have the latest list of
packages:

```sh
stack update
```

Verify Stack is using at least `lts-6.0` when installing by checking the
global project settings in `~/.stack/global-project/stack.yaml`.

Once that is complete, run:

```sh
stack install unused
```

This will install unused in the appropriate directory for Stack; you'll want
to ensure your `$PATH` reflects this.

### Installing by hand

This project is written in [Haskell] and uses [Stack].

Once you have these tools installed and the project cloned locally:

```sh
stack setup
stack install
```

This will generate a binary in `$HOME/.local/bin`; ensure this directory is in
your `$PATH`.

[Haskell]: https://www.haskell.org
[Stack]: http://www.haskellstack.org

### Install via Docker

Once [Docker is installed], create a binary within your `$PATH` to run the
image:

```bash
#!/usr/bin/env bash

docker run --rm -it -v $(pwd):/code joshuaclayton/unused unused $@
```

Note that, because Unused will be running inside of a virtual machine, it will
take longer to generate output than were you to install via
previously-mentioned methods.

[Docker is installed]: https://docs.docker.com/engine/installation

## Using Unused

`unused` attempts to read from common tags file locations (`.git/tags`,
`tags`, and `tmp/tags`).

In an application where the tags file exists, run:

```sh
unused
```

If you don't have a tags file, you can generate one by running:
```sh
git ls-files | xargs ctags
```

If you want to specify a custom tags file, or load tokens from somewhere else,
run:

```sh
cat .custom/tags | unused --stdin
```

To view more usage options, run:

```sh
unused --help
```

## Troubleshooting

### Ctags (and a corresponding workflow) isn't configured

[Exuberant Ctags] \(or another tool that will generate a tags file, like
[hasktags] for Haskell projects) is required to use `unused` correctly;
however, the version of `ctags` that ships with OS X (`/usr/bin/ctags`) is an
older version won't work with many languages (that BSD version of `ctags` says
it "makes a tags file for ex(1) from the specified C, Pascal, Fortran, YACC,
lex, and lisp sources.")

[hasktags]: https://hackage.haskell.org/package/hasktags

Installation via Homebrew includes the `ctags` dependency. You can also run
`brew install ctags` by hand.  If you're not on OS X, use your favorite package
manager and refer to the [Exuberant Ctags] site for download instructions.

[Exuberant Ctags]: http://ctags.sourceforge.net/

#### Ctags manual run

If you're using `ctags` to generate a `tags` file prior to running `unused` and
don't have a workflow around automatically generating a `tags` file, run:

```sh
git ls-files | xargs ctags -f tmp/tags
```

This will take your `.gitignore` into account and write the tags file to
`tmp/tags`. Be sure to write this to a location that's ignored by `git`.

While this process allows a developer to get started, it requires remembering
to run this command before running `unused`. Let's explore how to automate this
process.

#### Ctags automatic runs via `git` hooks

With `ctags` installed, you'll likely want to configure your workflow such that
your tags file gets updated periodically without any action on your part. I
recommend following the [instructions outlined by Tim Pope] on this matter,
which discusses a workflow coupled to `git` for managing the tags file. It
includes shell scripting that may not look "effortless"; however, the fact this
is automated helps to ensure `unused` is running against new versions of the
code as you (and other teammates, if you have any) are committing.

As he suggests, you'll want to run `git init` into the directories you want
this hook, and to manually run the hook:

```sh
git ctags
```

`unused` is configured to look for a tags file in three different directories,
including `.git/` as the article suggests, so no further configuration will be
necessary with `unused`.

[instructions outlined by Tim Pope]: http://tbaggery.com/2011/08/08/effortless-ctags-with-git.html

### "Calculating cache fingerprint" takes a long time

`unused` attempts to be intelligent at understanding if your codebase has
changed before running analysis (since it can be time-consuming on large
codebases). To do so, it calculates a "fingerprint" of the entire directory by
using `md5` (or `md5sum`), along with `find` and your `.gitignore` file.

If you're checking in artifacts (e.g. `node_modules/`, `dist/`, `tmp/`, or
similar), `unused` will likely take significantly longer to calculate the
fingerprint.

Per the `--help` documentation, you can disable caching with the `-C` flag:

```sh
$ unused -C
```

### "No results found" when expecting results

If you're expecting to see results but `unused` doesn't find anything, verify
that any artifacts `unused` uses (e.g. the `tags` file, wherever it's located)
or generates (e.g. in `PROJECT_ROOT/tmp/unused`) is `.gitignore`d.

What might be happening is, because unused searches for tokens with `ag`
(which honors `.gitignore`), it's running into checked-in versions of the
tokens from other files, resulting in duplicate occurrences that aren't
representative of the actual codebase. The most obvious might be the `tags`
file itself, although if you're using an IDE that runs any sort of analysis
and that's getting checked in somehow, that may cause it too.

One final piece to check is the number of tokens in the tags file itself; if
`ctags` is misconfigured and only a handful of tokens are being analyzed, they
all may have low removal likelihood and not display in the default results
(high-likelihood only).

### Analysis takes a long time due to a large number of terms found

In my experience, projects under 100,000LOC should have at most around 8,000
unique tokens found. This obviously depends on how you structure your
classes/modules/functions, but it'll likely be close.

If you're seeing more than 15,000 terms matched (I've seen upwards of 70,000),
this is very likely due to misconfiguration of `ctags` where it includes some
amount of build artifacts. In Ruby, this might be a `RAILS_ROOT/vendor`
directory, or if you're using NPM, `APP_ROOT/node_modules` or
`APP_ROOT/bower_components`.

When configuring `ctags`, be sure to include your `--exclude` directives; you
can [find an example here].

[find an example here]: https://github.com/joshuaclayton/dotfiles/commit/edf35f2a3ca2204a7c6796c3685b7da34bddf5fb#diff-6d7e423e99befb791a7db6ae51126747R76

## Custom Configuration

The first time you use `unused`, you might see a handful of false positives.
`unused` will look in two additional locations in an attempt to load
additional custom configuration to help improve this.

### Configuration format

```yaml
# Language or framework name
#   e.g. Rails, Ruby, Go, Play
- name: Framework or language
  # Collection of matches allowed to have one occurrence
  autoLowLikelihood:
    # Low likelihood match name
    - name: ActiveModel::Serializer
      # Flag to capture only capitalized names
      #   e.g. would match `ApplicationController`, not `with_comments`
      classOrModule: true

      # Matcher for `.*Serializer$`
      #   e.g. `UserSerializer`, `ProjectSerializer`
      termEndsWith: Serializer

      # Matcher for `^with_.*`
      #   e.g. `with_comments`, `with_previous_payments`
      termStartsWith: with_

      # Matcher for `^ApplicationController$`
      termEquals: ApplicationController

      # Matcher for `.*_factory.ex`
      #   e.g. `lib/appname/user_factory.ex`, `lib/appname/project_factory.ex`
      pathEndsWith: _factory.ex

      # Matcher for `^app/policies.*`
      #   e.g. `app/policies/user_policy.rb`, `app/policies/project_policy.rb`
      pathStartsWith: app/policies

      # list of termEquals
      # Matcher allowing any exact match from a list
      allowedTerms:
      - index?
      - edit?
      - create?
```

### `~/.unused.yml`

The first location is `~/.unused.yml`. This should hold widely-used
configuration roughly applicable across projects. Here's an example of what
might be present:

```yaml
- name: Rails
  autoLowLikelihood:
    - name: ActiveModel::Serializer
      termEndsWith: Serializer
      classOrModule: true
    - name: Pundit
      termEndsWith: Policy
      classOrModule: true
      pathEndsWith: .rb
    - name: Pundit Helpers
      allowedTerms:
        - Scope
        - index?
        - new?
        - create?
        - show?
        - edit?
        - destroy?
        - resolve
    - name: JSONAPI::Resources
      termEndsWith: Resource
      classOrModule: true
      pathStartsWith: app/resources
    - name: JSONAPI::Resources Helpers
      allowedTerms:
      - updatable_fields
      pathStartsWith: app/resources
```

I tend to work on different APIs, and the two libraries I most commonly use
have a fairly similar pattern when it comes to class naming. They both also
use that naming structure to identify serializers automatically, meaning they
very well may only be referenced once in the entire application (when they're
initially defined).

Similarly, with Pundit, an authorization library, naming conventions often
mean only one reference to the class name.

This is a file that might grow, but is focused on widely-used patterns across
codebases. You might even want to check it into your dotfiles.

### `APP_ROOT/.unused.yml`

The second location is `APP_ROOT/.unused.yml`. This is where any
project-specific settings might live. If you're working on a library before
extracting to a gem or package, you might have this configuration take that
into account.

### Validation

`unused` will attempt to parse both of these files, if it finds them. If
either is invalid either due to missing or mistyped keys, an error will be
displayed.

## Requirements

Unused leverages [Ag](https://github.com/ggreer/the_silver_searcher) to
analyze the codebase; as such, you'll need to have `ag` available in your
`$PATH`. This is set as an explicit dependency in Homebrew.

Alternatively, if you'd like to use
[RipGrep](https://github.com/BurntSushi/ripgrep), you can do so with the
`--search rg` flag. Be sure to have RipGrep installed first.

## Testing

To run the test suite, run:

```sh
stack test
```

## License

Copyright 2016-2018 Josh Clayton. See the [LICENSE](LICENSE).