Linguist

We use this library at GitHub to detect blob languages, highlight code, ignore binary files, suppress generated files in diffs, and generate language breakdown graphs.

Features

Language detection

Linguist defines a list of all languages known to GitHub in a yaml file. In order for a file to be highlighted, a language and a lexer must be defined there.

Most languages are detected by their file extension. For disambiguating between files with common extensions, we first apply some common-sense heuristics to pick out obvious languages. After that, we use a statistical classifier. This process can help us tell the difference between, for example, .h files which could be either C, C++, or Obj-C.

Linguist::FileBlob.new("lib/linguist.rb").language.name #=> "Ruby"

Linguist::FileBlob.new("bin/linguist").language.name #=> "Ruby"

See lib/linguist/language.rb and lib/linguist/languages.yml.

Syntax Highlighting

The actual syntax highlighting is handled by our Pygments wrapper, pygments.rb. It also provides a Lexer abstraction that determines which highlighter should be used on a file.

Stats

The Language stats bar that you see on every repository is built by aggregating the languages of each file in that repository. The top language in the graph determines the project's primary language.

The repository stats API, accessed through #languages, can be used on a directory:

project = Linguist::Repository.from_directory(".")
project.language.name  #=> "Ruby"
project.languages      #=> { "Ruby" => 0.98, "Shell" => 0.02 }

These stats are also printed out by the linguist binary. You can use the --breakdown flag, and the binary will also output the breakdown of files by language.

You can try running linguist on the lib/ directory in this repository itself:

$ bundle exec linguist lib/ --breakdown

100.00% Ruby

Ruby:
linguist/blob_helper.rb
linguist/classifier.rb
linguist/file_blob.rb
linguist/generated.rb
linguist/heuristics.rb
linguist/language.rb
linguist/md5.rb
linguist/repository.rb
linguist/samples.rb
linguist/tokenizer.rb
linguist.rb

Ignore vendored files

Checking other code into your git repo is a common practice. But this often inflates your project's language stats and may even cause your project to be labeled as another language. We are able to identify some of these files and directories and exclude them.

Linguist::FileBlob.new("vendor/plugins/foo.rb").vendored? # => true

See Linguist::BlobHelper#vendored? and lib/linguist/vendor.yml.

Generated file detection

Not all plain text files are true source files. Generated files like minified js and compiled CoffeeScript can be detected and excluded from language stats. As an extra bonus, these files are suppressed in diffs.

Linguist::FileBlob.new("underscore.min.js").generated? # => true

See Linguist::Generated#generated?.

Installation

github.com is usually running the latest version of the github-linguist gem that is released on RubyGems.org.

But for development you are going to want to checkout out the source. To get it, clone the repo and run Bundler to install its dependencies.

git clone https://github.com/github/linguist.git
cd linguist/
bundle install

To run the tests:

bundle exec rake test

Contributing

The majority of contributions won't need to touch any Ruby code at all. The master language list is just a YAML configuration file.

We try to only add languages once they have some usage on GitHub, so please note in-the-wild usage examples in your pull request.

Almost all bug fixes or new language additions should come with some additional code samples. Just drop them under samples/ in the correct subdirectory and our test suite will automatically test them. In most cases you shouldn't need to add any new assertions.

To update the samples.json after adding new files to samples/:

bundle exec rake samples

A note on language extensions

Linguist has a number of methods available to it for identifying the language of a particular file. The initial lookup is based upon the extension of the file, possible file extensions are defined in an array called extensions. Take a look at this example for example for Perl:

Perl:
  type: programming
  ace_mode: perl
  color: "#0298c3"
  extensions:
  - .pl
  - .PL
  - .perl
  - .ph
  - .plx
  - .pm
  - .pod
  - .psgi
  interpreters:
  - perl

Any of the extensions defined are valid but the first in this array should be the most popular.

Testing

Sometimes getting the tests running can be too much work, especially if you don't have much Ruby experience. It's okay: be lazy and let our build bot Travis run the tests for you. Just open a pull request and the bot will start cranking away.

Here's our current build status, which is hopefully green:

Releasing

If you are the current maintainer of this gem:

0. Create a branch for the release: git checkout -b cut-release-vxx.xx.xx
1. Make sure your local dependencies are up to date: bundle install
2. Ensure that samples are updated: bundle exec rake samples
3. Ensure that tests are green: bundle exec rake test
4. Bump gem version in lib/linguist/version.rb. For example, like this.
5. Make a PR to github/linguist. For example, #1238.
6. Build a local gem: gem build github-linguist.gemspec
7. Testing:
8. Bump the Gemfile and Gemfile.lock versions for an app which relies on this gem
9. Install the new gem locally
10. Test behavior locally, branch deploy, whatever needs to happen
11. Merge github/linguist PR
12. Tag and push: git tag vx.xx.xx; git push --tags
13. Push to rubygems.org -- gem push github-linguist-3.0.0.gem