Linguist

We use this library at GitHub to detect file language types for syntax highlighting, ignore binary files, suppress generated code in diffs and generate language breakdown graphs.

Features

Language detection

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

Most languages are detected by their file extension. This is the fastest and most common situation. For script files, which are usually extensionless, we do "deep content inspection"™ and check the shebang of the file. Checking the files contents may also be used for disambiguating between langauges. C/C++/Obj-C all use .h files. Looking for common keywords, we are usually able to guess the correct language.

In the actual GitHub app we deal with Grit::Blob objects, there is a simple FileBlob api you can use for testing.

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

file = Linguist::FileBlob.new("bin/linguist")
file.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, Albino. Linguist provides a Lexer abstraction that determines which highlighter should be used on a file.

We typical run on a prelease version of Pygments to get early access to new lexers. The lexers.yml file is a dump of the lexers we have available on our server.

MIME type detection

Most of the MIME types handling is done by the Ruby mime-types gem. But we have our own list of additions and overrides. To add or modify this list, see lib/linguist/mimes.yml.

MIME types are used to set the Content-Type of raw binary blobs which are served from a special raw.github.com domain. However, all text blobs are served as text/plain regardless of their type to ensure they open in the browser rather than downloading.

The MIME type also determines whether a blob is binary or plain text. So if you're seeing a blob that says "View Raw" and it is actually plain text, you probably just need to expliclity state the mime type and encoding.

file = Linguist::FileBlob.new("linguist.zip")
file.binary? #=> true

See lib/linguist/mimes.yml

Stats

The Language Graph is built by aggregating the programming languages we are able to detect. Collectively, these stats make up the Top Languages page.

The top language in your project's graph determines its primay language. If this doesn't seem right, open an issue and we'll have a look.

The repository stats API 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 binary. Try running linguist on itself:

$ bundle exec linguist lib/
100%  Ruby

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 indentified as another language. We are able to identify some of these files and directories and exclude them.

file = Linguist::FileBlob.new("vendor/plugins/foo.rb")
file.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 langauge stats. As an extra bonus, these files are supressed in Diffs.

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

See Linguist::BlobHelper#generated?

Contributing

1. Fork it.
2. Create a branch (git checkout -b detect-foo-language)
3. Make your changes
4. Run the tests (bundle install then bundle exec rake)
5. Commit your changes (git commit -am "Added detection for the new Foo language")
6. Push to the branch (git push origin detect-foo-language)
7. Create a Pull Request from your branch.
8. Promote it. Get others to drop in and 👍 it.