Manages lint execution. When you run 'arc lint' or 'arc diff', Arcanist attempts to run lint rules using a lint engine.

Lint engines are high-level strategic classes which do not contain any actual linting rules. Linting rules live in Linter classes. The lint engine builds and configures linters.

Most modern linters can be configured with an .arclint file, which is managed by the builtin ArcanistConfigurationDrivenLintEngine. Consult the documentation for more information on these files.

In the majority of cases, you do not need to write a custom lint engine. For example, to add new rules for a new language, write a linter instead. However, if you have a very advanced or specialized use case, you can write a custom lint engine by extending this class; custom lint engines are more powerful but much more complex than the builtin engines.

The lint engine is given a list of paths (generally, the paths that you modified in your change) and determines which linters to run on them. The linters themselves are responsible for actually analyzing file text and finding warnings and errors. For example, if the modified paths include some JS files and some Python files, you might want to run JSLint on the JS files and PyLint on the Python files.

You can also run multiple linters on a single file. For instance, you might run one linter on all text files to make sure they don't have trailing whitespace, or enforce tab vs space rules, or make sure there are enough curse words in them.

You can test an engine like this:

arc lint --engine YourLintEngineClassName --lintall some_file.py

...which will show you all the lint issues raised in the file.

See Arcanist User Guide: Customizing Lint, Unit Tests and Workflows for more information about configuring lint engines.