ormolu/CONTRIBUTING.md

Contributing

Issues (bugs, feature requests or otherwise feedback) may be reported in the GitHub issue tracker for this project. Pull requests are also welcome.

When contributing to this repository, please first discuss the change you wish to make via an issue, unless it's entirely trivial (typo fixes, etc.). If there is already an issue that describes the change you have in mind, comment on it indicating that you're going to work on that. This way we can avoid the situation when several people work on the same thing.

Please make sure that all non-trivial changes are described in commit messages and PR descriptions.

What to hack on?

Right now there are two options for people who want to contribute:

• Implementing rendering of AST. This is the main focus right now because we want to have a MVP which can render all syntactical constructions found in Haskell source code. Once that is achieved we'll polish the tool iteratively.
• Fixing bugs. If this seems more interesting than implementing rendering of AST, you are welcome to do this as well.

Implementing rendering of AST

The Ormolu.Printer.Combinators module provides a DSL for rendering of GHC AST. You'll probably only need this one module for writing new rendering functions. The module documents how to use the printing combinators it provides. Consult the Haddocks to learn more about them.

Create new modules corresponding to the things you want to render under Ormolu.Printer.Meat. For example, there are Ormolu.Printer.Meat.Type and Ormolu.Printer.Meat.Declaration.Data.

Concrete rendering functions get their names by appending p_ to the name of the type which describes a particular part of AST. For example, the function for rendering types is correspondingly:

p_hsType :: HsType GhcPs -> R ()

In general rendering functions like this take 1 or more arguments and produce R () which is a rendering action.

Testing

Testing has been taken good care of and now it amounts to just adding examples under data/examples. Each example is a pair of files: <example-name>.hs for input and <example-name>-out.hs for corresponding expected output.

Testing is performed as following:

• Given snippet of source code is parsed and pretty-printed.
• The result of printing is parsed back again and the AST is compared to the AST obtained from the original file. They should match.
• The output of printer is checked against the expected output.
• Idempotency property is verified: formatting already formatted code results in exactly the same output.

Examples can be organized in sub-directories, see the existing ones for inspiration.