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71 lines
2.8 KiB
Markdown
71 lines
2.8 KiB
Markdown
# Contributing
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Issues (bugs, feature requests or otherwise feedback) may be reported in
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[the GitHub issue tracker for this
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project](https://github.com/tweag/ormolu/issues). Pull requests are also
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welcome.
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When contributing to this repository, please first discuss the change you
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wish to make via an issue, unless it's entirely trivial (typo fixes, etc.).
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If there is already an issue that describes the change you have in mind,
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comment on it indicating that you're going to work on that. This way we can
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avoid the situation when several people work on the same thing.
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Please make sure that all non-trivial changes are described in commit
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messages and PR descriptions.
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## What to hack on?
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Right now there are two options for people who want to contribute:
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* [Implementing rendering of AST][cover-ast]. This is the main focus right
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now because we want to have a MVP which can render all syntactical
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constructions found in Haskell source code. Once that is achieved we'll
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polish the tool iteratively.
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* [Fixing bugs][bugs]. If this seems more interesting than implementing
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rendering of AST, you are welcome to do this as well.
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## Implementing rendering of AST
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The `Ormolu.Printer.Combinators` module provides a DSL for rendering of GHC
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AST. You'll probably only need this one module for writing new rendering
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functions. The module documents how to use the printing combinators it
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provides. Consult the Haddocks to learn more about them.
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Create new modules corresponding to the things you want to render under
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`Ormolu.Printer.Meat`. For example, there are `Ormolu.Printer.Meat.Type` and
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`Ormolu.Printer.Meat.Declaration.Data`.
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Concrete rendering functions get their names by appending `p_` to the name
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of the type which describes a particular part of AST. For example, the
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function for rendering types is correspondingly:
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```haskell
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p_hsType :: HsType GhcPs -> R ()
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```
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In general rendering functions like this take 1 or more arguments and
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produce `R ()` which is a rendering action.
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### Testing
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Testing has been taken good care of and now it amounts to just adding
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examples under `data/examples`. Each example is a pair of files:
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`<example-name>.hs` for input and `<example-name>-out.hs` for corresponding
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expected output.
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Testing is performed as following:
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* Given snippet of source code is parsed and pretty-printed.
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* The result of printing is parsed back again and the AST is compared to the
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AST obtained from the original file. They should match.
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* The output of printer is checked against the expected output.
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* Idempotency property is verified: formatting already formatted code
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results in exactly the same output.
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Examples can be organized in sub-directories, see the existing ones for
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inspiration.
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[cover-ast]: https://github.com/tweag/ormolu/issues?q=is%3Aissue+is%3Aopen+label%3Acovering-ghc-ast
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[bugs]: https://github.com/tweag/ormolu/issues?q=is%3Aissue+is%3Aopen+label%3Abug
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