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Contributing

Thanks for your help! Due to BuckleScript's nature, the contribution setup isn't all straightforward (though well documented). If something isn't working, please file an issue or ping us in Discord!

Setup

Prerequisites:

  • NodeJS
  • C compiler toolchain (you probably already have it installed)
  • OS: Mac/Linux (BuckleScript works on Windows, but developing the repo using Windows isn't tested. Contribution welcome!)

Build the vendored ocaml compiler

git submodule update --init && node scripts/buildocaml.js

Build everything in dev mode using vendored compiler

./scripts/ninja.js config && ./scripts/ninja.js build

scripts/ninja.js will generate many .ninja build files inside the jscomp directory which will be invoked by ./scripts/ninja.js build.

Editor support

Use this deprecated VSCode extension. The extension requires using an opam switch for ocaml 4.02.3, where merlin and ocp-indent are installed.

Building docs

./script/ninja.js docs

Edit file and test changes

In general, you'd edit files and rerun ./scripts/ninja.js build.

We have an optional watcher to auto rebuild on file changes. Suppose you are in jscomp:

node ../scripts/tasks.js

Troubleshooting broken builds

Try to run:

./scripts/ninja.js clean # it will remove files not in version control
./scripts/ninja.js config
./scripts/ninja.js build

Advanced: building everything in dev mode using a different compiler

This is primarily used when you need to test the repo with a different OCaml than the vendored one.

For example, you might be testing BuckleScript on the 4.06 OCaml compiler instead of 4.02. Clone our patched OCaml 4.06, then do:

git -C ocaml checkout 4.06.1+BS && node ./scripts/buildocaml.js

./scripts/ninja.js cleanbuild

Note: clean up is necessary since the binary artifacts between versions of compiler may be incompatible.

Using esy in development (experimental)

You can use esy to develop bucklescript. By default esy will do "out of source builds" which means that all the changes will happen outside the current directory. To be able to bspack the needed files and get sources that you can commit you will have to change the following in the esy.json.

-"buildsInSource": true,
+"buildsInSource": "unsafe",

When that is changed you just run the following command it will build everything you need.

esy

By default we depend on the 4.02.3+BS OCaml compiler. To be able to build with the 4.06.1+BS compiler we have a 4061.json file that just extends the esy.json and overrides the OCaml dependency. To use this file instead you simply run this command instead.

esy @4061

If there are problems building try to run one of the following depending on what you're building

esy clean
esy @4061 clean

Test on a Dummy Project

Go somewhere else and do this:

bsb -init foo -theme basic-reason
cd foo
npm run build

And whenever you modify a file in bucklescript, run this:

npm install -g .

Change the Vendored OCaml Compiler

This section is reserved for when you're making a change to the vendored ocaml compiler itself, in ocaml, and then testing on super-errors changes at the same time. If you're doing this for whatever reason, then the previous quick iteration workflow wouldn't work. Here's what you have to do after each change:

# at project root
cd ocaml && make -j9 world.opt && make install && cd ..
./scripts/ninja.js cleanbuild

Contributing to the runtime

BuckleScript runtime implementation is currently a mix of OCaml and JavaScript. (jscomp/runtime directory). The JavaScript code is defined in the .ml file using the bs.raw syntax extension.

The goal is to implement the runtime purely in OCaml and you can help!

Each new PR should include appropriate testing.

Currently all tests are in jscomp/test directory and you should either add/modify a test file which covers the part of the compiler you modified.

  • Add the filename in jscomp/test/test.mllib

  • Add a test suite. The specification is in jscomp/test/mt.ml. For example some simple tests would be like:

    let suites : _ Mt.pair_suites =
   ["hey", (fun _ -> Eq(true, 3 > 2));
       "hi", (fun _ -> Neq(2,3));
       "hello", (fun _ -> Approx(3.0, 3.0));
       "throw", (fun _ -> ThrowAny(fun _ -> raise 3))
       ]
let () = Mt.from_pair_suites __FILE__ suites

  • Run the tests: mocha -R list jscomp/test/your_test_file.js To build libs, tests and run all tests: make libs && make -C jscomp/test all && npm test

  • See the coverage: npm run cover

Contributing to Documentation

See https://github.com/BuckleScript/bucklescript.github.io

Contributing to the API Reference

The API reference is generated from doc comments in the source code. Here's a good example

Some tips and guidelines:

  • The first sentence or line should be a very short summary. This is used in indexes and by tools like merlin.
  • Ideally, every function should have at least one @example.
  • Cross-reference another definition with {! identifier}. But use them sparingly, they’re a bit verbose (currently, at least).
  • Wrap non-cross-referenced identifiers and other code in [ ... ].
  • Escape {, }, [, ] and @ using \.
  • It’s possible to use {%html ...} to generate custom html, but use this very, very sparingly.
  • A number of "documentation tags" are provided that would be nice to use, but unfortunately they’re often not supported for `external`s. Which is of course most of the API.
  • @param usually doesn’t work. Use {b <param>} ... instead
  • @returns usually doesn’t work. Use {b returns} ... instead.
  • Always use @deprecated when applicable.
  • Always use @raise when applicable.
  • Always provide a @see tag pointing to MDN for more information when available.

See Ocamldoc documentation for more details.

To generate the html, run make docs in jscomp/.

Html generation uses a custom generator located in odoc_gen/ and custom styles located in docs/api_static.

Make a Release

In release mode, assuming you have NodeJS and OCaml compiler with the right version installed:

node scripts/install.js

The build process will generate configure file with correct LIBDIR path, build all binaries and libraries and install the binaries into bin and lib files into lib.

First it will try to generate bin/config_whole_compiler.ml based on existing OCaml installation, if it fails, it will try to invoke node scripts/buildocaml.js to install an OCaml compiler from scratch, and retry again.

Publish Process

  • Run make force-snapshotml
  • Bump the compiler version

Code structure

The highlevel architecture is illustrated as below:

Lambda IR (OCaml compiler libs) ---+
  |   ^                            |
  |   |                     Lambda Passes (lam_* files)
  |   |             Optimization/inlining/dead code elimination
  |   \                            |
  |    \ --------------------------+
  |
  |  Self tail call elimination
  |  Constant folding + propagation
  V
JS IR (J.ml)  ---------------------+
  |   ^                            |
  |   |                     JS Passes (js_* files)
  |   |            Optimization/inlining/dead code elimination
  |   \                            |
  |    \  -------------------------+
  |
  |  Smart printer includes scope analysis
  |
  V
Javascript Code

Note that there is one design goal to keep in mind, never introduce any meaningless symbol unless real necessary, we do optimizations, however, it should also compile readable output code.

Contribution Licensing

Since BuckleScript is distributed under the terms of the LGPL Version 3, contributions that you make are licensed under the same terms. In order for us to be able to accept your contributions, we will need explicit confirmation from you that you are able and willing to provide them under these terms, and the mechanism we use to do this is called a Developer's Certificate of Origin DCO. This is very similar to the process used by the Linux(R) kernel, Samba, and many other major open source projects.

To participate under these terms, all that you must do is include a line like the following as the last line of the commit message for each commit in your contribution:

Signed-Off-By: Random J. Developer <random@developer.example.org>

You must use your real name (sorry, no pseudonyms, and no anonymous contributions).