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Contributing

Thank you for your interest in contributing to this library! Contributions are very appreciated.

If you want help or mentorship, reach out to us in a GitHub issue, or over Matrix in source-map on mozilla.org and introduce yourself.

Table of Contents

Filing Issues

If you are filing an issue for a bug or other misbehavior, please provide:

  • A test case. The more minimal the better, but sometimes a larger test case cannot be helped. This should be in the form of a gist, node script, repository, etc.

  • Steps to reproduce the bug. The more exact and specific the better.

  • The result you expected.

  • The actual result.

Building From Source

Install Node.js 18 or greater and then run

$ git clone https://github.com/mozilla/source-map.git
$ cd source-map/
$ npm install

There is no build step for the JavaScript: the package is used directly from source-map.js and lib/. The only generated files are lib/mappings.wasm and its glue, which are committed; see Updating the lib/mappings.wasm WebAssembly Module if you need to change them.

Submitting Pull Requests

Make sure that tests pass locally before creating a pull request.

Use a feature branch and pull request for each change, with logical commits. If your reviewer asks you to make changes before the pull request is accepted, fixup your existing commit(s) rather than adding follow up commits, and then force push to the remote branch to update the pull request.

Running Tests

The test suite is written for node.js. Install node.js 18 or greater and then run the tests with npm test:

$ npm test

> source-map@0.8.0 test
> git submodule update --init --recursive; node test/run-tests.js


190 / 190 tests passed.

Writing New Tests

To add new tests, create a new file named test/test-your-new-test-name.js and export your test functions with names that start with "test", for example:

exports["test issue #123: doing the foo bar"] = function (assert) {
  ...
};

The new tests will be located and run automatically when you run the full test suite.

The assert argument is a cut down version of node's assert module. You have access to the following assertion functions:

  • doesNotThrow

  • equal

  • ok

  • strictEqual

  • throws

(The reason for the restricted set of test functions is because we need the tests to run inside Firefox's test suite as well and Firefox has a shimmed version of the assert module.)

There are additional test utilities and helpers in ./test/util.js which you can use as well:

var util = require("./util");

Checking code coverage

It's fun to find ways to test lines of code that aren't visited by the tests yet.

$ npm run coverage
$ open coverage/index.html

This will allow you to browse to red sections of the code that need more attention.

Updating the lib/mappings.wasm WebAssembly Module

Ensure that you have the Rust toolchain installed:

$ curl https://sh.rustup.rs -sSf | sh

The exact toolchain version is pinned in wasm-mappings/rust-toolchain.toml and rustup will install it on demand, including the wasm32-unknown-unknown target. Note: The pin exists because CI rebuilds the committed artifacts and fails if they differ byte-for-byte, which only works if everyone builds with the same compiler.

Install wasm-pack version 0.15.0, the version CI uses, which vendors its own wasm-bindgen:

$ cargo install wasm-pack --version 0.15.0 --locked

You also need wasm-opt from binaryen version 132 on your PATH (for example brew install binaryen, or a release download). build.sh refuses to run with any other version: without one on PATH, wasm-pack falls back to downloading an older binaryen, whose output does not match the committed lib/mappings.wasm.

Make sure the crate's tests pass:

$ cd wasm-mappings/
$ cargo test

Then rebuild the shipped artifacts:

$ ./build.sh

This writes five files into lib/:

File Purpose
mappings.wasm the WebAssembly module itself
mappings-glue.js wasm-bindgen glue for Node (CommonJS)
mappings-glue.d.ts types for the above node glue file
mappings-glue-browser.mjs wasm-bindgen glue for browsers (ES module)
mappings-glue-browser.d.mts types for the above browser glue file

All five are generated and committed; do not edit them by hand. package.json's browser field swaps lib/read-wasm.js for lib/read-wasm-browser.js, which is what selects between the Node and browser glue.

Set PROFILING=1 to enable the crate's profiling feature, which wraps each query in a console.time / console.timeEnd pair:

$ PROFILING=1 ./build.sh

See further information in wasm-mappings/CONTRIBUTING.md.