[HowTo] Hacking on the CoffeeScript Compiler

Geoffrey Booth edited this page Apr 27, 2018 · 3 revisions

If you would like to help with CoffeeScript development, or would just like to play around with the compiler to see how it works, follow this guide to prepare your system.

Note: This has only been tested on Mac OS X. Details may vary for your particular platform.

Quick Start

git clone git://github.com/jashkenas/coffeescript.git
cd coffeescript
# …make your changes
bin/cake build:full
bin/coffee <your testing sample code>

For the full details, read on!

1. Prerequisites

Before you can play with the source, you’ll need a few things on your system first.

Node.js, including npm.

You need Node to run the CoffeeScript compiler.

The CoffeeScript Compiler

CoffeeScript is self-hosting. This means that the CoffeeScript compiler is written in.... CoffeeScript. If that makes your head hurt, welcome to the world of compilers and transpilers :)

npm install -g coffeescript

Note: You don’t technically need this, as CoffeeScript’s git repository includes a version of its own compiler in the bin directory that it uses during the build process. However, installing this puts CoffeeScript on your path and gives you the “official” version for playing around with things outside of the source directory.

2. Fetch the source

cd your_projects_dir
git clone git://github.com/jashkenas/coffeescript.git

3. Build the JavaScript files from the CoffeeScript source

cake build

This will use the pre-built CoffeeScript compiler archived in the bin/ folder to build all the CoffeeScript source files in src/ into their compiled JavaScript form in lib/.

Note that the bin/cake and bin/coffee scripts are not fully-concatenated “finished” scripts. In the source distribution as well as the installed version, these files simply point to the real source files in lib/.

4. Run a sanity check

When you make changes to the CoffeeScript source, it’s a good idea to do a

cake build:full

What this does is run cake build twice so that the compiler compiles itself with all your latest changes, then runs the CoffeeScript test suite. If you have broken something (and the test suite has adequate coverage), this should tell you. Note that this does not rebuild the parser; you need to also run cake build:parser to trigger that.

5. Backing out bad changes

When you’re working with a self-hosted compiler and using the latest version of the compiler to compile yourself, as CoffeeScript does, it’s easy to run into a situation where you can’t compile anymore because the compiler you just built has a fatal bug that you’ve introduced. When this occurs, it will usually manifest itself as the cake build process suddenly throwing errors, failed tests during cake test or cake build:full, or (even more insidiously), weird behaviors in CoffeeScript or some other program you’re using to test.

If this happens, don’t panic, and don’t start all over by blowing away your local repository and giving up! Just run

git checkout lib

This will revert the “built” CoffeeScript back to the way it was in the main repository. From here, you can look for what caused the problem and try to fix it. Just keep running the above command to get a working compiler until your compiler starts working, too.

6. Build the Parser

As stated in the prerequisites section, if you make any changes to src/grammar.coffee, you will need to build the parser from that grammar definition. To do this, run

cake build:parser

Be sure to run this after running cake build. When cake builds the parser, it puts it in the lib/ directory, so you don’t need to run cake build again.

7. Running tests

As you are hacking on the source, it’s a good idea to make sure you haven’t broken anything. Run

cake test

periodically for a sanity check. If you intend to submit a patch to the main CoffeeScript repository, make sure you add new tests to the test/ folder as necessary. Just follow an example that’s closest to what you are trying to do. The new tests will be picked up automatically by cake.

8. Installation

If you would like to make your compiler the official CoffeeScript compiler on your system, then

sudo cake install

ought to do the trick. A word of caution, though: only do this when you’re sure your compiler is in a stable state. Otherwise you will have to reinstall your official version.

9. Guidelines for submitting changes back to the master repository

  1. Don’t submit anything under the docs folder. The files under there will be rebuilt by the CoffeeScript team when a release is tagged.
  2. Changes without tests will generally not be accepted unless it’s a fix to a regression or you can make the argument that a test is more trouble than it’s worth

10. Preparing a new release

  1. Make sure that new features are properly documented. If not, try to do so by sending PRs. After those have been merged or otherwise fixed, proceed with the following steps.

  2. Update the version number in package.json.

  3. Write a change log entry in documentation/sections/changelog.md. The easiest way is to copy the previous entry and then adjust it.

    It is handy to base the change log entry on the commit log since the last version. If the last version is 1.9.9 you may run the following:

    git log 1.9.9.. –reverse –no-merges –pretty=medium >changes

    That’ll give you a nice little list of things that has happened since 1.9.9 in chronological order. Edit the changes file to remove commits that do not need to be mentioned explicitly in the change log and reduce related commits to single entries. Then turn them into nice little summarizing bullet points and move them over to documentation/sections/changelog.md. It helps visiting related issues and PRs on GitHub while doing this.

  4. Run cake release to rebuild the JavaScript files from the CoffeeScript source, which should include the new version number. It also runs the tests just to make sure that everything is good to go. It also rebuilds the documentation, including test.html and the annotated source. In short, everything.

  5. Commit all the changes. If you’re updating to 9.0.0, CoffeeScript 9.0.0 is a good commit message.

  6. Send a PR! (Amend and force-push changes requested by reviewers if needed.)

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