This article provides information that is relevant to people working on Emscripten itself, as opposed to those that use Emscripten in their own projects.
The information will be less relevant if you’re just using Emscripten, but may still be of interest.
Building Emscripten from source code
As a contributor you will need to build Emscripten from source in order to integrate fixes back into the main repositories.
Repositories and branches of interest
The Emscripten main repository is https://github.com/emscripten-core/emscripten. There are two main branches:
- master - The “master” branch. This is always safe to pull from and the test suite always passes.
- incoming - The branch for new code. Code in incoming is merged with the master only after it is code reviewed and has passed all the automated tests.
Emscripten’s compiler core (Fastcomp) is maintained in two other repositories, which use the same master/incoming branch approach:
When building Emscripten from source you should use the same branch (incoming, or master) for building all three repositories. The topic Branches explains how to ensure that the versions are kept in sync.
Patches should be submitted as pull requests to the incoming branch.
When submitting patches, please:
- Make pull requests to incoming, not master.
- Do not include merge commits in pull requests; include only commits with the new relevant code.
- Run all the automatic tests and make sure they pass. Some tests might not be required for very simple patches (for example, when just adding tests for new library functions). If you don’t have time to run all the tests, at least run a random subset of them (say, 100), see that link.
- “Add an automatic test to tests/runner.py if you add any new functionality or fix a bug.
- Record the tests that were run in the pull request or issue.
@kripken reviews all pull requests before merging.
Exceptions are sub-projects that are ‘owned’ by other people. These owners can push to incoming directly:
The Emscripten Compiler Frontend (emcc) is a python script that manages the entire compilation process:
- emcc calls Clang to convert C++ to bitcode,
llvm-opt to optimize it,
llvm-link to link it, etc.
- emscripten.py first runs the Fastcomp core compiler (previously it ran the old core compiler — src/compiler.js).
UglifyJS node.js script.