title: Patching changes to rules_nodejs layout: default toc: true

Patching changes

One advantage of open-source software is that you can make your own changes that suit your needs.

The @rules_nodejs module can simply be fetched from sources in place of the published distribution. For example, in place of

http_archive(
    name = "rules_nodejs",
    sha256 = "...",
    urls = ["https://github.com/bazelbuild/rules_nodejs/releases/download/5.0.0/rules_nodejs-core-5.0.0.tar.gz"],
)

you can just use a commit from your fork:

http_archive(
    name = "rules_nodejs",
    sha256 = "...",
    strip_prefix = "rules_nodejs-abcd123",
    url = "https://github.com/my-org/rules_nodejs/archive/abcd123.tar.gz",
)

The @build_bazel_rules_nodejs module distributed on GitHub releases is harder to work with. It has different content from the sources in this repo. This is true for packages published to @bazel/ on npm as well. These packages have only runtime bazel dependencies, but the sources depend on development dependencies. For example, the @bazel_skylib library is a development-time transitive dependency, while an npm package would have that dependency statically linked in.

If you have a small change, it‘s easiest to just patch the distributed artifacts rather than build from source. However if you’re doing active development in rules_nodejs or have a policy of not depending on release artifacts, it's possible to depend directly on sources. This is not yet documented; file an issue on our repo if you think you need this.

Patching the npm packages

The pattern we use most commonly is to use patch-package. To store your local changes to the npm packages follow the steps:

  1. npm i -D patch-package
  2. Edit the target package in your node_modules
  3. Run npx patch-package <npm package>. This will store the patch in the patches/ directory in the root of the workspace
  4. Add "postinstall": "patch-package" to the package.json in your repo to apply the patches when building dependencies (aka at npm install)

Patching the build_bazel_rules_nodejs release

build_bazel_rules_nodejs has a distribution format which is a tgz published to GitHub, and this can make it tricky to make casual changes without forking the project and building your own release artifacts.

Bazel has a handy patching mechanism that lets you easily apply a local patch to the release artifact for built-in rules: the patches attribute to http_archive.

First, make your changes in a clone of the rules_nodejs repo. Export a patch file simply using git diff:

git diff > my.patch

Then copy the patch file somewhere in your repo and point to it from your WORKSPACE file:

http_archive(
    name = "build_bazel_rules_nodejs",
    patch_args = ["-p1"],
    patches = ["//path/to/my.patch"],
    sha256 = "6d4edbf28ff6720aedf5f97f9b9a7679401bf7fca9d14a0fff80f644a99992b4",
    urls = ["https://github.com/bazelbuild/rules_nodejs/releases/download/0.32.2/rules_nodejs-0.32.2.tar.gz"],
)