Patches not applied when using Heroku's Node buildpack

This isn’t an issue with patch-package specifically, but I wanted to share it here nonetheless to help anyone else who might run into this.

When using Heroku’s Node buildpack, by default the following will happen during the build and startup process:

1. install all dependencies (including devDependencies) with yarn --production="false"
2. run build step
3. prune dev dependencies with yarn --production="true"
4. run the app

However, at step 3 when the dev dependencies are pruned, the buildpack also specifies the --ignore-scripts flag when calling yarn (since v119). This means patch-package will not run, because the postinstall/prepare scripts will not be ran. In turn, this means when the app runs, Node modules will not be patched (!).

The only workaround I’m aware of at the moment is to disable pruning of dev dependencies with YARN_PRODUCTION=false.

I can semi-understand why the buildpack would want to avoid invoking scripts, since the scripts were already run after step 1. In any case I’ve raised an issue with the buildpack to investigate what changes we can make there: https://github.com/heroku/heroku-buildpack-nodejs/issues/634

[naiyt]

Looks like with the latest version of the Heroku nodejs build script, you can accomplish this by using the heroku-postbuild step. That allows patch-package to work without losing the dev dependency pruning 🎉 .

Here’s what my package.json scripts look like now:

  "scripts": {
    "postinstall": "patch-package",
    "heroku-postbuild": "patch-package"
  }

[neokim]

heroku-postbuild didn’t work for me. Looks like during pruning dev dependencies which runs after heroku-postbuild, yarn restores the original version of packages. So I had to use heroku-cleanup instead which runs after pruning.

Actually, Heroku document says it runs after dependency caching, but it works for me anyway.