Post-build Clean Buildpack

A simple buildpack to run after all other buildpacks have completed, which removes a set of files defined in .slug-post-clean, so that they are not included in the finished slug.

Rationale

While this may seem to duplicate functionality provided by Heroku's .slugignore, there is a key difference: .slugignore'd files are removed after the repo is cloned, but before any buildpack is run. They can therefore not be involved in the build process itself.

However, it is not uncommon for there to exist files in the repo that are necessary for the build, but are not required at runtime. There may also be installable build dependencies that are not runtime dependencies.

In our case, a complex front-end build involves significant CSS, JS and image assets, along with a large installation of node modules, all of which are used only for building the production assets, but then remain part of the slug.

Usage

Add the buildpack to your app using the Heroku CLI: heroku buildpacks:add https://github.com/Lostmyname/heroku-buildpack-post-build-clean. The post-build-clean buildpack must be last in the buildpack order:

$ heroku buildpacks

=== test-app-12345 Buildpack URLs
1. heroku/nodejs
2. heroku/python
3. https://github.com/Lostmyname/heroku-buildpack-post-build-clean

The .slug-post-clean file supports single-file and single-directory patterns, as well as glob patterns, e.g.:

some_huge_file.psd
some/nested/directory
why_does_this_app_even_contain_a.tiff
your_frontend/build/*.map

Glob patterns are expanded using Bash syntax - not with a third-party library such as node-glob. You can see what your glob matches from bash with this command:

ls -d1 your/glob/pattern/*

Testing

The bin/compile script does all the heavy lifting for this package. It takes a single argument, $BUILD_DIR, the directory of your app. If you want to test it out locally and make sure your app still runs after the post-build cleanup, you can copy bin/compile into your app directory and run:

chmod +x compile; ./compile .