Use case

We are using patch-package to fix some nasty dependency issues, it works great during development. But it sometimes causes CircleCI failures when a partially patched node_modules folder is cached by CI.

The issue

1. Install patch-package and add it as prepare script, as instructed by README.
2. Patch module foo-bar using patch-package foo-bar. Commit the resulted patches/foo-bar+X.X.X.patch to repo.
3. When CI is run, CircleCI installs and patches the node_modules folder and saves the result to cache.
4. Modify module foo-bar and regenerate patch file.
5. CircleCI restores the previous cached node_modules folder (which has incorporated previous version of the patch).
6. CircleCI fails when applying new patch to node_modules:

**ERROR** Failed to apply patch for package foo-bar

  This error was caused because Git cannot apply the following patch file:

    patches/foo-bar+X.X.X.patch

  This is usually caused by inconsistent whitespace in the patch file.

Proposed solutions

1. Add a checksum file for the patches folder so we can easily check if patches has been changed before restoring cache from CI.

2. Or, add a operation that can revert applied patches, such as patch-package revert. So we can revert the patches and save the clean node_modules folder to cache.