I just spent the better part of an hour debugging a failing workflow, and it turned out the root cause was that the project's submodules had not been checked out recursively.

I had configured the checkout with:

    - uses: actions/checkout@v1
      with:
        submodules: true

I had inferred the true value for the submodules input from the action's documentation, which described the input as "Whether to recursively clone submodules; defaults to false". It turns out, setting the value to true checks out submodules, but not recursively. After searching through the closed issues, I discovered that for recursive checkout of submodules, the value needs to be recursive.

It would be very helpful if the action documentation could be updated to correctly indicate what value needs to be passed to get the documented behavior.