How to create GitHub Actions Workflow that works when code in any folder has been changed

I have a repository that contains many folders:

/folder_a
/folder_b
...
/folder_z

I want to create a GitHub Action workflow that is triggered whenever a PR is closed in which code within one of those folders has changed, in order to create a release that is tagged with the name of changed folder + a version number.

Example: if contents in folder_a has been changed in a PR, then when it gets merged it should create a release named folder_a_1.0.0 with the folder name as prefix.

I could create a workflow for each of the folders, but since there are many folders this approach wouldn't be very maintainable (example below with a re-usable release.yml workflow that contains the logic for creating the release and takes a prefix as input):

name: Release folder_a

on:
  pull_request:
    branches:
      - master
    paths:
      - "folder_a/**"

permissions:
  contents: write

jobs:
  release:
    uses: ./.github/workflows/release.yml
    secrets: inherit
    with:
      prefix: folder_a

Is there a way to use a single workflow to do the same job?

Solution

Your workflow needs an extra job that would feed names of all folders that changed into the release job. Because your reusable workflow ./.github/workflows/release.yml expects to be invoked with a single folder at a time, you need a matrix that would run your reusable workflow as many times as the number of changed folders:

name: Release folder_a

on:
  pull_request:
    branches:
      - master
    paths:
      - "folder_*/**"

permissions:
  contents: write

jobs:

  collect:
    runs-on:  ubuntu-latest
    outputs:
      outcomes: ${{ steps.collect.outputs.folders }}
    steps:
      - uses: actions/checkout@v4
      - id: collect
        run: |
          git diff --name-only ${{ github.base_ref }} ${{ github.head_ref }} | sed 's|/.*||' | uniq | jq -R -s -c 'split("\n")' > folders
          echo folders=$(cat folders) >> $GITHUB_OUTPUT

  release:
    needs: collect
    runs-on:  ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        folder: ${{ fromJSON(needs.collect.outputs.folders) }}
    uses: ./.github/workflows/release.yml
    secrets: inherit
    with:
      prefix: ${{ matrix.folder }}

Here git diff create a list of all files that changed on the PR relative to the base branch:

git diff --name-only ${{ github.base_ref }} ${{ github.head_ref }} 

folder_a/file_1
folder_a/file_2
folder_a/file_3
folder_b/file_1
folder_b/file_2

then sed removes everything after the "/" leaving just the folder name while uniq removes duplicates:

sed 's|/.*||' | uniq 

folder_a
folder_b

then jq slurps (-s) this output as raw text (-R) into a JSON list and outputs this list as a compact, one line JSON (-c):

jq -R -s -c 'split("\n")'

["folder_a","folder_b"]

This list is used as a folder matrix in the release job that invokes reusable workflow once per folder. Note, that the prefix input will not have a trailing "/"