How to compare with the main branch when a PR is created, and then with the last commit before a new push if the PR is already there?

[rafrafek]

I'm using tj-actions/changed-files@v45 and need some guidance. When a pull request (PR) is created, I want to compare the changes against the main branch. If the PR already exists and a new push is made, I want to compare against the previous commit instead (the last commit from the PR before the push). Additionally, I want to ensure this action only runs within pull requests. How can I achieve this?

My action definition so far:
https://github.com/rafrafek/github-actions-dynamic-matrix/blob/main/.github/workflows/ci.yml

My example PR that should trigger the changes:
https://github.com/rafrafek/github-actions-dynamic-matrix/pull/6/files

Action results - didn't find any changes, but it should as there is a change to a Dockerfile file:
https://github.com/rafrafek/github-actions-dynamic-matrix/actions/runs/10496631750/job/29077718779

[jackton1]

Hi, @rafrafek. This is already supported, so you wouldn't need to calculate the BASE_SHA.

To accomplish this, you will need to set the input since_last_remote_commit to true.

name: ci

on:
  pull_request:
    branches:
      - main
    types:
      - opened
      - synchronize

permissions:
  contents: read
  packages: write

jobs:
  prepare:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.prepare.outputs.matrix }}
      length: ${{ steps.prepare.outputs.length }}
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@v45
        with:
          since_last_remote_commit: true
          files: |
            **/Dockerfile

      - name: Prepare
        id: prepare
        shell: python
        run: |
           ...

Excerpt from the docs

      # -----------------------------------------------------------------------------------------------------------
      # Example 1
      # -----------------------------------------------------------------------------------------------------------
      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@v45
        # To compare changes between the current commit and the last pushed remote commit set `since_last_remote_commit: true`. e.g
        # with:
        #   since_last_remote_commit: true 

For more details see the inputs section in the documentation.

[jackton1]

If you want the directory names, you need to enable the dir_names input which returns the parent directory name rather than the full path, including the filename.

E.g

      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@v45
        with:
           since_last_remote_commit: true
           dir_names: true

[rafrafek]

Thank you so much for all your help! I copied this action definition from https://github.com/meysam81/github-actions-dynamic-matrix and I'll try to contact the author to also fix it upstream :)

[jackton1]

This action also supports matrix outputs. For more on that, see this example

[rafrafek]

Thank you!!

the output is a string separated by spaces and not a list

What if some of the paths contain a space? Like /foo/my dir/Dockerfile.

[rafrafek]

I think I figured it out. I'm using separator: "\\n":

      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@v45
        with:
          since_last_remote_commit: true
          separator: "\\n"
          files: |
            **/Dockerfile
      - name: Prepare
        id: prepare
        shell: python
        run: |
          import json
          import os
          from pathlib import Path
          from typing import Any, Generator


          def discover() -> Generator[str, Any, None]:
              all_changed_files = "${{ steps.changed-files.outputs.all_changed_files }}"
              if not all_changed_files:
                  return
              for changed in all_changed_files.split("\n"):
                  path = Path(changed)
                  if Path(path.parts[0]).is_dir():
                      yield path.parts[0]

But if handling spaces in paths is not required, it's better to use .split() rather than .split(" ") because in Python .split(" ") produces [''] and .split(): produces [].

I proposed the changes upstream: meysam81/github-actions-dynamic-matrix#1