Release find-changes action

.github/workflows/find-changes.yml

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+name: find-changes
+on:
+  pull_request:
+    paths:
+      - ".github/workflows/find-changes.yml"
+      - "find-changes/**/*"
+      - "!find-changes/README.md"
+
+jobs:
+  example:
+    name: Example
+    runs-on: [ubuntu-24.04]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Find changes
+        id: changes
+        uses: ./find-changes
+
+      - name: Echo changed files
+        shell: sh
+        run: |
+          echo ${{ steps.changes.outputs.array }}
+        # format: ["foo/bar", "baz"]
+        # getting the array is the difficult bit. Doing logic based on array contents can be done in local composite actions

find-changes/README.md

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+# Find changes
+
+This action outputs list of changed files as JSON. It works in `pull_request`, `merge_group`, and `push` events, supporting all merge types: `merge commit`, `squash`, and `rebase`.
+
+If you use this, you should have either [merge queues](https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue) (GitHub Enterprise feature) or `Require branches to be up to date before merging` branch protection rule enabled.
+
+## Usage example
+
+See [here](../.github/workflows/find-changes.yml).

find-changes/action.py

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+#!/usr/bin/env python3
+
+import os
+import subprocess
+import json
+import sys
+
+
+def fetch_diff_base(event_name, event_data):
+    """Ensure the git repository has enough history to perform the diff."""
+
+    valid_events = {"pull_request", "merge_group", "push"}
+
+    if event_name not in valid_events:
+        print(
+            f"find-changes only works on {', '.join(valid_events)} events.",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+    try:
+        # Determine what commit we need to fetch
+        target_commit = None
+
+        if event_name == "push" and event_data.get("before"):
+            target_commit = event_data["before"]
+        elif event_name in ("pull_request", "merge_group"):
+            return "HEAD~1"  # depends on actions/checkout with fetch-depth: 2 (handled in action.yml)
+
+        if target_commit:
+            # Fetch the specific commit we need
+            subprocess.run(
+                ["git", "fetch", "--depth=1", "--no-tags", "origin", target_commit],
+                check=True,
+                capture_output=True,
+                text=True,
+            )
+            print(f"Fetched diff base: {target_commit}")
+            return target_commit
+
+    except subprocess.CalledProcessError as e:
+        if (
+            event_name == "push"
+            and event_data.get("before") == "0000000000000000000000000000000000000000"
+        ):
+            print("Detected initial commit - returning empty change set")
+            return None
+
+        print(f"Warning: Error while fetching git history: {e.stderr}", file=sys.stderr)
+        sys.exit(1)
+
+
+def run_git_diff(comparison_point):
+    """Run git diff to get changed files."""
+    if comparison_point is None:
+        return []
+
+    try:
+        result = subprocess.run(
+            ["git", "diff", "--name-only", comparison_point],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        # Filter out empty lines and return array of changed files
+        return [file for file in result.stdout.splitlines() if file]
+    except subprocess.CalledProcessError:
+        print(f"Error running git diff against {comparison_point}", file=sys.stderr)
+        sys.exit(1)
+
+
+def get_event_data():
+    """Load GitHub event data from the event path file."""
+    event_path = os.environ.get("GITHUB_EVENT_PATH")
+    print(f"Reading event from {event_path}")
+
+    if not event_path:
+        print(
+            "Could not find event payload file.",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+    try:
+        with open(event_path) as f:
+            event_data = json.load(f)
+            if not event_data:
+                print("Event payload does not provide data.", file=sys.stderr)
+                sys.exit(1)
+            return event_data
+    except (IOError, json.JSONDecodeError) as e:
+        print(f"Error reading event data: {e}", file=sys.stderr)
+        sys.exit(1)
+
+
+def get_event_name():
+    """Get the GitHub event type from environment variables."""
+    return os.environ.get("GITHUB_EVENT_NAME")
+
+
+def main():
+    """Main function to output changed files in GitHub Actions format."""
+    event_name = get_event_name()
+    event_data = get_event_data()
+
+    # Fetch the diff base using the event data
+    diff_base = fetch_diff_base(event_name, event_data)
+
+    # Get an array of changed files using git diff
+    array = run_git_diff(diff_base)
+
+    # Write to GITHUB_OUTPUT file using the new approach
+    github_output = os.environ.get("GITHUB_OUTPUT")
+    if github_output:
+        files_output = json.dumps(array)
+        appending_mode = "a"
+        with open(github_output, appending_mode) as f:
+            f.write(f"array={files_output}\n")
+
+    # Log changed files
+    plural = "s" if len(array) != 1 else ""
+    if array:
+        print(f"Found {len(array)} change{plural}:")
+        for file in array:
+            print(file)
+    else:
+        print("No changes found")
+
+
+if __name__ == "__main__":
+    main()

find-changes/action.yml

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+name: "Find changes"
+description: "Outputs changed files in JSON format for downstream actions"
+
+runs:
+  using: "composite"
+  steps:
+    - if: github.event_name == 'pull_request' || github.event_name == 'merge_group'
+      name: Checkout
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 2
+
+    - if: github.event_name == 'push'
+      name: Checkout
+      uses: actions/checkout@v4
+
+    - name: Find changes
+      id: changes
+      shell: sh
+      run: |
+        "$GITHUB_ACTION_PATH/action.py"
+
+outputs:
+  array:
+    description: "JSON array of changed files"
+    value: ${{ steps.changes.outputs.array }}