feat: Add detect-changes action

README.md

@@ -22,6 +22,7 @@ particular step in a workflow.
 <!-- start:links: autogenerated by .scripts/local/update_readme_list.sh -->
 - [build-container-image](./build-container-image/README.md)
 - [build-product-image](./build-product-image/README.md)
+- [detect-changes](./detect-changes/README.md)
 - [free-disk-space](./free-disk-space/README.md)
 - [publish-helm-chart](./publish-helm-chart/README.md)
 - [publish-image](./publish-image/README.md)

detect-changes/README.md

@@ -0,0 +1,25 @@
+# `detect-changes`
+
+> Manifest: [detect-changes/action.yml][detect-changes]
+
+This action detects changed files by providing a list of glob patterns.
+It can be used in situations where the GHA native path filtering cannot be used.
+
+## Inputs and Outputs
+
+> [!TIP]
+> For descriptions of the inputs and outputs, see the complete [detect-changes] action.
+
+### Inputs
+
+| Input      | Required | Description                                                     |
+| ---------- | -------- | --------------------------------------------------------------- |
+| `patterns` | No       | A list of glob patterns to detect changes in. Defaults to ['*'] |
+
+### Outputs
+
+| Output      | Description                                                                                      |
+| ----------- | ------------------------------------------------------------------------------------------------ |
+| `detected`  | `'true'` or `'false'` indicating if any changed files were matched by the provided glob patterns |
+
+[detect-changes]: ./action.yaml

detect-changes/action.yaml

@@ -0,0 +1,35 @@
+---
+name: detect-changes
+description: Detect changed files by providing a list of glob patterns
+inputs:
+  patterns:
+    description: A list of glob patterns to detect changes in. Defaults to ['*'].
+    default: "['*']"
+outputs:
+  detected:
+    description: Returns if any changed files were matched by the provided glob patterns.
+    value: ${{ steps.check.outputs.MATCHED }}
+runs:
+  using: composite
+  steps:
+    - name: Check for changed files
+      id: check
+      env:
+        PATTERNS: ${{ inputs.patterns }}
+      shell: bash
+      run: |
+        set -euo pipefail
+
+        # This is cursed... we use `.[] | .` to remove quotes and any yaml formatting.
+        readarray -t GLOBS < <(echo -n "$PATTERNS" | yq '.[] | .')
+
+        MATCHED="false"
+        for GLOB in "${GLOBS[@]}"; do
+            if ! git diff --exit-code --name-only "${BASE_SHA}.." -- "$GLOB"; then
+              # When git diff exist with an error, that means there was a diff
+              # for the glob.
+              MATCHED="true"
+            fi
+        done
+
+        echo "MATCHED=$MATCHED" | tee -a "$GITHUB_OUTPUT"