🌱 Skip PR CI actions for docs/hacks changes (#2084)

When a PR only contains changes to root level markdown, or anything
under `docs/` or `hack/`, there is no need to run the CI github actions.

To satisfy branch protection rules that may exist that require the
"unit-test" job to run, the `ci-repo.yml` action looks up details about
a PR and will skip the unit test if it detects that the only changes
made in the PR are docs or hacks.

The ignores do not apply to pushes to main, pushes to release, or
workflow calls.

Signed-off-by: Scott J Dickerson <[email protected]>

.github/workflows/ci-global.yml

@@ -6,6 +6,10 @@ on:
       - "main"
 
   pull_request:
+    paths-ignore:
+      - "docs/**"
+      - "hack/**"
+      - "*.md"
     branches:
       - "main"
 

.github/workflows/ci-image-build.yml

@@ -2,6 +2,10 @@ name: CI (test image build for a PR with build related changes)
 
 on:
   pull_request:
+    paths-ignore:
+      - "docs/**"
+      - "hack/**"
+      - "*.md"
     branches:
       - "main"
       - "release-*"

.github/workflows/ci-repo.yml

@@ -20,26 +20,77 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  unit-test-lookup-image:
+  unit-test-lookup:
     runs-on: ubuntu-latest
     outputs:
       builder-image: ${{ steps.grepBuilder.outputs.builder }}
+      should-test: ${{ steps.check-changes.outputs.should-test }}
+
     steps:
       - uses: actions/checkout@v4
 
       - name: Lookup builder image from the project's Dockerfile
         id: grepBuilder
         run: |
           builder=$(grep 'as builder' Dockerfile | sed -e 's/^FROM \(.*\) as builder$/\1/')
-          echo "Builder image: \`$builder\`" >> "$GITHUB_STEP_SUMMARY"
           echo "builder=$builder" >> "$GITHUB_OUTPUT"
 
+      - name: Did docs and hacks change?
+        id: docs-and-hacks
+        uses: tj-actions/changed-files@v44
+        with:
+          files: |
+            docs/**
+            hack/**
+            *.md
+
+      - name: Check if only docs and hacks changes have been made in a PR
+        id: check-changes
+        env:
+          IS_PR: ${{ !!github.event.pull_request }}
+          ONLY_DOCS: ${{ steps.docs-and-hacks.outputs.only_modified }}
+        run: |
+          SHOULD_TEST=$(
+            if [[ $IS_PR == true ]] && [[ $ONLY_DOCS == true ]]; then
+              echo "false"
+            else
+              echo "true"
+            fi
+          )
+
+          echo "is-pr=$IS_PR" >> "$GITHUB_OUTPUT"
+          echo "changes_only_docs=${ONLY_DOCS:-false}" >> "$GITHUB_OUTPUT"
+          echo "should-test=$SHOULD_TEST" >> "$GITHUB_OUTPUT"
+
+      - name: Summarize findings
+        env:
+          ONLY_DOCS: ${{ steps.docs-and-hacks.outputs.only_modified }}
+          MODIFIED_FILES: ${{ steps.docs-and-hacks.outputs.all_modified_files }}
+        run: |
+          cat >> "$GITHUB_STEP_SUMMARY" <<EOF
+          ## Build container
+            - CI will run on container: \`${{ steps.grepBuilder.outputs.builder }}\`
+
+          ## Findings
+            - The action is PR triggered? \`${{ steps.check-changes.outputs.is-pr }}\`
+            - Changes are only to docs and hacks? \`${{ steps.check-changes.outputs.changes_only_docs }}\`
+            - Should the unit test run? \`${{ steps.check-changes.outputs.should-test }}\`
+          EOF
+
+          if [[ $ONLY_DOCS == true ]] && [[ -n "$MODIFIED_FILES" ]]; then
+            echo "## Modified docs and hacks files that do not impact the build" >> "$GITHUB_STEP_SUMMARY"
+            for file in ${MODIFIED_FILES}; do
+              echo "  - \`$file\`" >> "$GITHUB_STEP_SUMMARY"
+            done
+          fi
+
   unit-test:
     runs-on: ubuntu-latest
-    needs: unit-test-lookup-image
+    needs: unit-test-lookup
+    if: ${{ needs.unit-test-lookup.outputs.should-test == 'true' }}
 
     # Use the same container as the Dockerfile's "FROM * as builder"
-    container: ${{ needs.unit-test-lookup-image.outputs.builder-image }}
+    container: ${{ needs.unit-test-lookup.outputs.builder-image }}
 
     steps:
       - uses: actions/checkout@v4