ci: experiments with github actions

This PR exhibits experimental musings with github actions.

The objectives are:
* [x] try to avoid running a full test suite when only doc is updates
  (i.e. *.md files)
* [x] add some spell & grammar checking on doc (code is checked by a
  linter)
* [x] keep required checks, as they are desirable to properly check
  auto-merged PRs
* [ ] try to throttle macos runners and avoid failures due to the lower
  limit on macos runners

Signed-off-by: Frederic BIDON <[email protected]>

.github/workflows/go-test.yml

@@ -10,16 +10,85 @@ on:
   pull_request:
 
 jobs:
+  changes:
+    outputs:
+      notonlydoc: ${{ steps.filter.outputs.notonlydoc }}  # <- true if anything else than doc has been changed
+      doc: ${{ steps.filter.outputs.doc }}                # <- true if any doc has been changed
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: read
+
+    steps:
+    - uses: dorny/paths-filter@v3
+      id: filter
+      with:
+        filters: |
+          notonlydoc:
+          - '**/!(*.md)'                 # <- anything but markdown
+          doc:
+          - added|modified: '**.md'      # <- any markdown
+
+  merge-ok:
+    if: ${{ always() }}
+    name: MergeOK
+    needs: [changes, test_ok, doc_ok]
+    runs-on: ubuntu-latest
+    steps:
+    - run: |
+        not_doc_only="${{ needs.changes.outputs.notonlydoc }}"
+        doc="${{ needs.changes.outputs.doc }}"
+        merge_ok_doc="${{ needs.doc_ok.output.merge_status }}"
+        merge_ok_test="${{ needs.test_ok.output.merge_status }}"
+
+        if [[ "${not_doc_only}" != "true" && "${doc}" != "true" ]] ; then
+          echo "Change capture error. Should have not doc only, or docs or both."
+          exit 1
+        fi
+
+        if [[ "${not_doc_only}" == "true" && "${merge_ok_test}" != "true" ]] ; then
+          echo "Merge KO"
+          exit 1
+        fi
+
+        if [[ "${doc}" == "true" && "${merge_ok_doc}" != "true" ]] ; then
+          echo "Merge KO"
+          exit 1
+        fi
+
+        echo "Merge OK"
+
+  test_ok:
+    needs: [lint, test]
+    outputs:
+      merge_status: ${ steps.set_merge_ok.merge_status}
+    runs-on: ubuntu-latest
+    steps:
+    - run: |
+        echo "::set-output name=merge_status::true"
+
+  doc_ok:
+    needs: [spell-checking]
+    outputs:
+      merge_status: ${ steps.set_merge_ok.merge_status}
+    runs-on: ubuntu-latest
+    steps:
+    - run: |
+        echo "::set-output name=merge_status::true"
+
   lint:
     name: Lint
     runs-on: ubuntu-latest
+    needs: [changes]
+    if: ${{ needs.changes.outputs.notonlydoc == 'true' }}
+
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
         with:
           go-version: stable
           check-latest: true
           cache: true
+
       - name: golangci-lint
         uses: golangci/golangci-lint-action@v3
         with:
@@ -29,6 +98,8 @@ jobs:
 
   test:
     name: Unit tests
+    needs: [changes]
+    if: ${{ needs.changes.outputs.notonlydoc == 'true' }}
     runs-on: ${{ matrix.os }}
 
     strategy:
@@ -43,10 +114,13 @@ jobs:
         go-version: '${{ matrix.go_version }}'
         check-latest: true
         cache: true
-
     - uses: actions/checkout@v4
-
-    - run: go test -v -race -coverprofile="coverage-${{ matrix.os }}.${{ matrix.go_version }}.out" -covermode=atomic -coverpkg=$(go list)/... ./...
+    - run: >
+        go test -v -race
+        -coverprofile="coverage-${{ matrix.os }}.${{ matrix.go_version }}.out"
+        -covermode=atomic
+        -coverpkg=$(go list)/...
+        ./...
 
     - name: Upload coverage to codecov
       uses: codecov/codecov-action@v4
@@ -56,3 +130,16 @@ jobs:
         os: '${{ matrix.os }}'
         fail_ci_if_error: false
         verbose: true
+
+  spell-checking:
+    name: Doc spell checking
+    if: ${{ needs.changes.outputs.doc == 'true' }}
+    needs: [changes]
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: check-spelling/check-spelling@main
+      with:
+        only: '\.md$'
+        checkout: 1
+        #only_check_changed_files: 1