Add YAML file check (#858)

This adds a job to run `yamllint` on `*.{yaml,yml}` files in the repository. YAML files are currently found not only in the GitHub workflows directory; they're also in `docs/`, and we can imagine more YAML-based config files being added in the future.

Author: mhucka

.github/problem-matchers/yamllint.json

@@ -0,0 +1,22 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "yamllint",
+      "pattern": [
+        {
+          "regexp": "^(.*\\.ya?ml)$",
+          "file": 1
+        },
+        {
+          "regexp": "^\\s{2}(\\d+):(\\d+)\\s+(error|warning)\\s+(.*?)\\s+\\((.*)\\)$",
+          "line": 1,
+          "column": 2,
+          "severity": 3,
+          "message": 4,
+          "code": 5,
+          "loop": true
+        }
+      ]
+    }
+  ]
+}

.github/workflows/ci-file-checks.yaml

@@ -79,6 +79,8 @@ jobs:
       python_files: ${{steps.filter.outputs.python_files}}
       cc: ${{steps.filter.outputs.cc}}
       cc_files: ${{steps.filter.outputs.cc_files}}
+      yaml: ${{steps.filter.outputs.yaml}}
+      yaml_files: ${{steps.filter.outputs.yaml_files}}
     steps:
       # When invoked manually, use the given SHA to figure out the change list.
       - if: github.event_name == 'workflow_dispatch'
@@ -125,6 +127,10 @@ jobs:
                   - '**/*.cc'
                   - '**/*.h'
                   - '**/*.proto'
+            yaml:
+              - added|modified:
+                  - '**/*.yaml'
+                  - '**/*.yml'
 
   Setup:
     if: needs.Changes.outputs.python == 'true'
@@ -336,3 +342,27 @@ jobs:
             } >> "$GITHUB_STEP_SUMMARY"
           fi
           exit $exit_code
+
+  Yaml-lint:
+    if: needs.Changes.outputs.yaml == 'true'
+    name: YAML lint
+    needs: Changes
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Check out a copy of the TFQ git repository
+        uses: actions/checkout@v4
+
+      - name: Set up yamllint output problem matcher
+        run: echo '::add-matcher::.github/problem-matchers/yamllint.json'
+
+      - name: Find out the yamllint version
+        id: yamllint
+        run: |
+          version=$(yamllint --version)
+          echo "version=${version#yamllint }" >> "$GITHUB_OUTPUT"
+
+      - name: Run yamllint ${{steps.yamllint.outputs.version}}
+        run: |
+          set -x
+          # shellcheck disable=SC2086
+          yamllint --format github ${{needs.Changes.outputs.yaml_files}}