markdown linter gh action

.github/workflows/markdown-linter.yml

@@ -0,0 +1,52 @@
+name: 'Markdown linter'
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - '**.md'
+# Remove all permissions by default
+permissions: {}
+jobs:
+  markdown-linter:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - name: Install mardownlint
+        run: npm install -g [email protected]
+      - name: Checkout project
+        uses: actions/checkout@v3
+      - name: Execute markdownlint
+        env:
+          DIFF_URL: "${{github.event.pull_request.diff_url}}"
+          TEMP_FILE: "${{runner.temp}}/pr-${{github.event.number}}.diff"
+        run: |
+          # This request doesn't consume API calls.
+          curl -Lkso $TEMP_FILE $DIFF_URL
+          files_changed="$(sed -nr 's/[\-\+]{3} [ab]\/(.*)/\1/p' $TEMP_FILE | sort | uniq)"
+          md_files="$(echo "$files_changed" | grep -o ".*\.md$" | sort | uniq || true)"
+          # Create an empty file, useful when the PR changes ignored files
+          touch ${{runner.temp}}/output
+          exit_code=0
+          markdownlint -o ${{runner.temp}}/output ${md_files[@]} || exit_code=$?
+          while read -r line; do
+            # line format:
+            #   file:row[:column] message
+            # white space inside brackets is intentional to detect the message for the notice.
+            message="${line#*[ ]}"
+            file_row_column="${line%%[ ]*}"
+            # Split by ':'
+            readarray -d : -t strarr < <(printf '%s' "$file_row_column")
+            if [[ "${#strarr[@]}" -eq 3 ]]; then
+              echo "::warning file=${strarr[0]},line=${strarr[1]},col=${strarr[2]}::${message}"
+            elif [[ "${#strarr[@]}" -eq 2 ]]; then
+              echo "::warning file=${strarr[0]},line=${strarr[1]}::${message}"
+            else
+              echo "::warning:: Error processing: ${line}"
+            fi
+          done < ${{runner.temp}}/output
+          if [[ $exit_code -ne 0 ]]; then
+            echo "::error:: Please review linter messages"
+            exit "$exit_code"
+          fi