Use a problem matcher

.github/markdownlint-problem-matcher.json

@@ -0,0 +1,24 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "markdownlint",
+      "pattern": [
+        {
+          "code": 3,
+          "file": 1,
+          "line": 2,
+          "message": 4,
+          "regexp": "^(.+):(\\d+) (MD\\d+)/(.+)$"
+        },
+        {
+          "code": 4,
+          "column": 3,
+          "file": 1,
+          "line": 2,
+          "message": 5,
+          "regexp": "^(.+):(\\d+):(\\d+) (MD\\d+)/(.+)$"
+        }
+      ]
+    }
+  ]
+}

entrypoint.sh

@@ -5,41 +5,12 @@ MARKDOWNLINT="${MARKDOWNLINT}${INPUT_CONFIG_FILE:+ -c ${INPUT_CONFIG_FILE}}"
 MARKDOWNLINT="${MARKDOWNLINT}${INPUT_IGNORE_FILES:+ -i ${INPUT_IGNORE_FILES}}"
 MARKDOWNLINT="${MARKDOWNLINT}${INPUT_RULES:+ -r ${INPUT_RULES}}"
 
-# shellcheck disable=SC2086
-OUTPUT=$(${MARKDOWNLINT} ${INPUT_FILES} 2>&1)
-SUCCESS=$?
-echo "${OUTPUT}"
-
-if [ ${SUCCESS} -eq 0 ]; then
-  exit 0
-fi
-
-if [ "${GITHUB_EVENT_NAME}" = pull_request ]; then
-  comment=""
-  FILES=$(echo "${OUTPUT}" | cut -d: -f1 | sort | uniq)
-
-  for file in ${FILES}; do
-    comment="${comment}<details><summary><code>${file}</code></summary>
+echo '::add-matcher::.github/markdownlint-problem-matcher.json'
 
-\`\`\`
-$(echo "${OUTPUT}" | grep "^${file}:" | sed "s/^[^:]*:[[:space:]]*//")
-\`\`\`
-
-</details>"
-  done
-
-  COMMENT_BODY="#### Issues with Markdown/CommonMark files
-${comment}
-
-*Workflow: \`${GITHUB_WORKFLOW}\`, Action: \`${GITHUB_ACTION}\`*"
-  PAYLOAD=$(echo '{}' | jq --arg body "${COMMENT_BODY}" '.body = $body')
-  COMMENTS_URL=$(jq -r .pull_request.comments_url <"${GITHUB_EVENT_PATH}")
+# shellcheck disable=SC2086
+${MARKDOWNLINT} ${INPUT_FILES}
+readonly RC=$?
 
-  curl -sS \
-    -H "Authorization: token ${GITHUB_TOKEN}" \
-    -H 'Content-Type: application/json' \
-    -d "${PAYLOAD}" \
-    "${COMMENTS_URL}" >/dev/null
-fi
+echo '::remove-matcher owner=markdownlint::'
 
-exit ${SUCCESS}
+exit ${RC}