Use Github Actions to check PR messages (ouster-lidar#513)

* Repo settings now always squash merge
* Default commit message is lifted from PR description

.github/check_title_and_description.py

@@ -0,0 +1,34 @@
+import os
+import sys
+import re
+
+title_re = r'\A[0-9A-Z][\x20-\x7E]{0,88}([a-zA-Z0-9]|[\)])'
+description_re = r'(((\r)?\n[\20-\x7E]{0,100})+)?(\n)?'
+
+title = os.environ.get("TITLE")
+pr_number_string = os.environ.get("PR_NUMBER")
+pr_description = "\n" + os.environ.get("PR_BODY")
+
+# check title length with (PR number) added at end
+new_title = title + " (#" + pr_number_string + ")"
+
+error = False
+print(f"Checking PR title {repr(new_title)}...")
+if not re.fullmatch(title_re, new_title):
+    print(f"Error: Please revise the PR title {new_title} "
+            "to match the regex {title_re} where:\n"
+            "* the first letter is a capital letter or numeral 0-9\n"
+            "* title is more than 2 characters long\n"
+            "* the title is no longer than 90 characters including "
+            "the addition of (###) for the PR number")
+    error = True
+
+print(f"Checking PR description {repr(pr_description)}")
+if not re.fullmatch(description_re, pr_description):
+    print(f"Error: The PR description {repr(pr_description)}, "
+            "which will be treated as your commit message, does "
+            "not match the regex {description_re}")
+    error = True
+
+if error:
+    sys.exit(1)

.github/workflows/check-commit-message.yml

@@ -0,0 +1,19 @@
+name: check-merge-commit-message-on-PR
+
+run-name: Check merge commit messages by ${{ github.actor }} on ${{ github.ref }}
+on: [pull_request]
+
+jobs: 
+  check_title_and_description:
+    if: github.event_name == 'pull_request' && ! github.event.pull_request.draft
+    name: check PR title and description
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: check PR title and description
+        run: python .github/check_title_and_description.py
+        shell: bash
+        env:
+          TITLE: ${{ github.event.pull_request.title }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          PR_BODY: ${{ github.event.pull_request.body }}