Add GitHub Action.

.github/workflows/pull_request.yml

@@ -0,0 +1,23 @@
+name: Check changes
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install jsonschema
+    - name: Check changes
+      run: |
+        ./test-pr.py

.github/workflows/push.yml

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+name: Check full list
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install jsonschema
+    - name: Check full list
+      run: |
+        ./tools/check-list.py

test-pr.py

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+#!/usr/bin/env python3
+
+import json
+import os
+import re
+import shlex
+import sys
+import urllib.request
+
+
+def main():
+    with open(os.environ['GITHUB_EVENT_PATH']) as f:
+        event = json.load(f)
+
+    url = 'https://api.github.com/repos/{}/pulls/{}/files'.format(
+        os.environ['GITHUB_REPOSITORY'],
+        event['pull_request']['number'],
+    )
+
+    r = urllib.request.Request(url, headers={'Accept': 'application/json'})
+    f = urllib.request.urlopen(r)
+    files = json.load(f)
+    files = [x['filename'] for x in files]
+
+    addons_changed = []
+    schema_changed = False
+    checker_changed = False
+    for fname in files:
+        match = re.match(r'^addons/([^/]+)\.json$', fname)
+        if match:
+            addons_changed.append(match.group(1))
+        elif re.match(r'^schema/.+$', fname):
+            schema_changed = True
+        elif fname == 'tools/check-list.py':
+            checker_changed = True
+
+    if schema_changed or checker_changed:
+        return os.system('./tools/check-list.py')
+
+    if len(addons_changed) > 0:
+        return os.system('./tools/check-list.py {}'.format(
+            ' '.join([shlex.quote(a) for a in addons_changed]))
+        )
+
+    return 0
+
+
+if __name__ == '__main__':
+    # Sometimes, check-list.py returns 256. Apparently, sys.exit() will only
+    # accept 0-255, so we have to adjust. Weird.
+    if main() > 0:
+        sys.exit(1)