meta(gh): Add a status check for changelogs

.github/workflows/danger.yml

@@ -0,0 +1,13 @@
+name: "Danger"
+on: pull_request
+
+jobs:
+  build:
+    name: Changelogs
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+      - run: npx [email protected] ci
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

dangerfile.js

@@ -0,0 +1,24 @@
+const files = danger.git.modified_files;
+const hasChangelog = files.indexOf("CHANGELOG.md") !== -1;
+const hasPyChangelog = files.indexOf("py/CHANGELOG.md") !== -1;
+
+const ERROR_MESSAGE = `
+Please consider adding a changelog entry for the next release:
+
+For changes exposed to the Python package, please add an entry to \`py/CHANGELOG.md\`. This includes, but is not limited to event normalization, PII scrubbing, and the protocol.
+
+For changes to the Relay server, please add an entry to \`CHANGELOG.md\`:
+ 1. For new user-visible functionality under "Features"
+ 2. For user-visible bug fixes under "Bug Fixes"
+ 3. For features and bug fixes for internal operation (including processing mode) under "Internal"
+
+If none of the above apply, you can opt out by adding #skip-changelog to the PR description.
+`;
+
+const skipChangelog =
+  danger.github &&
+  (danger.github.pr.body + danger.github.pr.title).includes("#skip-changelog");
+
+if (!hasChangelog && !hasPyChangelog && !skipChangelog) {
+  error(ERROR_MESSAGE);
+}