Add script to check PR commit messages

Author: friendlyanon

.github/pull_request_template.md

@@ -1,3 +1,6 @@
 <!--
 Please make sure your Pull Request is targeting the develop branch.
+
+Please make sure your commit messages conform to the checks contained in
+.github/scripts/lint-commits.js.
 -->

.github/scripts/lint-commits.js

@@ -0,0 +1,98 @@
+"use strict";
+
+const { URL } = require("url");
+
+const titleRegex = /^(.+?)(?:(?:\r?\n){2}|$)/us;
+const titleOf = (message) => message.match(titleRegex)[1];
+const bodyOf = (message) => message.slice(titleOf(message).length).trimStart();
+
+const urlRegex = /^(?:https?|ftp):\/\//u;
+function isURL(string) {
+  if (urlRegex.test(string)) {
+    try {
+      new URL(string);
+      return true;
+    } catch {}
+  }
+
+  return false;
+}
+
+const checkers = [{
+  error: "Commit message must not contain carriage return (\\r) characters",
+  check: (message) => !message.includes("\r"),
+}, {
+  error: "Commit title must not contain newline (\\n) characters",
+  check: (message) => !titleOf(message).includes("\n"),
+}, {
+  error: "Commit title must be 50 characters long or less",
+  check: (message) => titleOf(message).length <= 50,
+}, {
+  error: "Commit title must start with an uppercase letter",
+  check(message) {
+    const firstChar = titleOf(message).charAt(0);
+    const firstCharUpper = firstChar.toUpperCase();
+    return firstChar === firstCharUpper
+      && "A" <= firstCharUpper
+      && firstCharUpper <= "Z";
+  },
+}, {
+  error: "Commit title must not end with a period",
+  check: (message) => titleOf(message).trimEnd().slice(-1) !== ".",
+}, {
+  error: "Commit body lines must be 72 characters long or less (except URLs)",
+  check(message) {
+    const body = bodyOf(message);
+    if (body.trimEnd() !== "") {
+      for (const line of body.split("\n")) {
+        if (line.length > 72 && !isURL(line)) {
+          return false;
+        }
+      }
+    }
+
+    return true;
+  },
+}];
+
+async function readJsonFromStdin() {
+  const chunks = [];
+  for await (const chunk of process.stdin) {
+    chunks.push(chunk);
+  }
+
+  return Buffer.concat(chunks).toString();
+}
+
+function runChecker({ check, error }) {
+  return check(this.message) ? [] : [error];
+}
+
+async function main() {
+  const commits = JSON.parse(await readJsonFromStdin());
+
+  let exitCode = 0;
+  for (const { commit, sha } of commits) {
+    const errors = checkers.flatMap(runChecker, commit);
+    if (errors.length === 0) {
+      continue;
+    }
+
+    if (exitCode !== 0) {
+      console.log("");
+    }
+    exitCode = 1;
+
+    console.log("Commit %s failed these checks:", sha);
+    for (const error of errors) {
+      console.log("  %s", error);
+    }
+  }
+
+  return exitCode;
+}
+
+main().catch((error) => {
+  console.error(error);
+  return 1;
+}).then((code) => { process.exitCode = code; });

.github/workflows/lint-commits.yml

@@ -0,0 +1,24 @@
+name: Lint commits
+
+on:
+  pull_request_target:
+    branches:
+    - develop
+
+jobs:
+  lint-commits:
+    if: github.repository_owner == 'friendlyanon'
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Get PR commits
+      id: commits
+      uses: IdanHo/get-pr-commits@d94b66d146a31ef91e54a2597dee4fb523157232
+      with: { token: "${{ github.token }}" }
+
+    - name: Check commits
+      run: |
+        node .github/scripts/lint-commits.js << 'JSON'
+        ${{ steps.commits.outputs.commits }}
+        JSON