ci: add automatic PR labeling from linked issues

.github/assets/label_pr.js

@@ -0,0 +1,65 @@
+// Filter function for labels we do not want on PRs automatically.
+function shouldIncludeLabel(label) {
+  const isStatus = label.startsWith("S-");
+  const isPreventStale = label === "M-prevent-stale";
+  const isDifficulty = label.startsWith("D-");
+
+  return !isStatus && !isPreventStale && !isDifficulty;
+}
+
+// Get the issue number from an issue link in the forms
+// `<keyword> <issue url>` or `<keyword> #<issue number>`.
+function getIssueLink(repoUrl, body) {
+  if (!body) return undefined;
+
+  const urlPattern = new RegExp(
+    `(close|closes|closed|fix|fixes|fixed|resolve|resolves|resolved) ${repoUrl}/issues/(?<issue_number>\\d+)`,
+    "i"
+  );
+  const issuePattern = new RegExp(
+    `(close|closes|closed|fix|fixes|fixed|resolve|resolves|resolved) #(?<issue_number>\\d+)`,
+    "i"
+  );
+
+  const urlRe = body.match(urlPattern);
+  const issueRe = body.match(issuePattern);
+  if (urlRe?.groups?.issue_number) {
+    return urlRe.groups.issue_number;
+  } else {
+    return issueRe?.groups?.issue_number;
+  }
+}
+
+module.exports = async ({ github, context }) => {
+  try {
+    const prNumber = context.payload.pull_request.number;
+    const prBody = context.payload.pull_request.body;
+    const repo = context.repo;
+
+    const repoUrl = context.payload.repository.html_url;
+    const issueNumber = getIssueLink(repoUrl, prBody);
+    if (!issueNumber) {
+      console.log("No issue reference found in PR description.");
+      return;
+    }
+
+    const issue = await github.rest.issues.get({
+      ...repo,
+      issue_number: issueNumber,
+    });
+
+    const issueLabels = issue.data.labels
+      .map((label) => label.name)
+      .filter(shouldIncludeLabel);
+    if (issueLabels.length > 0) {
+      await github.rest.issues.addLabels({
+        ...repo,
+        issue_number: prNumber,
+        labels: issueLabels,
+      });
+    }
+  } catch (err) {
+    console.error("Failed to label PR");
+    console.error(err);
+  }
+};

.github/workflows/label-pr.yml

@@ -0,0 +1,23 @@
+name: Label PRs
+
+on:
+  pull_request:
+    types: [opened]
+
+jobs:
+  label_prs:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Label PRs
+        uses: actions/github-script@v8
+        with:
+          script: |
+            const label_pr = require('./.github/assets/label_pr.js')
+            await label_pr({github, context})