Actions | Introduce auto-assign-pr workflow (#4275)

Author: cheenamalhotra

.github/scripts/auto-assign-pr.js

@@ -0,0 +1,133 @@
+// Auto-assign PR load balancer.
+//
+// Selects up to 2 assignees for a qualifying PR from a configurable pool,
+// balancing by current open-PR assignment count. Invoked by the
+// `auto-assign-pr.yml` workflow via `actions/github-script`.
+module.exports = async ({ github, context, core }) => {
+  const owner = context.repo.owner;
+  const repo = context.repo.repo;
+  const prNumber = context.issue.number;
+  const author = context.payload.pull_request.user.login;
+  const normalizeLogin = login => login.toLowerCase();
+  const parseCsvLogins = value => (value ?? '')
+    .split(',')
+    .map(entry => entry.trim())
+    .filter(entry => entry.length > 0);
+
+  // Fallback pool keeps behavior unchanged when no repo variable is configured.
+  const defaultPool = ['cheenamalhotra', 'paulmedynski', 'priyankatiwari08', 'benrr101', 'mdaigle', 'apoorvdeshmukh'];
+  const configuredPool = parseCsvLogins(process.env.PR_REVIEWER_POOL);
+  const rawPool = configuredPool.length > 0 ? configuredPool : defaultPool;
+  const seenPoolUsers = new Set();
+  const pool = [];
+  for (const user of rawPool) {
+    const normalized = normalizeLogin(user);
+    if (!seenPoolUsers.has(normalized)) {
+      seenPoolUsers.add(normalized);
+      pool.push(user);
+    }
+  }
+
+  let latestPr;
+  try {
+    const response = await github.rest.pulls.get({
+      owner,
+      repo,
+      pull_number: prNumber
+    });
+    latestPr = response.data;
+  } catch (error) {
+    throw new Error(`Failed to fetch latest PR details: ${error.message}`);
+  }
+
+  if (latestPr.state !== 'open' || latestPr.draft || !latestPr.milestone) {
+    console.log('PR is no longer assignment-eligible (not open, draft, or missing milestone).');
+    return;
+  }
+
+  const currentAssignees = (latestPr.assignees ?? []).map(a => a.login);
+
+  console.log(`PR Author: ${author}`);
+  console.log(`Event Name: ${context.eventName}; Is Fork PR: ${context.payload.pull_request.head.repo.fork === true}`);
+  console.log(`Current Assignees: ${currentAssignees.join(', ')}`);
+
+  if (currentAssignees.length >= 2) {
+    console.log('PR already has 2 or more assignees. No action needed.');
+    return;
+  }
+
+  const neededAssigneesCount = 2 - currentAssignees.length;
+
+  const candidates = pool.filter(user =>
+    normalizeLogin(user) !== normalizeLogin(author) &&
+    !currentAssignees.some(a => normalizeLogin(a) === normalizeLogin(user))
+  );
+
+  if (candidates.length === 0) {
+    console.log('No valid candidates left in the pool.');
+    return;
+  }
+
+  const workloads = {};
+  const canonicalCandidateByNormalized = {};
+  candidates.forEach(user => {
+    const normalized = normalizeLogin(user);
+    workloads[normalized] = 0;
+    canonicalCandidateByNormalized[normalized] = user;
+  });
+
+  try {
+    // Rank candidates by current assignment count across all open PRs.
+    const iterator = github.paginate.iterator(github.rest.pulls.list, {
+      owner,
+      repo,
+      state: 'open',
+      per_page: 100
+    });
+
+    for await (const response of iterator) {
+      for (const pr of response.data) {
+        if (pr.draft) continue;
+        if (pr.assignees) {
+          for (const assignee of pr.assignees) {
+            const login = normalizeLogin(assignee.login);
+            if (workloads[login] !== undefined) {
+              workloads[login]++;
+            }
+          }
+        }
+      }
+    }
+  } catch (error) {
+    throw new Error(`Failed to fetch open PRs for auto-assignment: ${error.message}`);
+  }
+
+  const workloadArray = candidates.map(user => {
+    const normalized = normalizeLogin(user);
+    return { user: canonicalCandidateByNormalized[normalized], count: workloads[normalized] };
+  });
+  console.log('Current Workloads:', workloadArray);
+
+  // Shuffle before sorting so ties are broken fairly instead of favoring pool order.
+  for (let i = workloadArray.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [workloadArray[i], workloadArray[j]] = [workloadArray[j], workloadArray[i]];
+  }
+
+  workloadArray.sort((a, b) => a.count - b.count);
+
+  const selectedAssignees = workloadArray.slice(0, neededAssigneesCount).map(w => w.user);
+  console.log(`Selected candidates: ${selectedAssignees.join(', ')}`);
+
+  if (selectedAssignees.length === 0) {
+    console.log('No assignees selected. No action needed.');
+    return;
+  }
+
+  await github.rest.issues.addAssignees({
+    owner,
+    repo,
+    issue_number: prNumber,
+    assignees: selectedAssignees
+  });
+};

.github/workflows/auto-assign-pr.yml

@@ -0,0 +1,38 @@
+name: Auto Assign PR Load Balancer
+
+on:
+  pull_request_target:
+    types: [opened, reopened, ready_for_review, milestoned]
+
+concurrency:
+  group: auto-assign-pr-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  load-balance-assignees:
+    # Only run for assignment-eligible PRs in the upstream repository. Use
+    # pull_request_target so the workflow only runs once per PR event.
+    # Exclude PRs from forks as GitHub Actions does not have permissions to assign users on PRs from forks.
+    if: github.repository == 'dotnet/SqlClient' && github.event.pull_request.state == 'open'  && github.event.pull_request.draft == false && github.event.pull_request.milestone != null && github.event.pull_request.head.repo.fork == false
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      issues: write
+      pull-requests: write
+    env:
+      PR_REVIEWER_POOL: ${{ vars.PR_REVIEWER_POOL }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          sparse-checkout: |
+            .github/scripts/auto-assign-pr.js
+          sparse-checkout-cone-mode: false
+          persist-credentials: false
+
+      - name: Calculate Workload and Apply
+        uses: actions/github-script@v9
+        with:
+          script: |
+            const script = require('./.github/scripts/auto-assign-pr.js');
+            await script({ github, context, core });