[ci] Tell stacked pull requests apart from hand-built chains (#17980)

.github/scripts/auto-label-pr/constants.js

@@ -13,6 +13,7 @@ module.exports = {
     'merging-to-release',
     'merging-to-beta',
     'chained-pr',
+    'stacked-pr',
     'core',
     'small-pr',
     'medium-pr',

.github/scripts/auto-label-pr/detectors.js

@@ -33,8 +33,41 @@ async function fetchPrFileContent(github, context, path) {
   }
 }
 
+// Check whether a pull request is part of a GitHub stack.
+//
+// GitHub's stacked pull request feature adds a `stack` object to the pull
+// request resource. It is present on every pull request in the stack -
+// including the bottom one, whose base is already `dev` - and is absent
+// entirely on standalone pull requests.
+//
+// The `pull_request_target` webhook payload is not guaranteed to carry this
+// field, so fall back to asking the API when it is missing. Guessing wrong
+// here is costly: a stacked pull request mistaken for a manually chained one
+// gets a label that blocks merging.
+async function isStackedPr(github, context) {
+  const pr = context.payload.pull_request;
+  if (pr.stack != null) {
+    return true;
+  }
+
+  try {
+    const { owner, repo } = context.repo;
+    const { data } = await github.rest.pulls.get({
+      owner,
+      repo,
+      pull_number: pr.number,
+    });
+    return data.stack != null;
+  } catch (error) {
+    // Treat an API failure as "not stacked" so a chained pull request still
+    // gets its blocking label rather than silently slipping through.
+    console.log('Failed to check stack membership:', error.message);
+    return false;
+  }
+}
+
 // Strategy: Merge branch detection
-async function detectMergeBranch(context) {
+async function detectMergeBranch(github, context) {
   const labels = new Set();
   const baseRef = context.payload.pull_request.base.ref;
 
@@ -42,7 +75,11 @@ async function detectMergeBranch(context) {
     labels.add('merging-to-release');
   } else if (baseRef === 'beta') {
     labels.add('merging-to-beta');
+  } else if (await isStackedPr(github, context)) {
+    // GitHub manages the merge order for a stack, so these are not blocked.
+    labels.add('stacked-pr');
   } else if (baseRef !== 'dev') {
+    // A chain built by hand: it must not merge until its base branch does.
     labels.add('chained-pr');
   }
 

.github/scripts/auto-label-pr/index.js

@@ -88,7 +88,7 @@ module.exports = async ({ github, context }) => {
 
   // Early exit for release and beta branches only
   if (baseRef === 'release' || baseRef === 'beta') {
-    const branchLabels = await detectMergeBranch(context);
+    const branchLabels = await detectMergeBranch(github, context);
     const finalLabels = Array.from(branchLabels);
 
     console.log('Computed labels (merge branch only):', finalLabels.join(', '));
@@ -118,7 +118,7 @@ module.exports = async ({ github, context }) => {
     deprecatedResult,
     maintainerAccess
   ] = await Promise.all([
-    detectMergeBranch(context),
+    detectMergeBranch(github, context),
     detectComponentPlatforms(changedFiles, apiData),
     detectNewComponents(github, context, prFiles),
     detectNewPlatforms(github, context, prFiles, apiData),

.github/scripts/auto-label-pr/tests/detectors.test.js

@@ -1,6 +1,7 @@
 const { describe, it } = require('node:test');
 const assert = require('node:assert/strict');
 const {
+  detectMergeBranch,
   detectNewPlatforms,
   detectNewComponents,
   detectPRSize,
@@ -36,6 +37,107 @@ const API_DATA = {
 const WITH_SCHEMA = 'CONFIG_SCHEMA = cv.Schema({})';
 const WITHOUT_SCHEMA = 'CODEOWNERS = ["@esphome/core"]';
 
+// ---------------------------------------------------------------------------
+// detectMergeBranch
+// ---------------------------------------------------------------------------
+
+// Builds a fresh context for detectMergeBranch tests instead of mutating the
+// shared CONTEXT fixture above (which other describe blocks rely on).
+function makeMergeContext(baseRef, { stack } = {}) {
+  const pull_request = { number: 1, base: { ref: baseRef } };
+  if (stack !== undefined) {
+    pull_request.stack = stack;
+  }
+  return {
+    repo: { owner: 'esphome', repo: 'esphome' },
+    payload: { pull_request }
+  };
+}
+
+// A GitHub API mock exposing only rest.pulls.get, with a call counter so
+// tests can assert whether the API fallback was actually invoked.
+function makeStackGithub({ stack = null, error = null } = {}) {
+  const state = { calls: 0 };
+  const github = {
+    rest: {
+      pulls: {
+        get: async () => {
+          state.calls++;
+          if (error) throw error;
+          return { data: { stack } };
+        }
+      }
+    }
+  };
+  return { github, state };
+}
+
+const STACK_INFO = { base: { ref: 'dev' }, id: 71540, number: 17978, position: 3, size: 3 };
+
+describe('detectMergeBranch', () => {
+  it('base ref release adds merging-to-release only and never checks the stack', async () => {
+    const { github, state } = makeStackGithub({ stack: STACK_INFO });
+    const context = makeMergeContext('release', { stack: STACK_INFO });
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['merging-to-release']);
+    assert.equal(state.calls, 0);
+  });
+
+  it('base ref beta adds merging-to-beta only and never checks the stack', async () => {
+    const { github, state } = makeStackGithub({ stack: STACK_INFO });
+    const context = makeMergeContext('beta', { stack: STACK_INFO });
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['merging-to-beta']);
+    assert.equal(state.calls, 0);
+  });
+
+  it('stack present on the webhook payload adds stacked-pr without calling the API', async () => {
+    const { github, state } = makeStackGithub();
+    const context = makeMergeContext('feature-branch', { stack: STACK_INFO });
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['stacked-pr']);
+    assert.equal(state.calls, 0);
+  });
+
+  it('stack absent from payload falls back to the API and adds stacked-pr', async () => {
+    const { github, state } = makeStackGithub({ stack: STACK_INFO });
+    const context = makeMergeContext('feature-branch');
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['stacked-pr']);
+    assert.equal(state.calls, 1);
+  });
+
+  it('bottom of a stack (base ref dev, stack present) still adds stacked-pr', async () => {
+    const { github, state } = makeStackGithub();
+    const context = makeMergeContext('dev', { stack: STACK_INFO });
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['stacked-pr']);
+    assert.equal(state.calls, 0);
+  });
+
+  it('not stacked, base ref not dev adds chained-pr', async () => {
+    const { github } = makeStackGithub({ stack: null });
+    const context = makeMergeContext('feature-branch');
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['chained-pr']);
+  });
+
+  it('not stacked, base ref dev adds no labels', async () => {
+    const { github } = makeStackGithub({ stack: null });
+    const context = makeMergeContext('dev');
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), []);
+  });
+
+  it('a failed stack lookup falls back to not-stacked, so a feature-branch base adds chained-pr', async () => {
+    const { github, state } = makeStackGithub({ error: new Error('API unavailable') });
+    const context = makeMergeContext('feature-branch');
+    const labels = await detectMergeBranch(github, context);
+    assert.deepEqual(Array.from(labels).sort(), ['chained-pr']);
+    assert.equal(state.calls, 1);
+  });
+});
+
 // ---------------------------------------------------------------------------
 // detectNewPlatforms
 // ---------------------------------------------------------------------------

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

@@ -35,7 +35,7 @@ jobs:
           # Scope the minted App token to the minimum needed by auto-label-pr/*.js.
           permission-contents: read       # repos.getContent for CODEOWNERS and file lookups in detectors.js
           permission-issues: write        # listLabelsOnIssue, addLabels, removeLabel, list/createComment
-          permission-pull-requests: write  # pulls.listFiles, list/create/update/dismissReview
+          permission-pull-requests: write  # pulls.get, pulls.listFiles, list/create/update/dismissReview
 
       - name: Auto Label PR
         uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0