fix(ios): parse the Xcode 27 <tagged-backtrace> time-profile stack

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 ## Unreleased
 
+- Fixed (ios): `perf cpu profile report --kind xctrace` on Xcode 27 no longer fails with
+  `Apple xctrace CPU report contained no samples` on a trace that holds thousands of samples. Xcode
+  27 exports each `time-profile` sample stack as `<tagged-backtrace>` instead of `<backtrace>`, and
+  the parser read only the old element, so every row resolved no stack at all. Both spellings now
+  parse through the same `id`/`ref` resolution, so a profile recorded with an older Xcode reports
+  what it did before. (#2860)
 - Changed (apple): a read-only runner command is resent inside the same request only when the
   runner refused it as `RUNNER_BUSY`. Before, any `COMMAND_FAILED` carrying `details.retriable:
   true` was sent up to three times. That flag tells a caller's own poll, such as `wait`, to try

packages/platform-apple/src/core/__tests__/perf-time-profile.test.ts

@@ -2,6 +2,58 @@ import assert from 'node:assert/strict';
 import { test } from 'vitest';
 import { parseAppleTimeProfileSummary } from '../perf-time-profile.ts';
 
+test('reads Xcode 27 tagged-backtrace stacks and skips stack sentinels', () => {
+  // xctrace 27 renamed the `time-profile` stack element to `<tagged-backtrace>` and kept the same
+  // `id`/`ref` reuse over frames and binaries. These row shapes come from a real 27.1 export; the
+  // symbols, binaries, and weights here are synthetic.
+  const summary = parseAppleTimeProfileSummary(
+    `<trace-query-result><node>
+      <row>
+        <weight id="weight-1">1000000</weight>
+        <tagged-backtrace id="stack-1">
+          <frame id="frame-1" name="hot"><binary id="binary-1" name="App"/></frame>
+          <frame name="caller"><binary name="Framework"/></frame>
+        </tagged-backtrace>
+      </row>
+      <row><weight ref="weight-1"/><tagged-backtrace ref="stack-1"/></row>
+      <row>
+        <weight ref="weight-1"/>
+        <tagged-backtrace id="stack-2" truncated="YES"><frame ref="frame-1"/></tagged-backtrace>
+      </row>
+      <row>
+        <weight ref="weight-1"/>
+        <tagged-backtrace id="stack-3">
+          <frame id="frame-2" name="warm"><binary ref="binary-1"/></frame>
+        </tagged-backtrace>
+      </row>
+      <row><weight ref="weight-1"/><sentinel/></row>
+    </node></trace-query-result>`,
+    2,
+  );
+
+  // `hot` is sampled as a stack definition, through a `<tagged-backtrace ref>`, and through a
+  // truncated stack whose innermost frame is a `<frame ref>`. `warm` reaches its binary only
+  // through `<binary ref>`, and the sentinel row carries a weight with no stack at all.
+  assert.deepEqual(summary, {
+    sampleCount: 4,
+    totalSampleWeightMs: 4,
+    topFunctions: [
+      {
+        symbol: 'hot',
+        binary: 'App',
+        selfSampleMs: 3,
+        selfSamplePercent: 75,
+      },
+      {
+        symbol: 'warm',
+        binary: 'App',
+        selfSampleMs: 1,
+        selfSamplePercent: 25,
+      },
+    ],
+  });
+});
+
 test('aggregates weighted innermost frames and follows xctrace references', () => {
   const summary = parseAppleTimeProfileSummary(
     `<trace-query-result><node><row>
@@ -44,6 +96,30 @@ test('aggregates rows exported from multiple trace runs', () => {
   assert.equal(summary.topFunctions[0]?.symbol, 'runTwo');
 });
 
+test('resolves a frame reference an earlier trace run defined', () => {
+  // A real `xctrace record --append-run` export numbers element ids with one counter across its
+  // runs, so a row of a later run refs a frame an earlier run defined. Scoping the id index per
+  // `<node>` would drop that row's frame instead of attributing it to the earlier symbol.
+  const summary = parseAppleTimeProfileSummary(
+    `<trace-query-result>
+      <node xpath="/trace-toc/run[1]"><row><weight>1000000</weight><tagged-backtrace><frame id="frame-1" name="shared"/></tagged-backtrace></row></node>
+      <node xpath="/trace-toc/run[2]"><row><weight>3000000</weight><tagged-backtrace><frame ref="frame-1"/></tagged-backtrace></row></node>
+    </trace-query-result>`,
+  );
+  assert.deepEqual(summary, {
+    sampleCount: 2,
+    totalSampleWeightMs: 4,
+    topFunctions: [
+      {
+        symbol: 'shared',
+        binary: undefined,
+        selfSampleMs: 4,
+        selfSamplePercent: 100,
+      },
+    ],
+  });
+});
+
 test('skips incomplete rows', () => {
   assert.deepEqual(
     parseAppleTimeProfileSummary(

packages/platform-apple/src/core/perf-time-profile.ts

@@ -4,6 +4,11 @@ import { findAllXmlNodes, indexXmlNodesById, resolveXmlReference } from './perf-
 
 const APPLE_TIME_PROFILE_FUNCTION_LIMIT = 10;
 
+// Xcode 27 renamed the `time-profile` stack element and its `engineering-type` to
+// `<tagged-backtrace>` while keeping the same `<frame>` children and `id`/`ref` reuse, so both
+// spellings carry one sampled stack.
+const APPLE_TIME_PROFILE_STACK_ELEMENT_NAMES = new Set(['backtrace', 'tagged-backtrace']);
+
 export type AppleTimeProfileFunction = {
   symbol: string;
   binary?: string;
@@ -78,14 +83,14 @@ function readRowWeightNs(row: XmlNode, nodesById: Map<string, XmlNode>): number
 }
 
 function readInnermostFrame(row: XmlNode, nodesById: Map<string, XmlNode>): XmlNode | undefined {
-  const backtrace = resolveXmlReference(
-    row.children.find((node) => node.name === 'backtrace'),
+  const stack = resolveXmlReference(
+    row.children.find((node) => APPLE_TIME_PROFILE_STACK_ELEMENT_NAMES.has(node.name)),
     nodesById,
   );
   // xctrace lists a sampled backtrace from the innermost frame outward. The first
   // frame therefore owns self time; a focused multi-frame test pins this ordering.
   return resolveXmlReference(
-    backtrace?.children.find((node) => node.name === 'frame'),
+    stack?.children.find((node) => node.name === 'frame'),
     nodesById,
   );
 }