core(fcp): handle negative request endTime (#13452)

Co-authored-by: Lukas Auer <lukas.auer@mstage.at>

lighthouse-core/computed/metrics/lantern-first-contentful-paint.js

@@ -150,7 +150,9 @@ class LanternFirstContentfulPaint extends LanternMetric {
     return dependencyGraph.cloneWithRelationships(node => {
       if (node.type === BaseNode.TYPES.NETWORK) {
         // Exclude all nodes that ended after paintTs (except for the main document which we always consider necessary)
-        if (node.endTime > paintTs && !node.isMainDocument()) return false;
+        // endTime is negative if request does not finish, make sure startTime isn't after paintTs in this case.
+        const endedAfterPaint = node.endTime > paintTs || node.startTime > paintTs;
+        if (endedAfterPaint && !node.isMainDocument()) return false;
 
         const url = node.record.url;
         // If the URL definitely wasn't render-blocking then we filter it out.

lighthouse-core/test/computed/metrics/lantern-first-contentful-paint-test.js

@@ -7,13 +7,16 @@
 
 const LanternFirstContentfulPaint = require('../../../computed/metrics/lantern-first-contentful-paint.js'); // eslint-disable-line max-len
 const assert = require('assert').strict;
+const networkRecordsToDevtoolsLog = require('../../network-records-to-devtools-log.js');
+const createTestTrace = require('../../create-test-trace.js');
 
 const trace = require('../../fixtures/traces/progressive-app-m60.json');
 const devtoolsLog = require('../../fixtures/traces/progressive-app-m60.devtools.log.json');
 
 /* eslint-env jest */
 describe('Metrics: Lantern FCP', () => {
   const gatherContext = {gatherMode: 'navigation'};
+
   it('should compute predicted value', async () => {
     const settings = {};
     const context = {settings, computedCache: new Map()};
@@ -30,4 +33,45 @@ describe('Metrics: Lantern FCP', () => {
     assert.ok(result.optimisticGraph, 'should have created optimistic graph');
     assert.ok(result.pessimisticGraph, 'should have created pessimistic graph');
   });
+
+  it('should handle negative request endTime', async () => {
+    const settings = {};
+    const context = {settings, computedCache: new Map()};
+    const devtoolsLog = networkRecordsToDevtoolsLog([
+      {
+        transferSize: 2000,
+        url: 'https://example.com/',
+        resourceType: 'Document',
+        priority: 'High',
+        startTime: 0,
+        endTime: 0.0000001, // Before FCP
+        timing: {sslStart: 50, sslEnd: 100, connectStart: 50, connectEnd: 100},
+      },
+      {
+        transferSize: 2000,
+        url: 'https://example.com/script.js',
+        resourceType: 'Script',
+        priority: 'High',
+        startTime: 0.000015, // After FCP
+        endTime: -1,
+        timing: {sslStart: 50, sslEnd: 100, connectStart: 50, connectEnd: 100},
+      },
+    ]);
+    const trace = createTestTrace({timeOrigin: 0, traceEnd: 2000});
+    const artifacts = {
+      trace,
+      devtoolsLog,
+      gatherContext,
+      settings,
+    };
+    const result = await LanternFirstContentfulPaint.request(artifacts, context);
+
+    const optimisticNodes = [];
+    result.optimisticGraph.traverse(node => optimisticNodes.push(node));
+    expect(optimisticNodes.map(node => node._record.url)).toEqual(['https://example.com/']);
+
+    const pessimisticNodes = [];
+    result.pessimisticGraph.traverse(node => pessimisticNodes.push(node));
+    expect(pessimisticNodes.map(node => node._record.url)).toEqual(['https://example.com/']);
+  });
 });

lighthouse-core/test/fixtures/lantern-baseline-accuracy.json

@@ -20,7 +20,7 @@
     "p95": 0.743897672766033
   },
   "roughEstimateOfLCP": {
-    "p50": 0.203757225433526,
+    "p50": 0.2028301886792453,
     "p90": 0.6962974535228871,
     "p95": 0.9262573279851898
   }