test_runner: exclude BRDA entries for ignored lines in LCOV reporter

When a line is marked with /* node:coverage ignore next */, the DA entry
for that line is correctly excluded from the LCOV output. However, the
corresponding BRDA entry was still being emitted, causing branch coverage
to report incorrect percentages when using the lcov reporter.

This commit adds:
- A new test fixture (brda_ignore_output.js) with a branch that has
  /* node:coverage ignore next */ to test the BRDA exclusion behavior
- A new test runner (lcov_reporter_brda_ignore.js) for the fixture
- A separate snapshot test case for this specific scenario
- Updates to lcov.js to filter BRDA entries for ignored lines

PR-URL: #62740

Author: Code Clawd

lib/internal/test_runner/reporter/lcov.js

@@ -2,6 +2,7 @@
 
 const { relative } = require('path');
 const Transform = require('internal/streams/transform');
+const { SafeSet } = require('internal/primordials');
 
 // This reporter is based on the LCOV format, as described here:
 // https://ltp.sourceforge.net/coverage/lcov/geninfo.1.php
@@ -68,7 +69,20 @@ class LcovReporter extends Transform {
         // Taken is either '-' if the basic block containing the branch was
         // never executed or a number indicating how often that branch was
         // taken.
+        // Build set of ignored line numbers from coverage data.
+        // A line is ignored if it appears with ignore=true in the file.lines array.
+        const ignoredLineSet = new SafeSet();
+        for (let k = 0; k < file.lines.length; k++) {
+          if (file.lines[k].ignore) {
+            ignoredLineSet.add(file.lines[k].line);
+          }
+        }
+
         for (let j = 0; j < file.branches.length; j++) {
+          // Skip branches that point to ignored lines.
+          if (ignoredLineSet.has(file.branches[j].line)) {
+            continue;
+          }
           lcov += `BRDA:${file.branches[j].line},${j},0,${file.branches[j].count}\n`;
         }
 
@@ -104,4 +118,4 @@ class LcovReporter extends Transform {
   }
 }
 
-module.exports = LcovReporter;
+module.exports = LcovReporter;

test/fixtures/test-runner/output/brda_ignore_output.js

@@ -0,0 +1,16 @@
+'use strict';
+require('../../../common');
+const test = require('node:test');
+
+function funcWithIgnoredBranch(value) {
+  /* node:coverage ignore next */
+  if (value > 0) { // This branch should be ignored
+    return 'positive';
+  } else {
+    return 'negative';
+  }
+}
+
+test('should not report BRDA for ignored branch', () => {
+  funcWithIgnoredBranch(1); // Only call one path of the branch
+});

test/fixtures/test-runner/output/lcov_reporter_brda_ignore.js

@@ -0,0 +1,16 @@
+'use strict';
+require('../../../common');
+const fixtures = require('../../../common/fixtures');
+const spawn = require('node:child_process').spawn;
+
+spawn(
+  process.execPath,
+  [
+    '--no-warnings',
+    '--experimental-test-coverage',
+    '--test-coverage-exclude=!test/**',
+    '--test-reporter', 'lcov',
+    fixtures.path('test-runner/output/brda_ignore_output.js'),
+  ],
+  { stdio: 'inherit' },
+);

test/fixtures/test-runner/output/lcov_reporter_brda_ignore.snapshot

@@ -0,0 +1,32 @@
+TN:
+SF:test/fixtures/test-runner/output/brda_ignore_output.js
+FN:5,funcWithIgnoredBranch
+FN:14,anonymous_1
+FNDA:1,funcWithIgnoredBranch
+FNDA:1,anonymous_1
+FNF:2
+FNH:2
+BRDA:1,0,0,1
+BRDA:5,1,0,1
+BRDA:9,2,0,0
+BRDA:14,3,0,1
+BRF:4
+BRH:3
+DA:1,1
+DA:2,1
+DA:3,1
+DA:4,1
+DA:5,1
+DA:6,1
+DA:8,1
+DA:9,1
+DA:10,0
+DA:11,0
+DA:12,1
+DA:13,1
+DA:14,1
+DA:15,1
+DA:16,1
+LH:14
+LF:16
+end_of_record

test/test-runner/test-output-lcov-reporter-brda-ignore.mjs

@@ -0,0 +1,13 @@
+import * as common from '../common/index.mjs';
+import * as fixtures from '../common/fixtures.mjs';
+import { spawnAndAssert, lcovTransform, ensureCwdIsProjectRoot } from '../common/assertSnapshot.js';
+
+if (!process.features.inspector) {
+  common.skip('inspector support required');
+}
+
+ensureCwdIsProjectRoot();
+await spawnAndAssert(
+  fixtures.path('test-runner/output/lcov_reporter_brda_ignore.js'),
+  lcovTransform,
+);