test_runner: support combining coverage reports

doc/api/cli.md

@@ -624,6 +624,10 @@ Use this flag to enable [ShadowRealm][] support.
 added:
   - v19.7.0
   - v18.15.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/47686
+    description: This option can be used with `--test`.
 -->
 
 When used in conjunction with the `node:test` module, a code coverage report is

doc/api/test.md

@@ -428,10 +428,6 @@ if (anAlwaysFalseCondition) {
 The test runner's code coverage functionality has the following limitations,
 which will be addressed in a future Node.js release:
 
-* Although coverage data is collected for child processes, this information is
-  not included in the coverage report. Because the command line test runner uses
-  child processes to execute test files, it cannot be used with
-  `--experimental-test-coverage`.
 * Source maps are not supported.
 * Excluding specific files or directories from the coverage report is not
   supported.

lib/internal/test_runner/coverage.js

@@ -1,13 +1,15 @@
 'use strict';
 const {
+  ArrayFrom,
   ArrayPrototypeMap,
   ArrayPrototypePush,
   JSONParse,
   MathFloor,
   NumberParseInt,
-  RegExp,
   RegExpPrototypeExec,
   RegExpPrototypeSymbolSplit,
+  SafeMap,
+  SafeSet,
   StringPrototypeIncludes,
   StringPrototypeLocaleCompare,
   StringPrototypeStartsWith,
@@ -23,9 +25,7 @@ const { setupCoverageHooks } = require('internal/util');
 const { tmpdir } = require('os');
 const { join, resolve } = require('path');
 const { fileURLToPath } = require('url');
-const kCoveragePattern =
-  `^coverage\\-${process.pid}\\-(\\d{13})\\-(\\d+)\\.json$`;
-const kCoverageFileRegex = new RegExp(kCoveragePattern);
+const kCoverageFileRegex = /^coverage-(\d+)-(\d{13})-(\d+)\.json$/;
 const kIgnoreRegex = /\/\* node:coverage ignore next (?<count>\d+ )?\*\//;
 const kLineEndingRegex = /\r?\n$/u;
 const kLineSplitRegex = /(?<=\r?\n)/u;
@@ -95,13 +95,6 @@ class TestCoverage {
     for (let i = 0; i < coverage.length; ++i) {
       const { functions, url } = coverage[i];
 
-      if (StringPrototypeStartsWith(url, 'node:') ||
-          StringPrototypeIncludes(url, '/node_modules/') ||
-          // On Windows some generated coverages are invalid.
-          !StringPrototypeStartsWith(url, 'file:')) {
-        continue;
-      }
-
       // Split the file source into lines. Make sure the lines maintain their
       // original line endings because those characters are necessary for
       // determining offsets in the file.
@@ -345,8 +338,7 @@ function mapRangeToLines(range, lines) {
 }
 
 function getCoverageFromDirectory(coverageDirectory) {
-  // TODO(cjihrig): Instead of only reading the coverage file for this process,
-  // combine all coverage files in the directory into a single data structure.
+  const result = new SafeMap();
   let dir;
 
   try {
@@ -359,13 +351,149 @@ function getCoverageFromDirectory(coverageDirectory) {
 
       const coverageFile = join(coverageDirectory, entry.name);
       const coverage = JSONParse(readFileSync(coverageFile, 'utf8'));
-      return coverage.result;
+
+      mergeCoverage(result, coverage.result);
     }
+
+    return ArrayFrom(result.values());
   } finally {
     if (dir) {
       dir.closeSync();
     }
   }
 }
 
+function mergeCoverage(merged, coverage) {
+  for (let i = 0; i < coverage.length; ++i) {
+    const newScript = coverage[i];
+    const { url } = newScript;
+
+    // Filter out core modules and the node_modules/ directory from results.
+    if (StringPrototypeStartsWith(url, 'node:') ||
+        StringPrototypeIncludes(url, '/node_modules/') ||
+        // On Windows some generated coverages are invalid.
+        !StringPrototypeStartsWith(url, 'file:')) {
+      continue;
+    }
+
+    const oldScript = merged.get(url);
+
+    if (oldScript === undefined) {
+      merged.set(url, newScript);
+    } else {
+      mergeCoverageScripts(oldScript, newScript);
+    }
+  }
+}
+
+function mergeCoverageScripts(oldScript, newScript) {
+  // Merge the functions from the new coverage into the functions from the
+  // existing (merged) coverage.
+  for (let i = 0; i < newScript.functions.length; ++i) {
+    const newFn = newScript.functions[i];
+    let found = false;
+
+    for (let j = 0; j < oldScript.functions.length; ++j) {
+      const oldFn = oldScript.functions[j];
+
+      if (newFn.functionName === oldFn.functionName &&
+          newFn.ranges?.[0].startOffset === oldFn.ranges?.[0].startOffset &&
+          newFn.ranges?.[0].endOffset === oldFn.ranges?.[0].endOffset) {
+        // These are the same functions.
+        found = true;
+
+        // If newFn is block level coverage, then it will:
+        // - Replace oldFn if oldFn is not block level coverage.
+        // - Merge with oldFn if it is also block level coverage.
+        // If newFn is not block level coverage, then it has no new data.
+        if (newFn.isBlockCoverage) {
+          if (oldFn.isBlockCoverage) {
+            // Merge the oldFn ranges with the newFn ranges.
+            mergeCoverageRanges(oldFn, newFn);
+          } else {
+            // Replace oldFn with newFn.
+            oldFn.isBlockCoverage = true;
+            oldFn.ranges = newFn.ranges;
+          }
+        }
+
+        break;
+      }
+    }
+
+    if (!found) {
+      // This is a new function to track. This is possible because V8 can
+      // generate a different list of functions depending on which code paths
+      // are executed. For example, if a code path dynamically creates a
+      // function, but that code path is not executed then the function does
+      // not show up in the coverage report. Unfortunately, this also means
+      // that the function counts in the coverage summary can never be
+      // guaranteed to be 100% accurate.
+      ArrayPrototypePush(oldScript.functions, newFn);
+    }
+  }
+}
+
+function mergeCoverageRanges(oldFn, newFn) {
+  const mergedRanges = new SafeSet();
+
+  // Keep all of the existing covered ranges.
+  for (let i = 0; i < oldFn.ranges.length; ++i) {
+    const oldRange = oldFn.ranges[i];
+
+    if (oldRange.count > 0) {
+      mergedRanges.add(oldRange);
+    }
+  }
+
+  // Merge in the new ranges where appropriate.
+  for (let i = 0; i < newFn.ranges.length; ++i) {
+    const newRange = newFn.ranges[i];
+    let exactMatch = false;
+
+    for (let j = 0; j < oldFn.ranges.length; ++j) {
+      const oldRange = oldFn.ranges[j];
+
+      if (doesRangeEqualOtherRange(newRange, oldRange)) {
+        // These are the same ranges, so keep the existing one.
+        oldRange.count += newRange.count;
+        mergedRanges.add(oldRange);
+        exactMatch = true;
+        break;
+      }
+
+      // Look at ranges representing missing coverage and add ranges that
+      // represent the intersection.
+      if (oldRange.count === 0 && newRange.count === 0) {
+        if (doesRangeContainOtherRange(oldRange, newRange)) {
+          // The new range is completely within the old range. Discard the
+          // larger (old) range, and keep the smaller (new) range.
+          mergedRanges.add(newRange);
+        } else if (doesRangeContainOtherRange(newRange, oldRange)) {
+          // The old range is completely within the new range. Discard the
+          // larger (new) range, and keep the smaller (old) range.
+          mergedRanges.add(oldRange);
+        }
+      }
+    }
+
+    // Add new ranges that do not represent missing coverage.
+    if (newRange.count > 0 && !exactMatch) {
+      mergedRanges.add(newRange);
+    }
+  }
+
+  oldFn.ranges = ArrayFrom(mergedRanges);
+}
+
+function doesRangeEqualOtherRange(range, otherRange) {
+  return range.startOffset === otherRange.startOffset &&
+         range.endOffset === otherRange.endOffset;
+}
+
+function doesRangeContainOtherRange(range, otherRange) {
+  return range.startOffset <= otherRange.startOffset &&
+         range.endOffset >= otherRange.endOffset;
+}
+
 module.exports = { setupCoverage };

src/node_options.cc

@@ -141,13 +141,6 @@ void EnvironmentOptions::CheckOptions(std::vector<std::string>* errors,
   }
 
   if (test_runner) {
-    if (test_runner_coverage) {
-      // TODO(cjihrig): This restriction can be removed once multi-process
-      // code coverage is supported.
-      errors->push_back(
-          "--experimental-test-coverage cannot be used with --test");
-    }
-
     if (syntax_check_only) {
       errors->push_back("either --test or --check can be used, not both");
     }

test/fixtures/v8-coverage/combined_coverage/common.js

@@ -0,0 +1,69 @@
+'use strict';
+function fnA() {
+  let cnt = 0;
+
+  try {
+    cnt++;
+    throw new Error('boom');
+    cnt++;
+  } catch (err) {
+    cnt++;
+  } finally {
+    if (false) {
+
+    }
+
+    return cnt;
+  }
+  cnt++;
+}
+
+function fnB(arr) {
+  for (let i = 0; i < arr.length; ++i) {
+    if (i === 2) {
+      continue;
+    } else {
+      fnE(1);
+    }
+  }
+}
+
+function fnC(arg1, arg2) {
+  if (arg1 === 1) {
+    if (arg2 === 3) {
+      return -1;
+    }
+
+    if (arg2 === 4) {
+      return 3;
+    }
+
+    if (arg2 === 5) {
+      return 9;
+    }
+  }
+}
+
+function fnD(arg) {
+  let cnt = 0;
+
+  if (arg % 2 === 0) {
+    cnt++;
+  } else if (arg === 1) {
+    cnt++;
+  } else if (arg === 3) {
+    cnt++;
+  } else {
+    fnC(1, 5);
+  }
+
+  return cnt;
+}
+
+function fnE(arg) {
+  const a = arg ?? 5;
+
+  return a;
+}
+
+module.exports = { fnA, fnB, fnC, fnD, fnE };

test/fixtures/v8-coverage/combined_coverage/first.test.js

@@ -0,0 +1,12 @@
+'use strict';
+const { test } = require('node:test');
+const common = require('./common');
+
+function notCalled() {
+}
+
+test('first 1', () => {
+  common.fnA();
+  common.fnD(100);
+  common.fnB([1, 2, 3]);
+});

test/fixtures/v8-coverage/combined_coverage/second.test.js

@@ -0,0 +1,8 @@
+'use strict';
+const { test } = require('node:test');
+const common = require('./common');
+
+test('second 1', () => {
+  common.fnB([1, 2, 3]);
+  common.fnD(3);
+});

test/fixtures/v8-coverage/combined_coverage/third.test.js

@@ -0,0 +1,8 @@
+'use strict';
+const { test } = require('node:test');
+const common = require('./common');
+
+test('third 1', () => {
+  common.fnC(1, 4);
+  common.fnD(99);
+});