fix: process coverage merging

This commit uses the [new merge algorithm][merge] to handle sub-processes. It fixes the issues reported in bcoe/v8-coverage-merge#7 and improves performance.

[merge]: https://github.com/demurgos/v8-coverage/blob/master/docs/merge.md

Author: demurgos

lib/report.js

@@ -4,7 +4,7 @@ const libReport = require('istanbul-lib-report')
 const reports = require('istanbul-reports')
 const { readdirSync, readFileSync } = require('fs')
 const { resolve, isAbsolute } = require('path')
-const v8CoverageMerge = require('v8-coverage-merge')
+const { mergeProcessCovs } = require('@c88/v8-coverage')
 const v8toIstanbul = require('v8-to-istanbul')
 
 class Report {
@@ -41,38 +41,47 @@ class Report {
     })
   }
   _getCoverageMapFromAllCoverageFiles () {
+    const v8ProcessCov = this._getMergedProcessCov()
+
     const map = libCoverage.createCoverageMap({})
-    const mergedResults = {}
-    this._loadReports().forEach((report) => {
-      report.result.forEach((result) => {
-        if (this.exclude.shouldInstrument(result.url) &&
-            (!this.omitRelative || isAbsolute(result.url))) {
-          if (mergedResults[result.url]) {
-            mergedResults[result.url] = v8CoverageMerge(
-              mergedResults[result.url],
-              result
-            )
-          } else {
-            mergedResults[result.url] = result
-          }
-        }
-      })
-    })
 
-    Object.keys(mergedResults).forEach((url) => {
+    for (const v8ScriptCov of v8ProcessCov.result) {
       try {
-        const result = mergedResults[url]
-        const path = resolve(this.resolve, result.url)
+        const path = resolve(this.resolve, v8ScriptCov.url)
         const script = v8toIstanbul(path)
-        script.applyCoverage(result.functions)
+        script.applyCoverage(v8ScriptCov.functions)
         map.merge(script.toIstanbul())
       } catch (err) {
-        console.warn(`file: ${url} error: ${err.stack}`)
+        console.warn(`file: ${v8ScriptCov.url} error: ${err.stack}`)
       }
-    })
+    }
 
     return map
   }
+
+  /**
+   * Returns the merged V8 process coverage.
+   *
+   * The result is computed from the individual process coverages generated
+   * by Node. It represents the sum of their counts.
+   *
+   * @return {ProcessCov} Merged V8 process coverage.
+   * @private
+   */
+  _getMergedProcessCov () {
+    const v8ProcessCovs = []
+    for (const v8ProcessCov of this._loadReports()) {
+      v8ProcessCovs.push(this._filterProcessCov(v8ProcessCov))
+    }
+    return mergeProcessCovs(v8ProcessCovs)
+  }
+
+  /**
+   * Returns the list of V8 process coverages generated by Node.
+   *
+   * @return {ProcessCov[]} Process coverages generated by Node.
+   * @private
+   */
   _loadReports () {
     const files = readdirSync(this.tempDirectory)
 
@@ -87,6 +96,28 @@ class Report {
       }
     })
   }
+
+  /**
+   * Returns a filtered process coverage.
+   *
+   * The result is a copy of the input, with script coverages filtered based
+   * on their `url` and the current inclusion rules.
+   * There is no deep cloning.
+   *
+   * @param v8ProcessCov V8 process coverage to filter.
+   * @return {v8ProcessCov} Filtered V8 process coverage.
+   * @private
+   */
+  _filterProcessCov (v8ProcessCov) {
+    const result = []
+    for (const v8ScriptCov of v8ProcessCov.result) {
+      if (this.exclude.shouldInstrument(v8ScriptCov.url) &&
+        (!this.omitRelative || isAbsolute(v8ScriptCov.url))) {
+        result.push(v8ScriptCov)
+      }
+    }
+    return { result }
+  }
 }
 
 module.exports = function (opts) {

package-lock.json

@@ -41,7 +41,7 @@
     "rimraf": "^2.6.2",
     "test-exclude": "^5.0.0",
     "uuid": "^3.3.2",
-    "v8-coverage-merge": "^1.1.2",
+    "@c88/v8-coverage": "^0.1.0",
     "v8-to-istanbul": "^1.2.0",
     "yargs": "^12.0.2",
     "yargs-parser": "^10.1.0"

package.json

@@ -8,17 +8,17 @@ second
 --------------------|----------|----------|----------|----------|-------------------|
 File                |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
 --------------------|----------|----------|----------|----------|-------------------|
-All files           |     92.5 |    69.23 |        0 |     92.5 |                   |
+All files           |    94.53 |     71.7 |        0 |    94.53 |                   |
  bin                |    83.72 |    57.14 |      100 |    83.72 |                   |
   c8.js             |    83.72 |    57.14 |      100 |    83.72 |... 22,40,41,42,43 |
- lib                |    93.71 |    62.96 |      100 |    93.71 |                   |
+ lib                |     96.6 |    62.07 |      100 |     96.6 |                   |
   parse-args.js     |    97.47 |    44.44 |      100 |    97.47 |             55,56 |
-  report.js         |    90.63 |    72.22 |      100 |    90.63 |... 70,71,85,86,87 |
- test/fixtures      |    95.16 |    83.33 |        0 |    95.16 |                   |
+  report.js         |    96.06 |       70 |      100 |    96.06 |    55,56,94,95,96 |
+ test/fixtures      |    95.16 |    94.12 |        0 |    95.16 |                   |
   async.js          |      100 |      100 |      100 |      100 |                   |
   multiple-spawn.js |      100 |      100 |      100 |      100 |                   |
   normal.js         |    85.71 |       75 |        0 |    85.71 |          14,15,16 |
-  subprocess.js     |      100 |    71.43 |      100 |      100 |              9,13 |
+  subprocess.js     |      100 |      100 |      100 |      100 |                   |
 --------------------|----------|----------|----------|----------|-------------------|
 ,"
 `;