feat: add experimental monocart reports (#521)

Author: cenfun

Diff for: README.md

@@ -43,6 +43,7 @@ Here is a list of common options. Run `c8 --help` for the full list and document
 | `--per-file` | check thresholds per file | `boolean` | `false` |
 | `--temp-directory` | directory V8 coverage data is written to and read from | `string` | `process.env.NODE_V8_COVERAGE` |
 | `--clean` | should temp files be deleted before script execution | `boolean` | `true` |
+| `--experimental-monocart` | see [section below](#using-monocart-coverage-reports-experimental) for more info | `boolean` | `false` |
 
 ## Checking for "full" source coverage using `--all`
 
@@ -119,6 +120,23 @@ The `--100` flag can be set for the `check-coverage` as well:
 c8 check-coverage --100
 ```
 
+## Using Monocart coverage reports (experimental)
+Monocart is an alternate library for outputting [v8 code coverage](https://v8.dev/blog/javascript-code-coverage) data as Istanbul reports.
+
+Monocart also provides reporters based directly on v8's byte-offset-based output. Such as, `console-details` and `v8`. This removes a complex transformation step and may be less bug prone for some environments.
+
+**Example usage:**
+
+```sh
+c8 --experimental-monocart --reporter=v8 --reporter=console-details node foo.js
+```
+
+NOTE: Monocart requires additional `monocart-coverage-reports` to be installed:
+
+```sh
+npm i monocart-coverage-reports --save-dev
+```
+
 ## Ignoring Uncovered Lines, Functions, and Blocks
 
 Sometimes you might find yourself wanting to ignore uncovered portions of your

Diff for: lib/commands/report.js

@@ -36,7 +36,8 @@ exports.outputReport = async function (argv) {
     src: argv.src,
     skipFull: argv.skipFull,
     excludeNodeModules: argv.excludeNodeModules,
-    mergeAsync: argv.mergeAsync
+    mergeAsync: argv.mergeAsync,
+    monocartArgv: (argv.experimentalMonocart || process.env.EXPERIMENTAL_MONOCART) ? argv : null
   })
   await report.run()
   if (argv.checkCoverage) await checkCoverages(argv, report)

Diff for: lib/parse-args.js

@@ -158,6 +158,11 @@ function buildYargs (withCommands = false) {
       describe: 'supplying --merge-async will merge all v8 coverage reports asynchronously and incrementally. ' +
         'This is to avoid OOM issues with Node.js runtime.'
     })
+    .option('experimental-monocart', {
+      default: false,
+      type: 'boolean',
+      describe: 'Use Monocart coverage reports'
+    })
     .pkgConf('c8')
     .demandCommand(1)
     .check((argv) => {

Diff for: lib/report.js

@@ -36,7 +36,8 @@ class Report {
     allowExternal = false,
     skipFull,
     excludeNodeModules,
-    mergeAsync
+    mergeAsync,
+    monocartArgv
   }) {
     this.reporter = reporter
     this.reporterOptions = reporterOptions || {}
@@ -60,6 +61,7 @@ class Report {
     this.src = this._getSrc(src)
     this.skipFull = skipFull
     this.mergeAsync = mergeAsync
+    this.monocartArgv = monocartArgv
   }
 
   _getSrc (src) {
@@ -73,6 +75,9 @@ class Report {
   }
 
   async run () {
+    if (this.monocartArgv) {
+      return this.runMonocart()
+    }
     const context = libReport.createContext({
       dir: this.reportsDirectory,
       watermarks: this.watermarks,
@@ -89,6 +94,141 @@ class Report {
     }
   }
 
+  async importMonocart () {
+    return import('monocart-coverage-reports')
+  }
+
+  async getMonocart () {
+    let MCR
+    try {
+      MCR = await this.importMonocart()
+    } catch (e) {
+      console.error('--experimental-monocart requires the plugin monocart-coverage-reports. Run: "npm i monocart-coverage-reports --save-dev"')
+      process.exit(1)
+    }
+    return MCR
+  }
+
+  async runMonocart () {
+    const MCR = await this.getMonocart()
+    if (!MCR) {
+      return
+    }
+
+    const argv = this.monocartArgv
+    const exclude = this.exclude
+
+    function getEntryFilter () {
+      return argv.entryFilter || argv.filter || function (entry) {
+        return exclude.shouldInstrument(fileURLToPath(entry.url))
+      }
+    }
+
+    function getSourceFilter () {
+      return argv.sourceFilter || argv.filter || function (sourcePath) {
+        if (argv.excludeAfterRemap) {
+          // console.log(sourcePath)
+          return exclude.shouldInstrument(sourcePath)
+        }
+        return true
+      }
+    }
+
+    function getReports () {
+      const reports = Array.isArray(argv.reporter) ? argv.reporter : [argv.reporter]
+      const reporterOptions = argv.reporterOptions || {}
+
+      return reports.map((reportName) => {
+        const reportOptions = {
+          ...reporterOptions[reportName]
+        }
+        if (reportName === 'text') {
+          reportOptions.skipEmpty = false
+          reportOptions.skipFull = argv.skipFull
+          reportOptions.maxCols = process.stdout.columns || 100
+        }
+        return [reportName, reportOptions]
+      })
+    }
+
+    // --all: add empty coverage for all files
+    function getAllOptions () {
+      if (!argv.all) {
+        return
+      }
+
+      const src = argv.src
+      const workingDirs = Array.isArray(src) ? src : (typeof src === 'string' ? [src] : [process.cwd()])
+      return {
+        dir: workingDirs,
+        filter: (filePath) => {
+          return exclude.shouldInstrument(filePath)
+        }
+      }
+    }
+
+    function initPct (summary) {
+      Object.keys(summary).forEach(k => {
+        if (summary[k].pct === '') {
+          summary[k].pct = 100
+        }
+      })
+      return summary
+    }
+
+    // adapt coverage options
+    const coverageOptions = {
+      logging: argv.logging,
+      name: argv.name,
+
+      reports: getReports(),
+
+      outputDir: argv.reportsDir,
+      baseDir: argv.baseDir,
+
+      entryFilter: getEntryFilter(),
+      sourceFilter: getSourceFilter(),
+
+      inline: argv.inline,
+      lcov: argv.lcov,
+
+      all: getAllOptions(),
+
+      clean: argv.clean,
+
+      // use default value for istanbul
+      defaultSummarizer: 'pkg',
+
+      onEnd: (coverageResults) => {
+        // for check coverage
+        this._allCoverageFiles = {
+          files: () => {
+            return coverageResults.files.map(it => it.sourcePath)
+          },
+          fileCoverageFor: (file) => {
+            const fileCoverage = coverageResults.files.find(it => it.sourcePath === file)
+            return {
+              toSummary: () => {
+                return initPct(fileCoverage.summary)
+              }
+            }
+          },
+          getCoverageSummary: () => {
+            return initPct(coverageResults.summary)
+          }
+        }
+      }
+    }
+    const coverageReport = new MCR.CoverageReport(coverageOptions)
+    coverageReport.cleanCache()
+
+    // read v8 coverage data from tempDirectory
+    await coverageReport.addFromDir(argv.tempDirectory)
+
+    // generate report
+    await coverageReport.generate()
+  }
+
   async getCoverageMapFromAllCoverageFiles () {
     // the merge process can be very expensive, and it's often the case that
     // check-coverage is called immediately after a report. We memoize the