fix: exclude CJS-MJS coverages from results

fix #14

lib/report.js

@@ -55,20 +55,51 @@ class Report {
     if (this._allCoverageFiles) return this._allCoverageFiles
 
     const v8ProcessCov = this._getMergedProcessCov()
-
     const map = libCoverage.createCoverageMap({})
+    const resultCountPerPath = new Map()
+    const possibleCjsEsmBridges = new Map()
 
     for (const v8ScriptCov of v8ProcessCov.result) {
       try {
         const path = resolve(this.resolve, v8ScriptCov.url)
         const script = v8toIstanbul(path, this.wrapperLength)
-        script.applyCoverage(v8ScriptCov.functions)
-        map.merge(script.toIstanbul())
+
+        if (resultCountPerPath.has(path)) {
+          resultCountPerPath.set(path, resultCountPerPath.get(path) + 1)
+        } else {
+          resultCountPerPath.set(path, 0)
+        }
+
+        // https://github.com/nodejs/node/blob/v12.0.0/lib/internal/modules/esm/create_dynamic_module.js#L12-L20
+        if (
+          v8ScriptCov.functions.length === 3 &&
+          v8ScriptCov.functions[0].functionName === '' &&
+          v8ScriptCov.functions[0].isBlockCoverage === true &&
+          v8ScriptCov.functions[1].functionName === 'get' &&
+          v8ScriptCov.functions[1].isBlockCoverage === false &&
+          v8ScriptCov.functions[2].functionName === 'set' &&
+          v8ScriptCov.functions[2].isBlockCoverage === true
+        ) {
+          possibleCjsEsmBridges.set(script, {
+            path,
+            functions: v8ScriptCov.functions
+          })
+        } else {
+          script.applyCoverage(v8ScriptCov.functions)
+          map.merge(script.toIstanbul())
+        }
       } catch (err) {
         console.warn(`file: ${v8ScriptCov.url} error: ${err.stack}`)
       }
     }
 
+    for (const [script, { path, functions }] of possibleCjsEsmBridges) {
+      if (resultCountPerPath.get(path) <= 1) {
+        script.applyCoverage(functions)
+        map.merge(script.toIstanbul())
+      }
+    }
+
     this._allCoverageFiles = map
     return this._allCoverageFiles
   }

package.json

@@ -42,7 +42,7 @@
     "rimraf": "^2.6.2",
     "test-exclude": "^5.0.0",
     "uuid": "^3.3.2",
-    "v8-to-istanbul": "^2.0.4",
+    "v8-to-istanbul": "^2.1.0",
     "yargs": "^13.1.0",
     "yargs-parser": "^10.1.0"
   },

test/fixtures/export.js

@@ -0,0 +1 @@
+module.exports = () => 'foo';

test/fixtures/export.mjs

@@ -4,4 +4,4 @@ export function foo () {
 
 export default function bar () {
   return 'bar'
-}
+}

test/fixtures/import.mjs

@@ -1,3 +1,5 @@
-import foo from './export'
+import fooEsm from './export.mjs'
+import fooCjs from './export.js'
 
-console.info(foo())
+console.info(fooEsm())
+console.info(fooCjs())

test/integration.js.snap

@@ -2,10 +2,12 @@
 
 exports[`c8 ESM Modules collects coverage for ESM modules 1`] = `
 ",bar
+foo
 ------------|----------|----------|----------|----------|-------------------|
 File        |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
 ------------|----------|----------|----------|----------|-------------------|
-All files   |       80 |      100 |       50 |       80 |                   |
+All files   |    84.62 |      100 |    66.67 |    84.62 |                   |
+ export.js  |      100 |      100 |      100 |      100 |                   |
  export.mjs |    71.43 |      100 |       50 |    71.43 |               2,3 |
  import.mjs |      100 |      100 |      100 |      100 |                   |
 ------------|----------|----------|----------|----------|-------------------|