feat: add a sources option allowing to bypass fs operations

index.d.ts

@@ -2,13 +2,23 @@
 
 import { Profiler } from 'inspector'
 import { CoverageMapData } from 'istanbul-lib-coverage'
+import { RawSourceMap } from 'source-map'
 
+declare type Sources =
+  | {
+      source: string
+    }
+  | {
+      source: string
+      originalSource: string
+      sourceMap: { sourcemap: RawSourceMap }
+    }
 declare class V8ToIstanbul {
   load(): Promise<void>
   applyCoverage(blocks: ReadonlyArray<Profiler.FunctionCoverage>): void
   toIstanbul(): CoverageMapData
 }
 
-declare function v8ToIstanbul(scriptPath: string, wrapperLength?: number): V8ToIstanbul
+declare function v8ToIstanbul(scriptPath: string, wrapperLength?: number, sources?: Sources): V8ToIstanbul
 
 export = v8ToIstanbul

index.js

@@ -1,5 +1,5 @@
 const V8ToIstanbul = require('./lib/v8-to-istanbul')
 
-module.exports = function (path, wrapperLength) {
-  return new V8ToIstanbul(path, wrapperLength)
+module.exports = function (path, wrapperLength, sources) {
+  return new V8ToIstanbul(path, wrapperLength, sources)
 }

lib/v8-to-istanbul.js

@@ -15,10 +15,11 @@ const isNode10 = !!process.version.match(/^v10/)
 const cjsWrapperLength = isNode10 ? require('module').wrapper[0].length : 0
 
 module.exports = class V8ToIstanbul {
-  constructor (scriptPath, wrapperLength) {
+  constructor (scriptPath, wrapperLength, sources) {
     assert(typeof scriptPath === 'string', 'scriptPath must be a string')
     this.path = parsePath(scriptPath)
     this.wrapperLength = wrapperLength === undefined ? cjsWrapperLength : wrapperLength
+    this.sources = sources || {}
     this.generatedLines = []
     this.branches = []
     this.functions = []
@@ -27,11 +28,13 @@ module.exports = class V8ToIstanbul {
     this.sourceTranspiled = undefined
   }
   async load () {
-    const rawSource = readFileSync(this.path, 'utf8')
-    // if we find a source-map (either inline, or a .map file) we load
-    // both the transpiled and original source, both of which are used during
-    // the backflips we perform to remap absolute to relative positions.
-    const rawSourceMap = convertSourceMap.fromSource(rawSource) || convertSourceMap.fromMapFileSource(rawSource, dirname(this.path))
+    const rawSource = this.sources.source || readFileSync(this.path, 'utf8')
+    const rawSourceMap = this.sources.sourceMap ||
+      // if we find a source-map (either inline, or a .map file) we load
+      // both the transpiled and original source, both of which are used during
+      // the backflips we perform to remap absolute to relative positions.
+      convertSourceMap.fromSource(rawSource) || convertSourceMap.fromMapFileSource(rawSource, dirname(this.path))
+
     if (rawSourceMap) {
       if (rawSourceMap.sourcemap.sources.length > 1) {
         console.warn('v8-to-istanbul: source-mappings from one to many files not yet supported')
@@ -44,7 +47,13 @@ module.exports = class V8ToIstanbul {
         }
         this.sourceMap = await new SourceMapConsumer(rawSourceMap.sourcemap)
 
-        const originalRawSource = readFileSync(this.path, 'utf8')
+        let originalRawSource
+        if (this.sources.originalSource) {
+          originalRawSource = this.sources.originalSource
+        } else {
+          originalRawSource = readFileSync(this.path, 'utf8')
+        }
+
         this.source = new CovSource(originalRawSource, this.wrapperLength)
         this.sourceTranspiled = new CovSource(rawSource, this.wrapperLength)
       }