feat: adds support for source-map production (#439)

README.md

@@ -51,6 +51,13 @@ and a `text-lcov` coverage report.
 nyc --reporter=lcov --reporter=text-lcov npm test
 ```
 
+## Accurate stack traces using source maps
+
+When `produce-source-map` is set to true, then the instrumented source files will
+include inline source maps for the instrumenter transform. When combined with
+[source-map-support](https://github.com/evanw/node-source-map-support),
+stack traces for instrumented code will reflect their original lines.
+
 ## Support for custom require hooks (babel, webpack, etc.)
 
 nyc supports custom require hooks like

index.js

@@ -39,6 +39,7 @@ if (/index\.covered\.js$/.test(__filename)) {
 
 function NYC (config) {
   config = config || {}
+  this.config = config
 
   this.subprocessBin = config.subprocessBin || path.resolve(__dirname, './bin/nyc.js')
   this._tempDirectory = config.tempDirectory || './.nyc_output'
@@ -84,8 +85,6 @@ function NYC (config) {
 
   this.processInfo = new ProcessInfo(config && config._processInfo)
   this.rootId = this.processInfo.root || this.generateUniqueID()
-  this.instrument = config.instrument
-  this.all = config.all
 }
 
 NYC.prototype._createTransform = function (ext) {
@@ -128,7 +127,9 @@ NYC.prototype.instrumenter = function () {
 }
 
 NYC.prototype._createInstrumenter = function () {
-  return this._instrumenterLib(this.cwd)
+  return this._instrumenterLib(this.cwd, {
+    produceSourceMap: this.config.produceSourceMap
+  })
 }
 
 NYC.prototype.addFile = function (filename) {
@@ -261,14 +262,15 @@ NYC.prototype._transformFactory = function (cacheDir) {
 
   return function (code, metadata, hash) {
     var filename = metadata.filename
+    var sourceMap = null
 
-    if (_this._sourceMap) _this._handleSourceMap(cacheDir, code, hash, filename)
+    if (_this._sourceMap) sourceMap = _this._handleSourceMap(cacheDir, code, hash, filename)
 
     try {
-      instrumented = instrumenter.instrumentSync(code, filename)
+      instrumented = instrumenter.instrumentSync(code, filename, sourceMap)
     } catch (e) {
       // don't fail external tests due to instrumentation bugs.
-      console.warn('failed to instrument', filename, 'with error:', e.message)
+      console.warn('failed to instrument', filename, 'with error:', e.stack)
       instrumented = code
     }
 
@@ -290,6 +292,7 @@ NYC.prototype._handleSourceMap = function (cacheDir, code, hash, filename) {
       this.sourceMapCache.registerMap(filename, sourceMap.sourcemap)
     }
   }
+  return sourceMap
 }
 
 NYC.prototype._handleJs = function (code, filename) {

lib/config-util.js

@@ -168,6 +168,11 @@ Config.buildYargs = function (cwd) {
       type: 'boolean',
       description: 'should nyc detect and handle source maps?'
     })
+    .option('produce-source-map', {
+      default: false,
+      type: 'boolean',
+      description: "should nyc's instrumenter produce source maps?"
+    })
     .option('instrument', {
       default: true,
       type: 'boolean',

lib/instrumenters/istanbul.js

@@ -1,13 +1,43 @@
-function InstrumenterIstanbul (cwd) {
-  var istanbul = InstrumenterIstanbul.istanbul()
+'use strict'
+
+var convertSourceMap = require('convert-source-map')
+var mergeSourceMap = require('merge-source-map')
 
-  return istanbul.createInstrumenter({
+function InstrumenterIstanbul (cwd, options) {
+  var istanbul = InstrumenterIstanbul.istanbul()
+  var instrumenter = istanbul.createInstrumenter({
     autoWrap: true,
     coverageVariable: '__coverage__',
     embedSource: true,
     noCompact: false,
-    preserveComments: true
+    preserveComments: true,
+    produceSourceMap: options.produceSourceMap
   })
+
+  return {
+    instrumentSync: function (code, filename, sourceMap) {
+      var instrumented = instrumenter.instrumentSync(code, filename)
+      // the instrumenter can optionally produce source maps,
+      // this is useful for features like remapping stack-traces.
+      // TODO: test source-map merging logic.
+      if (options.produceSourceMap) {
+        var lastSourceMap = instrumenter.lastSourceMap()
+        if (lastSourceMap) {
+          if (sourceMap) {
+            lastSourceMap = mergeSourceMap(
+              sourceMap.toObject(),
+              lastSourceMap
+            )
+          }
+          instrumented += '\n' + convertSourceMap.fromObject(lastSourceMap).toComment()
+        }
+      }
+      return instrumented
+    },
+    lastFileCoverage: function () {
+      return instrumenter.lastFileCoverage()
+    }
+  }
 }
 
 InstrumenterIstanbul.istanbul = function () {

package.json

@@ -88,6 +88,7 @@
     "istanbul-lib-source-maps": "^1.0.2",
     "istanbul-reports": "^1.0.0",
     "md5-hex": "^1.2.0",
+    "merge-source-map": "^1.0.2",
     "micromatch": "^2.3.11",
     "mkdirp": "^0.5.0",
     "resolve-from": "^2.0.0",
@@ -111,8 +112,8 @@
     "requirejs": "^2.3.0",
     "sanitize-filename": "^1.5.3",
     "sinon": "^1.15.3",
-    "source-map-support": "^0.4.2",
     "split-lines": "^1.0.0",
+    "source-map-support": "^0.4.6",
     "standard": "^8.0.0",
     "standard-version": "^3.0.0",
     "tap": "^8.0.0",
@@ -140,6 +141,7 @@
     "istanbul-lib-source-maps",
     "istanbul-reports",
     "md5-hex",
+    "merge-source-map",
     "micromatch",
     "mkdirp",
     "resolve-from",
@@ -155,4 +157,4 @@
       "find-up"
     ]
   }
-}
+}

test/fixtures/stack-trace.js

@@ -0,0 +1,16 @@
+'use strict';
+
+function blah() {
+  throw new Error('Blarrh')
+}
+
+var stack;
+try {
+  blah();
+} catch(err) {
+  stack = err.stack;
+}
+
+module.exports = function() {
+  return stack;
+}

test/src/nyc-test.js

@@ -1,6 +1,6 @@
 /* global describe, it */
 
-require('source-map-support').install()
+require('source-map-support').install({hookRequire: true})
 var _ = require('lodash')
 var ap = require('any-path')
 var configUtil = require('../../lib/config-util')
@@ -202,6 +202,28 @@ describe('nyc', function () {
       })
     })
 
+    describe('produce source map', function () {
+      it('handles stack traces', function () {
+        var nyc = new NYC(configUtil.loadConfig('--produce-source-map'))
+        nyc.reset()
+        nyc.wrap()
+
+        var check = require('../fixtures/stack-trace')
+        check().should.match(/stack-trace.js:4:/)
+      })
+
+      it('does not handle stack traces when disabled', function () {
+        var nyc = new NYC(configUtil.loadConfig())
+        nyc.reset()
+        nyc.wrap()
+
+        var check = require('../fixtures/stack-trace')
+        check().should.match(/stack-trace.js:1:/)
+      })
+
+      // TODO: add test for merge source-map logic.
+    })
+
     describe('compile handlers for custom extensions are assigned', function () {
       it('assigns a function to custom extensions', function () {
         var nyc = new NYC(configUtil.loadConfig([],