accept external source maps from transformers

packages/jest-runtime/src/__tests__/__snapshots__/transform-test.js.snap

@@ -1,3 +1,8 @@
+exports[`transform instruments with source map if preprocessor supplies it 1`] = `
+"({\"Object.<anonymous>\":function(module,exports,require,__dirname,__filename,global,jest){/* istanbul ignore next */var cov_25u22311x4 = function () {var path = \"/fruits/banana.js\",hash = \"2af15ff13eaa7e17fc0a001b1b75722b8fbeeb74\",global = new Function(\'return this\')(),gcv = \"__coverage__\",coverageData = { path: \"/fruits/banana.js\", statementMap: { \"0\": { start: { line: 1, column: 0 }, end: { line: 1, column: 7 } } }, fnMap: {}, branchMap: {}, s: { \"0\": 0 }, f: {}, b: {}, inputSourceMap: { mappings: \";AAAA\", version: 3 }, _coverageSchema: \"332fd63041d2c1bcb487cc26dd0d5f7d97098a6c\" },coverage = global[gcv] || (global[gcv] = {});if (coverage[path] && coverage[path].hash === hash) {return coverage[path];}coverageData.hash = hash;return coverage[path] = coverageData;}();++cov_25u22311x4.s[0];content;
+}});"
+`;
+
 exports[`transform transforms a file properly 1`] = `
 "({\"Object.<anonymous>\":function(module,exports,require,__dirname,__filename,global,jest){/* istanbul ignore next */var cov_25u22311x4 = function () {var path = \"/fruits/banana.js\",hash = \"04636d4ae73b4b3e24bf6fba39e08c946fd0afb5\",global = new Function(\'return this\')(),gcv = \"__coverage__\",coverageData = { path: \"/fruits/banana.js\", statementMap: { \"0\": { start: { line: 1, column: 0 }, end: { line: 1, column: 26 } } }, fnMap: {}, branchMap: {}, s: { \"0\": 0 }, f: {}, b: {}, _coverageSchema: \"332fd63041d2c1bcb487cc26dd0d5f7d97098a6c\" },coverage = global[gcv] || (global[gcv] = {});if (coverage[path] && coverage[path].hash === hash) {return coverage[path];}coverageData.hash = hash;return coverage[path] = coverageData;}();++cov_25u22311x4.s[0];module.exports = \"banana\";
 }});"

packages/jest-runtime/src/__tests__/transform-test.js

@@ -40,6 +40,25 @@ jest.mock(
   {virtual: true},
 );
 
+jest.mock(
+  'preprocessor-with-sourcemaps',
+  () => {
+    return {
+      getCacheKey: jest.fn((content, filename, configStr) => 'ab'),
+      process: (content, filename, config) => {
+        return ({
+          content: 'content',
+          sourceMap: {
+            mappings: ';AAAA',
+            version: 3,
+          },
+        });
+      },
+    };
+  },
+  {virtual: true},
+);
+
 jest.mock(
   'css-preprocessor',
   () => {
@@ -208,6 +227,16 @@ describe('transform', () => {
     expect(vm.Script.mock.calls[2][0]).toMatchSnapshot();
   });
 
+  it('instruments with source map if preprocessor supplies it', () => {
+    config = Object.assign(config, {
+      collectCoverage: true,
+      transform: [['^.+\\.js$', 'preprocessor-with-sourcemaps']],
+    });
+
+    transform('/fruits/banana.js', config);
+    expect(vm.Script.mock.calls[0][0]).toMatchSnapshot();
+  });
+
   it('reads values from the cache', () => {
     if (skipOnWindows.test()) {
       return;

packages/jest-runtime/src/transform.js

@@ -10,7 +10,7 @@
 'use strict';
 
 import type {Config, Path} from 'types/Config';
-import type {Transformer} from 'types/Transform';
+import type {Transformer, TransformedSource} from 'types/Transform';
 
 const createDirectory = require('jest-util').createDirectory;
 const crypto = require('crypto');
@@ -235,7 +235,7 @@ const stripShebang = content => {
 };
 
 const instrumentFile = (
-  content: string,
+  transformedSource: TransformedSource,
   filename: Path,
   config: Config,
 ): string => {
@@ -244,7 +244,7 @@ const instrumentFile = (
   const babel = require('babel-core');
   const babelPluginIstanbul = require('babel-plugin-istanbul').default;
 
-  return babel.transform(content, {
+  return babel.transform(transformedSource.content, {
     auxiliaryCommentBefore: ' istanbul ignore next ',
     babelrc: false,
     filename,
@@ -254,6 +254,7 @@ const instrumentFile = (
         {
           cwd: config.rootDir, // files outside `cwd` will not be instrumented
           exclude: [],
+          inputSourceMap: transformedSource.sourceMap,
         },
       ],
     ],
@@ -276,21 +277,32 @@ const transformSource = (
     return result;
   }
 
-  result = content;
+  let transformed: TransformedSource = {
+    content,
+    sourceMap: null,
+  };
 
   if (transform && shouldTransform(filename, config)) {
-    result = transform.process(result, filename, config, {
+    const processed = transform.process(content, filename, config, {
       instrument,
       watch: config.watch,
     });
+
+    if (typeof processed === 'string') {
+      transformed.content = processed;
+    } else {
+      transformed = processed;
+    }
   }
 
   // That means that the transform has a custom instrumentation
   // logic and will handle it based on `config.collectCoverage` option
-  const transformWillInstrument = transform && transform.canInstrument;
+  const transformDidInstrument = transform && transform.canInstrument;
 
-  if (!transformWillInstrument && instrument) {
-    result = instrumentFile(result, filename, config);
+  if (!transformDidInstrument && instrument) {
+    result = instrumentFile(transformed, filename, config);
+  } else {
+    result = transformed.content;
   }
 
   writeCacheFile(cacheFilePath, result);

types/Transform.js

@@ -11,6 +11,11 @@
 
 import type {Config, Path} from 'types/Config';
 
+export type TransformedSource = {|
+  content: string,
+  sourceMap: ?SourceMap,
+|};
+
 export type SourceMap = {|
   file: string,
   mappings: string,
@@ -41,5 +46,5 @@ export type Transformer = {|
     sourcePath: Path,
     config: Config,
     options?: TransformOptions,
-  ) => string,
+  ) => string | TransformedSource,
 |};