Sourcemap sourceRoot (#1141)

src/SourceMap.js

@@ -278,10 +278,8 @@ class SourceMap {
     }
   }
 
-  stringify(file) {
-    let generator = new SourceMapGenerator({
-      file: file
-    });
+  stringify(file, sourceRoot) {
+    let generator = new SourceMapGenerator({file, sourceRoot});
 
     this.eachMapping(mapping => generator.addMapping(mapping));
     Object.keys(this.sources).forEach(sourceName =>

src/packagers/SourceMapPackager.js

@@ -16,7 +16,12 @@ class SourceMapPackager extends Packager {
 
   async end() {
     let file = path.basename(this.bundle.name);
-    await this.write(this.sourceMap.stringify(file));
+    await this.write(
+      this.sourceMap.stringify(
+        file,
+        path.relative(this.options.outDir, this.options.rootDir)
+      )
+    );
     await super.end();
   }
 }

test/sourcemaps.js

@@ -2,13 +2,14 @@ const assert = require('assert');
 const fs = require('fs');
 const path = require('path');
 const mapValidator = require('sourcemap-validator');
-const {bundle, run, assertBundleTree} = require('./utils');
+const {bundler, bundle, run, assertBundleTree} = require('./utils');
 
 describe('sourcemaps', function() {
   it('should create a valid sourcemap as a child of a JS bundle', async function() {
-    let b = await bundle(__dirname + '/integration/sourcemap/index.js');
+    let b = bundler(__dirname + '/integration/sourcemap/index.js');
+    let bu = await b.bundle();
 
-    assertBundleTree(b, {
+    assertBundleTree(bu, {
       name: 'index.js',
       assets: ['index.js'],
       childBundles: [
@@ -26,8 +27,24 @@ describe('sourcemaps', function() {
       .readFileSync(path.join(__dirname, '/dist/index.map'))
       .toString();
     mapValidator(raw, map);
+    let mapObject = JSON.parse(map);
+    assert(
+      mapObject.sourceRoot ===
+        path.relative(b.options.outDir, b.options.rootDir),
+      'sourceRoot should be the root of the source files, relative to the output directory.'
+    );
+    assert(
+      fs.existsSync(
+        path.resolve(
+          b.options.outDir,
+          mapObject.sourceRoot,
+          mapObject.sources[0]
+        )
+      ),
+      'combining sourceRoot and sources object should resolve to the original file'
+    );
 
-    let output = run(b);
+    let output = run(bu);
     assert.equal(typeof output, 'function');
     assert.equal(output(), 'hello world');
   });