Parcel 2: CoffeeScript sourcemaps (#3282)

* Add sourcemaps to CoffeeScript transformer

* update sourcemap to use rawsourcemap output

packages/transformers/coffeescript/package.json

@@ -13,6 +13,8 @@
   },
   "dependencies": {
     "@parcel/plugin": "^2.0.0-alpha.0",
+    "@parcel/source-map": "^2.0.0-alpha.0",
+    "@parcel/utils": "^2.0.0-alpha.0",
     "coffeescript": "^2.0.3",
     "nullthrows": "^1.1.1",
     "semver": "^5.4.1"

packages/transformers/coffeescript/src/CoffeeScriptTransformer.js

@@ -1,11 +1,30 @@
+// @flow
 import {Transformer} from '@parcel/plugin';
+import SourceMap from '@parcel/source-map';
 import coffee from 'coffeescript';
+import {relativeUrl} from '@parcel/utils';
 
 export default new Transformer({
-  async transform({asset}) {
+  async transform({asset, options}) {
+    let sourceFileName: string = relativeUrl(
+      options.projectRoot,
+      asset.filePath
+    );
+
     asset.type = 'js';
-    let output = coffee.compile(await asset.getCode());
-    asset.setCode(output);
+    let output = coffee.compile(await asset.getCode(), {
+      filename: sourceFileName,
+      sourceMap: options.sourceMaps
+    });
+
+    // return from compile is based on sourceMaps option
+    if (options.sourceMaps) {
+      asset.setCode(output.js);
+      asset.setMap(SourceMap.fromRawSourceMap(output.v3SourceMap));
+    } else {
+      asset.setCode(output);
+    }
+
     return [asset];
   }
 });