add option decodeMappings to remapping

src/remapping.ts

@@ -16,7 +16,7 @@
 
 import buildSourceMapTree from './build-source-map-tree';
 import SourceMap from './source-map';
-import { SourceMapInput, SourceMapLoader } from './types';
+import { DecodedSourceMap, SourceMapInput, SourceMapLoader } from './types';
 
 /**
  * Traces through all the mappings in the root sourcemap, through the sources
@@ -27,14 +27,19 @@ import { SourceMapInput, SourceMapLoader } from './types';
  * it returns a falsey value, that source file is treated as an original,
  * unmodified source file.
  *
- * Pass `excludeContent` content to exclude any self-containing source file
- * content from the output sourcemap.
+ * Pass `excludeContent` to exclude any self-containing source file content
+ * from the output sourcemap.
+ *
+ * Pass `decodeMappings` to get a sourcemap with decoded mappings.
  */
 export default function remapping(
   input: SourceMapInput | SourceMapInput[],
   loader: SourceMapLoader,
-  excludeContent?: boolean
-): SourceMap {
+  excludeContent?: boolean,
+  decodeMappings?: boolean
+): SourceMap | DecodedSourceMap {
   const graph = buildSourceMapTree(input, loader);
-  return new SourceMap(graph.traceMappings(), !!excludeContent);
+  return !!decodeMappings
+    ? graph.traceMappings()
+    : new SourceMap(graph.traceMappings(), !!excludeContent);
 }

test/unit/remapping.ts

@@ -15,7 +15,7 @@
  */
 
 import remapping from '../../src/remapping';
-import { RawSourceMap } from '../../src/types';
+import { DecodedSourceMap, RawSourceMap } from '../../src/types';
 
 describe('remapping', () => {
   const rawMap: RawSourceMap = {
@@ -49,6 +49,16 @@ describe('remapping', () => {
     sourcesContent: ['\n\n  1 + 1;'],
     version: 3,
   };
+  const decodedMap: DecodedSourceMap = {
+    file: 'transpiled.min.js',
+    mappings: [[[0,0,2,2,0]]],
+    names: ['add'],
+    // TODO: support sourceRoot
+    // sourceRoot: '',
+    sources: ['helloworld.js'],
+    sourcesContent: ['\n\n  1 + 1;'],
+    version: 3,
+  };
 
   test('does not alter a lone sourcemap', () => {
     const map = remapping(rawMap, () => null);
@@ -155,4 +165,19 @@ describe('remapping', () => {
 
     expect(map).not.toHaveProperty('sourcesContent');
   });
+
+  test('returns decoded mappings if `decodeMappings` is set', () => {
+    const map = remapping(
+      rawMap,
+      (name: string) => {
+        if (name === 'transpiled.js') {
+          return transpiledMap;
+        }
+      },
+      false,
+      true
+    );
+
+    expect(map).toEqual(decodedMap);
+  });
 });