Accept filename-to-file-content hash as code parameter of generate.

packages/babel-generator/README.md

@@ -44,4 +44,47 @@ name                   | type     | default         | description
 sourceMaps             | boolean  | `false`         | Enable generating source maps
 sourceMapTarget        | string   |                 | The filename of the generated code that the source map will be associated with
 sourceRoot             | string   |                 | A root for all relative URLs in the source map
-sourceFileName         | string   |                 | The filename for the source code (i.e. the code in the `code` argument)
+sourceFileName         | string   |                 | The filename for the source code (i.e. the code in the `code` argument).  This will only be used if `code` is a string.
+
+## AST from Multiple Sources
+
+In most cases, Babel does a 1:1 transformation of input-file to output-file.  However,
+you may be dealing with AST constructed from multiple sources - JS files, templates, etc.
+If this is the case, and you want the sourcemaps to reflect the correct sources, you'll need
+to make some changes to your code.
+
+First, each node with a `loc` property (which indicates that node's original placement in the
+source document) must also include a `loc.filename` property, set to the source filename.
+
+Second, you should pass an object to `generate` as the `code` parameter.  Keys
+should be the source filenames, and values should be the source content.
+
+Here's an example of what that might look like:
+
+```js
+import {parse} from 'babylon';
+import traverse from "babel-traverse";
+import generate from 'babel-generator';
+
+function addFilename (ast, filename) {
+  traverse.cheap(ast, node => {
+    if (node.loc) { node.loc.source = sourcePath };
+  });
+}
+
+const a = 'var a = 1;';
+const b = 'var b = 2;';
+const astA = addFilename(parse(a), 'a.js');
+const astB = addFilename(parse(b), 'b.js');
+const ast = {
+  type: 'Program',
+  body: [].concat(astA.body, ast2.body)
+};
+
+const { code, map } = generate(ast, { /* options */ }, {
+  'a.js': a,
+  'b.js': b
+});
+
+// Sourcemap will point to both a.js and b.js where appropriate.
+```

packages/babel-generator/src/source-map.js

@@ -17,7 +17,13 @@ export default class SourceMap {
         sourceRoot: opts.sourceRoot
       });
 
-      this.map.setSourceContent(opts.sourceFileName, code);
+      if (typeof code === "string") {
+        this.map.setSourceContent(opts.sourceFileName, code);
+      } else if (typeof code === "object") {
+        Object.keys(code).forEach((sourceFileName) => {
+          this.map.setSourceContent(sourceFileName, code[sourceFileName]);
+        });
+      }
     } else {
       this.map = null;
     }