From ed6a339c168a8540b4ca2a0a3937b9379ca96417 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Oskar=20Segersv=C3=A4rd?= <victorystick@gmail.com>
Date: Tue, 29 Dec 2015 16:15:04 +0100
Subject: [PATCH 1/3] Add failing test

---
 .../handles-stringified-sourcemaps/_config.js  | 18 ++++++++++++++++++
 .../handles-stringified-sourcemaps/main.js     |  1 +
 2 files changed, 19 insertions(+)
 create mode 100644 test/function/handles-stringified-sourcemaps/_config.js
 create mode 100644 test/function/handles-stringified-sourcemaps/main.js

diff --git a/test/function/handles-stringified-sourcemaps/_config.js b/test/function/handles-stringified-sourcemaps/_config.js
new file mode 100644
index 0000000..a0220e9
--- /dev/null
+++ b/test/function/handles-stringified-sourcemaps/_config.js
@@ -0,0 +1,18 @@
+module.exports = {
+	options: {
+		plugins: [
+			{
+				transform: function ( code ) {
+					return {
+						code: code,
+						map: JSON.stringify({ mappings: '' })
+					};
+				}
+			}
+		]
+	},
+
+	bundleOptions: {
+		sourceMap: true
+	}
+};
diff --git a/test/function/handles-stringified-sourcemaps/main.js b/test/function/handles-stringified-sourcemaps/main.js
new file mode 100644
index 0000000..7a4e8a7
--- /dev/null
+++ b/test/function/handles-stringified-sourcemaps/main.js
@@ -0,0 +1 @@
+export default 42;

From f05bc8293f09b828eb9703cd6cd70e39a6cb4396 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Oskar=20Segersv=C3=A4rd?= <victorystick@gmail.com>
Date: Tue, 29 Dec 2015 16:16:42 +0100
Subject: [PATCH 2/3] Make failing test pass

---
 src/utils/transform.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/utils/transform.js b/src/utils/transform.js
index 761a217..5ddde28 100644
--- a/src/utils/transform.js
+++ b/src/utils/transform.js
@@ -25,6 +25,10 @@ export default function transform ( source, id, transformers ) {
 						map: null
 					};
 				}
+				// `result.map` can only be a string if `result` isn't
+				else if ( typeof result.map === 'string' ) {
+					result.map = JSON.parse( result.map );
+				}
 
 				sourceMapChain.push( result.map );
 				ast = result.ast;

From 9ce73156a2b26afa111da2b3ba1d5b5c65d86007 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Oskar=20Segersv=C3=A4rd?= <victorystick@gmail.com>
Date: Tue, 29 Dec 2015 16:19:30 +0100
Subject: [PATCH 3/3] Add description and comments

---
 test/function/handles-stringified-sourcemaps/_config.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/test/function/handles-stringified-sourcemaps/_config.js b/test/function/handles-stringified-sourcemaps/_config.js
index a0220e9..d09a3ce 100644
--- a/test/function/handles-stringified-sourcemaps/_config.js
+++ b/test/function/handles-stringified-sourcemaps/_config.js
@@ -1,10 +1,13 @@
 module.exports = {
+	description: 'handles transforms that return stringified source maps (#377)',
+
 	options: {
 		plugins: [
 			{
 				transform: function ( code ) {
 					return {
 						code: code,
+						// just stringify an otherwise acceptable source map
 						map: JSON.stringify({ mappings: '' })
 					};
 				}
@@ -12,6 +15,7 @@ module.exports = {
 		]
 	},
 
+	// ensure source maps are generated
 	bundleOptions: {
 		sourceMap: true
 	}