From 33eba896621d65ced6b24eb8722658f8d830f023 Mon Sep 17 00:00:00 2001
From: Lukas Taegert-Atkinson <lukastaegert@users.noreply.github.com>
Date: Thu, 16 May 2019 07:50:15 +0200
Subject: [PATCH] Allow transformers to return an empty string (#2861)

---
 src/utils/transform.ts                        |  6 +++---
 .../samples/transform-empty-string/_config.js | 21 +++++++++++++++++++
 .../samples/transform-empty-string/main.js    |  3 +++
 .../transform-empty-string/transformed.js     |  1 +
 4 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 test/function/samples/transform-empty-string/_config.js
 create mode 100644 test/function/samples/transform-empty-string/main.js
 create mode 100644 test/function/samples/transform-empty-string/transformed.js

diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index 56b1f321d10..84531218a80 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -76,21 +76,21 @@ export default function transform(
 			}
 		}
 
-		if (!result) return code;
-
 		if (typeof result === 'string') {
 			result = {
 				ast: undefined,
 				code: result,
 				map: undefined
 			};
-		} else {
+		} else if (result && typeof result === 'object') {
 			if (typeof result.map === 'string') {
 				result.map = JSON.parse(result.map);
 			}
 			if (typeof result.moduleSideEffects === 'boolean') {
 				moduleSideEffects = result.moduleSideEffects;
 			}
+		} else {
+			return code;
 		}
 
 		if (result.map && typeof (result.map as ExistingRawSourceMap).mappings === 'string') {
diff --git a/test/function/samples/transform-empty-string/_config.js b/test/function/samples/transform-empty-string/_config.js
new file mode 100644
index 00000000000..e6a15ba155f
--- /dev/null
+++ b/test/function/samples/transform-empty-string/_config.js
@@ -0,0 +1,21 @@
+const assert = require('assert');
+
+const sideEffects = [];
+
+module.exports = {
+	description: 'allows transformers to transform code to an empty string',
+	context: { sideEffects },
+	exports() {
+		assert.deepStrictEqual(sideEffects, ['this happens']);
+	},
+	options: {
+		plugins: {
+			name: 'test-plugin',
+			transform(code, id) {
+				if (id.endsWith('transformed.js')) {
+					return '';
+				}
+			}
+		}
+	}
+};
diff --git a/test/function/samples/transform-empty-string/main.js b/test/function/samples/transform-empty-string/main.js
new file mode 100644
index 00000000000..2a3a72d53c6
--- /dev/null
+++ b/test/function/samples/transform-empty-string/main.js
@@ -0,0 +1,3 @@
+import './transformed.js';
+
+sideEffects.push('this happens');
diff --git a/test/function/samples/transform-empty-string/transformed.js b/test/function/samples/transform-empty-string/transformed.js
new file mode 100644
index 00000000000..b302749e118
--- /dev/null
+++ b/test/function/samples/transform-empty-string/transformed.js
@@ -0,0 +1 @@
+sideEffects.push('should not happen');