chore: add module concatenation hint (vuejs#2503)

sirlancelot · haoqunjiang · commit 09305db48fbc · 2018-09-15T01:33:46.000+08:00
Allow Webpack to process this file as an ES Module, which allows
concatenating using ModuleConcatenationPlugin, resulting in a slightly
smaller bundle and removes the overhead of a runtime `require()`.

The export default null will get optimized away during tree-shaking.
diff --git a/packages/@vue/cli-service/lib/commands/build/setPublicPath.js b/packages/@vue/cli-service/lib/commands/build/setPublicPath.js
@@ -6,3 +6,6 @@ if (typeof window !== 'undefined') {
     __webpack_public_path__ = i[1] // eslint-disable-line
   }
 }
+
+// Indicate to webpack that this file can be concatenated
+export default null

Original file line number	Diff line number	Diff line change
`@@ -6,3 +6,6 @@ if (typeof window !== 'undefined') {`
`6`	`6`	`__webpack_public_path__ = i[1] // eslint-disable-line`
`7`	`7`	`}`
`8`	`8`	`}`
	`9`	`+`
	`10`	`+// Indicate to webpack that this file can be concatenated`
	`11`	`+export default null`