only remove valid sourcemapping URL comments (fixes #1132)

src/Bundle.js

@@ -420,7 +420,7 @@ export default class Bundle {
 		const bundleSourcemapChain = [];
 
 		code = transformBundle( code, this.plugins, bundleSourcemapChain, options )
-			.replace( new RegExp( `\\/\\/#\\s+${SOURCEMAPPING_URL}=.+\\n?`, 'g' ), '' );
+			.replace( new RegExp( `^\\/\\/#\\s+${SOURCEMAPPING_URL}=.+\\n?`, 'gm' ), '' );
 
 		if ( options.sourceMap ) {
 			timeStart( 'sourceMap' );

src/Module.js

@@ -72,7 +72,7 @@ export default class Module {
 		});
 
 		// remove existing sourceMappingURL comments
-		const pattern = new RegExp( `\\/\\/#\\s+${SOURCEMAPPING_URL}=.+\\n?`, 'g' );
+		const pattern = new RegExp( `^\\/\\/#\\s+${SOURCEMAPPING_URL}=.+\\n?`, 'gm' );
 		let match;
 		while ( match = pattern.exec( code ) ) {
 			this.magicString.remove( match.index, match.index + match[0].length );

test/function/sourcemapping-url-comment/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'only removes valid sourcemapping URL comments (#1132)'
+};

test/function/sourcemapping-url-comment/main.js

@@ -0,0 +1,3 @@
+////# sourceMappingURL=foo
+var val = 42;
+assert.equal( val, 42 );