perf: generate source maps only when explicitly set (#478)

lib/loader.js

@@ -16,10 +16,16 @@ module.exports = function(content, map) {
 	var root = query.root;
 	var moduleMode = query.modules || query.module;
 	var camelCaseKeys = query.camelCase || query.camelcase;
+	var sourceMap = query.sourceMap || false;
 	var resolve = createResolver(query.alias);
 
-	if(map !== null && typeof map !== "string") {
-		map = JSON.stringify(map);
+	if(sourceMap) {
+		if (map && typeof map !== "string") {
+			map = JSON.stringify(map);
+		}
+	} else {
+		// Some loaders (example `"postcss-loader": "1.x.x"`) always generates source map, we should remove it
+		map = null;
 	}
 
 	processCss(content, map, {
@@ -28,7 +34,8 @@ module.exports = function(content, map) {
 		to: loaderUtils.getCurrentRequest(this),
 		query: query,
 		minimize: this.minimize,
-		loaderContext: this
+		loaderContext: this,
+		sourceMap: sourceMap
 	}, function(err, result) {
 		if(err) return callback(err);
 

lib/processCss.js

@@ -200,12 +200,12 @@ module.exports = function processCss(inputSource, inputMap, options, callback) {
 		// we need a prefix to avoid path rewriting of PostCSS
 		from: "/css-loader!" + options.from,
 		to: options.to,
-		map: {
+		map: options.sourceMap ? {
 			prev: inputMap,
 			sourcesContent: true,
 			inline: false,
 			annotation: false
-		}
+		} : null
 	}).then(function(result) {
 		callback(null, {
 			source: result.css,

test/sourceMapTest.js

@@ -10,6 +10,24 @@ describe("source maps", function() {
 	testWithMap("falsy: undefined map doesn't cause an error", ".class { a: b c d; }", undefined, [
 		[1, ".class { a: b c d; }", ""]
 	]);
+    testWithMap("should don't generate sourceMap when `sourceMap: false` and map exist",
+		".class { a: b c d; }",
+        {
+            file: 'test.css',
+            mappings: 'AAAA,SAAS,SAAS,EAAE',
+            names: [],
+            sourceRoot: '',
+            sources: [ '/folder/test.css' ],
+            sourcesContent: [ '.class { a: b c d; }' ],
+            version: 3
+        },
+		[
+			[1, ".class { a: b c d; }", ""]
+		],
+		{
+            query: "?sourceMap=false"
+		}
+	);
 	testMap("generate sourceMap (1 loader)", ".class { a: b c d; }", undefined, {
 		loaders: [{request: "/path/css-loader"}],
 		options: { context: "/" },
@@ -95,4 +113,13 @@ describe("source maps", function() {
 			version: 3
 		}]
 	]);
+	testMap("don't generate sourceMap (1 loader)", ".class { a: b c d; }", undefined, {
+		loaders: [{request: "/path/css-loader"}],
+		options: { context: "/" },
+		resource: "/folder/test.css",
+		request: "/path/css-loader!/folder/test.css",
+		query: "?sourceMap=false"
+	}, [
+		[1, ".class { a: b c d; }", ""]
+	]);
 });