fix(compiler): Don't strip CSS source maps

Fix CSS source mapping for component by keeping `/*# sourceMappingURL= ... */` and  `/*# sourceURL= ... */` comments.

Relates to <angular/angular-cli#4199>.

Author: Zhicheng Wang

packages/compiler/src/style_url_resolver.ts

@@ -29,19 +29,20 @@ export function extractStyleUrls(
     resolver: UrlResolver, baseUrl: string, cssText: string): StyleWithImports {
   const foundUrls: string[] = [];
 
-  const modifiedCssText =
-      cssText.replace(CSS_COMMENT_REGEXP, '').replace(CSS_IMPORT_REGEXP, (...m: string[]) => {
-        const url = m[1] || m[2];
-        if (!isStyleUrlResolvable(url)) {
-          // Do not attempt to resolve non-package absolute URLs with URI scheme
-          return m[0];
-        }
-        foundUrls.push(resolver.resolve(baseUrl, url));
-        return '';
-      });
+  const modifiedCssText = cssText.replace(CSS_STRIPPABLE_COMMENT_REGEXP, '')
+                              .replace(CSS_IMPORT_REGEXP, (...m: string[]) => {
+                                const url = m[1] || m[2];
+                                if (!isStyleUrlResolvable(url)) {
+                                  // Do not attempt to resolve non-package absolute URLs with URI
+                                  // scheme
+                                  return m[0];
+                                }
+                                foundUrls.push(resolver.resolve(baseUrl, url));
+                                return '';
+                              });
   return new StyleWithImports(modifiedCssText, foundUrls);
 }
 
 const CSS_IMPORT_REGEXP = /@import\s+(?:url\()?\s*(?:(?:['"]([^'"]*))|([^;\)\s]*))[^;]*;?/g;
-const CSS_COMMENT_REGEXP = /\/\*[\s\S]+?\*\//g;
+const CSS_STRIPPABLE_COMMENT_REGEXP = /\/\*(?!#\s*(?:sourceURL|sourceMappingURL)=)[\s\S]+?\*\//g;
 const URL_WITH_SCHEMA_REGEXP = /^([^:/?#]+):/;

packages/compiler/test/style_url_resolver_spec.ts

@@ -51,6 +51,14 @@ export function main() {
       expect(styleWithImports.styleUrls).not.toContain('http://ng.io/3.css');
     });
 
+    it('should keep /*# sourceURL... */ and /*# sourceMappingURL... */ comments', () => {
+      const css =
+          `/*regular comment*/\n/*# sourceURL=.... */\n/*# sourceMappingURL=... *//*#sourceMappingURL=... */`;
+      const styleWithSourceMaps = extractStyleUrls(urlResolver, 'http://ng.io', css);
+      expect(styleWithSourceMaps.style.trim())
+          .toEqual('/*# sourceURL=.... */\n/*# sourceMappingURL=... *//*#sourceMappingURL=... */');
+    });
+
     it('should extract "@import url()" urls', () => {
       const css = `
       @import url('3.css');