fix(index): assign empty module.id to prevent contenthash from changing unnecessarily (#284)

* fix: add empty id to prevent contenthash from changing unnecessarily

* fix: updated tests

Author: lfre

src/index.js

@@ -42,6 +42,7 @@ class CssDependencyTemplate {
 class CssModule extends webpack.Module {
   constructor(dependency) {
     super(MODULE_TYPE, dependency.context);
+    this.id = '';
     this._identifier = dependency.identifier;
     this._identifierIndex = dependency.identifierIndex;
     this.content = dependency.content;
@@ -92,7 +93,7 @@ class CssModule extends webpack.Module {
     super.updateHash(hash);
     hash.update(this.content);
     hash.update(this.media || '');
-    hash.update(JSON.stringify(this.sourceMap || ''));
+    hash.update(this.sourceMap ? JSON.stringify(this.sourceMap) : '');
   }
 }
 

test/cases/composes-async/expected/1.css

@@ -1,4 +1,4 @@
-.base {
-  background: blue;
+.composed {
+  background: green;
 }
 

test/cases/composes-async/expected/2.css

@@ -1,4 +1,4 @@
-.composed {
-  background: green;
+.base {
+  background: blue;
 }