Fixed partial file updates producing duplicate styles

Author: samuelmaddock

lib/loader.js

@@ -92,7 +92,7 @@ module.exports = function (source, map) {
             });
 
             if ('_emitThemePartial' in loader) {
-                loader._emitThemePartial(result.css);
+                loader._emitThemePartial(loader.resourcePath, result.css);
             } else {
                 throw new Error('Theme loader missing _emitThemePartial function. Did you forget to include the ThemePlugin?');
             }

lib/plugin.js

@@ -69,24 +69,28 @@ function ThemePlugin(options) {
 
 ThemePlugin.prototype.apply = function apply(compiler) {
     const themes = this.options.themes;
-    const themePartials = [];
+    const themePartials = {};
 
     compiler.plugin('compilation', compilation => {
         compilation.plugin('normal-module-loader', (context, module) => {
-            context._emitThemePartial = (themeSource) => {
-                themePartials.push(themeSource);
+            context._emitThemePartial = (resourcePath, themeSource) => {
+                themePartials[resourcePath] = themeSource;
             };
         });
     });
 
     compiler.plugin('emit', (compilation, done) => {
-        if (themePartials.length === 0) {
+        const themePartialResources = Object.keys(themePartials);
+
+        if (themePartialResources.length === 0) {
             done();
             return;
         }
 
         // Concat theme partials
-        const source = themePartials.join('\n');
+        const source = themePartialResources
+            .map(resourcePath => themePartials[resourcePath])
+            .join('\n');
 
         generateThemes(themes, source).then(function (results) {
             const themeAssets = results.reduce((acc, theme) => {