support postcss.config.js

lib/builder/webpack/style-loader.js

@@ -18,16 +18,22 @@ export default function styleLoader (ext, loaders = [], isVueLoader = false) {
 
   // https://github.com/postcss/postcss-loader
   let postcssLoader
-  let postcssPlugins = this.options.build.postcss
-  if (!isVueLoader && Array.isArray(postcssPlugins) && postcssPlugins.length) {
+  if (!isVueLoader && this.options.build.postcss) {
     postcssLoader = {
       loader: 'postcss-loader',
       options: {
-        sourceMap: this.options.build.cssSourceMap,
-        plugins: () => postcssPlugins,
-        config: {}
+        sourceMap: this.options.build.cssSourceMap
       }
     }
+    if (Array.isArray(this.options.build.postcss)) {
+      // If array is provided set it as plugins
+      postcssLoader.options.plugins = this.options.build.postcss
+    } else if (typeof this.options.build.postcss.path === 'string') {
+      // If config object detected
+      postcssLoader.options.config = this.options.build.postcss
+    } else {
+      // Just let postcss-loader resolve it's config
+    }
   }
 
   // https://github.com/webpack-contrib/css-loader

lib/common/options.js

@@ -48,6 +48,14 @@ export default function Options (_options) {
     options.store = true
   }
 
+  // Prefer postcss.config.js if no explicit option was provided and it exists
+  if (Array.isArray(options.build.postcss) && options.build.postcss.length === 0) {
+    if (existsSync(join(options.srcDir, 'postcss.config.js') ||
+       existsSync(join(options.rootDir, 'postcss.config.js')))) {
+      options.build.postcss = true
+    }
+  }
+
   // Debug errors
   if (options.debug === undefined) {
     options.debug = options.dev