debug: Show what PostCSS configuration is used

lib/common/options.js

@@ -1,8 +1,12 @@
 import _ from 'lodash'
+import Debug from 'debug'
 import { join, resolve } from 'path'
 import { existsSync } from 'fs'
 import { isUrl, isPureObject } from 'utils'
 
+const debug = Debug('nuxt:build')
+debug.color = 2 // Force green color
+
 const Options = {}
 
 export default Options
@@ -96,6 +100,7 @@ Options.from = function (_options) {
 
     // Default postcss options
     if (postcssConfigPath) {
+      debug(`Using PostCSS config file: ${postcssConfigPath}`)
       options.build.postcss = {
         sourceMap: options.build.cssSourceMap,
         // https://github.com/postcss/postcss-loader/blob/master/lib/index.js#L79
@@ -104,6 +109,7 @@ Options.from = function (_options) {
         }
       }
     } else {
+      debug('Using PostCSS config from `build.postcss`')
       // Normalize & Apply default plugins
       if (Array.isArray(options.build.postcss)) {
         options.build.postcss = { plugins: options.build.postcss }