feat(cli): support custom postcss config

packages/vant-cli/src/common/index.ts

@@ -7,7 +7,12 @@ import {
   readFileSync,
   outputFileSync
 } from 'fs-extra';
-import { SRC_DIR, getVantConfig, WEBPACK_CONFIG_FILE } from './constant';
+import {
+  SRC_DIR,
+  getVantConfig,
+  ROOT_WEBPACK_CONFIG_FILE,
+  ROOT_POSTCSS_CONFIG_FILE
+} from './constant';
 
 export const EXT_REGEXP = /\.\w+$/;
 export const SFC_REGEXP = /\.(vue)$/;
@@ -96,8 +101,8 @@ export function normalizePath(path: string): string {
 }
 
 export function getWebpackConfig(): object {
-  if (existsSync(WEBPACK_CONFIG_FILE)) {
-    const config = require(WEBPACK_CONFIG_FILE);
+  if (existsSync(ROOT_WEBPACK_CONFIG_FILE)) {
+    const config = require(ROOT_WEBPACK_CONFIG_FILE);
 
     if (typeof config === 'function') {
       return config();
@@ -109,6 +114,14 @@ export function getWebpackConfig(): object {
   return {};
 }
 
+export function getPostcssConfig(): object {
+  if (existsSync(ROOT_POSTCSS_CONFIG_FILE)) {
+    return require(ROOT_POSTCSS_CONFIG_FILE);
+  }
+
+  return {};
+}
+
 export type ModuleEnv = 'esmodule' | 'commonjs';
 export type NodeEnv = 'production' | 'development' | 'test';
 export type BuildTarget = 'site' | 'package';
@@ -129,8 +142,8 @@ export function isDev() {
   return process.env.NODE_ENV === 'development';
 }
 
-// Smarter outputFileSync
-// Skip if content unchanged
+// smarter outputFileSync
+// skip output if file content unchanged
 export function smartOutputFile(filePath: string, content: string) {
   if (existsSync(filePath)) {
     const previousContent = readFileSync(filePath, 'utf-8');