add check for async plugins

Author: vasia

lib/compilers/postcss-compiler.js

@@ -5,27 +5,68 @@ const { plugins } = postcssrc.sync(ctx)
 const logger = require('../logger')
 const getVueJestConfig = require('../get-vue-jest-config')
 
+let prevCheckIsAsync = null
+function hasAsyncPlugin () {
+  if (prevCheckIsAsync !== null) {
+    return prevCheckIsAsync
+  }
+  const result = postcss(plugins)
+    .process('', {
+      from: undefined
+    })
+
+  if (result.processing) {
+    prevCheckIsAsync = true
+  }
+  for (const plugin of result.processor.plugins) {
+    const promise = result.run(plugin)
+    if (typeof promise === 'object' && typeof promise.then === 'function') {
+      prevCheckIsAsync = true
+      break
+    }
+  }
+  if (prevCheckIsAsync === null) {
+    prevCheckIsAsync = false
+  }
+
+  return prevCheckIsAsync
+}
+
+function catchError (error, filePath, jestConfig) {
+  if (!getVueJestConfig(jestConfig).hideStyleWarn) {
+    logger.warn(`There was an error rendering the POSTCSS in ${filePath}. `)
+    logger.warn(`Error while compiling styles: ${error}`)
+  }
+}
+
 module.exports = (content, filePath, jestConfig) => {
   let css = null
 
-  postcss(plugins)
+  const res = postcss(plugins)
     .process(content, {
       from: undefined
     })
-    .then(result => {
-      css = result.css || ''
-    })
-    .catch((e) => {
-      css = ''
-      if (!getVueJestConfig(jestConfig).hideStyleWarn) {
-        logger.warn(`There was an error rendering the POSTCSS in ${filePath}. `)
-        logger.warn(`Error while compiling styles: ${e}`)
-      }
-    })
 
-  while (css === null) { //eslint-disable-line
-    require('deasync').sleep(100)
+  if (hasAsyncPlugin()) {
+    res
+      .then(result => {
+        css = result.css || ''
+      })
+      .catch((e) => {
+        css = ''
+        catchError(e, filePath, jestConfig)
+      })
+
+    while (css === null) { //eslint-disable-line
+      require('deasync').sleep(100)
+    }
+
+    return css
   }
 
-  return css
+  try {
+    return res.css
+  } catch (e) {
+    catchError(e, filePath, jestConfig)
+  }
 }