feat: style-compiler should process one style block at a time

To keep API akin to template-compiler, style style-compiler should
process one style block at a time.

index.d.ts

@@ -13,7 +13,7 @@ declare module VueComponentCompiler {
    * @param styles List of styles to process.
    * @param file SFC file path
    */
-  export function compileStyles(styles: Array<StyleCompilerSource>, file: string, config: StyleCompilerConfig): Promise<Array<StyleCompilerOutput>>
+  export function compileStyle(style: StyleCompilerSource, file: string, config: StyleCompilerConfig): Promise<Array<StyleCompilerOutput>>
 
   /**
    * Compile template to render functions

src/index.js

@@ -1,6 +1,6 @@
 module.exports = {
   parse: require('./parser'),
-  compileStyles: require('./style-compiler'),
+  compileStyle: require('./style-compiler'),
   compileTemplate: require('./template-compiler'),
   assemble: require('./assemble'),
   generateScopeId: require('./gen-id')

src/style-compiler/index.js

@@ -4,7 +4,15 @@ const defaults = require('lodash.defaultsdeep')
 const trim = require('./plugins/trim')
 const scopeId = require('./plugins/scope-id')
 
-function compileStyle (style, filename, config) {
+module.exports = function compileStyle (style, filename, config) {
+  config = defaults(config, {
+    async: false,
+    needMap: true,
+    plugins: [],
+    options: {},
+    onWarn: message => console.warn(message)
+  })
+
   const plugins = [trim].concat(config.plugins)
   const options = Object.assign({
     to: filename,
@@ -48,17 +56,3 @@ function compileStyle (style, filename, config) {
 
   return (config.async) ? output.then(prepare) : prepare(output)
 }
-
-module.exports = function compileStyles (styles, filename, config) {
-  config = defaults(config, {
-    async: false,
-    needMap: true,
-    plugins: [],
-    options: {},
-    onWarn: message => console.warn(message)
-  })
-
-  const results = styles.map(style => compileStyle(style, filename, config))
-
-  return config.async ? Promise.all(results) : results
-}

test/style-compiler.test.js

@@ -7,6 +7,6 @@ test('should rewrite scoped style', () => {
       scoped: true
     }
   }
-  const compiled = compiler([style], 'foo.vue', { scopeId: 'xxx', needMap: false })
-  expect(compiled[0].code.indexOf('.foo[xxx]')).toBeGreaterThan(-1)
+  const compiled = compiler(style, 'foo.vue', { scopeId: 'xxx', needMap: false })
+  expect(compiled.code.indexOf('.foo[xxx]')).toBeGreaterThan(-1)
 })