fix: deep merge objects when extending package.json via plugins (#1070)

close #1053

packages/@vue/cli/__tests__/Generator.spec.js

@@ -49,7 +49,11 @@ test('api: extendPackage', async () => {
       list: [1],
       vue: {
         foo: 1,
-        bar: 2
+        bar: 2,
+        pluginOptions: {
+          graphqlMock: true,
+          apolloEngine: false
+        }
       }
     },
     plugins: [{
@@ -60,7 +64,10 @@ test('api: extendPackage', async () => {
           list: [2],
           vue: {
             foo: 2,
-            baz: 3
+            baz: 3,
+            pluginOptions: {
+              enableInSFC: true
+            }
           }
         })
       }
@@ -76,7 +83,12 @@ test('api: extendPackage', async () => {
     vue: {
       foo: 2,
       bar: 2,
-      baz: 3
+      baz: 3,
+      pluginOptions: {
+        graphqlMock: true,
+        apolloEngine: false,
+        enableInSFC: true
+      }
     }
   })
 })

packages/@vue/cli/lib/GeneratorAPI.js

@@ -2,6 +2,7 @@ const fs = require('fs')
 const ejs = require('ejs')
 const path = require('path')
 const globby = require('globby')
+const merge = require('deepmerge')
 const resolve = require('resolve')
 const isBinary = require('isbinaryfile')
 const yaml = require('yaml-front-matter')
@@ -105,7 +106,7 @@ class GeneratorAPI {
       } else if (Array.isArray(value) && Array.isArray(existing)) {
         pkg[key] = existing.concat(value)
       } else if (isObject(value) && isObject(existing)) {
-        pkg[key] = Object.assign({}, existing, value)
+        pkg[key] = merge(existing, value)
       } else {
         pkg[key] = value
       }