types(v-node-directive): changed expression type of VNodeDerective to optional string

fix vuejs#10871

Author: kawokas

types/test/options-test.ts

@@ -182,7 +182,7 @@ Vue.component('component', {
       },
       directives: [{
         name: 'a',
-        value: 'foo'
+        value: 'foo',
       }],
       domProps: {
         innerHTML: "baz"
@@ -478,3 +478,20 @@ Vue.component('functional-component-v-model', {
 
 
 Vue.component('async-es-module-component', () => import('./es-module'))
+
+Vue.component('directive-expression-optional-string', {
+  render(createElement) {
+    return createElement("div", {
+      directives: [
+        {
+          name: 'has-expression',
+          value: 2,
+          expression: '1 + 1',
+        }, {
+          name: 'no-expression',
+          value: 'foo',
+        },
+      ],
+    })
+  }
+});

types/vnode.d.ts

@@ -69,7 +69,7 @@ export interface VNodeDirective {
   name: string;
   value?: any;
   oldValue?: any;
-  expression?: any;
+  expression?: string;
   arg?: string;
   oldArg?: string;
   modifiers?: { [key: string]: boolean };