fix(types): accept primatives and falsy values in createElement children (#9154)

fixes #8498

Author: KaelWD

types/test/options-test.ts

@@ -281,6 +281,12 @@ Vue.component('provide-function', {
   })
 })
 
+Vue.component('component-with-slot', {
+  render (h): VNode {
+    return h('div', this.$slots.default)
+  }
+})
+
 Vue.component('component-with-scoped-slot', {
   render (h) {
     interface ScopedSlotProps {
@@ -301,6 +307,12 @@ Vue.component('component-with-scoped-slot', {
       h('child', {
         // Passing down all slots from parent
         scopedSlots: this.$scopedSlots
+      }),
+      h('child', {
+        // Passing down single slot from parent
+        scopedSlots: {
+          default: this.$scopedSlots.default
+        }
       })
     ])
   },
@@ -320,16 +332,22 @@ Vue.component('narrow-array-of-vnode-type', {
   render (h): VNode {
     const slot = this.$scopedSlots.default!({})
     if (typeof slot === 'string') {
+      // <template slot-scope="data">bare string</template>
       return h('span', slot)
     } else if (Array.isArray(slot)) {
+      // template with multiple children
       const first = slot[0]
-      if (!Array.isArray(first) && typeof first !== 'string') {
+      if (!Array.isArray(first) && typeof first !== 'string' && first) {
         return first
       } else {
         return h()
       }
-    } else {
+    } else if (slot) {
+      // <div slot-scope="data">bare VNode</div>
       return slot
+    } else {
+      // empty template, slot === undefined
+      return h()
     }
   }
 })

types/vnode.d.ts

@@ -1,9 +1,14 @@
 import { Vue } from "./vue";
 
-export type ScopedSlot = (props: any) => VNodeChildrenArrayContents | VNode | string;
+// Scoped slots can technically return anything if used from
+// a render function, but this is "good enough" for templates
+export type ScopedSlot = (props: any) => ScopedSlotChildren;
+export type ScopedSlotChildren = ScopedSlotArrayContents | VNode | string | undefined;
+export interface ScopedSlotArrayContents extends Array<ScopedSlotChildren> {}
 
-export type VNodeChildren = VNodeChildrenArrayContents | [ScopedSlot] | string;
-export interface VNodeChildrenArrayContents extends Array<VNode | string | VNodeChildrenArrayContents> {}
+// Relaxed type compatible with $createElement
+export type VNodeChildren = VNodeChildrenArrayContents | [ScopedSlot] | string | boolean | null | undefined;
+export interface VNodeChildrenArrayContents extends Array<VNodeChildren | VNode> {}
 
 export interface VNode {
   tag?: string;
@@ -27,7 +32,7 @@ export interface VNodeComponentOptions {
   Ctor: typeof Vue;
   propsData?: object;
   listeners?: object;
-  children?: VNodeChildren;
+  children?: VNode[];
   tag?: string;
 }