Reapply "simple & robust useData() impl"

This reverts commit 631f674.

examples/vue-full/renderer/app.ts

@@ -4,7 +4,8 @@ import { createSSRApp, h, markRaw, reactive, ref } from 'vue'
 import PageLayout from './PageLayout.vue'
 import { setPageContext } from './usePageContext'
 import type { PageContext } from 'vike/types'
-import { objectAssign } from './utils'
+import { setData } from './useData'
+import { isObject, objectAssign } from './utils'
 
 function createApp(pageContext: PageContext) {
   const { Page } = pageContext
@@ -22,13 +23,24 @@ function createApp(pageContext: PageContext) {
   // app.changePage() is called upon navigation, see +onRenderClient.ts
   objectAssign(app, {
     changePage: (pageContext: PageContext) => {
+      const data = pageContext.data ?? {}
+      assertDataIsObject(data)
+      Object.assign(dataReactive, data)
       Object.assign(pageContextReactive, pageContext)
       pageRef.value = markRaw(pageContext.Page)
     }
   })
 
+  const data = pageContext.data ?? {}
+  assertDataIsObject(data)
+  const dataReactive = reactive(data)
   const pageContextReactive = reactive(pageContext)
   setPageContext(app, pageContextReactive)
+  setData(app, dataReactive)
 
   return app
 }
+
+function assertDataIsObject(data: unknown): asserts data is Record<string, unknown> {
+  if (!isObject(data)) throw new Error('Return value of data() hook should be an object, undefined, or null')
+}

examples/vue-full/renderer/useData.ts

@@ -1,10 +1,19 @@
 // https://vike.dev/useData
 export { useData }
+export { setData }
 
-import { usePageContext } from './usePageContext'
+import { inject } from 'vue'
+import type { App } from 'vue'
+
+const key = Symbol()
 
 /** https://vike.dev/useData */
 function useData<Data>(): Data {
-  const { data } = usePageContext()
+  const data = inject(key)
+  if (!data) throw new Error('setData() not called')
   return data as any
 }
+
+function setData(app: App, data: unknown): void {
+  app.provide(key, data)
+}

examples/vue-full/renderer/utils.ts

@@ -5,3 +5,7 @@ export function objectAssign<Obj extends object, ObjAddendum>(
 ): asserts obj is Obj & ObjAddendum {
   Object.assign(obj, objAddendum)
 }
+
+export function isObject(value: unknown): value is Record<string, unknown> {
+  return typeof value === 'object' && value !== null
+}