wip: render fallback nodes for empty vfor

packages/runtime-vapor/src/apiCreateFor.ts

@@ -15,8 +15,10 @@ import { isArray, isObject, isString } from '@vue/shared'
 import { createComment, createTextNode } from './dom/node'
 import {
   type Block,
+  ForFragment,
   VaporFragment,
   insert,
+  remove,
   remove as removeBlock,
 } from './block'
 import { warn } from '@vue/runtime-dom'
@@ -77,7 +79,7 @@ export const createFor = (
   setup?: (_: {
     createSelector: (source: () => any) => (cb: () => void) => void
   }) => void,
-): VaporFragment => {
+): ForFragment => {
   const _insertionParent = insertionParent
   const _insertionAnchor = insertionAnchor
   if (isHydrating) {
@@ -94,7 +96,7 @@ export const createFor = (
   let currentKey: any
   // TODO handle this in hydration
   const parentAnchor = __DEV__ ? createComment('for') : createTextNode()
-  const frag = new VaporFragment(oldBlocks)
+  const frag = new ForFragment(oldBlocks)
   const instance = currentInstance!
   const canUseFastRemove = !!(flags & VaporVForFlags.FAST_REMOVE)
   const isComponent = !!(flags & VaporVForFlags.IS_COMPONENT)
@@ -123,6 +125,14 @@ export const createFor = (
     } else {
       parent = parent || parentAnchor!.parentNode
       if (!oldLength) {
+        // remove fallback nodes if needed
+        if (frag.fallback) {
+          const fallbackNodes = frag.nodes[0] as any
+          if (fallbackNodes) {
+            remove(fallbackNodes, parent!)
+          }
+        }
+
         // fast path for all new
         for (let i = 0; i < newLength; i++) {
           mount(source, i)
@@ -329,6 +339,11 @@ export const createFor = (
       frag.nodes.push(parentAnchor)
     }
 
+    // render fallback nodes if needed
+    if (isMounted && frag.fallback && newLength === 0) {
+      insert((frag.nodes[0] = frag.fallback()), parent!, parentAnchor)
+    }
+
     setActiveSub(prevSub)
   }
 

packages/runtime-vapor/src/block.ts

@@ -18,17 +18,24 @@ export type Block =
 
 export type BlockFn = (...args: any[]) => Block
 
-export class VaporFragment {
-  nodes: Block
+export class VaporFragment<T extends Block = Block> {
+  nodes: T
   anchor?: Node
   insert?: (parent: ParentNode, anchor: Node | null) => void
   remove?: (parent?: ParentNode) => void
+  fallback?: BlockFn
 
-  constructor(nodes: Block) {
+  constructor(nodes: T) {
     this.nodes = nodes
   }
 }
 
+export class ForFragment extends VaporFragment<Block[]> {
+  constructor(nodes: Block[]) {
+    super(nodes)
+  }
+}
+
 export class DynamicFragment extends VaporFragment {
   anchor: Node
   scope: EffectScope | undefined
@@ -67,14 +74,16 @@ export class DynamicFragment extends VaporFragment {
 
     if (this.fallback && !isValidBlock(this.nodes)) {
       parent && remove(this.nodes, parent)
-      // handle nested dynamic fragment
-      if (isFragment(this.nodes)) {
-        renderFallback(this.nodes, this.fallback, key)
-      } else {
-        this.nodes =
-          (this.scope || (this.scope = new EffectScope())).run(this.fallback) ||
-          []
-      }
+      const scope = this.scope || (this.scope = new EffectScope())
+      scope.run(() => {
+        // handle nested fragment
+        if (isFragment(this.nodes)) {
+          renderFallback(this.nodes, this.fallback!)
+        } else {
+          this.nodes = this.fallback!() || []
+        }
+      })
+
       parent && insert(this.nodes, parent, this.anchor)
     }
 
@@ -82,19 +91,21 @@ export class DynamicFragment extends VaporFragment {
   }
 }
 
-function renderFallback(
-  fragment: VaporFragment,
-  fallback: BlockFn,
-  key: any,
-): void {
+function renderFallback(fragment: VaporFragment, fallback: BlockFn): void {
+  if (!fragment.fallback) fragment.fallback = fallback
+
   if (fragment instanceof DynamicFragment) {
     const nodes = fragment.nodes
     if (isFragment(nodes)) {
-      renderFallback(nodes, fallback, key)
+      renderFallback(nodes, fallback)
     } else {
-      if (!fragment.fallback) fragment.fallback = fallback
-      fragment.update(fragment.fallback, key)
+      fragment.update(fragment.fallback)
     }
+  } else if (fragment instanceof ForFragment) {
+    // TODO handle nested ForFragment
+    fragment.nodes[0] = fallback() || []
+  } else {
+    // vdom slots
   }
 }