feat(vapor): forwarded slots

packages/compiler-vapor/__tests__/transforms/__snapshots__/vSlot.spec.ts.snap

@@ -103,6 +103,97 @@ export function render(_ctx) {
 }"
 `;
 
+exports[`compiler: transform slot > forwarded slots > <slot w/ nested component> 1`] = `
+"import { forwardedSlotCreator as _forwardedSlotCreator, resolveComponent as _resolveComponent, createComponentWithFallback as _createComponentWithFallback } from 'vue';
+
+export function render(_ctx) {
+  const _createForwardedSlot = _forwardedSlotCreator()
+  const _component_Comp = _resolveComponent("Comp")
+  const n2 = _createComponentWithFallback(_component_Comp, null, {
+    "default": () => {
+      const n1 = _createComponentWithFallback(_component_Comp, null, {
+        "default": () => {
+          const n0 = _createForwardedSlot("default", null)
+          return n0
+        }
+      })
+      return n1
+    }
+  }, true)
+  return n2
+}"
+`;
+
+exports[`compiler: transform slot > forwarded slots > <slot> tag only 1`] = `
+"import { forwardedSlotCreator as _forwardedSlotCreator, resolveComponent as _resolveComponent, createComponentWithFallback as _createComponentWithFallback } from 'vue';
+
+export function render(_ctx) {
+  const _createForwardedSlot = _forwardedSlotCreator()
+  const _component_Comp = _resolveComponent("Comp")
+  const n1 = _createComponentWithFallback(_component_Comp, null, {
+    "default": () => {
+      const n0 = _createForwardedSlot("default", null)
+      return n0
+    }
+  }, true)
+  return n1
+}"
+`;
+
+exports[`compiler: transform slot > forwarded slots > <slot> tag w/ template 1`] = `
+"import { forwardedSlotCreator as _forwardedSlotCreator, resolveComponent as _resolveComponent, createComponentWithFallback as _createComponentWithFallback } from 'vue';
+
+export function render(_ctx) {
+  const _createForwardedSlot = _forwardedSlotCreator()
+  const _component_Comp = _resolveComponent("Comp")
+  const n2 = _createComponentWithFallback(_component_Comp, null, {
+    "default": () => {
+      const n0 = _createForwardedSlot("default", null)
+      return n0
+    }
+  }, true)
+  return n2
+}"
+`;
+
+exports[`compiler: transform slot > forwarded slots > <slot> tag w/ v-for 1`] = `
+"import { forwardedSlotCreator as _forwardedSlotCreator, resolveComponent as _resolveComponent, createFor as _createFor, createComponentWithFallback as _createComponentWithFallback } from 'vue';
+
+export function render(_ctx) {
+  const _createForwardedSlot = _forwardedSlotCreator()
+  const _component_Comp = _resolveComponent("Comp")
+  const n3 = _createComponentWithFallback(_component_Comp, null, {
+    "default": () => {
+      const n0 = _createFor(() => (_ctx.b), (_for_item0) => {
+        const n2 = _createForwardedSlot("default", null)
+        return n2
+      })
+      return n0
+    }
+  }, true)
+  return n3
+}"
+`;
+
+exports[`compiler: transform slot > forwarded slots > <slot> tag w/ v-if 1`] = `
+"import { forwardedSlotCreator as _forwardedSlotCreator, resolveComponent as _resolveComponent, createIf as _createIf, createComponentWithFallback as _createComponentWithFallback } from 'vue';
+
+export function render(_ctx) {
+  const _createForwardedSlot = _forwardedSlotCreator()
+  const _component_Comp = _resolveComponent("Comp")
+  const n3 = _createComponentWithFallback(_component_Comp, null, {
+    "default": () => {
+      const n0 = _createIf(() => (_ctx.ok), () => {
+        const n2 = _createForwardedSlot("default", null)
+        return n2
+      })
+      return n0
+    }
+  }, true)
+  return n3
+}"
+`;
+
 exports[`compiler: transform slot > implicit default slot 1`] = `
 "import { resolveComponent as _resolveComponent, createComponentWithFallback as _createComponentWithFallback, template as _template } from 'vue';
 const t0 = _template("<div></div>")

packages/compiler-vapor/__tests__/transforms/vSlot.spec.ts

@@ -420,6 +420,35 @@ describe('compiler: transform slot', () => {
     })
   })
 
+  describe('forwarded slots', () => {
+    test('<slot> tag only', () => {
+      const { code } = compileWithSlots(`<Comp><slot/></Comp>`)
+      expect(code).toMatchSnapshot()
+    })
+
+    test('<slot> tag w/ v-if', () => {
+      const { code } = compileWithSlots(`<Comp><slot v-if="ok"/></Comp>`)
+      expect(code).toMatchSnapshot()
+    })
+
+    test('<slot> tag w/ v-for', () => {
+      const { code } = compileWithSlots(`<Comp><slot v-for="a in b"/></Comp>`)
+      expect(code).toMatchSnapshot()
+    })
+
+    test('<slot> tag w/ template', () => {
+      const { code } = compileWithSlots(
+        `<Comp><template #default><slot/></template></Comp>`,
+      )
+      expect(code).toMatchSnapshot()
+    })
+
+    test('<slot w/ nested component>', () => {
+      const { code } = compileWithSlots(`<Comp><Comp><slot/></Comp></Comp>`)
+      expect(code).toMatchSnapshot()
+    })
+  })
+
   describe('errors', () => {
     test('error on extraneous children w/ named default slot', () => {
       const onError = vi.fn()

packages/compiler-vapor/src/generate.ts

@@ -18,6 +18,7 @@ import {
   genCall,
 } from './generators/utils'
 import { setTemplateRefIdent } from './generators/templateRef'
+import { createForwardedSlotIdent } from './generators/slotOutlet'
 
 export type CodegenOptions = Omit<BaseCodegenOptions, 'optimizeImports'>
 
@@ -129,6 +130,12 @@ export function generate(
       `const ${setTemplateRefIdent} = ${context.helper('createTemplateRefSetter')}()`,
     )
   }
+  if (ir.hasForwardedSlot) {
+    push(
+      NEWLINE,
+      `const ${createForwardedSlotIdent} = ${context.helper('forwardedSlotCreator')}()`,
+    )
+  }
   push(...genBlockContent(ir.block, context, true))
   push(INDENT_END, NEWLINE)
 

packages/compiler-vapor/src/generators/slotOutlet.ts

@@ -5,12 +5,14 @@ import { genExpression } from './expression'
 import { type CodeFragment, NEWLINE, buildCodeFragment, genCall } from './utils'
 import { genRawProps } from './component'
 
+export const createForwardedSlotIdent = `_createForwardedSlot`
+
 export function genSlotOutlet(
   oper: SlotOutletIRNode,
   context: CodegenContext,
 ): CodeFragment[] {
   const { helper } = context
-  const { id, name, fallback } = oper
+  const { id, name, fallback, forwarded } = oper
   const [frag, push] = buildCodeFragment()
 
   const nameExpr = name.isStatic
@@ -26,7 +28,7 @@ export function genSlotOutlet(
     NEWLINE,
     `const n${id} = `,
     ...genCall(
-      helper('createSlot'),
+      forwarded ? createForwardedSlotIdent : helper('createSlot'),
       nameExpr,
       genRawProps(oper.props, context) || 'null',
       fallbackArg,

packages/compiler-vapor/src/ir/index.ts

@@ -65,6 +65,7 @@ export interface RootIRNode {
   directive: Set<string>
   block: BlockIRNode
   hasTemplateRef: boolean
+  hasForwardedSlot: boolean
 }
 
 export interface IfIRNode extends BaseIRNode {
@@ -208,6 +209,7 @@ export interface SlotOutletIRNode extends BaseIRNode {
   name: SimpleExpressionNode
   props: IRProps[]
   fallback?: BlockIRNode
+  forwarded?: boolean
   parent?: number
   anchor?: number
 }

packages/compiler-vapor/src/transform.ts

@@ -78,6 +78,7 @@ export class TransformContext<T extends AllNode = AllNode> {
 
   inVOnce: boolean = false
   inVFor: number = 0
+  inSlot: boolean = false
 
   comment: CommentNode[] = []
   component: Set<string> = this.ir.component
@@ -219,6 +220,7 @@ export function transform(
     directive: new Set(),
     block: newBlock(node),
     hasTemplateRef: false,
+    hasForwardedSlot: false,
   }
 
   const context = new TransformContext(ir, node, options)

packages/compiler-vapor/src/transforms/transformSlotOutlet.ts

@@ -99,13 +99,15 @@ export const transformSlotOutlet: NodeTransform = (node, context) => {
   }
 
   return () => {
+    if (context.inSlot) context.ir.hasForwardedSlot = true
     exitBlock && exitBlock()
     context.dynamic.operation = {
       type: IRNodeTypes.SLOT_OUTLET_NODE,
       id,
       name: slotName,
       props: irProps,
       fallback,
+      forwarded: context.inSlot,
     }
   }
 }

packages/compiler-vapor/src/transforms/vSlot.ts

@@ -248,7 +248,14 @@ function createSlotBlock(
   const block: SlotBlockIRNode = newBlock(slotNode)
   block.props = dir && dir.exp
   const exitBlock = context.enterBlock(block)
-  return [block, exitBlock]
+  context.inSlot = true
+  return [
+    block,
+    () => {
+      context.inSlot = false
+      exitBlock()
+    },
+  ]
 }
 
 function isNonWhitespaceContent(node: TemplateChildNode): boolean {

packages/runtime-core/src/helpers/renderSlot.ts

@@ -81,6 +81,10 @@ export function renderSlot(
   }
   openBlock()
   const validSlotContent = slot && ensureValidVNode(slot(props))
+
+  // handle forwarded vapor slot fallback
+  ensureVaporSlotFallback(validSlotContent, fallback)
+
   const slotKey =
     props.key ||
     // slot content array of a dynamic conditional slot may have a branch
@@ -124,3 +128,20 @@ export function ensureValidVNode(
     ? vnodes
     : null
 }
+
+export function ensureVaporSlotFallback(
+  vnodes: VNodeArrayChildren | null | undefined,
+  fallback?: () => VNodeArrayChildren,
+): void {
+  let vaporSlot: any
+  if (
+    vnodes &&
+    vnodes.length === 1 &&
+    isVNode(vnodes[0]) &&
+    (vaporSlot = vnodes[0].vs)
+  ) {
+    if (!vaporSlot.fallback && fallback) {
+      vaporSlot.fallback = fallback
+    }
+  }
+}

packages/runtime-core/src/index.ts

@@ -558,6 +558,10 @@ export { startMeasure, endMeasure } from './profiling'
  * @internal
  */
 export { initFeatureFlags } from './featureFlags'
+/**
+ * @internal
+ */
+export { ensureVaporSlotFallback } from './helpers/renderSlot'
 /**
  * @internal
  */