wip: disable time-slicing in compat mode

packages/runtime-core/src/createRenderer.ts

@@ -271,29 +271,7 @@ export function createRenderer(options: RendererOptions) {
     const doMount = () => {
       handle.runner = autorun(
         () => {
-          if (handle.prevTree) {
+          if (!handle.prevTree) {
-            // mounted
-            const { prevTree, current } = handle
-            if (__DEV__) {
-              pushWarningContext(current)
-            }
-            const nextTree = (handle.prevTree = current.children = renderFunctionalRoot(
-              current
-            ))
-            queuePostCommitHook(() => {
-              current.el = nextTree.el
-            })
-            patch(
-              prevTree as MountedVNode,
-              nextTree,
-              platformParentNode(current.el),
-              current as MountedVNode,
-              isSVG
-            )
-            if (__DEV__) {
-              popWarningContext()
-            }
-          } else {
             // initial mount
             if (__DEV__) {
               pushWarningContext(vnode)
@@ -308,6 +286,8 @@ export function createRenderer(options: RendererOptions) {
             if (__DEV__) {
               popWarningContext()
             }
+          } else {
+            updateFunctionalComponent(handle, isSVG)
           }
         },
         {
@@ -324,6 +304,30 @@ export function createRenderer(options: RendererOptions) {
     }
   }
 
+  function updateFunctionalComponent(handle: FunctionalHandle, isSVG: boolean) {
+    // mounted
+    const { prevTree, current } = handle
+    if (__DEV__) {
+      pushWarningContext(current)
+    }
+    const nextTree = (handle.prevTree = current.children = renderFunctionalRoot(
+      current
+    ))
+    queuePostCommitHook(() => {
+      current.el = nextTree.el
+    })
+    patch(
+      prevTree as MountedVNode,
+      nextTree,
+      platformParentNode(current.el),
+      current as MountedVNode,
+      isSVG
+    )
+    if (__DEV__) {
+      popWarningContext()
+    }
+  }
+
   function mountText(
     vnode: VNode,
     container: RenderNode | null,

packages/scheduler/src/experimental.ts

@@ -32,7 +32,7 @@ function flushAfterMicroTask() {
 }
 
 // Macrotask for time slicing
-const key = `__vueSchedulerTick`
+const key = `$vueTick`
 
 window.addEventListener(
   'message',
@@ -127,9 +127,11 @@ function flush(): void {
     } else {
       break
     }
-    const now = getNow()
+    if (!__COMPAT__) {
-    if (now - start > frameBudget && job.expiration > now) {
+      const now = getNow()
-      break
+      if (now - start > frameBudget && job.expiration > now) {
+        break
+      }
     }
   }
 
@@ -147,7 +149,7 @@ function flush(): void {
     }
     // some post commit hook triggered more updates...
     if (patchQueue.length > 0) {
-      if (getNow() - start > frameBudget) {
+      if (!__COMPAT__ && getNow() - start > frameBudget) {
         return flushAfterMacroTask()
       } else {
         // not out of budget yet, flush sync
@@ -162,6 +164,8 @@ function flush(): void {
     }
   } else {
     // got more job to do
+    // shouldn't reach here in compat mode, because the patchQueue is
+    // guarunteed to be drained
     flushAfterMacroTask()
   }
 }