feat(compiler): warn invalid children for transition and keep-alive

packages/compiler-dom/src/transforms/warnTransitionChildren.ts

@@ -0,0 +1,24 @@
+import { NodeTransform, NodeTypes, ElementTypes } from '@vue/compiler-core'
+import { TRANSITION } from '../runtimeHelpers'
+import { createDOMCompilerError, DOMErrorCodes } from '../errors'
+
+export const warnTransitionChildren: NodeTransform = (node, context) => {
+  if (
+    node.type === NodeTypes.ELEMENT &&
+    node.tagType === ElementTypes.COMPONENT
+  ) {
+    const component = context.isBuiltInComponent(node.tag)
+    if (
+      component === TRANSITION &&
+      (node.children.length > 1 || node.children[0].type === NodeTypes.FOR)
+    ) {
+      context.onError(
+        createDOMCompilerError(DOMErrorCodes.X_TRANSITION_INVALID_CHILDREN, {
+          start: node.children[0].loc.start,
+          end: node.children[node.children.length - 1].loc.end,
+          source: ''
+        })
+      )
+    }
+  }
+}