fix(compiler-sfc): add error handling for defineModel() without variable assignment

packages/compiler-core/src/errors.ts

@@ -90,7 +90,7 @@ export enum ErrorCodes {
   X_V_MODEL_ON_PROPS,
   X_INVALID_EXPRESSION,
   X_KEEP_ALIVE_INVALID_CHILDREN,
-
+  X_DEFINE_MODEL_NO_VARIABLE,
   // generic errors
   X_PREFIX_ID_NOT_SUPPORTED,
   X_MODULE_MODE_NOT_SUPPORTED,
@@ -179,6 +179,7 @@ export const errorMessages: Record<ErrorCodes, string> = {
   [ErrorCodes.X_INVALID_EXPRESSION]: `Error parsing JavaScript expression: `,
   [ErrorCodes.X_KEEP_ALIVE_INVALID_CHILDREN]: `<KeepAlive> expects exactly one child component.`,
   [ErrorCodes.X_VNODE_HOOKS]: `@vnode-* hooks in templates are no longer supported. Use the vue: prefix instead. For example, @vnode-mounted should be changed to @vue:mounted. @vnode-* hooks support has been removed in 3.4.`,
+  [ErrorCodes.X_DEFINE_MODEL_NO_VARIABLE]: `defineModel() must be assigned to a variable. For example: const model = defineModel()`,
 
   // generic errors
   [ErrorCodes.X_PREFIX_ID_NOT_SUPPORTED]: `"prefixIdentifiers" option is not supported in this build of compiler.`,

packages/compiler-sfc/__tests__/compileScript/defineModel.spec.ts

@@ -1,4 +1,4 @@
-import { BindingTypes } from '@vue/compiler-core'
+import { BindingTypes, ErrorCodes, errorMessages } from '@vue/compiler-core'
 import { assertCode, compileSFCScript as compile } from '../utils'
 
 describe('defineModel()', () => {
@@ -269,4 +269,14 @@ describe('defineModel()', () => {
       modelValue: BindingTypes.SETUP_REF,
     })
   })
+
+  test('error when defineModel is not assigned to a variable', () => {
+    expect(() =>
+      compile(`
+        <script setup>
+        defineModel()
+        </script>
+      `),
+    ).toThrow(errorMessages[ErrorCodes.X_DEFINE_MODEL_NO_VARIABLE])
+  })
 })

packages/compiler-sfc/src/script/defineModel.ts

@@ -2,7 +2,12 @@ import type { LVal, Node, TSType } from '@babel/types'
 import type { ScriptCompileContext } from './context'
 import { inferRuntimeType } from './resolveType'
 import { UNKNOWN_TYPE, isCallOf, toRuntimeTypeString } from './utils'
-import { BindingTypes, unwrapTSNode } from '@vue/compiler-dom'
+import {
+  BindingTypes,
+  ErrorCodes,
+  errorMessages,
+  unwrapTSNode,
+} from '@vue/compiler-dom'
 
 export const DEFINE_MODEL = 'defineModel'
 
@@ -22,6 +27,10 @@ export function processDefineModel(
     return false
   }
 
+  if (!declId) {
+    ctx.error(errorMessages[ErrorCodes.X_DEFINE_MODEL_NO_VARIABLE], node)
+  }
+
   ctx.hasDefineModelCall = true
 
   const type =