fix(language-core): add undefined to first param type of optional model emits (#5171)

Author: KazariEX

Diff for: packages/language-core/lib/codegen/script/scriptSetup.ts

@@ -524,6 +524,9 @@ function* generateModelEmit(
 			const [propName, localName] = getPropAndLocalName(scriptSetup, defineModel);
 			yield `'update:${propName}': [value: `;
 			yield* generateDefinePropType(scriptSetup, propName, localName, defineModel);
+			if (!defineModel.required) {
+				yield ` | undefined`;
+			}
 			yield `]${endOfLine}`;
 		}
 		yield `}${endOfLine}`;

Diff for: test-workspace/tsc/passedFixtures/vue3.4/defineModel/main.vue

@@ -13,12 +13,12 @@ const ScriptSetupExact = defineComponent({
 		g: PropType<string>;
 	},
 	emits: {} as {
-		"update:modelValue": (_:string) => void
-		"update:c": (_:number) => void
-		"update:d": (_:number) => void
-		"update:e": (_:string) => void
-		"update:f": (_:string) => void
-		"update:g": (_:string) => void
+		"update:modelValue": (_: string | undefined) => void
+		"update:c": (_: number) => void
+		"update:d": (_: number | undefined) => void
+		"update:e": (_: string | undefined) => void
+		"update:f": (_: string) => void
+		"update:g": (_: string | undefined) => void
 	},
 	setup() {
 		return {};
@@ -32,11 +32,11 @@ exactType(ScriptSetup, ScriptSetupExact);
 	<ScriptSetup 
 		:c="0"
 		f=""
-		@update:model-value="(x) => exactType(x, {} as string)"
+		@update:model-value="(x) => exactType(x, {} as string | undefined)"
 		@update:c="(x) => exactType(x, {} as number)"
-		@update:d="(x) => exactType(x, {} as number)"
-		@update:e="(x) => exactType(x, {} as string)"
+		@update:d="(x) => exactType(x, {} as number | undefined)"
+		@update:e="(x) => exactType(x, {} as string | undefined)"
 		@update:f="(x) => exactType(x, {} as string)"
-		@update:g="(x) => exactType(x, {} as string)"
+		@update:g="(x) => exactType(x, {} as string | undefined)"
 	/>
 </template>

Diff for: test-workspace/tsc/passedFixtures/vue3/defineModel/main.vue

@@ -13,12 +13,12 @@ const ScriptSetupExact = defineComponent({
 		'g'?: string,
 	},
 	__typeEmits: {} as {
-		'update:modelValue': [modelValue:string];
-		'update:c': [c:number];
-		'update:d': [d:number];
-		'update:e': [e:string];
-		'update:f': [f:string];
-		'update:g': [g:string];
+		'update:modelValue': [modelValue: string | undefined];
+		'update:c': [c: number];
+		'update:d': [d: number | undefined];
+		'update:e': [e: string];
+		'update:f': [f: string | undefined];
+		'update:g': [g: string | undefined];
 	},
 	setup() {
 		return {};
@@ -32,11 +32,11 @@ exactType(ScriptSetup, ScriptSetupExact);
 	<ScriptSetup
 		:c="0"
 		e=""
-		@update:model-value="(x) => exactType(x, {} as string)"
+		@update:model-value="(x) => exactType(x, {} as string | undefined)"
 		@update:c="(x) => exactType(x, {} as number)"
-		@update:d="(x) => exactType(x, {} as number)"
+		@update:d="(x) => exactType(x, {} as number | undefined)"
 		@update:e="(x) => exactType(x, {} as string)"
-		@update:f="(x) => exactType(x, {} as string)"
-		@update:g="(x) => exactType(x, {} as string)"
+		@update:f="(x) => exactType(x, {} as string | undefined)"
+		@update:g="(x) => exactType(x, {} as string | undefined)"
 	/>
 </template>