fix(language-core): correct type narrowing from script to template (#4689)

Author: KazariEX

packages/language-core/lib/codegen/script/template.ts

@@ -18,18 +18,21 @@ export function* generateTemplate(
 
 	if (!options.vueCompilerOptions.skipTemplateCodegen) {
 		if (isClassComponent) {
-			yield `__VLS_template() {${newLine}`;
+			yield `__VLS_template = (() => {${newLine}`;
 		}
 		else {
-			yield `function __VLS_template() {${newLine}`;
+			yield `const __VLS_template = (() => {${newLine}`;
 		}
 		const templateCodegenCtx = createTemplateCodegenContext(new Set());
+		yield `const __VLS_template_return = () => {${newLine}`;
 		yield* generateCtx(options, isClassComponent);
 		yield* generateTemplateContext(options, templateCodegenCtx);
 		yield* generateExportOptions(options);
 		yield* generateConstNameOption(options);
+		yield `}${endOfLine}`;
 		yield* generateInternalComponent(options, ctx, templateCodegenCtx);
-		yield `}${newLine}`;
+		yield `return __VLS_template_return${endOfLine}`;
+		yield `})()${endOfLine}`;
 	}
 	else {
 		yield `function __VLS_template() {${newLine}`;

packages/tsc/tests/__snapshots__/dts.spec.ts.snap

@@ -656,7 +656,7 @@ export {};
 `;
 
 exports[`vue-tsc-dts > Input: template-slots/component.vue, Output: template-slots/component.vue.d.ts 1`] = `
-"declare function __VLS_template(): {
+"declare const __VLS_template: () => {
     slots: {
         "no-bind"?(_: {}): any;
         default?(_: {
@@ -687,7 +687,7 @@ type __VLS_WithTemplateSlots<T, S> = T & {
 
 exports[`vue-tsc-dts > Input: template-slots/component-define-slots.vue, Output: template-slots/component-define-slots.vue.d.ts 1`] = `
 "import { VNode } from 'vue';
-declare function __VLS_template(): {
+declare const __VLS_template: () => {
     slots: Readonly<{
         default: (props: {
             num: number;
@@ -729,7 +729,7 @@ type __VLS_WithTemplateSlots<T, S> = T & {
 `;
 
 exports[`vue-tsc-dts > Input: template-slots/component-destructuring.vue, Output: template-slots/component-destructuring.vue.d.ts 1`] = `
-"declare function __VLS_template(): {
+"declare const __VLS_template: () => {
     slots: Readonly<{
         bottom: (props: {
             num: number;
@@ -755,7 +755,7 @@ type __VLS_WithTemplateSlots<T, S> = T & {
 `;
 
 exports[`vue-tsc-dts > Input: template-slots/component-no-script.vue, Output: template-slots/component-no-script.vue.d.ts 1`] = `
-"declare function __VLS_template(): {
+"declare const __VLS_template: () => {
     slots: {
         "no-bind"?(_: {}): any;
         default?(_: {

test-workspace/tsc/passedFixtures/vue3/#4391/comp.vue

@@ -0,0 +1,5 @@
+<script lang="ts" setup>
+defineProps<{
+	foo: number;
+}>();
+</script>

test-workspace/tsc/passedFixtures/vue3/#4391/main.vue

@@ -0,0 +1,12 @@
+<script lang="ts" setup>
+import Comp from './comp.vue';
+
+let value!: number | undefined;
+if (!value) {
+	throw new Error('undefined');
+}
+</script>
+
+<template>
+	<Comp :foo="value"></Comp>
+</template>