fix: return ast from compile

Svelte 4 does it and language tools assumes it's there

Author: dummdidumm

.changeset/poor-hats-design.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: return ast from `compile` (like Svelte 4 does)

packages/svelte/src/compiler/index.js

@@ -44,7 +44,7 @@ export function compile(source, options) {
 		const analysis = analyze_component(parsed, source, combined_options);
 
 		const result = transform_component(analysis, source, combined_options);
-		return result;
+		return { ...result, ast: to_public_ast(source, parsed, options.modernAst) };
 	} catch (e) {
 		if (e instanceof CompileError) {
 			handle_compile_error(e, options.filename, source);
@@ -121,7 +121,16 @@ export function parse(source, options = {}) {
 		throw e;
 	}
 
-	if (options.modern) {
+	return to_public_ast(source, ast, options.modern);
+}
+
+/**
+ * @param {string} source
+ * @param {import('#compiler').Root} ast
+ * @param {boolean | undefined} modern
+ */
+function to_public_ast(source, ast, modern) {
+	if (modern) {
 		// remove things that we don't want to treat as public API
 		return walk(ast, null, {
 			_(node, { next }) {

packages/svelte/src/compiler/types/index.d.ts

@@ -46,6 +46,8 @@ export interface CompileResult {
 		 */
 		runes: boolean;
 	};
+	/** The AST */
+	ast: any;
 }
 
 export interface Warning {
@@ -184,6 +186,13 @@ export interface CompileOptions extends ModuleCompileOptions {
 	 * @default false
 	 */
 	hmr?: boolean;
+	/**
+	 * If `true`, returns the modern version of the AST.
+	 * Will become `true` by default in Svelte 6, and the option will be removed in Svelte 7.
+	 *
+	 * @default false
+	 */
+	modernAst?: boolean;
 }
 
 export interface ModuleCompileOptions {

packages/svelte/types/index.d.ts

@@ -542,6 +542,8 @@ declare module 'svelte/compiler' {
 			 */
 			runes: boolean;
 		};
+		/** The AST */
+		ast: any;
 	}
 
 	interface Warning {
@@ -676,6 +678,13 @@ declare module 'svelte/compiler' {
 		 * @default false
 		 */
 		hmr?: boolean;
+		/**
+		 * If `true`, returns the modern version of the AST.
+		 * Will become `true` by default in Svelte 6, and the option will be removed in Svelte 7.
+		 *
+		 * @default false
+		 */
+		modernAst?: boolean;
 	}
 
 	interface ModuleCompileOptions {
@@ -2477,6 +2486,13 @@ declare module 'svelte/types/compiler/interfaces' {
 		 * @default false
 		 */
 		hmr?: boolean;
+		/**
+		 * If `true`, returns the modern version of the AST.
+		 * Will become `true` by default in Svelte 6, and the option will be removed in Svelte 7.
+		 *
+		 * @default false
+		 */
+		modernAst?: boolean;
 	}
 
 	interface ModuleCompileOptions {