fix: return ast from compile (#11191)

Svelte 4 does it and language tools assumes it's there
This also uncovered another case of how ridicoulus the old AST was

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

@@ -44,6 +44,7 @@ export function compile(source, options) {
 		const analysis = analyze_component(parsed, source, combined_options);
 
 		const result = transform_component(analysis, source, combined_options);
+		result.ast = to_public_ast(source, parsed, options.modernAst);
 		return result;
 	} catch (e) {
 		if (e instanceof CompileError) {
@@ -121,7 +122,16 @@ 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/legacy.js

@@ -141,29 +141,37 @@ export function convert(source, ast) {
 				};
 
 				if (node.pending) {
-					const first = /** @type {import('#compiler').BaseNode} */ (node.pending.nodes.at(0));
-					const last = /** @type {import('#compiler').BaseNode} */ (node.pending.nodes.at(-1));
+					const first = node.pending.nodes.at(0);
+					const last = node.pending.nodes.at(-1);
 
-					pendingblock.start = first.start;
-					pendingblock.end = last.end;
+					pendingblock.start = first?.start ?? source.indexOf('}', node.expression.end) + 1;
+					pendingblock.end = last?.end ?? pendingblock.start;
 					pendingblock.skip = false;
 				}
 
 				if (node.then) {
-					const first = /** @type {import('#compiler').BaseNode} */ (node.then.nodes.at(0));
-					const last = /** @type {import('#compiler').BaseNode} */ (node.then.nodes.at(-1));
+					const first = node.then.nodes.at(0);
+					const last = node.then.nodes.at(-1);
 
-					thenblock.start = pendingblock.end ?? first.start;
-					thenblock.end = last.end;
+					thenblock.start =
+						pendingblock.end ?? first?.start ?? source.indexOf('}', node.expression.end) + 1;
+					thenblock.end =
+						last?.end ?? source.lastIndexOf('}', pendingblock.end ?? node.expression.end) + 1;
 					thenblock.skip = false;
 				}
 
 				if (node.catch) {
-					const first = /** @type {import('#compiler').BaseNode} */ (node.catch.nodes.at(0));
-					const last = /** @type {import('#compiler').BaseNode} */ (node.catch.nodes.at(-1));
-
-					catchblock.start = thenblock.end ?? pendingblock.end ?? first.start;
-					catchblock.end = last.end;
+					const first = node.catch.nodes.at(0);
+					const last = node.catch.nodes.at(-1);
+
+					catchblock.start =
+						thenblock.end ??
+						pendingblock.end ??
+						first?.start ??
+						source.indexOf('}', node.expression.end) + 1;
+					catchblock.end =
+						last?.end ??
+						source.lastIndexOf('}', thenblock.end ?? pendingblock.end ?? node.expression.end) + 1;
 					catchblock.skip = false;
 				}
 

packages/svelte/src/compiler/phases/3-transform/index.js

@@ -20,7 +20,8 @@ export function transform_component(analysis, source, options) {
 			warnings: transform_warnings(source, options.filename, analysis.warnings),
 			metadata: {
 				runes: analysis.runes
-			}
+			},
+			ast: /** @type {any} */ (null) // set afterwards
 		};
 	}
 
@@ -62,7 +63,8 @@ export function transform_component(analysis, source, options) {
 		warnings: transform_warnings(source, options.filename, analysis.warnings), // TODO apply preprocessor sourcemap
 		metadata: {
 			runes: analysis.runes
-		}
+		},
+		ast: /** @type {any} */ (null) // set afterwards
 	};
 }
 
@@ -80,7 +82,8 @@ export function transform_module(analysis, source, options) {
 			warnings: transform_warnings(source, analysis.name, analysis.warnings),
 			metadata: {
 				runes: true
-			}
+			},
+			ast: /** @type {any} */ (null) // set afterwards
 		};
 	}
 
@@ -105,7 +108,8 @@ export function transform_module(analysis, source, options) {
 		warnings: transform_warnings(source, analysis.name, analysis.warnings),
 		metadata: {
 			runes: true
-		}
+		},
+		ast: /** @type {any} */ (null) // set afterwards
 	};
 }
 

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

@@ -541,6 +541,8 @@ declare module 'svelte/compiler' {
 			 */
 			runes: boolean;
 		};
+		/** The AST */
+		ast: any;
 	}
 
 	interface Warning {
@@ -675,6 +677,13 @@ 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 {
@@ -2476,6 +2485,13 @@ 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 {