fix: preserve node locations for better sourcemaps

.changeset/gentle-views-matter.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: preserve node locations for better sourcemaps

packages/svelte/src/compiler/phases/1-parse/index.js

@@ -1,4 +1,6 @@
 /** @import { AST } from '#compiler' */
+/** @import { Location } from 'locate-character' */
+/** @import * as ESTree from 'estree' */
 // @ts-expect-error acorn type definitions are borked in the release we use
 import { isIdentifierStart, isIdentifierChar } from 'acorn';
 import fragment from './state/fragment.js';
@@ -218,31 +220,45 @@ export class Parser {
 		return result;
 	}
 
-	/** @param {any} allow_reserved */
-	read_identifier(allow_reserved = false) {
+	/**
+	 * @returns {ESTree.Identifier & { start: number, end: number, loc: { start: Location, end: Location } }}
+	 */
+	read_identifier() {
 		const start = this.index;
+		let end = start;
+		let name = '';
 
-		let i = this.index;
+		const code = /** @type {number} */ (this.template.codePointAt(this.index));
 
-		const code = /** @type {number} */ (this.template.codePointAt(i));
-		if (!isIdentifierStart(code, true)) return null;
+		if (isIdentifierStart(code, true)) {
+			let i = this.index;
+			end += code <= 0xffff ? 1 : 2;
 
-		i += code <= 0xffff ? 1 : 2;
+			while (end < this.template.length) {
+				const code = /** @type {number} */ (this.template.codePointAt(end));
 
-		while (i < this.template.length) {
-			const code = /** @type {number} */ (this.template.codePointAt(i));
-
-			if (!isIdentifierChar(code, true)) break;
-			i += code <= 0xffff ? 1 : 2;
-		}
+				if (!isIdentifierChar(code, true)) break;
+				end += code <= 0xffff ? 1 : 2;
+			}
 
-		const identifier = this.template.slice(this.index, (this.index = i));
+			name = this.template.slice(start, end);
+			this.index = end;
 
-		if (!allow_reserved && is_reserved(identifier)) {
-			e.unexpected_reserved_word(start, identifier);
+			if (is_reserved(name)) {
+				e.unexpected_reserved_word(start, name);
+			}
 		}
 
-		return identifier;
+		return {
+			type: 'Identifier',
+			name,
+			start,
+			end,
+			loc: {
+				start: state.locator(start),
+				end: state.locator(end)
+			}
+		};
 	}
 
 	/** @param {RegExp} pattern */

packages/svelte/src/compiler/phases/1-parse/read/context.js

@@ -1,11 +1,9 @@
-/** @import { Location } from 'locate-character' */
 /** @import { Pattern } from 'estree' */
 /** @import { Parser } from '../index.js' */
 import { match_bracket } from '../utils/bracket.js';
 import { parse_expression_at } from '../acorn.js';
 import { regex_not_newline_characters } from '../../patterns.js';
 import * as e from '../../../errors.js';
-import { locator } from '../../../state.js';
 
 /**
  * @param {Parser} parser
@@ -15,20 +13,13 @@ export default function read_pattern(parser) {
 	const start = parser.index;
 	let i = parser.index;
 
-	const name = parser.read_identifier();
+	const id = parser.read_identifier();
 
-	if (name !== null) {
+	if (id.name !== '') {
 		const annotation = read_type_annotation(parser);
 
 		return {
-			type: 'Identifier',
-			name,
-			start,
-			loc: {
-				start: /** @type {Location} */ (locator(start)),
-				end: /** @type {Location} */ (locator(parser.index))
-			},
-			end: parser.index,
+			...id,
 			typeAnnotation: annotation
 		};
 	}