fix: preserve comments when parsing JS AST (#609)

* follow esrap implementation

* add test

* Create short-chicken-sell.md

---------

Co-authored-by: Manuel <[email protected]>

Author: eltigerchino

.changeset/short-chicken-sell.md

@@ -0,0 +1,5 @@
+---
+"sv": patch
+---
+
+fix: preserve comments when parsing JS AST

packages/core/tests/utils.ts

@@ -170,3 +170,16 @@ test('integration - simple 2', () => {
 		}"
 	`);
 });
+
+test('integration - preserves comments', () => {
+	const code = dedent`
+	  /** @type {string} */
+    let foo = 'bar';
+    `;
+	const ast = parseScript(code);
+
+	expect(serializeScript(ast, code)).toMatchInlineSnapshot(`
+		"/** @type {string} */
+		let foo = 'bar';"
+	`);
+});

packages/core/tooling/index.ts

@@ -77,22 +77,20 @@ export function parseScript(content: string): TsEstree.Program {
 
 	Walker.walk(ast as TsEstree.Node, null, {
 		_(commentNode, { next }) {
-			let comment = comments.shift();
+			let comment: TsEstree.Comment;
 
-			while (comment && comment.start! < commentNode.start!) {
-				commentNode.leadingComments ??= [];
-				commentNode.leadingComments.push(comment);
-				comment = comments.shift();
+			while (comments[0] && commentNode.start && comments[0].start! < commentNode.start) {
+				comment = comments.shift()!;
+				(commentNode.leadingComments ??= []).push(comment);
 			}
 
 			next();
 
-			comment = comments.shift();
-			if (comment) {
-				const slice = content.slice(commentNode.end, comment.start);
+			if (comments[0]) {
+				const slice = content.slice(commentNode.end, comments[0].start);
 
 				if (/^[,) \t]*$/.test(slice)) {
-					commentNode.trailingComments = [comment];
+					commentNode.trailingComments = [comments.shift()!];
 				}
 			}
 		}