Fix microsoft/vscode#53159

src/parser/cssParser.ts

@@ -1003,6 +1003,7 @@ export class Parser {
 		node.addChild(this._parseUnknownAtRuleName());
 
 		const isTopLevel = () => curlyDepth === 0 && parensDepth === 0 && bracketsDepth === 0;
+		let curlyLCount = 0;
 		let curlyDepth = 0;
 		let parensDepth = 0;
 		let bracketsDepth = 0;
@@ -1024,10 +1025,22 @@ export class Parser {
 						return this.finish(node);
 					}
 				case TokenType.CurlyL:
+					curlyLCount++;
 					curlyDepth++;
 					break;
 				case TokenType.CurlyR:
 					curlyDepth--;
+					// End of at-rule, consume CurlyR and return node
+					if (curlyLCount > 0 && curlyDepth === 0) {
+						this.consumeToken();
+
+						if (bracketsDepth > 0) {
+							return this.finish(node, ParseError.RightSquareBracketExpected);
+						} else if (parensDepth > 0) {
+							return this.finish(node, ParseError.RightParenthesisExpected);
+						}
+						break done;
+					}
 					if (curlyDepth < 0) {
 						// The property value has been terminated without a semicolon, and
 						// this is the last declaration in the ruleset.

src/test/css/parser.test.ts

@@ -90,6 +90,16 @@ suite('CSS - Parser', () => {
 		assertError('@unknown-rule (foo) { .bar {}', parser, parser._parseStylesheet.bind(parser), ParseError.RightCurlyExpected);
 	});
 
+	test('stylesheet - unknown rules node ends properly. Microsoft/vscode#53159', function () {
+		let parser = new Parser();
+		const node = assertNode('@unknown-rule (foo) {} .foo {}', parser, parser._parseStylesheet.bind(parser));
+
+		const unknownAtRule = node.getChild(0);
+		assert.equal(unknownAtRule.type, nodes.NodeType.UnknownAtRule);
+		assert.equal(unknownAtRule.offset, 0);
+		assert.equal(node.getChild(0).length, 13);
+	});
+
 	test('stylesheet /panic/', function () {
 		let parser = new Parser();
 		assertError('#boo, far } \n.far boo {}', parser, parser._parseStylesheet.bind(parser), ParseError.LeftCurlyExpected);