fix: Handle backslashes before opening curly braces (#20)

https://linear.app/n8n/issue/PAY-2317

src/ExpressionSplitter.ts

@@ -13,13 +13,17 @@ export interface ExpressionCode {
 
 export type ExpressionChunk = ExpressionCode | ExpressionText;
 
-const OPEN_BRACKET = /(?<escape>\\|)(?<brackets>\{\{)/;
-const CLOSE_BRACKET = /(?<escape>\\|)(?<brackets>\}\})/;
+const OPEN_BRACKET = /(?<brackets>\{\{)/;
+const CLOSE_BRACKET = /(?<brackets>\}\})/;
 
 export const escapeCode = (text: string): string => {
 	return text.replace('\\}}', '}}');
 };
 
+const normalizeBackslashes = (text: string): string => {
+	return text.replace(/\\\\/g, '\\');
+};
+
 export const splitExpression = (expression: string): ExpressionChunk[] => {
 	const chunks: ExpressionChunk[] = [];
 	let searchingFor: 'open' | 'close' = 'open';
@@ -51,16 +55,21 @@ export const splitExpression = (expression: string): ExpressionChunk[] => {
 			}
 			break;
 		}
-		if (res.groups.escape) {
-			buffer += expr.slice(0, res.index + 3);
-			index += res.index + 3;
+
+		const beforeMatch = expr.slice(0, res.index);
+		const backslashCount = beforeMatch.match(/\\*$/)?.[0]?.length ?? 0;
+		const isEscaped = backslashCount % 2 === 1;
+
+		if (isEscaped) {
+			buffer += expr.slice(0, res.index + '{{'.length);
+			index += res.index + '{{'.length;
 		} else {
 			buffer += expr.slice(0, res.index);
 
 			if (searchingFor === 'open') {
 				chunks.push({
 					type: 'text',
-					text: buffer,
+					text: normalizeBackslashes(buffer),
 				});
 				searchingFor = 'close';
 				activeRegex = CLOSE_BRACKET;

test/ExpressionExtension.test.ts → test/ExpressionSplitter.test.ts

@@ -36,12 +36,30 @@ describe('tmpl Expression Parser', () => {
 			]);
 		});
 
-		test('Escaped closinging bracket', () => {
+		test('Escaped closing bracket', () => {
 			expect(splitExpression('test {{ code.test("\\}}") }}')).toEqual([
 				{ type: 'text', text: 'test ' },
 				{ type: 'code', text: ' code.test("}}") ', hasClosingBrackets: true },
 			]);
 		});
+
+		test('Escaped backslashes before double opening curly braces', () => {
+			const expr =
+				'C:\\\\Users\\\\Administrator\\\\Desktop\\\\abc\\\\{{ $json.files[0].fileName }}';
+			const result = splitExpression(expr);
+
+			expect(result).toEqual([
+				{
+					type: 'text',
+					text: 'C:\\Users\\Administrator\\Desktop\\abc\\',
+				},
+				{
+					type: 'code',
+					text: ' $json.files[0].fileName ',
+					hasClosingBrackets: true,
+				},
+			]);
+		});
 	});
 
 	describe('Compatible joining', () => {