fix: string escape detection in util.ts

closes #45

Author: cyyynthia

src/util.ts

@@ -36,6 +36,12 @@ export type TomlValue = TomlPrimitive | TomlValue[] | TomlTable
 export type TomlTableWithoutBigInt = { [key: string]: TomlValueWithoutBigInt }
 export type TomlValueWithoutBigInt = Exclude<TomlPrimitive, bigint> | TomlValueWithoutBigInt[] | TomlTableWithoutBigInt
 
+function isEscaped(str: string, ptr: number) {
+	let i = 0
+	while (str[ptr - ++i] === '\\');
+	return --i && (i % 2)
+}
+
 export function indexOfNewline (str: string, start = 0, end = str.length) {
 	let idx = str.indexOf('\n', start)
 	if (str[idx - 1] === '\r') idx--
@@ -102,7 +108,7 @@ export function getStringEnd (str: string, seek: number) {
 
 	seek += target.length - 1
 	do seek = str.indexOf(target, ++seek)
-	while (seek > -1 && first !== "'" && str[seek - 1] === '\\' && (str[seek - 2] !== '\\' || str[seek - 3] === '\\'))
+	while (seek > -1 && first !== "'" && isEscaped(str, seek))
 
 	if (seek > -1) {
 		seek += target.length

test/parse.test.ts

@@ -57,6 +57,15 @@ it('handles escapes in strings', () => {
 	// Reference: https://github.com/squirrelchat/smol-toml/issues/37
 	expect(parse('key = "value \\\\\\" value"')).toStrictEqual({ key: 'value \\" value' })
 	expect(parse('key = "value \\\\\\\\\\" value"')).toStrictEqual({ key: 'value \\\\" value' })
+
+	// Reference: https://github.com/squirrelchat/smol-toml/issues/45
+	expect(parse('key = "\\\\"')).toStrictEqual({ key: '\\' })
+	expect(parse('key = "\\\\\\\\"')).toStrictEqual({ key: '\\\\' })
+	expect(parse('key = "\\\\\\\\\\\\"')).toStrictEqual({ key: '\\\\\\' })
+
+	expect(parse('key = ["\\\\"]')).toStrictEqual({ key: [ '\\' ] })
+	expect(parse('key = ["\\\\\\\\"]')).toStrictEqual({ key: [ '\\\\' ] })
+	expect(parse('key = ["\\\\\\\\\\\\"]')).toStrictEqual({ key: [ '\\\\\\' ] })
 })
 
 it('rejects unspecified values', () => {