From 81db3798101d82d4df2b03e37875b35f13dc1f57 Mon Sep 17 00:00:00 2001
From: Daniel Duan <daniel@duan.ca>
Date: Tue, 30 Dec 2025 23:21:38 -0800
Subject: [PATCH] Defer basic-string escape validation in tokenizer

Stop validating escape sequences while scanning double-quoted strings.
Validation remains in unpacking, reducing work during parsing of large inputs.
---
 Sources/TOMLDecoder/Parsing/Parser.swift | 59 ++----------------------
 1 file changed, 3 insertions(+), 56 deletions(-)

diff --git a/Sources/TOMLDecoder/Parsing/Parser.swift b/Sources/TOMLDecoder/Parsing/Parser.swift
index 64ad65f..7f145b9 100644
--- a/Sources/TOMLDecoder/Parsing/Parser.swift
+++ b/Sources/TOMLDecoder/Parsing/Parser.swift
@@ -253,9 +253,6 @@ struct Parser {
 
                 if ch == CodeUnits.doubleQuote {
                     var i = start + 1
-                    var expectedHexDigit = 0
-                    var localExpectedHexDigit = 0
-                    var localEscape = false
 
                     // 8x unrolling for double-quoted strings
                     while i + 8 <= range.upperBound {
@@ -272,71 +269,21 @@ struct Parser {
 
                     while i < range.upperBound {
                         let ch = bytes[i]
-                        if localEscape {
-                            localEscape = false
-                            if ch == CodeUnits.lowerB || ch == CodeUnits.lowerT
-                                || ch == CodeUnits.lowerN || ch == CodeUnits.lowerF
-                                || ch == CodeUnits.lowerR || ch == CodeUnits.doubleQuote
-                                || ch == CodeUnits.backslash
-                            {
-                                i += 1
-                                continue
-                            }
-
-                            if ch == CodeUnits.lowerU {
-                                localExpectedHexDigit = 4
-                                i += 1
-                                continue
-                            }
-
-                            if ch == CodeUnits.upperU {
-                                localExpectedHexDigit = 8
-                                i += 1
-                                continue
-                            }
-
-                            // Set error flag and break
-                            expectedHexDigit = -1
-                            break
-                        }
-
-                        if localExpectedHexDigit > 0 {
-                            localExpectedHexDigit -= 1
-                            if ch.isHexDigit {
+                        if ch == CodeUnits.backslash {
+                            i += 1
+                            if i < range.upperBound {
                                 i += 1
                                 continue
                             }
-                            // Set error flag and break
-                            expectedHexDigit = -2
                             break
                         }
 
-                        if ch == CodeUnits.backslash {
-                            localEscape = true
-                            i += 1
-                            continue
-                        }
-
-                        if ch == CodeUnits.singleQuote {
-                            i += 1
-                            continue
-                        }
-
                         if ch == CodeUnits.lf || ch == CodeUnits.doubleQuote {
                             break
                         }
                         i += 1
                     }
 
-                    expectedHexDigit = localExpectedHexDigit
-
-                    if expectedHexDigit == -1 {
-                        throw TOMLError(
-                            .syntax(lineNumber: lineNumber, message: "expected escape char"))
-                    }
-                    if expectedHexDigit == -2 {
-                        throw TOMLError(.syntax(lineNumber: lineNumber, message: "expect hex char"))
-                    }
                     if i >= range.upperBound || bytes[i] != CodeUnits.doubleQuote {
                         throw TOMLError(
                             .syntax(lineNumber: lineNumber, message: "unterminated quote"))