From 5d9f418c8950cc8cbedc5272f10440067c9764a0 Mon Sep 17 00:00:00 2001
From: Rex Morgan <rex@rexmorgan.net>
Date: Fri, 19 Jun 2026 20:56:24 -0400
Subject: [PATCH] fix: preserve backslashes in template literal text (issue
 #462)

Backslashes in template literal text are no longer treated as escape
sequences unless they appear as \\ immediately before a {{ expression.
The pattern \\{{ still collapses to a single literal backslash followed
by the evaluated expression (per Handlebars.js spec), but \\ elsewhere
in template text passes through verbatim.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 source/Handlebars.Test/IssueTests.cs          | 42 +++++++++++++++++++
 source/Handlebars/Compiler/Lexer/Tokenizer.cs | 14 ++++++-
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/source/Handlebars.Test/IssueTests.cs b/source/Handlebars.Test/IssueTests.cs
index 31136117..cb8b2a18 100644
--- a/source/Handlebars.Test/IssueTests.cs
+++ b/source/Handlebars.Test/IssueTests.cs
@@ -733,5 +733,47 @@ public void UnrecognisedExpressionThrowsOutOfMemoryException()
 
             Assert.Throws<HandlebarsCompilerException>(()=> Handlebars.Compile(source));
         }
+
+        // Issue: https://github.com/Handlebars-Net/Handlebars.Net/issues/462
+        // Compile replaces \\ (double backslash) with \ (single backslash)
+        [Fact]
+        public void Issue462_DoubleBackslashPreservedInOutput()
+        {
+            var handlebars = Handlebars.Create();
+            // Template contains two backslashes as literal text
+            var compiledTemplate = handlebars.Compile(@"\\");
+            var result = compiledTemplate(null);
+            Assert.Equal(@"\\", result);
+        }
+
+        [Fact]
+        public void Issue462_SingleBackslashPreservedInOutput()
+        {
+            var handlebars = Handlebars.Create();
+            var compiledTemplate = handlebars.Compile(@"\");
+            var result = compiledTemplate(null);
+            Assert.Equal(@"\", result);
+        }
+
+        [Fact]
+        public void Issue462_DoubleBackslashBeforeExpressionStillCollapses()
+        {
+            // \\{{name}} should still produce a single literal backslash followed by the evaluated expression
+            var handlebars = Handlebars.Create();
+            var compiledTemplate = handlebars.Compile(@"\\{{name}}");
+            var result = compiledTemplate(new { name = "World" });
+            Assert.Equal(@"\World", result);
+        }
+
+        [Fact]
+        public void Issue462_DoubleBackslashInMixedTemplate()
+        {
+            // Template with backslashes mixed: \\to preserves both backslashes (not before {{),
+            // but \\{{name}} collapses to single backslash + evaluated expression (spec behavior)
+            var handlebars = Handlebars.Create();
+            var compiledTemplate = handlebars.Compile(@"path\\to\\{{name}}");
+            var result = compiledTemplate(new { name = "file" });
+            Assert.Equal(@"path\\to\file", result);
+        }
     }
 }
\ No newline at end of file
diff --git a/source/Handlebars/Compiler/Lexer/Tokenizer.cs b/source/Handlebars/Compiler/Lexer/Tokenizer.cs
index d0d051c7..1f03b8b0 100644
--- a/source/Handlebars/Compiler/Lexer/Tokenizer.cs
+++ b/source/Handlebars/Compiler/Lexer/Tokenizer.cs
@@ -122,8 +122,18 @@ private static IEnumerable<Token> Parse(ExtendedStringReader source)
                 {
                     if ((char)node == '\\' && (char)source.Peek() == '\\')
                     {
-                        source.Read();
-                        buffer.Append('\\');
+                        source.Read(); // consume second '\'
+                        if ((char)source.Peek() == '{')
+                        {
+                            // \\{{ → single literal backslash followed by evaluated expression
+                            buffer.Append('\\');
+                        }
+                        else
+                        {
+                            // \\ not followed by {{ → preserve both backslashes verbatim
+                            buffer.Append('\\');
+                            buffer.Append('\\');
+                        }
                         node = source.Read();
                     }
                     else if ((char)node == '\\' && (char)source.Peek() == '{')