fix: preserve backslashes in template literal text (issue #462)

source/Handlebars.Test/IssueTests.cs

@@ -734,6 +734,48 @@ 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);
+        }
+
         // Issue: https://github.com/Handlebars-Net/Handlebars.Net/issues/539
         // Parent context (../) resolves to wrong value inside a custom block helper used within #each
         [Fact]

source/Handlebars/Compiler/Lexer/Tokenizer.cs

@@ -12,7 +12,7 @@
         private static readonly Parser PartialParser = new PartialParser();
         private static readonly Parser BlockWordParser = new BlockWordParser();
         private static readonly Parser BlockParamsParser = new BlockParamsParser();
         //TODO: structure parser
 
         public static IEnumerable<Token> Tokenize(ExtendedStringReader source)
         {
@@ -122,8 +122,18 @@
                 {
                     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() == '{')