Fix escaping of the path

Cesium.Parser.Tests/PreprocessorTests/PreprocessorTests.cs

@@ -15,10 +15,11 @@ private static async Task DoTest(string source, Dictionary<string, string>? stan
 
     private static async Task<string> DoPreprocess(string source, Dictionary<string, string>? standardHeaders = null, Dictionary<string, IList<IToken<CPreprocessorTokenType>>>? defines = null)
     {
-        var lexer = new CPreprocessorLexer(source);
+        var filePath = "c:\\a\\b\\c.c";
+        var lexer = new CPreprocessorLexer(filePath, source);
         var includeContext = new IncludeContextMock(standardHeaders ?? new Dictionary<string, string>());
         var definesContext = new InMemoryDefinesContext(defines ?? new Dictionary<string, IList<IToken<CPreprocessorTokenType>>>());
-        var preprocessor = new CPreprocessor(source, lexer, includeContext, definesContext);
+        var preprocessor = new CPreprocessor(filePath, lexer, includeContext, definesContext);
         var result = await preprocessor.ProcessSource();
         return result;
     }
@@ -432,5 +433,11 @@ public Task DoubleHashOperator() => DoTest(
     public Task LineDefine() => DoTest(
 @"
 int x = __LINE__;
+");
+
+    [Fact]
+    public Task FileDefine() => DoTest(
+@"
+char* x = __FILE__;
 ");
 }

Cesium.Parser.Tests/PreprocessorTests/verified/PreprocessorTests.FileDefine.verified.txt

@@ -0,0 +1,2 @@
+
+char* x = "c:\\a\\b\\c.c";

Cesium.Preprocessor/CPreprocessor.cs

@@ -248,7 +248,7 @@ private IEnumerable<IToken<CPreprocessorTokenType>> ReplaceMacro(IToken<CPreproc
             {
                 if (objectMacro.Name == "__FILE__")
                 {
-                    yield return new Token<CPreprocessorTokenType>(token.Range, token.Location, "\"" + token.Location.File?.Path + "\"", PreprocessingToken);
+                    yield return new Token<CPreprocessorTokenType>(token.Range, token.Location, "\"" + token.Location.File?.Path.Replace("\\", "\\\\") + "\"", PreprocessingToken);
                     yield break;
                 }