Improve the error handling of the Parse method so we can correctly diagnose the issue in the driver.

src/Generator/Driver.cs

@@ -55,8 +55,19 @@ namespace Cxxi
 
             var parser = new Parser(Options);
             parser.HeaderParsed += (file, result) =>
-                Console.WriteLine(result.Success ? "  Parsed '" + file + "'." :
-                                            "  Could not parse '" + file + "'.");
+                {
+                    switch (result.Kind)
+                    {
+                        case ParserResultKind.Success:
+                            Console.WriteLine("  Parsed '{0}'", file);
+                            break;
+                        case ParserResultKind.Error:
+                            Console.WriteLine("  Error parsing '{0}'", file);
+                            break;
+                        case ParserResultKind.FileNotFound:
+                            Console.WriteLine("  File '{0}' was not found", file);
+                            break;
+                    }
 
             parser.ParseHeaders(Options.Headers);
             Library = parser.Library;

src/Parser/Parser.cpp

@@ -13,6 +13,7 @@
 #include <clang/Config/config.h>
 #include <clang/AST/ASTContext.h>
 #include <clang/AST/DeclTemplate.h>
+#include <clang/Lex/DirectoryLookup.h>
 #include <clang/Lex/HeaderSearch.h>
 #include <clang/Lex/PreprocessingRecord.h>
 #include <clang/Frontend/Utils.h>
@@ -1429,7 +1430,7 @@ ParserResult^ Parser::Parse(const std::string& File)
 
     if (File.empty())
     {
-        res->Success = false;
+        res->Kind = ParserResultKind::FileNotFound;
         return res;
     }
 
@@ -1438,6 +1439,15 @@ ParserResult^ Parser::Parse(const std::string& File)
     auto DiagClient = new DiagnosticConsumer();
     C->getDiagnostics().setClient(DiagClient);
 
+    // Check that the file is reachable.
+    const clang::DirectoryLookup *Dir;
+    if (!C->getPreprocessor().getHeaderSearchInfo().LookupFile(File, /*isAngled*/true,
+        nullptr, Dir, nullptr, nullptr, nullptr, nullptr))
+    {
+        res->Kind = ParserResultKind::FileNotFound;
+        return res;
+    }
+
     // Create a virtual file that includes the header. This gets rid of some
     // Clang warnings about parsing an header file as the main file.
 
@@ -1471,13 +1481,13 @@ ParserResult^ Parser::Parse(const std::string& File)
 
     if(DiagClient->getNumErrors() != 0)
     {
-        res->Success = false;
+        res->Kind = ParserResultKind::Error;
         return res;
     }
 
     AST = &C->getASTContext();
     WalkAST();
 
-    res->Success = true;
+    res->Kind = ParserResultKind::Success;
     return res;
  }

src/Parser/Parser.h

@@ -61,6 +61,13 @@ public value struct ParserDiagnostic
     System::String^ Message;
 };
 
+public enum struct ParserResultKind
+{
+    Success,
+    Error,
+    FileNotFound
+};
+
 public ref struct ParserResult
 {
     ParserResult()
@@ -68,7 +75,7 @@ public ref struct ParserResult
         Diagnostics = gcnew List<ParserDiagnostic>(); 
     }
 
-    bool Success;
+    ParserResultKind Kind;
     Cxxi::Library^ Library;
     List<ParserDiagnostic>^ Diagnostics;
 };