Make it an error if a field has the same name as a table.

Change-Id: Ie5a3bb5a3643cd48e1cc75fe170a7b8a7c2cc8ed
Tested: on Linux.

src/idl_parser.cpp

@@ -608,7 +608,7 @@ CheckedError Parser::AddField(StructDef &struct_def, const std::string &name,
 CheckedError Parser::ParseField(StructDef &struct_def) {
   std::string name = attribute_;
 
-  if (name == struct_def.name)
+  if (structs_.Lookup(name))
     return Error("field name can not be the same as table/struct name");
 
   std::vector<std::string> dc = doc_comment_;

tests/test.cpp

@@ -1101,7 +1101,7 @@ void ErrorTest() {
   TestError("table X { Y:[[int]]; }", "nested vector");
   TestError("table X { Y:1; }", "illegal type");
   TestError("table X { Y:int; Y:int; }", "field already");
-  TestError("table X { X:int; }", "same as table");
+  TestError("table Y {} table X { Y:int; }", "same as table");
   TestError("struct X { Y:string; }", "only scalar");
   TestError("struct X { Y:int (deprecated); }", "deprecate");
   TestError("union Z { X } table X { Y:Z; } root_type X; { Y: {}, A:1 }",