Fixed flatc silently accepting non-scalars as default values.

Bug: 17304016
Change-Id: I4873f8ef32fbb2657f15fc53a2c8f767e10f2d96
Tested: on Linux

src/idl_parser.cpp

@@ -364,6 +364,8 @@ void Parser::ParseField(StructDef &struct_def) {
 
   if (token_ == '=') {
     Next();
+    if (!IsScalar(type.base_type))
+      Error("default values currently only supported for scalars");
     ParseSingleValue(field.value);
   }
 

tests/test.cpp

@@ -489,6 +489,7 @@ void ErrorTest() {
   TestError("union X { Y }", "referenced");
   TestError("union Z { X } struct X { Y:int; }", "only tables");
   TestError("table X { Y:[int]; YLength:int; }", "clash");
+  TestError("table X { Y:string = 1; }", "scalar");
 }
 
 // Additional parser testing not covered elsewhere.