[Sema] Emit diagnostic only once

If the TypeRepr is marked invalid, the function isn't called a second time

Author: JaSpa

lib/Sema/TypeCheckType.cpp

@@ -395,6 +395,7 @@ Type TypeChecker::applyGenericArguments(Type type, SourceLoc loc,
     if (!type->is<ErrorType>())
       diagnose(loc, diag::not_a_generic_type, type)
           .fixItRemove(generic->getAngleBrackets());
+    generic->setInvalid();
     return type;
   }
 

test/Generics/function_decls.swift

@@ -38,7 +38,4 @@ public class A<X> {
 
 protocol P { associatedtype A }
 
-// FIXME: only emit this diagnostic once
-func f12<T : P>(x: T) -> T.A<Int> {}
-// expected-error @-1 {{cannot specialize non-generic type 'T.A'}}
-// expected-error @-2 {{cannot specialize non-generic type 'T.A'}}
+func f12<T : P>(x: T) -> T.A<Int> {} //expected-error{{cannot specialize non-generic type 'T.A'}}{{29-34=}}