[QoI] Improve diagnostics for unbound generic types (#7178)

Since the type is declared in other modules, we should use Decl instead
of its location.

Author: rintaro

lib/Sema/TypeCheckType.cpp

@@ -707,7 +707,7 @@ static void diagnoseUnboundGenericType(TypeChecker &tc, Type ty,SourceLoc loc) {
         diag.fixItInsertAfter(loc, genericArgsToAdd);
     }
   }
-  tc.diagnose(unbound->getDecl()->getLoc(), diag::generic_type_declared_here,
+  tc.diagnose(unbound->getDecl(), diag::generic_type_declared_here,
               unbound->getDecl()->getName());
 }
 

test/Constraints/generics.swift

@@ -439,3 +439,7 @@ func sr3525_2(t: SR_3525<Int>) {
 func sr3525_3<T>(t: SR_3525<T>) {
   let _ = sr3525_arg_gen(&t) // expected-error {{cannot pass immutable value as inout argument: 't' is a 'let' constant}}
 }
+
+class testStdlibType {
+  let _: Array // expected-error {{reference to generic type 'Array' requires arguments in <...>}} {{15-15=<Any>}}
+}