Fix error handling in issubclass

Summary: Due to the use of `untype`, we were reporting two errors when issubclass got a first argument that isn't a type. We only need one.

Reviewed By: stroxler

Differential Revision: D68291059

fbshipit-source-id: 9d756ebaf22bc65bcf5cbf7c69d833d398ae4e56

pyre2/pyre2/bin/alt/narrow.rs

@@ -180,8 +180,10 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                     self.distribute_narrow_op_over_tuple(&NarrowOp::IsSubclass, &right, v.range())
                 {
                     self.narrow(ty, &distributed_op)
-                } else if let Some(right) = self.unwrap_class_object_or_error(&right, v.range()) {
-                    Type::type_form(self.intersect(&self.untype(ty.clone(), v.range()), &right))
+                } else if let Some(left) = self.untype_opt(ty.clone(), v.range())
+                    && let Some(right) = self.unwrap_class_object_or_error(&right, v.range())
+                {
+                    Type::type_form(self.intersect(&left, &right))
                 } else {
                     ty.clone()
                 }
@@ -192,8 +194,10 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                     self.distribute_narrow_op_over_tuple(&NarrowOp::IsSubclass, &right, v.range())
                 {
                     self.narrow(ty, &distributed_op.negate())
-                } else if let Some(right) = self.unwrap_class_object_or_error(&right, v.range()) {
-                    Type::type_form(self.subtract(&self.untype(ty.clone(), v.range()), &right))
+                } else if let Some(left) = self.untype_opt(ty.clone(), v.range())
+                    && let Some(right) = self.unwrap_class_object_or_error(&right, v.range())
+                {
+                    Type::type_form(self.subtract(&left, &right))
                 } else {
                     ty.clone()
                 }

pyre2/pyre2/bin/test/narrow.rs

@@ -546,6 +546,15 @@ def f(x: type[B] | type[int]):
     "#,
 );
 
+testcase!(
+    test_issubclass_error,
+    r#"
+def f(x: int):
+    if issubclass(x, int):  # E: EXPECTED int <: type
+        return True
+    "#,
+);
+
 testcase!(
     test_typeguard_instance_method,
     r#"