add Enum::get_members helper

Summary: Before this logic was in the narrowing code, I think it makes more sense to move it into the Enum strict so that it can be reused.

Reviewed By: rchen152

Differential Revision: D68280404

fbshipit-source-id: 589e01c92a92f24d8aea9c87bea4f8d42eeca0fd

pyre2/pyre2/bin/alt/answers.rs

@@ -1039,14 +1039,15 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
     fn subtract_enum_member(&self, cls: &ClassType, name: &Name) -> Type {
         let e = self.get_enum(cls).unwrap();
         self.unions(
-            &cls.class_object()
-                .fields()
-                .iter()
+            &e.get_members()
+                .into_iter()
                 .filter_map(|f| {
-                    if *f == *name {
+                    if let Lit::Enum(box (_, ref member_name)) = f
+                        && *member_name == *name
+                    {
                         None
                     } else {
-                        e.get_member(f).map(Type::Literal)
+                        Some(Type::Literal(f))
                     }
                 })
                 .collect::<Vec<_>>(),

pyre2/pyre2/bin/alt/classes.rs

@@ -143,6 +143,15 @@ impl Enum {
     pub fn class_type(&self) -> &ClassType {
         &self.0
     }
+
+    pub fn get_members(&self) -> SmallSet<Lit> {
+        self.0
+            .class_object()
+            .fields()
+            .iter()
+            .filter_map(|f| self.get_member(f))
+            .collect()
+    }
 }
 
 fn is_unbound_function(ty: &Type) -> bool {