Don't consider class name for similarity in naming errors

Summary:
When we require a fully qualified label name `FooClass#bar_label`, we should only consider the `#bar_label` text in the similarity calculation.

Previously, we'd suggest `FooClass#unrelated` as a match for `foo`, rather than `FooClass#foo`.

Reviewed By: vsiles

Differential Revision: D39329902

fbshipit-source-id: 15faf0d4f9c928e2b6fa7db40ab87f41847ecb8e

Author: Wilfred

hphp/hack/src/typing/typing.ml

@@ -2065,14 +2065,18 @@ module EnumClassLabelOps = struct
           Cls.consts cls
           |> List.filter ~f:(fun (name, _) ->
                  not (String.equal name SN.Members.mClass))
-          |> List.map ~f:(fun (name, const) ->
-                 ( (if full then
-                     Render.strip_ns enum_name ^ "#" ^ name
-                   else
-                     "#" ^ name),
-                   const.cc_pos ))
         in
-        let most_similar = Env.most_similar label_name consts fst in
+        let most_similar =
+          match Env.most_similar label_name consts fst with
+          | Some (name, const) ->
+            Some
+              ( (if full then
+                  Render.strip_ns enum_name ^ "#" ^ name
+                else
+                  "#" ^ name),
+                const.cc_pos )
+          | None -> None
+        in
         Errors.add_typing_error
           Typing_error.(
             enum

hphp/hack/test/typecheck/enum_class_label/missing_label.php

@@ -0,0 +1,10 @@
+<?hh
+
+enum class VeryLongClassName: mixed {
+  int f = 1;
+  int foobar = 1;
+}
+
+function foo(): void {
+  $x = VeryLongClassName#foobarr;
+}

hphp/hack/test/typecheck/enum_class_label/missing_label.php.exp

@@ -0,0 +1,6 @@
+File "missing_label.php", line 9, characters 8-32:
+Enum class `VeryLongClassName` does not contain a label named `foobarr`. (Typing[4394])
+  File "missing_label.php", line 3, characters 12-28:
+  `VeryLongClassName` is defined here
+  File "missing_label.php", line 5, characters 7-12:
+  Did you mean `VeryLongClassName#foobar`?