Extract is_override_method check

Summary:
Instead of inlining the name of the override decorator
we support directly into typeCheck.ml, let's encode
it in a helper function of the Statement.Define module,
consistent with how we handle other special decorators
like `final`.

Reviewed By: kinto0

Differential Revision: D43055549

fbshipit-source-id: ca34452c739196f4e4f9feede216b88da8cb3ed5

source/analysis/typeCheck.ml

@@ -5347,9 +5347,7 @@ module State (Context : Context) = struct
           errors
       in
       let check_override_decorator errors =
-        let override_decorator_name = "pyre_extensions.override" in
-        let has_override_decorator = StatementDefine.has_decorator define override_decorator_name in
-        if has_override_decorator then
+        if StatementDefine.is_override_method define then
           match define with
           | { Ast.Statement.Define.signature = { parent = Some parent; _ }; _ } -> (
               let possibly_overridden_attribute =

source/ast/statement.ml

@@ -408,6 +408,8 @@ and Define : sig
 
     val is_final_method : t -> bool
 
+    val is_override_method : t -> bool
+
     val is_class_method : t -> bool
 
     val is_class_property : t -> bool
@@ -496,6 +498,8 @@ and Define : sig
 
   val is_final_method : t -> bool
 
+  val is_override_method : t -> bool
+
   val is_class_method : t -> bool
 
   val is_class_property : t -> bool
@@ -661,6 +665,8 @@ end = struct
 
     let is_final_method signature = has_decorator signature "typing.final"
 
+    let is_override_method signature = has_decorator signature "pyre_extensions.override"
+
     let is_dunder_method signature =
       let name = unqualified_name signature in
       String.is_prefix ~prefix:"__" name && String.is_suffix ~suffix:"__" name
@@ -859,6 +865,8 @@ end = struct
 
   let is_final_method { signature; _ } = Signature.is_final_method signature
 
+  let is_override_method { signature; _ } = Signature.is_override_method signature
+
   let is_dunder_method { signature; _ } = Signature.is_dunder_method signature
 
   let is_class_method { signature; _ } = Signature.is_class_method signature

source/ast/statement.mli

@@ -161,6 +161,8 @@ and Define : sig
 
     val is_final_method : t -> bool
 
+    val is_override_method : t -> bool
+
     val is_class_method : t -> bool
 
     val is_class_property : t -> bool
@@ -243,6 +245,8 @@ and Define : sig
 
   val is_final_method : t -> bool
 
+  val is_override_method : t -> bool
+
   val is_class_method : t -> bool
 
   val is_class_property : t -> bool