[enums] Parsing of unknown members (...)

Summary:
This adds parsing support for Flow Enums with unknown members.

The error for using this when the option is not enabled is part of the next diff.

Whether an enum has unknown members is logically part of the enum body, so I've put it as part of this AST node, though this does cause a bit of repetition.

Syntax:

```
enum E {
  A,
  B,
  ...
}
```
The `...` must be last, and cannot have a trialing comma.

Reviewed By: Hans-Halverson

Differential Revision: D24152192

fbshipit-source-id: a7194ae00d3971146e965a35a132fe050f3a06a6

src/parser/enum_parser.ml

@@ -26,6 +26,7 @@ end = struct
   type acc = {
     members: members;
     seen_names: SSet.t;
+    has_unknown_members: bool;
   }
 
   type init =
@@ -38,7 +39,7 @@ end = struct
   let empty_members =
     { boolean_members = []; number_members = []; string_members = []; defaulted_members = [] }
 
-  let empty_acc = { members = empty_members; seen_names = SSet.empty }
+  let empty_acc = { members = empty_members; seen_names = SSet.empty; has_unknown_members = false }
 
   let end_of_member_init env =
     match Peek.token env with
@@ -123,7 +124,7 @@ end = struct
   let is_a_to_z c = c >= 'a' && c <= 'z'
 
   let enum_member ~enum_name ~explicit_type acc env =
-    let { members; seen_names } = acc in
+    let { members; seen_names; _ } = acc in
     let (member_loc, (id, init)) = member_raw env in
     let (id_loc, { Identifier.name = member_name; _ }) = id in
     (* if we parsed an empty name, something has gone wrong and we should abort analysis *)
@@ -184,12 +185,32 @@ end = struct
     match Peek.token env with
     | T_RCURLY
     | T_EOF ->
-      {
-        boolean_members = List.rev acc.members.boolean_members;
-        number_members = List.rev acc.members.number_members;
-        string_members = List.rev acc.members.string_members;
-        defaulted_members = List.rev acc.members.defaulted_members;
-      }
+      ( {
+          boolean_members = List.rev acc.members.boolean_members;
+          number_members = List.rev acc.members.number_members;
+          string_members = List.rev acc.members.string_members;
+          defaulted_members = List.rev acc.members.defaulted_members;
+        },
+        acc.has_unknown_members )
+    | T_ELLIPSIS ->
+      let loc = Peek.loc env in
+      Eat.token env;
+      (match Peek.token env with
+      | T_RCURLY
+      | T_EOF ->
+        ()
+      | T_COMMA ->
+        Expect.token env T_COMMA;
+        let trailing_comma =
+          match Peek.token env with
+          | T_RCURLY
+          | T_EOF ->
+            true
+          | _ -> false
+        in
+        error_at env (loc, Parse_error.EnumInvalidEllipsis { trailing_comma })
+      | _ -> error_at env (loc, Parse_error.EnumInvalidEllipsis { trailing_comma = false }));
+      enum_members ~enum_name ~explicit_type { acc with has_unknown_members = true } env
     | _ ->
       let acc = enum_member ~enum_name ~explicit_type acc env in
       (match Peek.token env with
@@ -202,14 +223,16 @@ end = struct
       | _ -> Expect.token env T_COMMA);
       enum_members ~enum_name ~explicit_type acc env
 
-  let string_body ~env ~enum_name ~is_explicit string_members defaulted_members comments =
+  let string_body
+      ~env ~enum_name ~is_explicit ~has_unknown_members string_members defaulted_members comments =
     let initialized_len = List.length string_members in
     let defaulted_len = List.length defaulted_members in
     let defaulted_body () =
       StringBody
         {
           StringBody.members = StringBody.Defaulted defaulted_members;
           explicitType = is_explicit;
+          has_unknown_members;
           comments;
         }
     in
@@ -218,6 +241,7 @@ end = struct
         {
           StringBody.members = StringBody.Initialized string_members;
           explicitType = is_explicit;
+          has_unknown_members;
           comments;
         }
     in
@@ -272,7 +296,7 @@ end = struct
             []
         in
         Expect.token env T_LCURLY;
-        let members = enum_members ~enum_name ~explicit_type empty_acc env in
+        let (members, has_unknown_members) = enum_members ~enum_name ~explicit_type empty_acc env in
         Expect.token env T_RCURLY;
         let trailing =
           match Peek.token env with
@@ -287,28 +311,45 @@ end = struct
           match explicit_type with
           | Some Enum_common.Boolean ->
             BooleanBody
-              { BooleanBody.members = members.boolean_members; explicitType = true; comments }
+              {
+                BooleanBody.members = members.boolean_members;
+                explicitType = true;
+                has_unknown_members;
+                comments;
+              }
           | Some Enum_common.Number ->
             NumberBody
-              { NumberBody.members = members.number_members; explicitType = true; comments }
+              {
+                NumberBody.members = members.number_members;
+                explicitType = true;
+                has_unknown_members;
+                comments;
+              }
           | Some Enum_common.String ->
             string_body
               ~env
               ~enum_name
               ~is_explicit:true
+              ~has_unknown_members
               members.string_members
               members.defaulted_members
               comments
           | Some Enum_common.Symbol ->
-            SymbolBody { SymbolBody.members = members.defaulted_members; comments }
+            SymbolBody
+              { SymbolBody.members = members.defaulted_members; has_unknown_members; comments }
           | None ->
             let bools_len = List.length members.boolean_members in
             let nums_len = List.length members.number_members in
             let strs_len = List.length members.string_members in
             let defaulted_len = List.length members.defaulted_members in
             let empty () =
               StringBody
-                { StringBody.members = StringBody.Defaulted []; explicitType = false; comments }
+                {
+                  StringBody.members = StringBody.Defaulted [];
+                  explicitType = false;
+                  has_unknown_members;
+                  comments;
+                }
             in
             begin
               match (bools_len, nums_len, strs_len, defaulted_len) with
@@ -318,6 +359,7 @@ end = struct
                   ~env
                   ~enum_name
                   ~is_explicit:false
+                  ~has_unknown_members
                   members.string_members
                   members.defaulted_members
                   comments
@@ -329,7 +371,12 @@ end = struct
                       (loc, Parse_error.EnumBooleanMemberNotInitialized { enum_name; member_name }))
                   members.defaulted_members;
                 BooleanBody
-                  { BooleanBody.members = members.boolean_members; explicitType = false; comments }
+                  {
+                    BooleanBody.members = members.boolean_members;
+                    explicitType = false;
+                    has_unknown_members;
+                    comments;
+                  }
               | (0, _, 0, _) when nums_len >= defaulted_len ->
                 List.iter
                   (fun (loc, { DefaultedMember.id = (_, { Identifier.name = member_name; _ }) }) ->
@@ -338,7 +385,12 @@ end = struct
                       (loc, Parse_error.EnumNumberMemberNotInitialized { enum_name; member_name }))
                   members.defaulted_members;
                 NumberBody
-                  { NumberBody.members = members.number_members; explicitType = false; comments }
+                  {
+                    NumberBody.members = members.number_members;
+                    explicitType = false;
+                    has_unknown_members;
+                    comments;
+                  }
               | _ ->
                 error_at env (name_loc, Parse_error.EnumInconsistentMemberValues { enum_name });
                 empty ()

src/parser/estree_translator.ml

@@ -1032,7 +1032,7 @@ with type t = Impl.t = struct
       let open Statement.EnumDeclaration in
       let enum_body =
         match body with
-        | (loc, BooleanBody { BooleanBody.members; explicitType; comments }) ->
+        | (loc, BooleanBody { BooleanBody.members; explicitType; has_unknown_members; comments }) ->
           node
             ?comments
             "EnumBooleanBody"
@@ -1048,8 +1048,9 @@ with type t = Impl.t = struct
                     node "EnumBooleanMember" loc [("id", identifier id); ("init", bool value)])
                   members );
               ("explicitType", bool explicitType);
+              ("hasUnknownMembers", bool has_unknown_members);
             ]
-        | (loc, NumberBody { NumberBody.members; explicitType; comments }) ->
+        | (loc, NumberBody { NumberBody.members; explicitType; has_unknown_members; comments }) ->
           node
             ?comments
             "EnumNumberBody"
@@ -1064,8 +1065,9 @@ with type t = Impl.t = struct
                       [("id", identifier id); ("init", number_literal init)])
                   members );
               ("explicitType", bool explicitType);
+              ("hasUnknownMembers", bool has_unknown_members);
             ]
-        | (loc, StringBody { StringBody.members; explicitType; comments }) ->
+        | (loc, StringBody { StringBody.members; explicitType; has_unknown_members; comments }) ->
           let members =
             match members with
             | StringBody.Defaulted defaulted_members ->
@@ -1083,8 +1085,12 @@ with type t = Impl.t = struct
             ?comments
             "EnumStringBody"
             loc
-            [("members", array members); ("explicitType", bool explicitType)]
-        | (loc, SymbolBody { SymbolBody.members; comments }) ->
+            [
+              ("members", array members);
+              ("explicitType", bool explicitType);
+              ("hasUnknownMembers", bool has_unknown_members);
+            ]
+        | (loc, SymbolBody { SymbolBody.members; has_unknown_members; comments }) ->
           node
             ?comments
             "EnumSymbolBody"
@@ -1095,6 +1101,7 @@ with type t = Impl.t = struct
                   (fun (loc, { DefaultedMember.id }) ->
                     node "EnumDefaultedMember" loc [("id", identifier id)])
                   members );
+              ("hasUnknownMembers", bool has_unknown_members);
             ]
       in
       node ?comments "EnumDeclaration" loc [("id", identifier id); ("body", enum_body)]

src/parser/flow_ast.ml

@@ -697,6 +697,7 @@ and Statement : sig
       type 'M t = {
         members: ('M BooleanLiteral.t, 'M) InitializedMember.t list;
         explicitType: bool;
+        has_unknown_members: bool;
         comments: ('M, unit) Syntax.t option;
       }
       [@@deriving show]
@@ -706,6 +707,7 @@ and Statement : sig
       type 'M t = {
         members: ('M NumberLiteral.t, 'M) InitializedMember.t list;
         explicitType: bool;
+        has_unknown_members: bool;
         comments: ('M, unit) Syntax.t option;
       }
       [@@deriving show]
@@ -715,6 +717,7 @@ and Statement : sig
       type 'M t = {
         members: ('M StringLiteral.t, 'M) members;
         explicitType: bool;
+        has_unknown_members: bool;
         comments: ('M, unit) Syntax.t option;
       }
 
@@ -727,6 +730,7 @@ and Statement : sig
     module SymbolBody : sig
       type 'M t = {
         members: 'M DefaultedMember.t list;
+        has_unknown_members: bool;
         comments: ('M, unit) Syntax.t option;
       }
       [@@deriving show]

src/parser/flow_ast_mapper.ml

@@ -745,7 +745,7 @@ class ['loc] mapper =
 
     method enum_boolean_body (body : 'loc Ast.Statement.EnumDeclaration.BooleanBody.t) =
       let open Ast.Statement.EnumDeclaration.BooleanBody in
-      let { members; explicitType = _; comments } = body in
+      let { members; explicitType = _; has_unknown_members = _; comments } = body in
       let members' = map_list this#enum_boolean_member members in
       let comments' = this#syntax_opt comments in
       if members == members' && comments == comments' then
@@ -755,7 +755,7 @@ class ['loc] mapper =
 
     method enum_number_body (body : 'loc Ast.Statement.EnumDeclaration.NumberBody.t) =
       let open Ast.Statement.EnumDeclaration.NumberBody in
-      let { members; explicitType = _; comments } = body in
+      let { members; explicitType = _; has_unknown_members = _; comments } = body in
       let members' = map_list this#enum_number_member members in
       let comments' = this#syntax_opt comments in
       if members == members' && comments == comments' then
@@ -765,7 +765,7 @@ class ['loc] mapper =
 
     method enum_string_body (body : 'loc Ast.Statement.EnumDeclaration.StringBody.t) =
       let open Ast.Statement.EnumDeclaration.StringBody in
-      let { members; explicitType = _; comments } = body in
+      let { members; explicitType = _; has_unknown_members = _; comments } = body in
       let members' =
         match members with
         | Defaulted members -> Defaulted (map_list this#enum_defaulted_member members)
@@ -779,13 +779,13 @@ class ['loc] mapper =
 
     method enum_symbol_body (body : 'loc Ast.Statement.EnumDeclaration.SymbolBody.t) =
       let open Ast.Statement.EnumDeclaration.SymbolBody in
-      let { members; comments } = body in
+      let { members; has_unknown_members = _; comments } = body in
       let members' = map_list this#enum_defaulted_member members in
       let comments' = this#syntax_opt comments in
       if members == members' && comments == comments' then
         body
       else
-        { members = members'; comments = comments' }
+        { body with members = members'; comments = comments' }
 
     method enum_defaulted_member (member : 'loc Ast.Statement.EnumDeclaration.DefaultedMember.t) =
       let open Ast.Statement.EnumDeclaration.DefaultedMember in

src/parser/parse_error.ml

@@ -32,6 +32,7 @@ type t =
       member_name: string;
     }
   | EnumInvalidMemberSeparator
+  | EnumInvalidEllipsis of { trailing_comma: bool }
   | EnumNumberMemberNotInitialized of {
       enum_name: string;
       member_name: string;
@@ -231,6 +232,11 @@ module PP = struct
         suggestion
         enum_name
     | EnumInvalidMemberSeparator -> "Enum members are separated with `,`. Replace `;` with `,`."
+    | EnumInvalidEllipsis { trailing_comma } ->
+      if trailing_comma then
+        "The `...` must come at the end of the enum body. Remove the trailing comma."
+      else
+        "The `...` must come after all enum members. Move it to the end of the enum body."
     | EnumNumberMemberNotInitialized { enum_name; member_name } ->
       Printf.sprintf
         "Number enum members need to be initialized, e.g. `%s = 1,` in enum `%s`."