Allow declaration files to declare generator functions

src/parser/parser_flow.ml

@@ -481,10 +481,12 @@ end = struct
       match param_list_or_type env with
       | ParamList (rest, params) ->
         Expect.token env T_ARROW;
+        let generator = false in
         let returnType = _type env in
         let end_loc = fst returnType in
         Loc.btwn start_loc end_loc, Type.(Function Function.({
           params;
+          generator;
           returnType;
           rest;
           typeParameters = None;
@@ -496,10 +498,12 @@ end = struct
       let typeParameters = type_parameter_declaration env in
       let rest, params = function_param_list env in
       Expect.token env T_ARROW;
+      let generator = false in
       let returnType = _type env in
       let end_loc = fst returnType in
       Loc.btwn start_loc end_loc, Type.(Function Function.({
         params;
+        generator;
         returnType;
         rest;
         typeParameters;
@@ -510,10 +514,12 @@ end = struct
         let typeParameters = type_parameter_declaration env in
         let rest, params = function_param_list env in
         Expect.token env T_COLON;
+        let generator = false in
         let returnType = _type env in
         let loc = Loc.btwn start_loc (fst returnType) in
         loc, Type.Function.({
           params;
+          generator;
           returnType;
           rest;
           typeParameters;
@@ -2853,7 +2859,9 @@ end = struct
           })) in
 
       let declare_function env start_loc =
+        let async = Declaration.async env in
         Expect.token env T_FUNCTION;
+        let generator = Declaration.generator env async in
         let id = Parse.identifier env in
         let start_sig_loc = Peek.loc env in
         let typeParameters = Type.type_parameter_declaration env in
@@ -2864,6 +2872,7 @@ end = struct
         let loc = Loc.btwn start_sig_loc end_loc in
         let value = loc, Ast.Type.(Function {Function.
           params;
+          generator;
           returnType;
           rest;
           typeParameters;

src/parser/spider_monkey_ast.ml

@@ -125,6 +125,7 @@ and Type : sig
 
     type t = {
       params: Param.t list;
+      generator: bool;
       returnType: Type.t;
       rest: Param.t option;
       typeParameters: Type.ParameterDeclaration.t option;

src/typing/type_inference_js.ml

@@ -771,8 +771,7 @@ let rec convert cx map = Ast.Type.(function
         mk_nominal_type_ cx reason map (c, params)
     )
 
-  (* TODO: unsupported generators *)
-  | loc, Function { Function.params; returnType; rest; typeParameters } ->
+  | loc, Function { Function.params; generator; returnType; rest; typeParameters } ->
     let typeparams, map_ = mk_type_param_declarations cx ~map typeParameters in
     let map = SMap.fold SMap.add map_ map in
 
@@ -797,6 +796,21 @@ let rec convert cx map = Ast.Type.(function
             ((snd name).Ast.Identifier.name) :: rev_pnames
         | None -> rev_tlist, rev_pnames
       ) in
+    let ret = convert cx map returnType in
+    let ret =
+      if generator then
+        let reason = mk_reason "generator type" loc in
+        let yield = Flow_js.mk_tvar cx (prefix_reason "yield of " reason) in
+        let return = Flow_js.mk_tvar cx (prefix_reason "return of " reason) in
+        let next = Flow_js.mk_tvar cx (prefix_reason "next of " reason) in
+        let gt = Flow_js.get_builtin_typeapp
+          cx
+          reason
+          "Generator"
+          [yield; return; next] in
+        Flow_js.flow cx (ret, gt);
+        gt
+      else ret in
     let ft =
       FunT (
         mk_reason "function type" loc,
@@ -806,7 +820,7 @@ let rec convert cx map = Ast.Type.(function
           this_t = Flow_js.mk_tvar cx (mk_reason "this" loc);
           params_tlist = (List.rev rev_params_tlist);
           params_names = Some (List.rev rev_params_names);
-          return_t = convert cx map returnType;
+          return_t = ret;
           closure_t = 0
         })
     in

tests/generators/generators.exp

@@ -27,4 +27,16 @@ generators.js:21:10,11: string
 This type is incompatible with
 generators.js:28:22,28: boolean
 
-Found 6 errors
+generators.js:31:37,42: number
+This type is incompatible with
+generators.js:23:13,18: string
+
+generators.js:31:45,50: string
+This type is incompatible with
+[LIB] core.js:306:37,39: union type
+
+generators.js:33:29,29: number
+This type is incompatible with
+generators.js:31:53,59: boolean
+
+Found 9 errors

tests/generators/generators.js

@@ -27,3 +27,12 @@ if (typeof infer_stmt_next === "undefined") {
 } else {
   (infer_stmt_next : boolean) // error: string ~> boolean
 }
+
+declare function *decl(): Generator<number, string, boolean>;
+for (var x: string of decl()) {} // error: number ~> string
+var decl_next = decl().next(0).value; // error: number ~> boolean
+if (typeof decl_next === "undefined") {
+} else if (typeof decl_next === "number") {
+} else {
+  (decl_next : boolean) // error: string ~> boolean
+}