[indexed-access] Type normalizer support for indexed access

Summary:
Add custom behaviour rather than just piggy-backing off of `$ElementType<...>`. This will be required anyway to support optional indexed access, which does not have a legacy analog.

In the future, we will eliminate `$ElementType<...>` and rename/replace `ElementType` in the code with `IndexedAccessType`, and remove the `is_indexed_access`.

Reviewed By: panagosg7

Differential Revision: D26891740

fbshipit-source-id: 633824572ec619b4f450c07960164a39ae9d108a

src/common/ty/ty.ml

@@ -53,6 +53,10 @@ type t =
   | Utility of utility
   | Mu of int * t
   | CharSet of string
+  | IndexedAccess of {
+      _object: t;
+      index: t;
+    }
 
 and tvar = RVar of int [@@unboxed]
 
@@ -437,15 +441,16 @@ class ['A] comparator_ty =
       | Generic _ -> 14
       | TypeOf _ -> 15
       | Utility _ -> 16
-      | Tup _ -> 17
-      | Arr _ -> 18
-      | Fun _ -> 19
-      | Obj _ -> 20
-      | Inter _ -> 21
-      | Union _ -> 22
-      | Mu _ -> 23
-      | InlineInterface _ -> 24
-      | CharSet _ -> 25
+      | IndexedAccess _ -> 17
+      | Tup _ -> 18
+      | Arr _ -> 19
+      | Fun _ -> 20
+      | Obj _ -> 21
+      | Inter _ -> 22
+      | Union _ -> 23
+      | Mu _ -> 24
+      | InlineInterface _ -> 25
+      | CharSet _ -> 26
 
     method tag_of_decl _ =
       function
@@ -657,7 +662,8 @@ let rec mk_exact ty =
   | Union _
   | Inter _
   | TypeOf _
-  | Utility _ ->
+  | Utility _
+  | IndexedAccess _ ->
     Utility (Exact ty)
 
 let mk_array ~readonly ~literal t =

src/common/ty/ty_debug.ml

@@ -244,6 +244,8 @@ and dump_t ?(depth = 10) t =
         (spf "{ %s %s }" (dump_list (dump_prop ~depth) if_props) dict)
     | TypeOf v -> spf "Typeof (%s)" (builtin_value v)
     | Utility u -> dump_utility ~depth u
+    | IndexedAccess { _object; index } ->
+      spf "IndexedAccess (%s) (%s)" (dump_t ~depth _object) (dump_t ~depth index)
     | Mu (i, t) -> spf "Mu (%d, %s)" i (dump_t ~depth t)
     | CharSet s -> spf "CharSet (%s)" s
 
@@ -317,6 +319,7 @@ let string_of_ctor_t = function
   | InlineInterface _ -> "InlineInterface"
   | TypeOf _ -> "Typeof"
   | Utility _ -> "Utility"
+  | IndexedAccess _ -> "IndexedAccess"
   | Mu _ -> "Mu"
   | CharSet _ -> "CharSet"
 
@@ -398,6 +401,8 @@ let json_of_elt ~strip_root =
           ])
       | TypeOf b -> [("name", json_of_builtin_value b)]
       | Utility u -> json_of_utility u
+      | IndexedAccess { _object; index } ->
+        [("object", json_of_t _object); ("index", json_of_t index)]
       | Mu (i, t) -> [("mu_var", int_ i); ("type", json_of_t t)]
       | CharSet s -> [("literal", JSON_String s)])
   and json_of_tvar (RVar i) = Hh_json.[("id", int_ i)]

src/common/ty/ty_printer.ml

@@ -98,6 +98,8 @@ let layout_of_elt ?(size = 5000) ?(with_comments = true) ~exact_by_default elt =
     | Union (t1, t2, ts) -> type_union ~depth (t1 :: t2 :: ts)
     | Inter (t1, t2, ts) -> type_intersection ~depth (t1 :: t2 :: ts)
     | Utility s -> utility ~depth s
+    | IndexedAccess { _object; index } ->
+      fuse [type_ ~depth _object; Atom "["; type_ ~depth index; Atom "]"]
     | Tup ts ->
       list
         ~wrap:(Atom "[", Atom "]")

src/common/ty/ty_serializer.ml

@@ -100,6 +100,10 @@ let type_ options =
     | Union (t0, t1, ts) as t -> union t (t0, t1, ts)
     | Inter (t0, t1, ts) -> intersection (t0, t1, ts)
     | Utility s -> utility s
+    | IndexedAccess { _object; index } ->
+      let%bind _object = type_ _object in
+      let%map index = type_ index in
+      (Loc.none, T.IndexedAccess { T.IndexedAccess._object; index; comments = None })
     | InlineInterface i -> inline_interface i
     | CharSet s ->
       let id = id_from_string "CharSet" in

src/services/autocomplete/autocompleteService_js.ml

@@ -85,6 +85,7 @@ let lsp_completion_of_type =
   | Arr _
   | TypeOf _
   | Utility _
+  | IndexedAccess _
   | Mu _
   | CharSet _ ->
     Some Lsp.Completion.Variable

src/typing/flow_js.ml

@@ -6865,7 +6865,7 @@ struct
           | PropertyType x ->
             let reason_op = replace_desc_reason (RProperty (Some x)) reason in
             GetPropT (use_op, reason, Named (reason_op, x), tout)
-          | ElementType t -> GetElemT (use_op, reason, t, tout)
+          | ElementType { index_type; _ } -> GetElemT (use_op, reason, index_type, tout)
           | Bind t -> BindT (use_op, reason, mk_boundfunctioncalltype t None [] tout, true)
           | SpreadType (options, todo_rev, head_slice) ->
             Object.(

src/typing/merge_js.ml

@@ -900,12 +900,12 @@ module ContextOptimizer = struct
         | PropertyType s ->
           SigHash.add_name sig_hash s;
           t
-        | ElementType t' ->
-          let t'' = self#type_ cx map_cx t' in
-          if t'' == t' then
+        | ElementType { index_type; is_indexed_access } ->
+          let index_type' = self#type_ cx map_cx index_type in
+          if index_type' == index_type then
             t
           else
-            ElementType t''
+            ElementType { index_type = index_type'; is_indexed_access }
         | Bind t' ->
           let t'' = self#type_ cx map_cx t' in
           if t'' == t' then

src/typing/resolvableTypeJob.ml

@@ -235,7 +235,7 @@ and collect_of_type ?log_unresolved cx acc = function
 and collect_of_destructor ?log_unresolved cx acc = function
   | NonMaybeType -> acc
   | PropertyType _ -> acc
-  | ElementType t -> collect_of_type ?log_unresolved cx acc t
+  | ElementType { index_type; _ } -> collect_of_type ?log_unresolved cx acc index_type
   | Bind t -> collect_of_type ?log_unresolved cx acc t
   | ReadOnlyType -> acc
   | SpreadType (_, ts, head_slice) ->

src/typing/ty_members.ml

@@ -191,6 +191,7 @@ let rec members_of_ty : Ty.t -> Ty.t member_info NameUtils.Map.t * string list =
   | InlineInterface _
   | TypeOf _
   | Utility _
+  | IndexedAccess _
   | Mu _
   | CharSet _ ->
     (NameUtils.Map.empty, [])

src/typing/ty_normalizer.ml

@@ -1741,9 +1741,12 @@ end = struct
       | T.NonMaybeType -> return (Ty.Utility (Ty.NonMaybeType ty))
       | T.ReadOnlyType -> return (Ty.Utility (Ty.ReadOnly ty))
       | T.ValuesType -> return (Ty.Utility (Ty.Values ty))
-      | T.ElementType t' ->
-        let%map ty' = type__ ~env t' in
-        Ty.Utility (Ty.ElementType (ty, ty'))
+      | T.ElementType { index_type; is_indexed_access } ->
+        let%map index_type' = type__ ~env index_type in
+        if is_indexed_access then
+          Ty.IndexedAccess { _object = ty; index = index_type' }
+        else
+          Ty.Utility (Ty.ElementType (ty, index_type'))
       | T.CallType ts ->
         let%map tys = mapM (type__ ~env) ts in
         Ty.Utility (Ty.Call (ty, tys))

src/typing/type.ml

@@ -1290,7 +1290,11 @@ module rec TypeTerm : sig
   and destructor =
     | NonMaybeType
     | PropertyType of name
-    | ElementType of t
+    | ElementType of {
+        index_type: t;
+        (* For type normalizer purposes - in the future ElementType will be removed. *)
+        is_indexed_access: bool;
+      }
     | Bind of t
     | ReadOnlyType
     | SpreadType of

src/typing/type_annotation.ml

@@ -265,7 +265,9 @@ let rec convert cx tparams_map =
             (IndexedTypeAccess { _object = reason_of_t object_type; index = reason_of_t index_type })
         in
         EvalT
-          (object_type, TypeDestructorT (use_op, reason, ElementType index_type), mk_eval_id cx loc)
+          ( object_type,
+            TypeDestructorT (use_op, reason, ElementType { index_type; is_indexed_access = true }),
+            mk_eval_id cx loc )
     in
     ((loc, t), IndexedAccess { IndexedAccess._object; index; comments })
   (* TODO *)
@@ -496,7 +498,13 @@ let rec convert cx tparams_map =
             | ([t; e], targs) ->
               let reason = mk_reason (RType (OrdinaryName "$ElementType")) loc in
               reconstruct_ast
-                (EvalT (t, TypeDestructorT (use_op reason, reason, ElementType e), mk_eval_id cx loc))
+                (EvalT
+                   ( t,
+                     TypeDestructorT
+                       ( use_op reason,
+                         reason,
+                         ElementType { index_type = e; is_indexed_access = false } ),
+                     mk_eval_id cx loc ))
                 targs
             | _ -> assert false)
       (* $NonMaybeType<T> acts as the type T without null and void *)

src/typing/type_asserts.ml

@@ -50,6 +50,7 @@ let check_type_visitor wrap =
       | TypeOf _
       | Generic _
       | Utility _
+      | IndexedAccess _
       | CharSet _
       | InlineInterface _ ->
         ()

src/typing/type_mapper.ml

@@ -518,12 +518,12 @@ class virtual ['a, 'phase] t =
       | NonMaybeType
       | PropertyType _ ->
         t
-      | ElementType t' ->
-        let t'' = self#type_ cx map_cx t' in
-        if t'' == t' then
+      | ElementType { index_type; is_indexed_access } ->
+        let index_type' = self#type_ cx map_cx index_type in
+        if index_type' == index_type then
           t
         else
-          ElementType t''
+          ElementType { index_type = index_type'; is_indexed_access }
       | Bind t' ->
         let t'' = self#type_ cx map_cx t' in
         if t'' == t' then

src/typing/type_sig_merge.ml

@@ -638,7 +638,12 @@ and merge_annot file = function
     let obj = merge file obj in
     let elem = merge file elem in
     let id = Type.Eval.id_of_aloc_id (Context.make_aloc_id file.cx loc) in
-    Type.(EvalT (obj, TypeDestructorT (use_op, reason, Type.ElementType elem), id))
+    Type.(
+      EvalT
+        ( obj,
+          TypeDestructorT
+            (use_op, reason, Type.ElementType { index_type = elem; is_indexed_access = false }),
+          id ))
   | NonMaybeType (loc, t) ->
     let reason = Reason.(mk_reason (RType (OrdinaryName "$NonMaybeType")) loc) in
     let use_op = Type.Op (Type.TypeApplication { type' = reason }) in

src/typing/type_visitor.ml

@@ -206,7 +206,7 @@ class ['a, 'phase] t =
       | ReactElementRefType ->
         acc
       | ReactConfigType default_props -> self#type_ cx pole_TODO acc default_props
-      | ElementType t -> self#type_ cx pole_TODO acc t
+      | ElementType { index_type; _ } -> self#type_ cx pole_TODO acc index_type
       | Bind t -> self#type_ cx pole_TODO acc t
       | SpreadType (_, ts, head_slice) ->
         let acc = self#list (self#object_kit_spread_operand cx) acc ts in

tests/type_at_pos_indexed_access/.flowconfig

@@ -0,0 +1,2 @@
+[options]
+indexed_access=true

tests/type_at_pos_indexed_access/.testconfig

@@ -0,0 +1 @@
+shell: test.sh

tests/type_at_pos_indexed_access/test.js

@@ -0,0 +1,4 @@
+type O = {a: number};
+
+type T = O['a'];
+//   ^

tests/type_at_pos_indexed_access/test.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+queries_in_file "type-at-pos" "test.js"

tests/type_at_pos_indexed_access/type_at_pos_indexed_access.exp

@@ -0,0 +1,5 @@
+test.js:3:6
+Flags:
+type T = O["a"]
+test.js:3:6,3:6
+