model x.foo++ with a new Number Val.write_state

Summary:
This diff fixes duplicate errors we see on things like:

```
//flow
type O = {foo?: number};

declare var o: O;
o.foo++;
```
as mentioned in the previous diff.

These duplicate errors were caused because we were unifying the read of o.foo with the write of o.foo. `o.foo++` always creates a number, so this effectively unified `void | number` with `number`. The reason we unified the reads and writes is because we set the write of `o.foo++` in the env builder at the location of `o.foo`.

Since these operations always produce a number, there is no real reason to record a location and use the env to look it up. Instead we, introduce a new Val.write_state that represents a number. This allows us to avoid the clashing key issue entirely.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D35200715

fbshipit-source-id: 97557c2ab6e0a981a6012392ea673a112ec7ab80

src/analysis/env_builder/__tests__/env_builder_refinement_test.ml

@@ -62,6 +62,7 @@ let print_values refinement_of_id =
     | Global name -> "Global " ^ name
     | Unreachable _ -> "unreachable"
     | Undefined _ -> "undefined"
+    | Number _ -> "number"
     | DeclaredFunction l -> Printf.sprintf "declared function %s" (L.debug_to_string l)
   in
   fun values ->
@@ -4472,13 +4473,13 @@ x.a;
         (2, 4) to (2, 5): (`x`)
       };
       (4, 0) to (4, 3) => {
-        (3, 2) to (3, 5): (some property)
+        number
       };
       (5, 0) to (5, 1) => {
         (2, 4) to (2, 5): (`x`)
       };
       (5, 0) to (5, 3) => {
-        (4, 0) to (4, 3): (some property)
+        number
       }] |}]
 
 let%expect_test "op_assign_heap" =

src/analysis/env_builder/env_api.ml

@@ -44,6 +44,7 @@ module type S = sig
     | Projection of L.t
     | Unreachable of L.t
     | Undefined of L.t Reason.virtual_reason
+    | Number of L.t Reason.virtual_reason
     | DeclaredFunction of L.t
 
   and write_locs = write_loc list
@@ -195,6 +196,7 @@ module Make
     | Projection of L.t
     | Unreachable of L.t
     | Undefined of L.t Reason.virtual_reason
+    | Number of L.t Reason.virtual_reason
     | DeclaredFunction of L.t
 
   and write_locs = write_loc list
@@ -315,6 +317,7 @@ module Make
     | Projection _ -> []
     | Unreachable _ -> []
     | Undefined r -> [Reason.poly_loc_of_reason r]
+    | Number r -> [Reason.poly_loc_of_reason r]
     | DeclaredFunction l -> [l]
 
   let rec refinements_of_write_loc ({ refinement_of_id; _ } as env) write_loc =
@@ -365,6 +368,7 @@ module Make
       | Projection l -> Printf.sprintf "projection at %s" (L.debug_to_string l)
       | Unreachable _ -> "unreachable"
       | Undefined _ -> "undefined"
+      | Number _ -> "number"
       | DeclaredFunction l -> Printf.sprintf "declared function %s" (L.debug_to_string l)
       | Write reason ->
         let loc = Reason.poly_loc_of_reason reason in

src/analysis/env_builder/name_resolver.ml

@@ -159,6 +159,8 @@ module Make
 
     val undefined : L.t virtual_reason -> t
 
+    val number : L.t virtual_reason -> t
+
     val undeclared_class : L.t virtual_reason -> string -> t
 
     val merge : t -> t -> t
@@ -227,6 +229,7 @@ module Make
           val_t: t;
         }
       | Undefined of ALoc.t virtual_reason
+      | Number of ALoc.t virtual_reason
       | DeclaredFunction of ALoc.t
 
     and t = {
@@ -274,6 +277,8 @@ module Make
 
     let undefined r = mk_with_write_state (Undefined r)
 
+    let number r = mk_with_write_state (Number r)
+
     let undeclared_class def name = mk_with_write_state (UndeclaredClass { def; name })
 
     let projection loc = mk_with_write_state @@ Projection loc
@@ -323,6 +328,7 @@ module Make
       match t with
       | Uninitialized _
       | Undefined _
+      | Number _
       | DeclaredFunction _
       | Undeclared _
       | DeclaredButSkipped _
@@ -360,6 +366,7 @@ module Make
       match t with
       | Uninitialized _
       | Undefined _
+      | Number _
       | DeclaredFunction _
       | Undeclared _
       | DeclaredButSkipped _
@@ -396,6 +403,7 @@ module Make
           | Uninitialized l when WriteSet.cardinal vals <= 1 ->
             Env_api.Uninitialized (mk_reason RUninitialized l)
           | Undefined r -> Env_api.Undefined r
+          | Number r -> Env_api.Number r
           | DeclaredFunction l -> Env_api.DeclaredFunction l
           | Undeclared (name, loc)
           | DeclaredButSkipped (name, loc) ->
@@ -431,6 +439,7 @@ module Make
         | Undeclared _ -> []
         | DeclaredButSkipped _ -> []
         | Undefined _ -> []
+        | Number _ -> []
         | DeclaredFunction _ -> []
         | Uninitialized _ -> [v]
         | UndeclaredClass _ -> [v]
@@ -1677,8 +1686,18 @@ module Make
             ignore @@ this#expression argument;
             ignore @@ this#pattern_expression argument;
             let val_reason = mk_reason RSomeProperty loc in
-            let assigned_val = Val.one val_reason in
-            this#assign_member ~update_entry:true member loc assigned_val val_reason
+            let assigned_val = Val.number val_reason in
+            (* We explicitly write a number instead of using the location of the write to avoid
+             * location clashes between the read of the member and the write of the member. If
+             * we don't do this then expressions like o.x++ will attempt to unify the read of o.x
+             * with the write of o.x that happens in that update expression *)
+            (match RefinementKey.lookup_of_member member ~allow_optional:false with
+            | Some lookup ->
+              this#map_val_with_lookup
+                lookup
+                (fun _ -> assigned_val)
+                ~create_val_for_heap:(Some (fun () -> assigned_val))
+            | _ -> ())
           | _ -> (* given 'o()++`, read o *) ignore @@ this#expression argument
         end;
         expr

src/typing/new_env.ml

@@ -234,6 +234,7 @@ module New_env = struct
           | (Env_api.Undefined reason, _)
           | (Env_api.Uninitialized reason, _) ->
             Type.(VoidT.make reason |> with_trust Trust.bogus_trust)
+          | (Env_api.Number reason, _) -> Type.(NumT.make reason |> with_trust Trust.bogus_trust)
           | (Env_api.DeclaredFunction loc, _) -> provider_type_for_def_loc ~intersect:true env loc
           | (Env_api.Undeclared (_name, def_loc), (ForType | ForTypeof)) ->
             Base.Option.value_exn (Loc_env.find_write env def_loc)
@@ -353,6 +354,7 @@ module New_env = struct
       Base.List.exists
         ~f:(function
           | Env_api.With_ALoc.Undefined _ -> true
+          | Env_api.With_ALoc.Number _ -> true
           | Env_api.With_ALoc.DeclaredFunction _ -> true
           | Env_api.With_ALoc.Uninitialized _ -> true
           | Env_api.With_ALoc.UndeclaredClass _ -> true