Move reason construction to inference env

Summary:
When we solve a type variable we record this fact in the provenance of the type letting us keep track of both where the type variable originally came from and the flow of the type through typing.

This diff moves the place where we modify the reason from `Typing_env` to `Typing_inference_env` since `get_type` is the fundamental function in which we are getting solutions for type variables and moving the logic there eliminates the possibility of subtle provenance bugs

Reviewed By: andrewjkennedy

Differential Revision: D63749779

fbshipit-source-id: a7170046f6e21aea8632abc13f51a85120d3d182

Author: Michael Thomas

hphp/hack/src/typing/env/typing_env.ml

@@ -91,23 +91,6 @@ let log_env_change name ?(level = 1) old_env new_env =
 
 let expand_var env r v =
   let (inference_env, ty_solution) = Inf.expand_var env.inference_env r v in
-  (* When we have a concrete solution r, record the flow of that solution as a
-     prefix to the original type variables's reason; when we linearize the
-     path, we should then see the path of the relevant uppper / lower bounds
-     as the prefix for any flow through typing.
-     We don't record the flow when we are pointing at another tyvar on the
-     heap since we would end up with a chain of flows representing unification
-  *)
-  let ty_solution =
-    if
-      (not (is_tyvar ty_solution))
-      && TypecheckerOptions.using_extended_reasons env.genv.tcopt
-    then
-      map_reason ty_solution ~f:(fun solution ->
-          Typing_reason.(solved v ~solution ~in_:r))
-    else
-      ty_solution
-  in
   ({ env with inference_env }, ty_solution)
 
 let fresh_type_reason ?variance env p r =
@@ -268,10 +251,7 @@ let get_type env r var =
 let expand_type env ty =
   match deref ty with
   | (reason, Tvar tvid) -> expand_var env reason tvid
-  | _ ->
-    (* If this expansion was applied to a concrete type, don't modify the
-       reason *)
-    (env, ty)
+  | _ -> (env, ty)
 
 let expand_internal_type env ty =
   match ty with

hphp/hack/src/typing/typing_inference_env.ml

@@ -292,7 +292,7 @@ let add env ?(tyvar_pos = Pos.none) v ty =
   let env = update_tyvar_occurrences env v ty in
   env
 
-let get_type env r v =
+let get_type env reason_in tvid_in =
   let rec get r v aliases =
     let shorten_paths () =
       Tvid.Set.fold (fun v' env -> add env v' (mk (r, Tvar v))) aliases env
@@ -307,6 +307,16 @@ let get_type env r v =
                "Two type variables are aliasing each other!";
         get r v' (Tvid.Set.add v aliases)
       | _ ->
+        (* When we have a concrete solution r, record the flow of that solution as a
+           prefix to the original type variables's reason; when report in an error
+           we should then see the path of the relevant uppper / lower bounds
+           as the prefix for any flow through typing.
+           We don't record the flow when we are pointing at another tyvar on the
+           heap since we would end up with a chain of flows representing unification *)
+        let ty =
+          map_reason ty ~f:(fun solution ->
+              Typing_reason.(solved tvid_in ~solution ~in_:reason_in))
+        in
         let env = shorten_paths () in
         (env, ty)
     end
@@ -315,7 +325,7 @@ let get_type env r v =
       let env = shorten_paths () in
       (env, mk (r, Tvar v))
   in
-  get r v Tvid.Set.empty
+  get reason_in tvid_in Tvid.Set.empty
 
 let create_tyvar_constraints variance =
   let (appears_covariantly, appears_contravariantly) =

hphp/hack/src/typing/typing_reason.ml

@@ -2233,8 +2233,8 @@ let rec to_string : type a. string -> a t_ -> (Pos_or_decl.t * string) list =
           ^ (strip_ns class_name |> Markdown_lite.md_codify)
           ^ " must match exactly (it is invariant)" );
       ]
-  (* If type originated with an unannotated lambda parameter with type variable type,
-   * suggested annotating the lambda parameter. Otherwise defer to original reason. *)
+    (* If type originated with an unannotated lambda parameter with type variable type,
+     * suggested annotating the lambda parameter. Otherwise defer to original reason. *)
   | Lambda_param
       ( _,
         ( From_witness_decl (Solve_fail _)

hphp/hack/test/typecheck/aktuple/unify_error1.php.exp

@@ -2,7 +2,7 @@ ERROR: File "unify_error1.php", line 13, characters 12-16:
 Invalid argument (Typing[4110])
   File "unify_error1.php", line 3, characters 19-21:
   Expected `int`
-  File "unify_error1.php", line 8, characters 14-14:
+  File "unify_error1.php", line 10, characters 14-17:
   But got `num`
 ERROR: File "unify_error1.php", line 13, characters 12-16:
 Invalid argument (Typing[4110])

hphp/hack/test/typecheck/aktuple/unify_error2.php.exp

@@ -2,7 +2,7 @@ ERROR: File "unify_error2.php", line 13, characters 14-18:
 Invalid argument (Typing[4110])
   File "unify_error2.php", line 3, characters 21-25:
   Expected `float`
-  File "unify_error2.php", line 8, characters 14-14:
+  File "unify_error2.php", line 10, characters 14-17:
   But got `num`
 ERROR: File "unify_error2.php", line 13, characters 14-18:
 Invalid argument (Typing[4110])

hphp/hack/test/typecheck/aktuple/unify_error3.php.exp

@@ -2,7 +2,7 @@ ERROR: File "unify_error3.php", line 13, characters 12-16:
 Invalid argument (Typing[4110])
   File "unify_error3.php", line 3, characters 19-21:
   Expected `int`
-  File "unify_error3.php", line 8, characters 14-14:
+  File "unify_error3.php", line 10, characters 14-17:
   But got `num`
 ERROR: File "unify_error3.php", line 13, characters 12-16:
 Invalid argument (Typing[4110])

hphp/hack/test/typecheck/aktuple/unify_ok.php.exp

@@ -8,5 +8,5 @@ ERROR: File "unify_ok.php", line 15, characters 15-19:
 Invalid argument (Typing[4110])
   File "unify_ok.php", line 4, characters 22-27:
   Expected `string`
-  File "unify_ok.php", line 9, characters 14-14:
+  File "unify_ok.php", line 11, characters 14-17:
   But got `num`

hphp/hack/test/typecheck/constraints/classmeth_constraints_bad.php.exp

@@ -1,9 +1,5 @@
 ERROR: File "classmeth_constraints_bad.php", line 11, characters 6-6:
-Invalid argument (Typing[4323])
-  File "classmeth_constraints_bad.php", line 6, characters 34-34:
-  `T` is a constrained type parameter
-  File "classmeth_constraints_bad.php", line 6, characters 39-42:
-  This type constraint is violated
+Invalid argument (Typing[4110])
   File "classmeth_constraints_bad.php", line 6, characters 39-42:
   Expected `Base`
   File "classmeth_constraints_bad.php", line 11, characters 6-6:

hphp/hack/test/typecheck/new_inference/eager_solve/stack_overflow_array.php.exp

@@ -2,55 +2,55 @@ File "stack_overflow_array.php", line 25, characters 3-13:
   dict<int, (bool | dict<string, dict<int, dict<(string | _ | _ | _), (_ | _ | _ | (nonnull & (_ | _)) | dict<nothing, nothing>)>>>)>
 ERROR: File "stack_overflow_array.php", line 15, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<nothing, nothing> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 15, characters 3-24:
 This is not an object of type `KeyedContainer`, this is a bool (Typing[4370])
   File "stack_overflow_array.php", line 12, characters 17-21:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 16, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, ((_ & nonnull) | dict<nothing, nothing>)> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 16, characters 3-28:
 This is not an object of type `KeyedContainer`, this is a bool (Typing[4370])
   File "stack_overflow_array.php", line 12, characters 17-21:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 17, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, dict<int, ((_ & nonnull) | dict<nothing, nothing>)>> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 17, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, dict<int, dict<nothing, nothing>>> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 17, characters 3-33:
 This is not an object of type `KeyedContainer`, this is a bool (Typing[4370])
   File "stack_overflow_array.php", line 12, characters 17-21:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 20, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, dict<int, dict<(string | _), (_ | (_ & nonnull) | dict<nothing, nothing>)>>> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 20, characters 3-24:
 This is not an object of type `KeyedContainer`, this is a bool (Typing[4370])
   File "stack_overflow_array.php", line 12, characters 17-21:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 21, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, ((nonnull & _) | dict<int, dict<(string | _), (_ | (_ & nonnull) | dict<nothing, nothing>)>>)> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 21, characters 3-28:
 This is not an object of type `KeyedContainer`, this is a bool (Typing[4370])
   File "stack_overflow_array.php", line 12, characters 17-21:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 22, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, dict<int, ((_ & nonnull) | dict<(string | _), (_ | (_ & nonnull) | dict<nothing, nothing>)>)>> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 22, characters 3-13:
 This is not an object of type `KeyedContainer`, this is a bool or an object of type dict<string, dict<int, ((dict<_, _> & nonnull) | dict<(string | _), (_ | (_ & nonnull) | dict<nothing, nothing>)>)>> (Typing[4324])
-  File "stack_overflow_array.php", line 12, characters 17-21:
+  File "stack_overflow_array.php", line 14, characters 14-19:
   Definition is here
 ERROR: File "stack_overflow_array.php", line 22, characters 3-33:
 This is not an object of type `KeyedContainer`, this is a bool (Typing[4370])

hphp/hack/test/typecheck/readonly/call.php.exp

@@ -9,4 +9,4 @@ This function is readonly, so it must be marked readonly at declaration time to
 ERROR: File "call.php", line 29, characters 4-12:
 This function is readonly, so it must be marked readonly at declaration time to be called. (Typing[4428])
   File "call.php", line 4, characters 10-27:
-  Did you mean to annotate this typehint as a (readonly function(): void)?
+  Did you mean to declaring this as a `readonly` function?