[flow] Kill UnionRep.specialized_reason

Summary:
I don't think the reason patching here creates any more value. Most of the time, we patch it to be `literal union`, which is probably less helpful than the underlying reasons.

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D56642933

fbshipit-source-id: 37f922037190d2b5ce5feb5729219ef0125328b8

src/typing/speculation_kit.ml

@@ -838,12 +838,7 @@ module Make (Flow : INPUT) : OUTPUT = struct
             cx
             ~trace
             (Error_message.EIncompatibleWithUseOp
-               {
-                 reason_lower = TypeUtil.reason_of_t l;
-                 reason_upper =
-                   UnionRep.specialized_reason ~reason_of_t:TypeUtil.reason_of_t reason_op rep;
-                 use_op;
-               }
+               { reason_lower = TypeUtil.reason_of_t l; reason_upper = reason_op; use_op }
             );
           true
         | DefT (_, ObjT _)
@@ -856,27 +851,26 @@ module Make (Flow : INPUT) : OUTPUT = struct
 
   and shortcut_enum cx trace reason_op use_op l rep =
     let quick_subtype = TypeUtil.quick_subtype in
-    quick_mem_result cx trace reason_op use_op l rep @@ UnionRep.quick_mem_enum ~quick_subtype l rep
+    quick_mem_result cx trace reason_op use_op l @@ UnionRep.quick_mem_enum ~quick_subtype l rep
 
   and shortcut_disjoint_union cx trace reason_op use_op l rep =
     let quick_subtype = TypeUtil.quick_subtype in
-    quick_mem_result cx trace reason_op use_op l rep
+    quick_mem_result cx trace reason_op use_op l
     @@ UnionRep.quick_mem_disjoint_union
          ~quick_subtype
          l
          rep
          ~find_resolved:(Context.find_resolved cx)
          ~find_props:(Context.find_props cx)
 
-  and quick_mem_result cx trace reason_op use_op l rep = function
+  and quick_mem_result cx trace reason_op use_op l = function
     | UnionRep.Yes ->
       (* membership check succeeded *)
       true
     (* Our work here is done, so no need to continue. *)
     | UnionRep.No ->
       (* membership check failed *)
-      let r = UnionRep.specialized_reason ~reason_of_t:TypeUtil.reason_of_t reason_op rep in
-      rec_flow cx trace (l, UseT (use_op, DefT (r, EmptyT)));
+      rec_flow cx trace (l, UseT (use_op, DefT (reason_op, EmptyT)));
       true
     (* Our work here is done, so no need to continue. *)
     | UnionRep.Conditional t ->

src/typing/subtyping_kit.ml

@@ -986,12 +986,7 @@ module Make (Flow : INPUT) : OUTPUT = struct
                  cx
                  ~trace
                  (Error_message.EIncompatibleWithUseOp
-                    {
-                      reason_lower = reason_l;
-                      reason_upper =
-                        UnionRep.specialized_reason ~reason_of_t:TypeUtil.reason_of_t reason_u rep;
-                      use_op;
-                    }
+                    { reason_lower = reason_l; reason_upper = reason_u; use_op }
                  );
              true
            | _ -> false ->

src/typing/type.ml

@@ -2381,9 +2381,6 @@ and UnionRep : sig
   (** build a rep from list of members *)
   val make : ?source_aloc:ALoc.id -> TypeTerm.t -> TypeTerm.t -> TypeTerm.t list -> t
 
-  (** replace reason with specialized desc, if any *)
-  val specialized_reason : reason_of_t:(TypeTerm.t -> reason) -> reason -> t -> reason
-
   (** members in declaration order *)
   val members : t -> TypeTerm.t list
 
@@ -2584,13 +2581,6 @@ end = struct
     else
       rep
 
-  let specialized_reason ~reason_of_t r { specialization; _ } =
-    match !specialization with
-    | Some Empty -> replace_desc_reason REmpty r
-    | Some (Singleton t) -> reason_of_t t
-    | Some (EnumUnion _) -> replace_desc_reason RUnionEnum r
-    | _ -> r
-
   (********** Optimizations **********)
 
   let is_optimized_finally { specialization; _ } = !specialization <> None

tests/bigint/bigint.exp

@@ -344,7 +344,7 @@ Unsupported key in object literal. Only identifier, string literal, and number l
 
 Error --------------------------------------------------------------------------------------------------- unions.js:5:10
 
-Cannot return `x` because number literal `1` [1] is incompatible with literal union [2]. [incompatible-return]
+Cannot return `x` because number literal `1` [1] is incompatible with `bigints` [2]. [incompatible-return]
 
    unions.js:5:10
    5|   return x; // fast path error
@@ -361,7 +361,7 @@ References:
 
 Error --------------------------------------------------------------------------------------------------- unions.js:5:10
 
-Cannot return `x` because number literal `2` [1] is incompatible with literal union [2]. [incompatible-return]
+Cannot return `x` because number literal `2` [1] is incompatible with `bigints` [2]. [incompatible-return]
 
    unions.js:5:10
    5|   return x; // fast path error
@@ -378,7 +378,7 @@ References:
 
 Error --------------------------------------------------------------------------------------------------- unions.js:9:10
 
-Cannot return `x` because bigint literal `1n` [1] is incompatible with literal union [2]. [incompatible-return]
+Cannot return `x` because bigint literal `1n` [1] is incompatible with `nums` [2]. [incompatible-return]
 
    unions.js:9:10
    9|   return x; // fast path error
@@ -395,7 +395,7 @@ References:
 
 Error --------------------------------------------------------------------------------------------------- unions.js:9:10
 
-Cannot return `x` because bigint literal `2n` [1] is incompatible with literal union [2]. [incompatible-return]
+Cannot return `x` because bigint literal `2n` [1] is incompatible with `nums` [2]. [incompatible-return]
 
    unions.js:9:10
    9|   return x; // fast path error

tests/conditional_type/conditional_type.exp

@@ -141,7 +141,7 @@ References:
 
 Error --------------------------------------------------------------------------------------------- distributive.js:26:4
 
-Cannot cast `2` to `one_or_three` because number [1] is incompatible with literal union [2]. [incompatible-cast]
+Cannot cast `2` to `one_or_three` because number [1] is incompatible with union type [2]. [incompatible-cast]
 
    distributive.js:26:4
    26|   (2: one_or_three); // error: 2 ~> 1|3
@@ -155,7 +155,7 @@ References:
 
 Error --------------------------------------------------------------------------------------------- distributive.js:28:4
 
-Cannot cast `4` to `one_or_three` because number [1] is incompatible with literal union [2]. [incompatible-cast]
+Cannot cast `4` to `one_or_three` because number [1] is incompatible with union type [2]. [incompatible-cast]
 
    distributive.js:28:4
    28|   (4: one_or_three); // error: 4 ~> 1|3

tests/dom/dom.exp

@@ -28,8 +28,8 @@ References:
 
 Error ------------------------------------------------------------------------------------------ ClipboardEvent.js:10:45
 
-Cannot call `ClipboardEvent` with `'invalid'` bound to `type` because string [1] is incompatible with literal union [2].
-[incompatible-call]
+Cannot call `ClipboardEvent` with `'invalid'` bound to `type` because string [1] is incompatible with
+`ClipboardEventTypes` [2]. [incompatible-call]
 
    ClipboardEvent.js:10:45
     10|     const invalidEvent = new ClipboardEvent('invalid'); // invalid
@@ -95,7 +95,7 @@ References:
 Error ------------------------------------------------------------------------------------------------- Element.js:14:28
 
 Cannot call `element.scrollIntoView` with object literal bound to `arg` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2] in property `behavior`.
+ - Either string [1] is incompatible with union type [2] in property `behavior`.
  - Or object literal [3] is incompatible with boolean [4].
 
    Element.js:14:28
@@ -117,7 +117,7 @@ References:
 Error ------------------------------------------------------------------------------------------------- Element.js:15:28
 
 Cannot call `element.scrollIntoView` with object literal bound to `arg` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2] in property `block`.
+ - Either string [1] is incompatible with union type [2] in property `block`.
  - Or object literal [3] is incompatible with boolean [4].
 
    Element.js:15:28
@@ -206,7 +206,7 @@ References:
 Error --------------------------------------------------------------------------------------------- HTMLElement.js:22:28
 
 Cannot call `element.scrollIntoView` with object literal bound to `arg` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2] in property `behavior`.
+ - Either string [1] is incompatible with union type [2] in property `behavior`.
  - Or object literal [3] is incompatible with boolean [4].
 
    HTMLElement.js:22:28
@@ -228,7 +228,7 @@ References:
 Error --------------------------------------------------------------------------------------------- HTMLElement.js:23:28
 
 Cannot call `element.scrollIntoView` with object literal bound to `arg` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2] in property `block`.
+ - Either string [1] is incompatible with union type [2] in property `block`.
  - Or object literal [3] is incompatible with boolean [4].
 
    HTMLElement.js:23:28
@@ -536,7 +536,7 @@ References:
 Error ----------------------------------------------------------------------------------------- HTMLInputElement.js:10:8
 
 Cannot call `el.setRangeText` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2].
+ - Either string [1] is incompatible with `SelectionMode` [2].
  - Or number [3] is incompatible with undefined [4].
 
    HTMLInputElement.js:10:8
@@ -1011,7 +1011,7 @@ References:
 Error ---------------------------------------------------------------------------------------------- traversal.js:188:14
 
 Cannot call `document.createNodeIterator` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2] in the return value of property `acceptNode`.
+ - Either string [1] is incompatible with union type [2] in the return value of property `acceptNode`.
  - Or number [3] is incompatible with number literal `133` [4].
 
    traversal.js:188:14
@@ -1387,7 +1387,7 @@ References:
 Error ---------------------------------------------------------------------------------------------- traversal.js:195:14
 
 Cannot call `document.createTreeWalker` because: [incompatible-call]
- - Either string [1] is incompatible with literal union [2] in the return value of property `acceptNode`.
+ - Either string [1] is incompatible with union type [2] in the return value of property `acceptNode`.
  - Or number [3] is incompatible with number literal `133` [4].
 
    traversal.js:195:14

tests/enforce_union_optimized/enforce_union_optimized.exp

@@ -158,7 +158,7 @@ Cannot use type without exactly 1 type argument. [nonpolymorphic-type-app]
 
 Error ---------------------------------------------------------------------------------------------------- import.js:4:1
 
-Cannot cast `3` to `T1` because number [1] is incompatible with literal union [2]. [incompatible-cast]
+Cannot cast `3` to `T1` because number [1] is incompatible with `T1` [2]. [incompatible-cast]
 
    import.js:4:1
    4| 3 as T1; // error 3 ~> 1 | 2

tests/enum_perf/enum_perf.exp

@@ -1,6 +1,6 @@
 Error ----------------------------------------------------------------------------------------------------- yuge.js:23:5
 
-Cannot cast empty string to `ErrorCode` because string [1] is incompatible with literal union [2]. [incompatible-cast]
+Cannot cast empty string to `ErrorCode` because string [1] is incompatible with `ErrorCode` [2]. [incompatible-cast]
 
    yuge.js:23:5
    23|     '' as ErrorCode; // also, error pos omits this line completely

tests/fetch/fetch.exp

@@ -318,7 +318,7 @@ References:
 
 Error -------------------------------------------------------------------------------------------------- request.js:6:35
 
-Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with literal union [2] in property
+Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with `CacheType` [2] in property
 `cache`. This property is invariantly typed. See
 https://flow.org/en/docs/faq/#why-cant-i-pass-a-string-to-a-function-that-takes-a-string-number. [incompatible-call]
 
@@ -337,8 +337,8 @@ References:
 
 Error -------------------------------------------------------------------------------------------------- request.js:6:35
 
-Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with literal union [2] in property
-`credentials`. This property is invariantly typed. See
+Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with `CredentialsType` [2] in
+property `credentials`. This property is invariantly typed. See
 https://flow.org/en/docs/faq/#why-cant-i-pass-a-string-to-a-function-that-takes-a-string-number. [incompatible-call]
 
    request.js:6:35
@@ -451,7 +451,7 @@ References:
 
 Error -------------------------------------------------------------------------------------------------- request.js:6:35
 
-Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with literal union [2] in property
+Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with `ModeType` [2] in property
 `mode`. This property is invariantly typed. See
 https://flow.org/en/docs/faq/#why-cant-i-pass-a-string-to-a-function-that-takes-a-string-number. [incompatible-call]
 
@@ -470,7 +470,7 @@ References:
 
 Error -------------------------------------------------------------------------------------------------- request.js:6:35
 
-Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with literal union [2] in property
+Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with `RedirectType` [2] in property
 `redirect`. This property is invariantly typed. See
 https://flow.org/en/docs/faq/#why-cant-i-pass-a-string-to-a-function-that-takes-a-string-number. [incompatible-call]
 
@@ -508,8 +508,8 @@ References:
 
 Error -------------------------------------------------------------------------------------------------- request.js:6:35
 
-Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with literal union [2] in property
-`referrerPolicy`. This property is invariantly typed. See
+Cannot call `Request` with `c` bound to `init` because undefined [1] is incompatible with `ReferrerPolicyType` [2] in
+property `referrerPolicy`. This property is invariantly typed. See
 https://flow.org/en/docs/faq/#why-cant-i-pass-a-string-to-a-function-that-takes-a-string-number. [incompatible-call]
 
    request.js:6:35
@@ -548,7 +548,7 @@ Error --------------------------------------------------------------------------
 
 Cannot call `h.text().then` because: [incompatible-call]
  - Either `Buffer` [1] is incompatible with string [2] in the first parameter.
- - Or function [3] is incompatible with literal union [4].
+ - Or function [3] is incompatible with union type [4].
 
    request.js:24:10
      24| h.text().then((t: Buffer) => t); // incorrect
@@ -573,7 +573,7 @@ Error --------------------------------------------------------------------------
 
 Cannot call `h.arrayBuffer().then` because: [incompatible-call]
  - Either `ArrayBuffer` [1] is incompatible with `Buffer` [2] in the first parameter.
- - Or function [3] is incompatible with literal union [4].
+ - Or function [3] is incompatible with union type [4].
 
    request.js:26:17
      26| h.arrayBuffer().then((ab: Buffer) => ab); // incorrect
@@ -742,7 +742,7 @@ Error --------------------------------------------------------------------------
 
 Cannot call `h.text().then` because: [incompatible-call]
  - Either `Buffer` [1] is incompatible with string [2] in the first parameter.
- - Or function [3] is incompatible with literal union [4].
+ - Or function [3] is incompatible with union type [4].
 
    response.js:42:10
      42| h.text().then((t: Buffer) => t); // incorrect
@@ -767,7 +767,7 @@ Error --------------------------------------------------------------------------
 
 Cannot call `h.arrayBuffer().then` because: [incompatible-call]
  - Either `ArrayBuffer` [1] is incompatible with `Buffer` [2] in the first parameter.
- - Or function [3] is incompatible with literal union [4].
+ - Or function [3] is incompatible with union type [4].
 
    response.js:44:17
      44| h.arrayBuffer().then((ab: Buffer) => ab); // incorrect

tests/interface/interface.exp

@@ -59,7 +59,7 @@ Multiple indexers are not supported. [unsupported-syntax]
 
 Error -------------------------------------------------------------------------------------------------- indexer.js:40:3
 
-Cannot get `x['xxx']` because string `xxx` [1] is incompatible with literal union [2]. [incompatible-type]
+Cannot get `x['xxx']` because string `xxx` [1] is incompatible with `Keys` [2]. [incompatible-type]
 
    indexer.js:40:3
    40|   x['xxx']; // ERROR
@@ -81,7 +81,7 @@ Cannot assign `1` to `x['a']` because property `a` is not writable. [cannot-writ
 
 Error -------------------------------------------------------------------------------------------------- indexer.js:46:3
 
-Cannot get `x['xxx']` because string `xxx` [1] is incompatible with literal union [2]. [incompatible-type]
+Cannot get `x['xxx']` because string `xxx` [1] is incompatible with `Keys` [2]. [incompatible-type]
 
    indexer.js:46:3
    46|   x['xxx']; // ERROR
@@ -103,7 +103,7 @@ Cannot get `x['a']` because an index signature declaring the expected key / valu
 
 Error -------------------------------------------------------------------------------------------------- indexer.js:52:3
 
-Cannot assign `1` to `x['xxx']` because string `xxx` [1] is incompatible with literal union [2]. [incompatible-type]
+Cannot assign `1` to `x['xxx']` because string `xxx` [1] is incompatible with `Keys` [2]. [incompatible-type]
 
    indexer.js:52:3
    52|   x['xxx'] = 1; // ERROR
@@ -324,7 +324,7 @@ Cannot assign `1` to `x['a']` because property `a` is not writable. [cannot-writ
 
 Error ------------------------------------------------------------------------------------------------- indexer.js:179:5
 
-Cannot get `x[true]` because boolean [1] is incompatible with literal union [2]. [incompatible-type]
+Cannot get `x[true]` because boolean [1] is incompatible with `Keys` [2]. [incompatible-type]
 
    indexer.js:179:5
    179|   x[true]; // ERROR