[flow] Singleton types get a with "generalizable" field

Summary:
In the following code under natural inference
```
const x1 = "a";
const o1 = {f: x1};
```
we would like to infer
```
x1: "a" // SingletonStrT("a")
o1: {f:string} // ObjT {f: StrGeneralT}
```

At the same time, an annotated version of this code:
```
const x2: "a" = "a";
const o2 = {f: x2};
```
should yield
```
x2: "a" // SingletonStrT("a")
o2: {f:"a"} // ObjT {f: SingletonStrT("a")}
```
Note the difference between `o1` and `o2`. To enable this behavior we need to be able to distinguish between the two types of `SingletonStrT` that we infer for `x1` and `x2`.

The key difference is whether we should allow a `SingletonStrT` to "generalize" to `StrGeneralT`.

Roughly, a string literal type is generalizable iff it does not originate from an annotation, or a value under `as const`, or `Object.freeze()`.

This diff adds a field `from_annot` to `SingletonStrT`, `SingletonNumT`, etc, and populates it accordingly. This field has no impact yet in typechecking behavior. It will only be used later to inform the generalization process.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D66659579

fbshipit-source-id: 148f2e35de53debc600d17f735dc51cbd771d190

src/typing/annotation_inference.ml

@@ -771,11 +771,11 @@ module rec ConsGen : S = struct
       BoolModuleT.at (loc_of_reason reason)
     (* !x when x is falsy *)
     | (DefT (_, BoolT_UNSOUND false), Annot_NotT reason)
-    | (DefT (_, SingletonBoolT false), Annot_NotT reason)
+    | (DefT (_, SingletonBoolT { value = false; _ }), Annot_NotT reason)
     | (DefT (_, StrT_UNSOUND (_, OrdinaryName "")), Annot_NotT reason)
-    | (DefT (_, SingletonStrT (OrdinaryName "")), Annot_NotT reason)
+    | (DefT (_, SingletonStrT { value = OrdinaryName ""; _ }), Annot_NotT reason)
     | (DefT (_, NumT_UNSOUND (_, (0., _))), Annot_NotT reason)
-    | (DefT (_, SingletonNumT (0., _)), Annot_NotT reason)
+    | (DefT (_, SingletonNumT { value = (0., _); _ }), Annot_NotT reason)
     | (DefT (_, NullT), Annot_NotT reason)
     | (DefT (_, VoidT), Annot_NotT reason) ->
       let reason = replace_desc_reason (RBooleanLit true) reason in
@@ -1152,11 +1152,12 @@ module rec ConsGen : S = struct
     (*****************************)
     | (DefT (reason, NumericStrKeyT (_, s)), _) ->
       elab_t cx (DefT (reason, StrT_UNSOUND (None, OrdinaryName s))) op
-    | (DefT (reason, SingletonStrT key), _) ->
+    | (DefT (reason, SingletonStrT { value = key; _ }), _) ->
       elab_t cx (DefT (reason, StrT_UNSOUND (None, key))) op
-    | (DefT (reason, SingletonNumT lit), _) ->
+    | (DefT (reason, SingletonNumT { value = lit; _ }), _) ->
       elab_t cx (DefT (reason, NumT_UNSOUND (None, lit))) op
-    | (DefT (reason, SingletonBoolT b), _) -> elab_t cx (DefT (reason, BoolT_UNSOUND b)) op
+    | (DefT (reason, SingletonBoolT { value = b; _ }), _) ->
+      elab_t cx (DefT (reason, BoolT_UNSOUND b)) op
     | (NullProtoT reason, _) -> elab_t cx (DefT (reason, NullT)) op
     (********************)
     (* Function Statics *)

src/typing/debug_js.ml

@@ -345,10 +345,12 @@ let rec dump_t_ (depth, tvars) cx t =
           )
         t
     | DefT (_, NumericStrKeyT (_, s)) -> p ~extra:s t
-    | DefT (_, SingletonStrT s) -> p ~extra:(spf "%S" (display_string_of_name s)) t
-    | DefT (_, SingletonNumT (_, s)) -> p ~extra:s t
-    | DefT (_, SingletonBoolT b) -> p ~extra:(spf "%B" b) t
-    | DefT (_, SingletonBigIntT (_, s)) -> p ~extra:s t
+    | DefT (_, SingletonStrT { from_annot; value = s }) ->
+      p ~extra:(spf "%S (from_annot=%b)" (display_string_of_name s) from_annot) t
+    | DefT (_, SingletonNumT { from_annot; value = (_, s) }) ->
+      p ~extra:(s ^ spf " (from_annot=%b)" from_annot) t
+    | DefT (_, SingletonBoolT { value = b; _ }) -> p ~extra:(spf "%B" b) t
+    | DefT (_, SingletonBigIntT { value = (_, s); _ }) -> p ~extra:s t
     | NamespaceT { namespace_symbol; values_type; types_tmap } ->
       p
         t

src/typing/env_resolution.ml

@@ -206,7 +206,10 @@ let resolve_hint cx loc hint =
       UnionT (mk_reason (RCustom "providers") loc, UnionRep.make t1 t2 ts)
     | WriteLocHint (kind, loc) -> Type_env.checked_find_loc_env_write cx kind loc
     | StringLiteralType name ->
-      DefT (mk_reason (RIdentifier (OrdinaryName name)) loc, SingletonStrT (OrdinaryName name))
+      DefT
+        ( mk_reason (RIdentifier (OrdinaryName name)) loc,
+          SingletonStrT { from_annot = true; value = OrdinaryName name }
+        )
     | ReactFragmentType ->
       Flow_js_utils.ImportExportUtils.get_implicitly_imported_react_type
         cx

src/typing/flow_js.ml

@@ -1433,16 +1433,16 @@ struct
           ) ->
           (match (drop_generic key, flags.obj_kind) with
           (* If we have a literal string and that property exists *)
-          | (DefT (_, (StrT_UNSOUND (_, x) | SingletonStrT x)), _) when Context.has_prop cx mapr x
-            ->
+          | (DefT (_, (StrT_UNSOUND (_, x) | SingletonStrT { value = x; _ })), _)
+            when Context.has_prop cx mapr x ->
             ()
           (* If we have a dictionary, try that next *)
           | (_, Indexed { key = expected_key; _ }) ->
             rec_flow_t ~use_op cx trace (mod_reason_of_t (Fun.const reason_op) key, expected_key)
           | _ ->
             let (prop, suggestion) =
               match drop_generic key with
-              | DefT (_, (StrT_UNSOUND (_, prop) | SingletonStrT prop)) ->
+              | DefT (_, (StrT_UNSOUND (_, prop) | SingletonStrT { value = prop; _ })) ->
                 (Some prop, prop_typo_suggestion cx [mapr] (display_string_of_name prop))
               | _ -> (None, None)
             in
@@ -1461,9 +1461,12 @@ struct
             HasOwnPropT
               ( use_op,
                 reason_op,
-                ( ( DefT (_, (StrT_UNSOUND (_, x) | SingletonStrT x))
-                  | GenericT { bound = DefT (_, (StrT_UNSOUND (_, x) | SingletonStrT x)); _ } ) as
-                key
+                ( ( DefT (_, (StrT_UNSOUND (_, x) | SingletonStrT { value = x; _ }))
+                  | GenericT
+                      {
+                        bound = DefT (_, (StrT_UNSOUND (_, x) | SingletonStrT { value = x; _ }));
+                        _;
+                      } ) as key
                 )
               )
           ) ->
@@ -3965,7 +3968,9 @@ struct
               let r = reason_of_t value_t in
               match index with
               | None -> NumModuleT.why r
-              | Some i -> DefT (r, SingletonNumT (float_of_int i, string_of_int i))
+              | Some i ->
+                DefT
+                  (r, SingletonNumT { from_annot = true; value = (float_of_int i, string_of_int i) })
             in
             Slice_utils.mk_mapped_prop_type
               ~use_op
@@ -5268,7 +5273,7 @@ struct
                  suggestion = None;
                }
             )
-        | ( DefT (reason, (NumT_UNSOUND (_, (value, _)) | SingletonNumT (value, _))),
+        | ( DefT (reason, (NumT_UNSOUND (_, (value, _)) | SingletonNumT { value = (value, _); _ })),
             WriteComputedObjPropCheckT { reason_key; _ }
           ) ->
           let kind = Flow_intermediate_error_types.InvalidObjKey.kind_of_num_value value in

src/typing/flow_js_utils.ml

@@ -306,7 +306,7 @@ let ground_subtype = function
     )
     when String.starts_with ~prefix:prefix2 prefix1 ->
     true
-  | ( DefT (_, (StrT_UNSOUND (None, OrdinaryName s) | SingletonStrT (OrdinaryName s))),
+  | ( DefT (_, (StrT_UNSOUND (None, OrdinaryName s) | SingletonStrT { value = OrdinaryName s; _ })),
       UseT (_, StrUtilT { reason = _; op = StrPrefix prefix; remainder = None })
     )
     when String.starts_with ~prefix s ->
@@ -316,7 +316,7 @@ let ground_subtype = function
     )
     when String.ends_with ~suffix:suffix2 suffix1 ->
     true
-  | ( DefT (_, (StrT_UNSOUND (None, OrdinaryName s) | SingletonStrT (OrdinaryName s))),
+  | ( DefT (_, (StrT_UNSOUND (None, OrdinaryName s) | SingletonStrT { value = OrdinaryName s; _ })),
       UseT (_, StrUtilT { reason = _; op = StrSuffix suffix; remainder = None })
     )
     when String.ends_with ~suffix s ->
@@ -1015,7 +1015,7 @@ let obj_key_mirror cx o reason_op =
   in
   let map_field key t =
     let reason = replace_desc_reason (RStringLit key) reason_op in
-    map_t (DefT (reason, SingletonStrT key)) t
+    map_t (DefT (reason, SingletonStrT { from_annot = true; value = key })) t
   in
   let props_tmap =
     Context.find_props cx o.props_tmap
@@ -2699,8 +2699,12 @@ module GetPropT_kit (F : Get_prop_helper_sig) = struct
           add_output cx Error_message.(EInternal (loc, PropRefComputedLiteral));
           F.error_type cx trace reason_op
         | GenericT
-            { bound = DefT (_, (NumT_UNSOUND (_, (value, _)) | SingletonNumT (value, _))); _ }
-        | DefT (_, (NumT_UNSOUND (_, (value, _)) | SingletonNumT (value, _))) ->
+            {
+              bound =
+                DefT (_, (NumT_UNSOUND (_, (value, _)) | SingletonNumT { value = (value, _); _ }));
+              _;
+            }
+        | DefT (_, (NumT_UNSOUND (_, (value, _)) | SingletonNumT { value = (value, _); _ })) ->
           let reason_prop = reason_of_t elem_t in
           let kind = Flow_intermediate_error_types.InvalidObjKey.kind_of_num_value value in
           add_output cx (Error_message.EObjectComputedPropertyAccess (reason_op, reason_prop, kind));
@@ -2749,8 +2753,10 @@ let array_elem_check
   in
   let (can_write_tuple, value, use_op) =
     match l with
-    | DefT (index_reason, (NumT_UNSOUND (_, (float_value, _)) | SingletonNumT (float_value, _))) ->
-    begin
+    | DefT
+        ( index_reason,
+          (NumT_UNSOUND (_, (float_value, _)) | SingletonNumT { value = (float_value, _); _ })
+        ) -> begin
       match elements with
       | None -> (false, elem_t, use_op)
       | Some elements ->
@@ -2843,19 +2849,21 @@ let array_elem_check
   (value, is_tuple, use_op, react_dro)
 
 let propref_for_elem_t = function
-  | OpaqueT (reason, { super_t = Some (DefT (_, SingletonStrT name)); _ })
-  | GenericT { bound = DefT (_, (SingletonStrT name | StrT_UNSOUND (_, name))); reason; _ }
-  | DefT (reason, (SingletonStrT name | StrT_UNSOUND (_, name))) ->
+  | OpaqueT (reason, { super_t = Some (DefT (_, SingletonStrT { value = name; _ })); _ })
+  | GenericT
+      { bound = DefT (_, (SingletonStrT { value = name; _ } | StrT_UNSOUND (_, name))); reason; _ }
+  | DefT (reason, (SingletonStrT { value = name; _ } | StrT_UNSOUND (_, name))) ->
     let reason = replace_desc_reason (RProperty (Some name)) reason in
     mk_named_prop ~reason ~from_indexed_access:true name
-  | OpaqueT (reason_num, { super_t = Some (DefT (_, SingletonNumT (value, raw))); _ })
+  | OpaqueT (reason_num, { super_t = Some (DefT (_, SingletonNumT { value = (value, raw); _ })); _ })
   | GenericT
       {
-        bound = DefT (_, (NumT_UNSOUND (_, (value, raw)) | SingletonNumT (value, raw)));
+        bound =
+          DefT (_, (NumT_UNSOUND (_, (value, raw)) | SingletonNumT { value = (value, raw); _ }));
         reason = reason_num;
         _;
       }
-  | DefT (reason_num, (NumT_UNSOUND (_, (value, raw)) | SingletonNumT (value, raw)))
+  | DefT (reason_num, (NumT_UNSOUND (_, (value, raw)) | SingletonNumT { value = (value, raw); _ }))
     when Js_number.is_float_safe_integer value ->
     let reason = replace_desc_reason (RProperty (Some (OrdinaryName raw))) reason_num in
     let name = OrdinaryName (Dtoa.ecma_string_of_float value) in
@@ -2868,7 +2876,7 @@ let keylist_of_props props reason_op =
       match name with
       | OrdinaryName _ ->
         let reason = replace_desc_new_reason (RStringLit name) reason_op in
-        DefT (reason, SingletonStrT name) :: acc
+        DefT (reason, SingletonStrT { from_annot = true; value = name }) :: acc
       | InternalName _ -> acc)
     props
     []
@@ -2984,9 +2992,9 @@ let flow_unary_arith cx l reason kind =
   | (Minus, DefT (lreason, NumT_UNSOUND (_, lit))) ->
     let (reason, lit) = unary_negate_lit ~annot_loc:(loc_of_reason reason) lreason lit in
     DefT (reason, NumT_UNSOUND (None, lit))
-  | (Minus, DefT (lreason, SingletonNumT lit)) ->
+  | (Minus, DefT (lreason, SingletonNumT { from_annot; value = lit })) ->
     let (reason, lit) = unary_negate_lit ~annot_loc:(loc_of_reason reason) lreason lit in
-    DefT (reason, SingletonNumT lit)
+    DefT (reason, SingletonNumT { from_annot; value = lit })
   | (Minus, DefT (_, NumGeneralT _)) -> l
   | (Minus, DefT (_, BigIntT_UNSOUND (_, (value, raw)))) ->
     let (value, raw) = Flow_ast_utils.negate_bigint_literal (value, raw) in
@@ -3330,7 +3338,7 @@ end = struct
 
   let on_concretized_bad_non_element_normalization normalization_cx = function
     | DefT (invalid_type_reason, BoolT_UNSOUND false)
-    | DefT (invalid_type_reason, SingletonBoolT false)
+    | DefT (invalid_type_reason, SingletonBoolT { value = false; _ })
     | DefT (invalid_type_reason, NullT)
     | DefT (invalid_type_reason, VoidT) ->
       TypeCollector.add normalization_cx.type_collector (AnyT.error normalization_cx.result_reason);
@@ -3373,7 +3381,7 @@ end = struct
              invalid_type_reasons = Nel.one generic_reason;
            }
         )
-    | DefT (reason, SingletonStrT (OrdinaryName "svg")) ->
+    | DefT (reason, SingletonStrT { value = OrdinaryName "svg"; _ }) ->
       TypeCollector.add
         normalization_cx.type_collector
         (DefT (reason, RendersT (InstrinsicRenders "svg")))

src/typing/object_kit.ml

@@ -68,7 +68,7 @@ module Kit (Flow : Flow_common.S) : OBJECT = struct
          (fun (keys, indexers) t ->
            match t with
            | DefT (r, StrT_UNSOUND (_, name))
-           | DefT (r, SingletonStrT name) ->
+           | DefT (r, SingletonStrT { value = name; _ }) ->
              ((name, r) :: keys, indexers)
            | DefT (_, EmptyT) -> (keys, indexers)
            | _ -> (keys, t :: indexers))

src/typing/predicate_kit.ml

@@ -545,16 +545,16 @@ and intersect =
    * handling a few cases here explicitly. *)
   let ground_types_differ t1 t2 =
     match (C.unwrap t1, C.unwrap t2) with
-    | ( DefT (_, (SingletonStrT v1 | StrT_UNSOUND (_, v1))),
-        DefT (_, (SingletonStrT v2 | StrT_UNSOUND (_, v2)))
+    | ( DefT (_, (SingletonStrT { value = v1; _ } | StrT_UNSOUND (_, v1))),
+        DefT (_, (SingletonStrT { value = v2; _ } | StrT_UNSOUND (_, v2)))
       ) ->
       v1 <> v2
-    | ( DefT (_, (SingletonNumT v1 | NumT_UNSOUND (_, v1))),
-        DefT (_, (SingletonNumT v2 | NumT_UNSOUND (_, v2)))
+    | ( DefT (_, (SingletonNumT { value = v1; _ } | NumT_UNSOUND (_, v1))),
+        DefT (_, (SingletonNumT { value = v2; _ } | NumT_UNSOUND (_, v2)))
       ) ->
       v1 <> v2
-    | ( DefT (_, (SingletonBoolT v1 | BoolT_UNSOUND v1)),
-        DefT (_, (SingletonBoolT v2 | BoolT_UNSOUND v2))
+    | ( DefT (_, (SingletonBoolT { value = v1; _ } | BoolT_UNSOUND v1)),
+        DefT (_, (SingletonBoolT { value = v2; _ } | BoolT_UNSOUND v2))
       ) ->
       v1 <> v2
     | (_, _) -> false
@@ -1146,16 +1146,16 @@ and sentinel_prop_test_generic key cx trace result_collector orig_obj =
   in
   let sentinel_of_literal = function
     | DefT (_, StrT_UNSOUND (_, value))
-    | DefT (_, SingletonStrT value) ->
+    | DefT (_, SingletonStrT { value; _ }) ->
       Some UnionEnum.(One (Str value))
     | DefT (_, NumT_UNSOUND (_, value))
-    | DefT (_, SingletonNumT value) ->
+    | DefT (_, SingletonNumT { value; _ }) ->
       Some UnionEnum.(One (Num value))
     | DefT (_, BoolT_UNSOUND value)
-    | DefT (_, SingletonBoolT value) ->
+    | DefT (_, SingletonBoolT { value; _ }) ->
       Some UnionEnum.(One (Bool value))
     | DefT (_, BigIntT_UNSOUND (_, value))
-    | DefT (_, SingletonBigIntT value) ->
+    | DefT (_, SingletonBigIntT { value; _ }) ->
       Some UnionEnum.(One (BigInt value))
     | DefT (_, VoidT) -> Some UnionEnum.(One Void)
     | DefT (_, NullT) -> Some UnionEnum.(One Null)
@@ -1223,10 +1223,10 @@ and concretize_and_run_sentinel_prop_test
              | UnionEnum.One enum ->
                let def =
                  match enum with
-                 | UnionEnum.Str v -> SingletonStrT v
-                 | UnionEnum.Num v -> SingletonNumT v
-                 | UnionEnum.Bool v -> SingletonBoolT v
-                 | UnionEnum.BigInt v -> SingletonBigIntT v
+                 | UnionEnum.Str v -> SingletonStrT { from_annot = true; value = v }
+                 | UnionEnum.Num v -> SingletonNumT { from_annot = true; value = v }
+                 | UnionEnum.Bool v -> SingletonBoolT { from_annot = true; value = v }
+                 | UnionEnum.BigInt v -> SingletonBigIntT { from_annot = true; value = v }
                  | UnionEnum.Void -> VoidT
                  | UnionEnum.Null -> NullT
                in
@@ -1258,10 +1258,10 @@ and concretize_and_run_sentinel_prop_test
                    (fun enum acc ->
                      let def =
                        match enum with
-                       | UnionEnum.Str v -> SingletonStrT v
-                       | UnionEnum.Num v -> SingletonNumT v
-                       | UnionEnum.Bool v -> SingletonBoolT v
-                       | UnionEnum.BigInt v -> SingletonBigIntT v
+                       | UnionEnum.Str v -> SingletonStrT { from_annot = true; value = v }
+                       | UnionEnum.Num v -> SingletonNumT { from_annot = true; value = v }
+                       | UnionEnum.Bool v -> SingletonBoolT { from_annot = true; value = v }
+                       | UnionEnum.BigInt v -> SingletonBigIntT { from_annot = true; value = v }
                        | UnionEnum.Void -> VoidT
                        | UnionEnum.Null -> NullT
                      in
@@ -1311,7 +1311,7 @@ and eq_test cx _trace result_collector (sense, left, right) =
   let expected_loc = loc_of_t right in
   match right with
   | DefT (_, StrT_UNSOUND (_, value))
-  | DefT (_, SingletonStrT value) ->
+  | DefT (_, SingletonStrT { value; _ }) ->
     let filtered =
       if sense then
         Type_filter.string_literal cx expected_loc sense value left
@@ -1320,7 +1320,7 @@ and eq_test cx _trace result_collector (sense, left, right) =
     in
     report_filtering_result_to_predicate_result filtered result_collector
   | DefT (_, NumT_UNSOUND (_, value))
-  | DefT (_, SingletonNumT value) ->
+  | DefT (_, SingletonNumT { value; _ }) ->
     let filtered =
       if sense then
         Type_filter.number_literal cx expected_loc sense value left
@@ -1329,7 +1329,7 @@ and eq_test cx _trace result_collector (sense, left, right) =
     in
     report_filtering_result_to_predicate_result filtered result_collector
   | DefT (_, BoolT_UNSOUND true)
-  | DefT (_, SingletonBoolT true) ->
+  | DefT (_, SingletonBoolT { value = true; _ }) ->
     let filtered =
       if sense then
         Type_filter.true_ cx left
@@ -1338,7 +1338,7 @@ and eq_test cx _trace result_collector (sense, left, right) =
     in
     report_filtering_result_to_predicate_result filtered result_collector
   | DefT (_, BoolT_UNSOUND false)
-  | DefT (_, SingletonBoolT false) ->
+  | DefT (_, SingletonBoolT { value = false; _ }) ->
     let filtered =
       if sense then
         Type_filter.false_ cx left
@@ -1347,7 +1347,7 @@ and eq_test cx _trace result_collector (sense, left, right) =
     in
     report_filtering_result_to_predicate_result filtered result_collector
   | DefT (_, BigIntT_UNSOUND (_, value))
-  | DefT (_, SingletonBigIntT value) ->
+  | DefT (_, SingletonBigIntT { value; _ }) ->
     let filtered =
       if sense then
         Type_filter.bigint_literal cx expected_loc sense value left