[flow][refactor] Create a separate use_op for switch test so we don't…

… have to hardcode RCustom description

Summary: Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D56608188

fbshipit-source-id: dfc2f9186e7cd485ca531f88a7f170f5c13da891

src/typing/errors/flow_intermediate_error.ml

@@ -576,6 +576,14 @@ let rec make_intermediate_error :
       | Op (DeleteProperty { prop; lhs }) -> root loc frames lhs (RootCannotDelete (desc prop))
       | Op (RefinementCheck { test; discriminant }) ->
         root loc frames test (RootCannotCheckAgainst { test = desc test; discriminant })
+      | Op (SwitchRefinementCheck { test; discriminant }) ->
+        let root_loc = loc_of_aloc test in
+        root_with_loc_and_specific_loc
+          loc
+          frames
+          root_loc
+          root_loc
+          (RootCannotCheckAgainstSwitchDiscriminant discriminant)
       | Op (MatchingProp { op; obj; key; sentinel_reason }) ->
         root loc frames op (RootCannotCompareWithProperty { sentinel = sentinel_reason; obj; key })
       | Op (EvalMappedType { mapped_type }) ->
@@ -1263,6 +1271,11 @@ let to_printable_error :
     | RootCannotCast { lower; upper } -> [text "Cannot cast "; desc lower; text " to "; desc upper]
     | RootCannotCheckAgainst { test; discriminant } ->
       [text "Invalid check of "; desc test; text " against "; ref discriminant]
+    | RootCannotCheckAgainstSwitchDiscriminant discriminant_loc ->
+      [
+        text "Invalid check of case test against ";
+        hardcoded_string_desc_ref "switch discriminant" discriminant_loc;
+      ]
     | RootCannotCoerce { from; target } ->
       [text "Cannot coerce "; desc from; text " to "; desc target]
     | RootCannotConformToCommonInterface -> [text "Cannot conform to common interface module"]

src/typing/errors/flow_intermediate_error_types.ml

@@ -255,6 +255,7 @@ type 'loc root_message =
       test: 'loc virtual_reason_desc;
       discriminant: 'loc virtual_reason;
     }
+  | RootCannotCheckAgainstSwitchDiscriminant of 'loc
   | RootCannotCoerce of {
       from: 'loc virtual_reason_desc;
       target: 'loc virtual_reason_desc;

src/typing/flow_js.ml

@@ -120,9 +120,9 @@ let strict_equatable_error cond_context (l, r) =
   let comparison_error =
     lazy
       (match cond_context with
-      | Some (SwitchTest { case_test_reason; switch_discriminant_reason }) ->
+      | Some (SwitchTest { case_test_loc; switch_discriminant_loc }) ->
         let use_op =
-          Op (RefinementCheck { test = case_test_reason; discriminant = switch_discriminant_reason })
+          Op (SwitchRefinementCheck { test = case_test_loc; discriminant = switch_discriminant_loc })
         in
         Error_message.EIncompatibleWithUseOp
           { reason_lower = reason_of_t l; reason_upper = reason_of_t r; use_op }
@@ -8976,6 +8976,7 @@ struct
                 true
               | Cast _
               | RefinementCheck _
+              | SwitchRefinementCheck _
               | ClassExtendsCheck _
               | ClassMethodDefinition _
               | ClassImplementsCheck _

src/typing/statement.ml

@@ -1130,14 +1130,13 @@ module Make
                          }
                      )
                    in
-                   let case_test_reason = mk_reason (RCustom "case test") (fst expr) in
-                   let switch_discriminant_reason =
-                     mk_reason (RCustom "switch discriminant") (fst discriminant)
-                   in
                    let (_, fake_ast) =
                      condition
                        cx
-                       ~cond:(SwitchTest { case_test_reason; switch_discriminant_reason })
+                       ~cond:
+                         (SwitchTest
+                            { case_test_loc = fst expr; switch_discriminant_loc = fst discriminant }
+                         )
                        fake
                    in
                    let expr_ast =

src/typing/type.ml

@@ -432,6 +432,10 @@ module rec TypeTerm : sig
         test: 'loc virtual_reason;
         discriminant: 'loc virtual_reason;
       }
+    | SwitchRefinementCheck of {
+        test: 'loc;
+        discriminant: 'loc;
+      }
     | MatchingProp of {
         op: 'loc virtual_reason;
         obj: 'loc virtual_reason;
@@ -1008,8 +1012,8 @@ module rec TypeTerm : sig
 
   and cond_context =
     | SwitchTest of {
-        case_test_reason: reason;
-        switch_discriminant_reason: reason;
+        case_test_loc: ALoc.t;
+        switch_discriminant_loc: ALoc.t;
       }
     | OtherTest
 
@@ -4142,6 +4146,7 @@ let string_of_root_use_op (type a) : a virtual_root_use_op -> string = function
   | SetProperty _ -> "SetProperty"
   | UpdateProperty _ -> "UpdateProperty"
   | RefinementCheck _ -> "RefinementCheck"
+  | SwitchRefinementCheck _ -> "SwitchRefinementCheck"
   | MatchingProp _ -> "MatchingProp"
   | EvalMappedType _ -> "EvalMappedType"
   | TypeGuardIncompatibility _ -> "TypeGuardIncompatibility"

src/typing/typeUtil.ml

@@ -455,6 +455,8 @@ let rec mod_loc_of_virtual_use_op f =
       UpdateProperty { lhs = mod_reason lhs; prop = mod_reason prop }
     | RefinementCheck { test; discriminant } ->
       RefinementCheck { test = mod_reason test; discriminant = mod_reason discriminant }
+    | SwitchRefinementCheck { test; discriminant } ->
+      SwitchRefinementCheck { test = f test; discriminant = f discriminant }
     | MatchingProp { op; obj; key; sentinel_reason } ->
       MatchingProp
         {