[swift] Fix crash in model when more than two args are passed

Summary: We expected the model for DerivedEnumEquals to expect 2 arguments, but on complex enums this isn't always the case.

Reviewed By: ezgicicek

Differential Revision: D89719686

fbshipit-source-id: 10c6a0dc0a95dc180586a090cb101e80d7aee105

Author: dulmarod

infer/src/pulse/PulseModelsSwift.ml

@@ -117,9 +117,15 @@ let builtins_matcher builtin args : unit -> unit DSL.model_monad =
   | DynamicCall ->
       let arg, args = ProcnameDispatcherBuiltins.expect_at_least_1_arg args builtin_s in
       dynamic_call arg args
-  | DerivedEnumEquals ->
-      let arg1, arg2 = ProcnameDispatcherBuiltins.expect_2_args args builtin_s in
-      derived_enum_equals arg1 arg2
+  | DerivedEnumEquals -> (
+      let arg1, arg2, args = ProcnameDispatcherBuiltins.expect_at_least_2_args args builtin_s in
+      (* we are modelling the case for simple enums where there are two args here, in the case
+         of complex enums there can be more args, but we are not modelling that yet. *)
+      match args with
+      | [] ->
+          derived_enum_equals arg1 arg2
+      | _ ->
+          unknown args )
 
 
 let matchers : matcher list =

infer/tests/codetoanalyze/swift/frontend/student.swift

@@ -266,3 +266,22 @@ func using_enums_with_saturday_ok() {
     let today = Day.saturday
     assert(isWeekend(today) == true)
 }
+
+// Example that shows we do not crash on complex enums
+// We haven't yet checked that we translate correctly the semantics of this code,
+// but it doesn't crash and it doesn't have typechecking errors.
+enum CoverPictureModel: Equatable {
+    case empty
+    case upload(imageName: String)
+}
+class Profile {
+    public private(set) var coverPictureModel: CoverPictureModel = .empty {
+        didSet {
+            guard coverPictureModel != oldValue else { return }
+            updateCollectionViewForItems(["coverPicture"])
+        }
+    }
+    func updateCollectionViewForItems(_ items: [String]) {
+        print("Updating collection view for items: \(items)")
+    }
+}