[ConstraintSystem] Move SK_MissingSynthesizableConformance before SK_UnappliedFunction

This would make sure that if property is non-Sendable we'd pick
a method if it's Sendable instead.

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -978,6 +978,10 @@ enum ScoreKind: unsigned int {
   SK_ValueToPointerConversion,
   /// A closure/function conversion to an autoclosure parameter.
   SK_FunctionToAutoClosureConversion,
+  /// A type with a missing conformance(s) that has be synthesized
+  /// or diagnosed later, such types are allowed to appear in
+  /// a valid solution.
+  SK_MissingSynthesizableConformance,
   /// An unapplied reference to a function. The purpose of this
   /// score bit is to prune overload choices that are functions
   /// when a solution has already been found using property.
@@ -988,12 +992,8 @@ enum ScoreKind: unsigned int {
   /// ambiguity tie-breakers should go after this; anything else
   /// should be added above.
   SK_UnappliedFunction,
-  /// A type with a missing conformance(s) that has be synthesized
-  /// or diagnosed later, such types are allowed to appear in
-  /// a valid solution.
-  SK_MissingSynthesizableConformance,
 
-  SK_LastScoreKind = SK_MissingSynthesizableConformance,
+  SK_LastScoreKind = SK_UnappliedFunction,
 };
 
 /// The number of score kinds.

test/Concurrency/sendable_disambiguation.swift

@@ -25,3 +25,24 @@ do {
     _ = SendableOnly(value: v) // Ok
   }
 }
+
+do {
+  class K {
+    func value() {}
+  }
+
+  struct X {
+    var fn: (Int) -> K
+    func fn(_: Int) -> Int { 42 }
+  }
+
+  func sendable<T>(_ fn: (Int) -> T) -> T { fn(42) }
+  func sendable<T: Sendable>(_ fn: (Int) -> T) -> T { fn(0) }
+
+  func test(x: X) {
+    let res = sendable(x.fn) // Ok (non-ambiguous and non-Sendable overload)
+    res.value() // To make sure that previous expression picks a property
+    let _: K = sendable(x.fn) // Ok (picks `sendable<T>` with a property)
+    let _: Int = sendable(x.fn) // Ok (picks `sendable<T: Sendable>` with a method)
+  }
+}