[CSOptimizer] All the candidates should match Any parameter type

If the parameter is `Any` we assume that all candidates are
convertible to it, which makes it a perfect match. The solver
would then decide whether erasing to an existential is preferable.

Resolves: rdar://157644867

Author: xedin

lib/Sema/CSOptimizer.cpp

@@ -1388,6 +1388,12 @@ static void determineBestChoicesInContext(
         }
       }
 
+      // If the parameter is `Any` we assume that all candidates are
+      // convertible to it, which makes it a perfect match. The solver
+      // would then decide whether erasing to an existential is preferable.
+      if (paramType->isAny())
+        return 1;
+
       // Check protocol requirement(s) if this parameter is a
       // generic parameter type.
       if (genericSig && paramType->isTypeParameter()) {

test/Constraints/disfavored.swift

@@ -35,3 +35,15 @@ func test(s: String, answer: Int) {
   let r2c = f2(s)
   let _: A = r2c
 }
+
+do {
+  @available(*, deprecated)
+  @_disfavoredOverload
+  func test(v: Int) {}
+
+  func test(v: Any) {}
+
+  func call(v: Int) {
+    test(v: v) // Ok (the overload that takes `Int` is disfavored)
+  }
+}