From 9cd9619a57f757ecb8c917faaa49341d7ac252c2 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Thu, 7 Dec 2023 18:00:55 -0800
Subject: [PATCH] [CSBindings] Unwrap optionals from contextual function type
 used as a key path type

The key path is going to be implicitly wrapped into a contextual
optional type.

Resolves: rdar://72864716
Resolves: https://github.com/apple/swift/issues/56393
---
 lib/Sema/CSBindings.cpp        |  5 +++--
 test/Constraints/keypath.swift | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/Sema/CSBindings.cpp b/lib/Sema/CSBindings.cpp
index 3974ef89fcc3e..80d0fe1ddfd78 100644
--- a/lib/Sema/CSBindings.cpp
+++ b/lib/Sema/CSBindings.cpp
@@ -634,8 +634,9 @@ void BindingSet::finalize(
         assert(isKnownKeyPathType(bindingTy) || bindingTy->is<FunctionType>());
 
         // Functions don't have capability so we can simply add them.
-        if (bindingTy->is<FunctionType>())
-          updatedBindings.insert(binding);
+        if (auto *fnType = bindingTy->getAs<FunctionType>()) {
+          updatedBindings.insert(binding.withType(fnType));
+        }
       }
 
       // Note that even though key path literal maybe be invalid it's
diff --git a/test/Constraints/keypath.swift b/test/Constraints/keypath.swift
index dd5e7c811b3ca..6f80de5250ba2 100644
--- a/test/Constraints/keypath.swift
+++ b/test/Constraints/keypath.swift
@@ -304,3 +304,17 @@ func test_invalid_argument_to_keypath_subscript() {
     // expected-error@-1 {{cannot use value of type 'A' as a key path subscript index; argument must be a key path}}
   }
 }
+
+extension Collection {
+  func prefix<R: RangeExpression>(
+    _ range: R,
+    while predicate: ((Element) -> Bool)? = nil
+  ) -> SubSequence where R.Bound == Self.Index {
+    fatalError()
+  }
+}
+
+// https://github.com/apple/swift/issues/56393
+func keypathToFunctionWithOptional() {
+  _ = Array("").prefix(1...4, while: \.isNumber) // Ok
+}