From 7ad80b8ce016b51d9069c73dce904eb210f7ef5f Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Mon, 26 Feb 2024 13:08:58 -0800
Subject: [PATCH] [CSApply] Optional chaining forces key path component to be
 r-value

Key path components with optional chaining unlike other places
don't propagate l-value through optionals.

Resolves: rdar://123638701
---
 lib/Sema/CSApply.cpp       |  3 ++-
 test/SILGen/keypaths.swift | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/Sema/CSApply.cpp b/lib/Sema/CSApply.cpp
index f3145e09554ff..db66fa8f4dda9 100644
--- a/lib/Sema/CSApply.cpp
+++ b/lib/Sema/CSApply.cpp
@@ -5116,7 +5116,8 @@ namespace {
           !componentTy->getWithoutSpecifierType()->isEqual(leafTy)) {
         auto component = KeyPathExpr::Component::forOptionalWrap(leafTy);
         resolvedComponents.push_back(component);
-        componentTy = OptionalType::get(componentTy);
+        // Optional chaining forces the component to be r-value.
+        componentTy = OptionalType::get(componentTy->getWithoutSpecifierType());
       }
 
       // Set the resolved components, and cache their types.
diff --git a/test/SILGen/keypaths.swift b/test/SILGen/keypaths.swift
index c45191840b2bd..b6881a4d58c2b 100644
--- a/test/SILGen/keypaths.swift
+++ b/test/SILGen/keypaths.swift
@@ -652,3 +652,23 @@ struct Test {
   var codingPath: [any CodingKey] { codingStack.map(\.key) }
   // CHECK: keypath $KeyPath<CodingStackEntry, URICoderCodingKey>, (root $CodingStackEntry; stored_property #CodingStackEntry.key : $URICoderCodingKey)
 }
+
+// rdar://123638701 - Make sure that optional chaining forces loads.
+func test_optional_chaining_with_function_conversion() {
+  class Storage {}
+
+  class Elements {
+    var db: Storage = Storage()
+  }
+
+  class Source {
+    var elements: Elements? = nil
+  }
+
+  func test(data: [Source]) {
+    // CHECK: {{.*}} = keypath $KeyPath<Source, Optional<Storage>>
+    _ = data.compactMap(\.elements?.db)
+    // CHECK: {{.*}} = keypath $KeyPath<Source, Storage>
+    _ = data.compactMap(\.elements!.db)
+  }
+}