From fcf6ed7fba2669517bc91188cfeb070388c9a917 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Thu, 18 Jul 2024 20:44:28 -0700
Subject: [PATCH] [Concurrency] Don't warn about re-stating inherited
 unavailable conformances to `Sendable`.

The unavailability check was not using the root conformance, which is where
the extension declaration with the unavailability attribute is for inherited
conformances, leading to bogus warnings about re-stating unchecked conformances
to `Sendable`.

(cherry picked from commit 69b2435babc7d0424b59be3ead52e05a12a2a072)
---
 lib/Sema/TypeCheckConcurrency.cpp                | 6 +++++-
 test/Concurrency/concurrent_value_checking.swift | 8 ++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/Sema/TypeCheckConcurrency.cpp b/lib/Sema/TypeCheckConcurrency.cpp
index 3c61f01bfd987..b116b1a432086 100644
--- a/lib/Sema/TypeCheckConcurrency.cpp
+++ b/lib/Sema/TypeCheckConcurrency.cpp
@@ -6186,7 +6186,11 @@ bool swift::checkSendableConformance(
     return false;
 
   // If this is an always-unavailable conformance, there's nothing to check.
-  if (auto ext = dyn_cast<ExtensionDecl>(conformanceDC)) {
+  // We always use the root conformance for this check, because inherited
+  // conformances need to walk back to the original declaration for the
+  // superclass conformance to find an unavailable attribute.
+  if (auto ext = dyn_cast<ExtensionDecl>(
+          conformance->getRootConformance()->getDeclContext())) {
     if (AvailableAttr::isUnavailable(ext))
       return false;
   }
diff --git a/test/Concurrency/concurrent_value_checking.swift b/test/Concurrency/concurrent_value_checking.swift
index 7d0f4c2ae22a6..57b0b6dfe79ed 100644
--- a/test/Concurrency/concurrent_value_checking.swift
+++ b/test/Concurrency/concurrent_value_checking.swift
@@ -380,6 +380,14 @@ final class C7<T>: Sendable { }
 
 class C9: Sendable { } // expected-warning{{non-final class 'C9' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
 
+@available(*, unavailable)
+extension HasUnavailableSendable : @unchecked Sendable { }
+
+class HasUnavailableSendable {
+}
+
+class NoRestated: HasUnavailableSendable {} // okay
+
 @globalActor
 struct SomeActor {
   static let shared = A1()