From cd3e96a320497c40995a33eb52633e8a7af171a8 Mon Sep 17 00:00:00 2001
From: Jamie <2119834+jamieQ@users.noreply.github.com>
Date: Fri, 1 Aug 2025 05:48:37 -0500
Subject: [PATCH] [Sema]: fix @discardableResult interaction with implicit
 @Sendable conversions

Updates existing diagnostic handling to look through function
conversions when suppressing diagnostics for unused functions that are
return values from callees marked with @discardableResult.
---
 lib/Sema/TypeCheckStmt.cpp                    | 21 ++++++++++++++++++-
 .../attr_discardableResult_async_await.swift  | 20 ++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/lib/Sema/TypeCheckStmt.cpp b/lib/Sema/TypeCheckStmt.cpp
index 7e78556aafb6f..bff6cec1bee7e 100644
--- a/lib/Sema/TypeCheckStmt.cpp
+++ b/lib/Sema/TypeCheckStmt.cpp
@@ -1886,7 +1886,26 @@ void TypeChecker::checkIgnoredExpr(Expr *E) {
                     : valueE;
 
     if (auto *Fn = dyn_cast<ApplyExpr>(expr)) {
-      if (auto *calledValue = Fn->getCalledValue()) {
+      /// Some concurrency-related things may have intermediate conversions that
+      /// we want to look through, e.g.
+      ///
+      /// ```swift
+      /// @discardableResult
+      /// @MainActor
+      /// func foo() -> () -> Void {
+      ///   return {}
+      /// }
+      ///
+      /// @MainActor
+      /// func test() {
+      ///   foo()
+      ///   // ^ return value implicitly wapped in a `@Sendable` conversion
+      /// }
+      /// ```
+      /// Attempt to look through function conversions when resolving the
+      /// called value.
+      if (auto *calledValue =
+              Fn->getCalledValue(/*skipFunctionConversions=*/true)) {
         if (auto *FD = dyn_cast<AbstractFunctionDecl>(calledValue)) {
           if (FD->getAttrs().hasAttribute<DiscardableResultAttr>()) {
             isDiscardable = true;
diff --git a/test/Concurrency/attr_discardableResult_async_await.swift b/test/Concurrency/attr_discardableResult_async_await.swift
index d8f3e7f822cc6..d3475bad09248 100644
--- a/test/Concurrency/attr_discardableResult_async_await.swift
+++ b/test/Concurrency/attr_discardableResult_async_await.swift
@@ -14,3 +14,23 @@ func mainActorAsyncDiscardable() async -> Int { 0 }
 func consumesMainActorAsyncDiscardable() async {
   await mainActorAsyncDiscardable() // ok
 }
+
+// https://github.com/swiftlang/swift/issues/83463
+
+@MainActor
+@discardableResult
+func returnsDiscardableFunc() -> () -> Void { return {} }
+
+@MainActor
+func testDiscardsSyncFuncWithImplicitSendableConversion() {
+    returnsDiscardableFunc()
+}
+
+@MainActor
+@discardableResult
+func mainActorAsyncReturnsDiscardableFunc() async -> () -> Void { return {} }
+
+@MainActor
+func discardsAsyncFuncWithImplicitSendableConversion() async {
+  await mainActorAsyncReturnsDiscardableFunc()
+}