[llvm-branch-commits] [clang] release/21.x: [clang][ObjC] Fix incorrect return type inference for discarded blocks (#154109) (PR #154210)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/154210

Backport ec4e6aa

Requested by: @ojhunt

>From 26939b2293cafb83da0794c926321a20e0c6b017 Mon Sep 17 00:00:00 2001
From: Oliver Hunt <oliver at apple.com>
Date: Mon, 18 Aug 2025 14:38:50 -0700
Subject: [PATCH] [clang][ObjC] Fix incorrect return type inference for
 discarded blocks (#154109)

When parsing a block expression we were not entering a new eval context
and as a result when parsing the block body we continue to treat any
return statements as discarded so infer a `void` result.

This fixes the problem by introducing an evaluation context around the
parsing of the body.

(cherry picked from commit ec4e6aaac4612af26322b2b10b8f518ecf053c74)
---
 clang/lib/Parse/ParseExpr.cpp                     |  3 ++-
 .../SemaObjCXX/discarded-block-type-inference.mm  | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaObjCXX/discarded-block-type-inference.mm

diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index bc238a9517a37..3515343202de1 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -3342,7 +3342,8 @@ ExprResult Parser::ParseBlockLiteralExpression() {
     Actions.ActOnBlockError(CaretLoc, getCurScope());
     return ExprError();
   }
-
+  EnterExpressionEvaluationContextForFunction PotentiallyEvaluated(
+       Actions, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
   StmtResult Stmt(ParseCompoundStatementBody());
   BlockScope.Exit();
   if (!Stmt.isInvalid())
diff --git a/clang/test/SemaObjCXX/discarded-block-type-inference.mm b/clang/test/SemaObjCXX/discarded-block-type-inference.mm
new file mode 100644
index 0000000000000..8e2587724a7f6
--- /dev/null
+++ b/clang/test/SemaObjCXX/discarded-block-type-inference.mm
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -fobjc-arc -fblocks %s
+
+void  block_receiver(int (^)() );
+
+int f1() {
+  if constexpr (0)
+    (block_receiver)(^{ return 2; });
+  return 1;
+}
+
+int f2() {
+  if constexpr (0)
+    return (^{ return 2; })();
+  return 1;
+}