[clang] [Sema][ObjC] Treat unknown selector messages as unrecoverable errors under ARC (PR #146803)

[Akira Hatanaka via cfe-commits]

https://github.com/ahatanak updated https://github.com/llvm/llvm-project/pull/146803

>From c74ab1b752c4d6f0f52bfb682b0d0949c2912230 Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanak at gmail.com>
Date: Wed, 2 Jul 2025 15:51:54 -0700
Subject: [PATCH 1/3] [Sema][ObjC] Treat unknown selector messages as
 unrecoverable errors under ARC

Fixes a CodeGen crash observed when C++ auto variable types remained
non-deduced due to a message being sent with an unknown selector under
ARC.

By treating these instances as an unrecoverable error, we prevent the
compiler from proceeding to CodeGen with fundamentally incorrect code.

rdar://144394403
---
 clang/lib/Basic/DiagnosticIDs.cpp | 6 +++++-
 clang/test/SemaObjCXX/arc-0x.mm   | 7 ++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index dcf0c6cb54282..04a7f7732429d 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -832,7 +832,11 @@ bool DiagnosticIDs::isUnrecoverable(unsigned DiagID) const {
       DiagID == diag::err_unavailable_message)
     return false;
 
-  // Currently we consider all ARC errors as recoverable.
+  // Currently we consider all ARC errors except err_arc_may_not_respond as
+  // recoverable.
+  if (DiagID == diag::err_arc_may_not_respond)
+    return true;
+
   if (isARCDiagnostic(DiagID))
     return false;
 
diff --git a/clang/test/SemaObjCXX/arc-0x.mm b/clang/test/SemaObjCXX/arc-0x.mm
index ac788686a7374..bcaa5da6b9283 100644
--- a/clang/test/SemaObjCXX/arc-0x.mm
+++ b/clang/test/SemaObjCXX/arc-0x.mm
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -fobjc-arc -fobjc-runtime-has-weak -fobjc-weak -verify -fblocks -fobjc-exceptions %s
+// RUN: %clang_cc1 -std=c++11 -fobjc-arc -fobjc-runtime-has-weak -fobjc-weak -verify -fblocks -fobjc-exceptions -emit-llvm -o - %s
 
 // "Move" semantics, trivial version.
 void move_it(__strong id &&from) {
@@ -14,6 +14,11 @@ @interface A
 // don't warn about this
 extern "C" A* MakeA();
 
+void test_nonexistent_method(A *a) {
+  // This used to crash in codegen.
+  auto a1 = [a foo]; // expected-error {{no visible @interface for 'A' declares the selector 'foo'}}
+}
+
 // Ensure that deduction works with lifetime qualifiers.
 void deduction(id obj) {
   auto a = [[A alloc] init];

>From 83714a8717387020b48fef8ed6e21f5a3650c70d Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanak at gmail.com>
Date: Wed, 2 Jul 2025 17:35:35 -0700
Subject: [PATCH 2/3] Call isARCDiagnostic first

---
 clang/lib/Basic/DiagnosticIDs.cpp | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index 04a7f7732429d..fb18c767a7de5 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -834,10 +834,7 @@ bool DiagnosticIDs::isUnrecoverable(unsigned DiagID) const {
 
   // Currently we consider all ARC errors except err_arc_may_not_respond as
   // recoverable.
-  if (DiagID == diag::err_arc_may_not_respond)
-    return true;
-
-  if (isARCDiagnostic(DiagID))
+  if (isARCDiagnostic(DiagID) && DiagID != diag::err_arc_may_not_respond)
     return false;
 
   if (isCodegenABICheckDiagnostic(DiagID))

>From 7205f2be2c1afa1473b6de72433834cb27d6a74b Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanak at gmail.com>
Date: Thu, 3 Jul 2025 08:26:23 -0700
Subject: [PATCH 3/3] Explain why err_arc_may_not_respond needs to be treated
 as unrecoverable

---
 clang/lib/Basic/DiagnosticIDs.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index fb18c767a7de5..73f24a82d4c75 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -832,8 +832,11 @@ bool DiagnosticIDs::isUnrecoverable(unsigned DiagID) const {
       DiagID == diag::err_unavailable_message)
     return false;
 
-  // Currently we consider all ARC errors except err_arc_may_not_respond as
-  // recoverable.
+  // All ARC errors are currently considered recoverable, with the exception of
+  // err_arc_may_not_respond. This specific error is treated as unrecoverable
+  // because sending a message with an unknown selector could lead to crashes
+  // within CodeGen if the resulting expression is used to initialize a C++
+  // auto variable, where type deduction is required.
   if (isARCDiagnostic(DiagID) && DiagID != diag::err_arc_may_not_respond)
     return false;