[clang] [clang] Don't emit the warn_dangling_lifetime_pointer diagnostic for the assignment case. (PR #97408)

[Haojian Wu via cfe-commits]

https://github.com/hokein updated https://github.com/llvm/llvm-project/pull/97408

>From d1ea90918702fec85714bdd9caa68942eb4a4218 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Tue, 2 Jul 2024 14:12:36 +0200
Subject: [PATCH 1/2] [clang] Don't emit the warn_dangling_lifetime_pointer
 diagnostic for the assignment case.

The lifetime_pointer case is handled before the assignment case. In some
scenario where we have the gsl::Pointer attr, we will end up with
emitting the `-Wdangling-gsl` warning for the assignment case. This
means we can not use `-Wno-dangling-assignment` to suppress the
newly-added warning.
---
 clang/lib/Sema/CheckExprLifetime.cpp              |  2 +-
 .../test/SemaCXX/suppress-dangling-assignment.cpp | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaCXX/suppress-dangling-assignment.cpp

diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index fea0239f7bc36..03bf87a7cf5e6 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -1023,7 +1023,7 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         return false;
       }
 
-      if (IsGslPtrInitWithGslTempOwner && DiagLoc.isValid()) {
+      if (InitEntity && IsGslPtrInitWithGslTempOwner && DiagLoc.isValid()) {
         SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
             << DiagRange;
         return false;
diff --git a/clang/test/SemaCXX/suppress-dangling-assignment.cpp b/clang/test/SemaCXX/suppress-dangling-assignment.cpp
new file mode 100644
index 0000000000000..11625d3272b83
--- /dev/null
+++ b/clang/test/SemaCXX/suppress-dangling-assignment.cpp
@@ -0,0 +1,15 @@
+
+// RUN: %clang_cc1 -std=c++20 -verify -Wno-dangling-assignment %s
+// expected-no-diagnostics
+
+namespace std {
+// std::basic_string has a hard-coded gsl::owner attr.
+struct basic_string {
+  const char* c_str();
+};
+}  // namespace std
+
+void test(const char* a) {
+  // verify that the dangling-assignment diagnostic are suppressed. 
+  a = std::basic_string().c_str();
+}

>From 95233e150d4344411d41539c57a3e921d621ea0b Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Tue, 2 Jul 2024 14:35:47 +0200
Subject: [PATCH 2/2] Refine the test, verifing that  we emit the
 "-Wdangling-assignment" warning.

---
 .../test/SemaCXX/suppress-dangling-assignment.cpp | 15 ---------------
 clang/test/SemaCXX/warn-dangling-local.cpp        | 11 +++++++++++
 2 files changed, 11 insertions(+), 15 deletions(-)
 delete mode 100644 clang/test/SemaCXX/suppress-dangling-assignment.cpp

diff --git a/clang/test/SemaCXX/suppress-dangling-assignment.cpp b/clang/test/SemaCXX/suppress-dangling-assignment.cpp
deleted file mode 100644
index 11625d3272b83..0000000000000
--- a/clang/test/SemaCXX/suppress-dangling-assignment.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-
-// RUN: %clang_cc1 -std=c++20 -verify -Wno-dangling-assignment %s
-// expected-no-diagnostics
-
-namespace std {
-// std::basic_string has a hard-coded gsl::owner attr.
-struct basic_string {
-  const char* c_str();
-};
-}  // namespace std
-
-void test(const char* a) {
-  // verify that the dangling-assignment diagnostic are suppressed. 
-  a = std::basic_string().c_str();
-}
diff --git a/clang/test/SemaCXX/warn-dangling-local.cpp b/clang/test/SemaCXX/warn-dangling-local.cpp
index a946b8a241a38..2808a4c01f88d 100644
--- a/clang/test/SemaCXX/warn-dangling-local.cpp
+++ b/clang/test/SemaCXX/warn-dangling-local.cpp
@@ -26,3 +26,14 @@ void g() {
   const int a[] = {a[0]};
   const int b[] = {a[0]};
 }
+
+namespace std {
+// std::basic_string has a hard-coded gsl::owner attr.
+struct basic_string {
+  const char* c_str();
+};
+}  // namespace std
+void test(const char* a) {
+  // verify we're emitting the `-Wdangling-assignment` warning.
+  a = std::basic_string().c_str(); // expected-warning {{object backing the pointer a will be destroyed at the end of the full-expression}}
+}