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

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Haojian Wu (hokein)

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/97408.diff


2 Files Affected:

- (modified) clang/lib/Sema/CheckExprLifetime.cpp (+1-1) 
- (added) clang/test/SemaCXX/suppress-dangling-assignment.cpp (+15) 


``````````diff
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();
+}

``````````

</details>


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