[clang] [attributes][-Wunsafe-buffer-usage] Support adding unsafe_buffer_usage attribute to struct fields (PR #101585)

[Malavika Samak via cfe-commits]

================
@@ -0,0 +1,113 @@
+// RUN: %clang_cc1 -std=c++20 -Wunsafe-buffer-usage \
+// RUN:            -fsafe-buffer-usage-suggestions -verify %s
+
+using size_t = __typeof(sizeof(int));
+
+namespace std {
+  class type_info;
+  class bad_cast;
+  class bad_typeid;
+
+  template <typename T> class span {
+
+  private:
+    T *elements;
+    size_t size_;
+
+  public:
+    span(T *, size_t){}
+
+    constexpr T* data() const noexcept {
+      return elements;
+    }
+
+    constexpr size_t size() const noexcept {
+      return size_;
+    }
+
+  };
+}
+
+struct A {
+    [[clang::unsafe_buffer_usage]]
+    int *ptr;
+
+    size_t sz;
+};
+
+struct B {
+   A a;
+ 
+   [[clang::unsafe_buffer_usage]]
+   int buf[];
+};
+
+union Union {
+  [[clang::unsafe_buffer_usage]]
+  int *ptr1;
+
+  int ptr2;
+};
+
+struct C {
+  Union ptr; 
+};
+
+struct D { 
+  [[clang::unsafe_buffer_usage]]
+  int *ptr, *ptr2;
+
+  [[clang::unsafe_buffer_usage]]
+  int buf[10];
+ 
+  size_t sz;
+  
+};
+
+void foo(int *ptr);
+
+void foo_safe(std::span<int> sp);
+
+void test_attribute_union(C c) {
+  int *p = c.ptr.ptr1; //expected-warning{{field ptr1 prone to unsafe buffer manipulation}}
+
+  // TODO: Warn here about the field
----------------
malavikasamak wrote:

So after some off-line discussion, we have converged to not provide this special handling for Unions. That means, just like struct fields, the warning will only be issued if the specific union field bears explicitly bears attribute. 

https://github.com/llvm/llvm-project/pull/101585