[libcxx] [llvm] [libc++] Diagnose when nullptrs are passed to string APIs (PR #122790)

[Nikolas Klauser via llvm-commits]

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@@ -1037,13 +1037,14 @@ public:
 #  endif // _LIBCPP_CXX03_LANG
 
   template <__enable_if_t<__is_allocator<_Allocator>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* _LIBCPP_DIAGNOSE_NONNULL __s) {
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philnik777 wrote:

Yes. `_Nonnull` makes passing a nullptr erroneus behaviour, but not UB. That's why I chose that over `[[gnu::nonnull]]`.

https://github.com/llvm/llvm-project/pull/122790