[libcxx-commits] [libcxx] [libc++][format] LWG4106: `basic_format_args` should not be default-constructible (PR #97250)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

<details>
<summary>Changes</summary>

See [LWG4106](https://cplusplus.github.io/LWG/issue4106) and [P3341R0](https://wg21.link/p3341r0).

The test coverage for the empty state of `basic_format_args` in `get.pass.cpp` is to be completely removed, because the non-default-constructibility is covered in `ctor.pass.cpp`.

---
Full diff: https://github.com/llvm/llvm-project/pull/97250.diff


3 Files Affected:

- (modified) libcxx/include/__format/format_args.h (-2) 
- (modified) libcxx/test/std/utilities/format/format.arguments/format.args/ctor.pass.cpp (+2-7) 
- (modified) libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp (-5) 


``````````diff
diff --git a/libcxx/include/__format/format_args.h b/libcxx/include/__format/format_args.h
index a5fde36a29817..07923570f3893 100644
--- a/libcxx/include/__format/format_args.h
+++ b/libcxx/include/__format/format_args.h
@@ -28,8 +28,6 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 template <class _Context>
 class _LIBCPP_TEMPLATE_VIS basic_format_args {
 public:
-  basic_format_args() noexcept = default;
-
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI basic_format_args(const __format_arg_store<_Context, _Args...>& __store) noexcept
       : __size_(sizeof...(_Args)) {
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.args/ctor.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.args/ctor.pass.cpp
index c0575c545bde3..bb542a8e63ecf 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.args/ctor.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.args/ctor.pass.cpp
@@ -9,12 +9,12 @@
 
 // <format>
 
-// basic_format_args() noexcept;
 // template<class... Args>
 //   basic_format_args(const format-arg-store<Context, Args...>& store) noexcept;
 
 #include <format>
 #include <cassert>
+#include <type_traits>
 
 #include "test_macros.h"
 
@@ -24,12 +24,7 @@ void test() {
   char c        = 'c';
   nullptr_t p   = nullptr;
   using Context = std::basic_format_context<CharT*, CharT>;
-  {
-    ASSERT_NOEXCEPT(std::basic_format_args<Context>{});
-
-    std::basic_format_args<Context> format_args{};
-    assert(!format_args.get(0));
-  }
+  static_assert(!std::is_default_constructible_v<std::basic_format_args<Context>>);
   {
     auto store = std::make_format_args<Context>(i);
     ASSERT_NOEXCEPT(std::basic_format_args<Context>{store});
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
index c590cebf48acc..af8d7eff6f6b8 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
@@ -82,11 +82,6 @@ void test_string_view(From value) {
 template <class CharT>
 void test() {
   using Context = std::basic_format_context<CharT*, CharT>;
-  {
-    const std::basic_format_args<Context> format_args{};
-    ASSERT_NOEXCEPT(format_args.get(0));
-    assert(!format_args.get(0));
-  }
 
   using char_type = typename Context::char_type;
   std::basic_string<char_type> empty;

``````````

</details>


https://github.com/llvm/llvm-project/pull/97250