libstdc++: Make std::basic_format_context non-copyable [PR114387]

Users are not supposed to create objects of this type, and there's no
reason it needs to be copyable. LWG 4061 makes it non-copyable and
non-default constructible.

libstdc++-v3/ChangeLog:

	PR libstdc++/114387
	* include/std/format (basic_format_context): Define copy
	operations as deleted, as per LWG 4061.
	* testsuite/std/format/context.cc: New test.

1 files changed, 36 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/std/format/context.cc b/libstdc++-v3/testsuite/std/format/context.cc
new file mode 100644
index 0000000..5cc5e9c
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/format/context.cc
@@ -0,0 +1,36 @@
+// { dg-do compile { target c++20 } }
+
+#include <format>
+
+template<typename Context>
+concept format_context_reqs = std::is_destructible_v<Context>
+  && (!std::is_default_constructible_v<Context>)
+  && (!std::is_copy_constructible_v<Context>)
+  && (!std::is_move_constructible_v<Context>)
+  && (!std::is_copy_assignable_v<Context>)
+  && (!std::is_move_assignable_v<Context>)
+  && requires (Context& ctx, const Context& cctx) {
+    typename Context::iterator;
+    typename Context::char_type;
+    requires std::same_as<typename Context::template formatter_type<int>,
+			  std::formatter<int, typename Context::char_type>>;
+    { ctx.locale() } -> std::same_as<std::locale>;
+    { ctx.out() } -> std::same_as<typename Context::iterator>;
+    { ctx.advance_to(ctx.out()) } -> std::same_as<void>;
+    { cctx.arg(1) } -> std::same_as<std::basic_format_arg<Context>>;
+  };
+
+template<typename Out, typename charT>
+constexpr bool
+check(std::basic_format_context<Out, charT>*)
+{
+  using context = std::basic_format_context<Out, charT>;
+  static_assert( format_context_reqs<context> );
+  static_assert( std::is_same_v<typename context::iterator, Out> );
+  static_assert( std::is_same_v<typename context::char_type, charT> );
+  return true;
+}
+
+static_assert( check( (std::format_context*)nullptr) );
+static_assert( check( (std::wformat_context*)nullptr) );
+static_assert( check( (std::basic_format_context<char*, char>*)nullptr) );