[libc++][NFC] Move format_to_n_result.

[Mordante]

Summary

Places format_to_n_result to its own file. While working on D112361 it
turns out the type will be used outside the format header.

[Mordante]

Fixes building on Apple. (Basically disabling the build.)

[Mordante]

Fixes modular build.

[• Quuxplusone]

libcxx/include/__format/format_to_n_result.h

25–28

FWIW, I think this TODO is obvious. I'm not worried that we'll forget to eliminate _LIBCPP_HAS_NO_CONCEPTS once that becomes possible. :)

libcxx/include/format

581

LGTM, ship it (once CI passes).
But FWIW, for any header where we're doing the "granular" thing, I would strongly prefer that the top-level header contain nothing but #include directives (and boilerplate). That is, I think you should follow up, as soon as you get the cycles, by moving format, formatted_size, etc., into their own headers.

I also don't understand why you're splitting up struct format_to_n_result from the format_to_n function itself; shouldn't they go together into <__format/format_to_n.h>?

[Mordante]

Thanks for the review!

libcxx/include/__format/format_to_n_result.h

25–28

True but this is the comment I've used before and try to keep it consistent ;-)
I would really love to get rid of this TODO...

libcxx/include/format

581

I'm not going to mvoe the format functions for now. I'm happy to add a TODO FMT for now. The reason not to do it now it to avoid merge conflicts with the P2216 patches under review now. (I've some more patches not yet under review, so I strongly prefer to wait with this until it won't cause needless rebase issues.)

I moved only the struct to a new header since it will be used in the __format/buffer.h header and in format. This is part of the PoC P2216 patch D112361. Currently I'm reworking that patch to patches in that stack to have small modular patches.

libcxx/include/CMakeLists.txt

set(files
   __errc
   __format/format_arg.h
   __format/format_args.h
   __format/format_context.h
   __format/format_error.h
   __format/format_fwd.h
   __format/format_parse_context.h
   __format/format_string.h
+  __format/format_to_n_result.h
   __format/formatter.h
   __format/formatter_bool.h
   __format/formatter_char.h
   __format/formatter_integer.h
   __format/formatter_integral.h
   __format/formatter_string.h
   __format/parser_std_format_spec.h
   __function_like.h

libcxx/include/__format/format_to_n_result.h

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FORMAT_FORMAT_TO_N_RESULT_H
+#define _LIBCPP___FORMAT_FORMAT_TO_N_RESULT_H
+
+#include <__config>
+#include <__iterator/incrementable_traits.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+#if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+template <class _OutIt>
+struct _LIBCPP_TEMPLATE_VIS format_to_n_result {
+  _OutIt out;
+  iter_difference_t<_OutIt> size;
+};
+
+#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_FORMAT_TO_N_RESULT_H

libcxx/include/format

 #include <__debug>
 #include <__format/format_arg.h>
 #include <__format/format_args.h>
 #include <__format/format_context.h>
 #include <__format/format_error.h>
 #include <__format/format_fwd.h>
 #include <__format/format_parse_context.h>
 #include <__format/format_string.h>
+#include <__format/format_to_n_result.h>
 #include <__format/formatter.h>
 #include <__format/formatter_bool.h>
 #include <__format/formatter_char.h>
 #include <__format/formatter_integer.h>
 #include <__format/formatter_string.h>
 #include <__format/parser_std_format_spec.h>
 #include <__variant/monostate.h>
 #include <array>

 }
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 template <class... _Args>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT wstring
 format(wstring_view __fmt, const _Args&... __args) {
   return _VSTD::vformat(__fmt, _VSTD::make_wformat_args(__args...));
 }
 #endif
 
-template <class _OutIt>
-struct _LIBCPP_TEMPLATE_VIS format_to_n_result {
-  _OutIt out;
-  iter_difference_t<_OutIt> size;
-};
-
 template <output_iterator<const char&> _OutIt, class... _Args>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT format_to_n_result<_OutIt>
 format_to_n(_OutIt __out_it, iter_difference_t<_OutIt> __n, string_view __fmt,
             const _Args&... __args) {
   // TODO FMT Improve PoC: using std::string is inefficient.
   string __str = _VSTD::vformat(__fmt, _VSTD::make_format_args(__args...));
   iter_difference_t<_OutIt> __s = __str.size();
   iter_difference_t<_OutIt> __m =

libcxx/include/module.modulemap

module __format {
         private header "__format/format_context.h"
         export optional
         export locale
       }
       module format_error           { private header "__format/format_error.h"           }
       module format_fwd             { private header "__format/format_fwd.h"             }
       module format_parse_context   { private header "__format/format_parse_context.h"   }
       module format_string          { private header "__format/format_string.h"          }
+      module format_to_n_result     { private header "__format/format_to_n_result.h"     }
       module formatter              { private header "__format/formatter.h"              }
       module formatter_bool         { private header "__format/formatter_bool.h"         }
       module formatter_char         { private header "__format/formatter_char.h"         }
       module formatter_integer      { private header "__format/formatter_integer.h"      }
       module formatter_integral     { private header "__format/formatter_integral.h"     }
       module formatter_string       { private header "__format/formatter_string.h"       }
       module parser_std_format_spec { private header "__format/parser_std_format_spec.h" }
     }

libcxx/test/libcxx/diagnostics/detail.headers/format/format_to_n_result.module.verify.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__format/format_to_n_result.h'}}
+#include <__format/format_to_n_result.h>