[libc++][NFC] Move format_error to its own header.

[• Quuxplusone]

I don't see anything stylistically wrong with this, but I'd like to see a rationale for why it's a good idea. What does having-this-in-a-separate-header buy us, physically?

libcxx/include/__format/format_error.h

11–12

_LIBCPP___FORMAT_FORMAT_ERROR_H

[Mordante]

Thanks for the review!

In D101723#2732299, @Quuxplusone wrote:

I don't see anything stylistically wrong with this, but I'd like to see a rationale for why it's a good idea. What does having-this-in-a-separate-header buy us, physically?

I personally like small headers/files. I find them easier to navigate than large files. Since it seems libc++ is moving in that direction I'm happy to oblige. In this case there's another reason. Locally I've more std::format patches. Managing patch series where parts are stored in separate files makes it easier when rebasing the series. (These patches will be up for review in a later stage, for new I'm still improving them.)

libcxx/include/__format/format_error.h

11–12

Will fix.

[Mordante]

Addresses review comments.

[Mordante]

friendly ping.

[Mordante]

Rebase.

[zoecarver]

libcxx/include/format

81

I don't feel too strongly, but I think it might be better to move basic_format_parse_context into its own header, and format_error along with it.

[Mordante]

Rebased to fix applying D93593.

libcxx/include/CMakeLists.txt

 set(files
   __availability
   __bit_reference
   __bits
   __bsd_locale_defaults.h
   __bsd_locale_fallbacks.h
   __config
   __debug
   __errc
+  __format/format_error.h
   __functional_03
   __functional_base
   __functional_base_03
   __hash_table
   __iterator/concepts.h
   __iterator/incrementable_traits.h
   __iterator/iter_move.h
   __iterator/iterator_traits.h

libcxx/include/__format/format_error.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_ERROR_H
+#define _LIBCPP__FORMAT_FORMAT_ERROR_H
+
+#include <__config>
+#include <stdexcept>
+
+#ifdef _LIBCPP_NO_EXCEPTIONS
+#include <cstdlib>
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+class _LIBCPP_EXCEPTION_ABI format_error : public runtime_error {
+public:
+  _LIBCPP_INLINE_VISIBILITY explicit format_error(const string& __s)
+      : runtime_error(__s) {}
+  _LIBCPP_INLINE_VISIBILITY explicit format_error(const char* __s)
+      : runtime_error(__s) {}
+  virtual ~format_error() noexcept;
+};
+
+_LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY void
+__throw_format_error(const char* __s) {
+#ifndef _LIBCPP_NO_EXCEPTIONS
+  throw format_error(__s);
+#else
+  (void)__s;
+  _VSTD::abort();
+#endif
+}
+
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP__FORMAT_FORMAT_ERROR_H

libcxx/include/format

namespace std {
   };
   using format_parse_context = basic_format_parse_context<char>;
   using wformat_parse_context = basic_format_parse_context<wchar_t>;
 }
 
 */
 
 #include <__config>
-#include <stdexcept>
+#include <__format/format_error.h>
 #include <string_view>
 #include <version>
 
-#ifdef _LIBCPP_NO_EXCEPTIONS
-#include <cstdlib>
-#endif
-
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
-class _LIBCPP_EXCEPTION_ABI format_error : public runtime_error {
-public:
-  _LIBCPP_INLINE_VISIBILITY explicit format_error(const string& __s)
-      : runtime_error(__s) {}
-  _LIBCPP_INLINE_VISIBILITY explicit format_error(const char* __s)
-      : runtime_error(__s) {}
-  virtual ~format_error() noexcept;
-};
-
 // 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) && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
 
-_LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY void
-__throw_format_error(const char* __s) {
-#ifndef _LIBCPP_NO_EXCEPTIONS
-  throw format_error(__s);
-#else
-  (void)__s;
-  _VSTD::abort();
-#endif
-}
-
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS basic_format_parse_context {
 public:
   using char_type = _CharT;
   using const_iterator =
       typename basic_string_view<_CharT>::const_iterator;
   using iterator = const_iterator;
 
 public:
   _LIBCPP_INLINE_VISIBILITY