[PATCH v5 02/10] libstdc++: Add header mdspan to the build-system.

[Luc Grosheintz]

On 4/29/25 3:11 PM, Jonathan Wakely wrote:
> On Tue, 29 Apr 2025 at 13:59, Luc Grosheintz <luc.grosheintz@gmail.com> wrote:
>>
>> Creates a nearly empty header mdspan and adds it to the build-system and
>> Doxygen config file.
>>
>> libstdc++-v3/ChangeLog:
>>
>>          * doc/doxygen/user.cfg.in: Add <mdspan>.
>>          * include/Makefile.am: Ditto.
>>          * include/Makefile.in: Ditto.
>>          * include/precompiled/stdc++.h: Ditto.
>>          * include/std/mdspan: New file.
>>
>> Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
>> ---
>>   libstdc++-v3/doc/doxygen/user.cfg.in      |  1 +
>>   libstdc++-v3/include/Makefile.am          |  1 +
>>   libstdc++-v3/include/Makefile.in          |  1 +
>>   libstdc++-v3/include/precompiled/stdc++.h |  1 +
>>   libstdc++-v3/include/std/mdspan           | 48 +++++++++++++++++++++++
>>   5 files changed, 52 insertions(+)
>>   create mode 100644 libstdc++-v3/include/std/mdspan
>>
>> diff --git a/libstdc++-v3/doc/doxygen/user.cfg.in b/libstdc++-v3/doc/doxygen/user.cfg.in
>> index 19ae67a67ba..e926c6707f6 100644
>> --- a/libstdc++-v3/doc/doxygen/user.cfg.in
>> +++ b/libstdc++-v3/doc/doxygen/user.cfg.in
>> @@ -880,6 +880,7 @@ INPUT                  = @srcdir@/doc/doxygen/doxygroups.cc \
>>                            include/list \
>>                            include/locale \
>>                            include/map \
>> +                         include/mdspan \
>>                            include/memory \
>>                            include/memory_resource \
>>                            include/mutex \
>> diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
>> index 537774c2668..1140fa0dffd 100644
>> --- a/libstdc++-v3/include/Makefile.am
>> +++ b/libstdc++-v3/include/Makefile.am
>> @@ -38,6 +38,7 @@ std_freestanding = \
>>          ${std_srcdir}/generator \
>>          ${std_srcdir}/iterator \
>>          ${std_srcdir}/limits \
>> +       ${std_srcdir}/mdspan \
>>          ${std_srcdir}/memory \
>>          ${std_srcdir}/numbers \
>>          ${std_srcdir}/numeric \
>> diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
>> index 7b96b2207f8..c96e981acd6 100644
>> --- a/libstdc++-v3/include/Makefile.in
>> +++ b/libstdc++-v3/include/Makefile.in
>> @@ -396,6 +396,7 @@ std_freestanding = \
>>          ${std_srcdir}/generator \
>>          ${std_srcdir}/iterator \
>>          ${std_srcdir}/limits \
>> +       ${std_srcdir}/mdspan \
>>          ${std_srcdir}/memory \
>>          ${std_srcdir}/numbers \
>>          ${std_srcdir}/numeric \
>> diff --git a/libstdc++-v3/include/precompiled/stdc++.h b/libstdc++-v3/include/precompiled/stdc++.h
>> index f4b312d9e47..e7d89c92704 100644
>> --- a/libstdc++-v3/include/precompiled/stdc++.h
>> +++ b/libstdc++-v3/include/precompiled/stdc++.h
>> @@ -228,6 +228,7 @@
>>   #include <flat_map>
>>   #include <flat_set>
>>   #include <generator>
>> +#include <mdspan>
>>   #include <print>
>>   #include <spanstream>
>>   #include <stacktrace>
>> diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
>> new file mode 100644
>> index 00000000000..4094a416d1e
>> --- /dev/null
>> +++ b/libstdc++-v3/include/std/mdspan
>> @@ -0,0 +1,48 @@
>> +// <mdspan> -*- C++ -*-
>> +
>> +// Copyright (C) 2025 Free Software Foundation, Inc.
> 
> I've just noticed that this file claims to be copyright FSF, but if
> you're contributing under the https://gcc.gnu.org/dco.html terms
> rather than via a copyright assignment to the FSF, then that's
> incorrect.
> 
> Please see the <expected> header for the DCO-compatible way to mention
> that the header is covered by copyright without being overly precise.
> 
> Otherwise these patches look good and I'll start pushing them this
> week - thanks!

That's exciting to hear! I'll fix the issues and strip anything layout
related from this series.

I'm slightly nervous because the first time I used <mdspan> outside of
the test harness I was greeted with an error due to not including a
header inside <mdspan>; and because I was using PCH, it didn't cause an
error during testing.

I've since reconfigured with `--disable-libstdcxx-pch` and also run
with `--target_board='unix/-Wall/-Wextra/-pedantic'`.

Is there more I can do to make sure the patches are correct?

> 
> 
>> +//
>> +// This file is part of the GNU ISO C++ Library.  This library is free
>> +// software; you can redistribute it and/or modify it under the
>> +// terms of the GNU General Public License as published by the
>> +// Free Software Foundation; either version 3, or (at your option)
>> +// any later version.
>> +
>> +// This library is distributed in the hope that it will be useful,
>> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> +// GNU General Public License for more details.
>> +
>> +// Under Section 7 of GPL version 3, you are granted additional
>> +// permissions described in the GCC Runtime Library Exception, version
>> +// 3.1, as published by the Free Software Foundation.
>> +
>> +// You should have received a copy of the GNU General Public License and
>> +// a copy of the GCC Runtime Library Exception along with this program;
>> +// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
>> +// <http://www.gnu.org/licenses/>.
>> +
>> +/** @file mdspan
>> + *  This is a Standard C++ Library header.
>> + */
>> +
>> +#ifndef _GLIBCXX_MDSPAN
>> +#define _GLIBCXX_MDSPAN 1
>> +
>> +#ifdef _GLIBCXX_SYSHDR
>> +#pragma GCC system_header
>> +#endif
>> +
>> +#define __glibcxx_want_mdspan
>> +#include <bits/version.h>
>> +
>> +#ifdef __glibcxx_mdspan
>> +
>> +namespace std _GLIBCXX_VISIBILITY(default)
>> +{
>> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
>> +
>> +_GLIBCXX_END_NAMESPACE_VERSION
>> +}
>> +#endif
>> +#endif
>> --
>> 2.49.0
>>
>