C++: add -std={c,gnu}++{current,future}

Tue Aug 30 12:20:17 GMT 2022

On Wed, Jul 13, 2022 at 03:29:04PM -0400, Nathan Sidwell via Gcc-patches wrote:
> Inspired by a user question.  Jason, thoughts?

FWIW, this makes sense.  I mean, how could I be against a patch
quoting Macbeth?!

> Since C++ is such a moving target, Microsoft have /std:c++latest
> (AFAICT clang does not), to select the currently implemented version
> of the working paper.  But the use of 'std:latest' is somewhat
> ambiguous -- the current std is C++20 -- that's the latest std, the
> next std will more than likely but not necessarily be C++23.  So this
> adds:
> 
>   -std=c++current -- the current std (c++20)
>   -std=c++future -- the working paper (c++2b)
> 
> also adds gnu++current and gnu++future to select the gnu-extended
> variants.
> 
> nathan
> 
> -- 
> Nathan Sidwell

> From 9671f4d5e7efa130280b6d50fb4e9e8492d5b587 Mon Sep 17 00:00:00 2001
> From: Nathan Sidwell <nathan@acm.org>
> Date: Wed, 13 Jul 2022 12:11:40 -0700
> Subject: [PATCH] C++: add -std={c,gnu}++{current,future}
> 
> Since C++ is such a moving target, Microsoft have /std:c++latest
> (AFAICT clang does not), to select the currently implemented version
> of the working paper.  But the use of 'std:latest' is somewhat
> ambiguous -- the current std is C++20 -- that's the latest std, the
> next std will more than likely but not necessarily be C++23.  So this
> adds:
> 
>   -std=c++current -- the current std (c++20)
>   -std=c++future -- the working paper (c++2b)
> 
> also adds gnu++current and gnu++future to select the gnu-extended
> variants.
> 
> 	gcc/
> 	* doc/invoke.texi (-std=): Document new c++ current & future
> 	options.
> 	gcc/c-family/
> 	* c.opt (-std={c,gnu}++{current,future}: New alias options.
> 	gcc/testsuite/
> 	* g++.dg/gnu-current.C: New.
> 	* g++.dg/gnu-future.C: New.
> 	* g++.dg/std-current.C: New.
> 	* g++.dg/std-future.C: New.
> ---
>  gcc/c-family/c.opt                 | 16 ++++++++++++++++
>  gcc/doc/invoke.texi                | 23 +++++++++++++++++++++++
>  gcc/testsuite/g++.dg/gnu-current.C |  7 +++++++
>  gcc/testsuite/g++.dg/gnu-future.C  |  7 +++++++
>  gcc/testsuite/g++.dg/std-current.C | 11 +++++++++++
>  gcc/testsuite/g++.dg/std-future.C  |  8 ++++++++
>  6 files changed, 72 insertions(+)
>  create mode 100644 gcc/testsuite/g++.dg/gnu-current.C
>  create mode 100644 gcc/testsuite/g++.dg/gnu-future.C
>  create mode 100644 gcc/testsuite/g++.dg/std-current.C
>  create mode 100644 gcc/testsuite/g++.dg/std-future.C
> 
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 44e1a60ce24..9292029a967 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -2321,6 +2321,14 @@ std=c++23
>  C++ ObjC++ Undocumented
>  Conform to the ISO 2023 C++ draft standard (experimental and incomplete support).
>  
> +std=c++current
> +C++ ObjC++ Alias(std=c++20) Undocumented
> +Conform to the current ISO C++ standard (C++20).
> +
> +std=c++future
> +C++ ObjC++ Alias(std=c++23) Undocumented
> +Conform to a future ISO C++ standard (C++2b, experimentatl and incomplete support).

Since the option says 23, why not use 23 here as well instead of 2b?
And below too.

> +
>  std=c11
>  C ObjC
>  Conform to the ISO 2011 C standard.
> @@ -2407,6 +2415,14 @@ std=gnu++23
>  C++ ObjC++ Undocumented
>  Conform to the ISO 2023 C++ draft standard with GNU extensions (experimental and incomplete support).
>  
> +std=gnu++current
> +C++ ObjC++ Alias(std=gnu++20) Undocumented
> +Conform to the current ISO C++ standard with GNU extensions (C++20).
> +
> +std=gnu++future
> +C++ ObjC++ Alias(std=gnu++23) Undocumented
> +Conform to a future ISO C++ standard with GNU extensions (C++2b, experimentatl and incomplete support).
> +
>  std=gnu11
>  C ObjC
>  Conform to the ISO 2011 C standard with GNU extensions.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index d5ff1018372..1c0edb9df68 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -2462,6 +2462,17 @@ GNU dialect of @option{-std=c++17}.
>  This is the default for C++ code.
>  The name @samp{gnu++1z} is deprecated.
>  
> +@item gnu++current
> +@itemx gnu++current
> +GNU dialect of the current C++ standard, currently @option{-std=gnu++20}.
> +The C++ version selected by this option is a moving target.
> +
> +@item gnu++future
> +@itemx gnu++future
> +GNU dialect of the next C++ standard, currently @option{-std=gnu++2b}.
> +The C++ version selected by this option is a moving target (as are the
> +semantics of that proposed version).
> +
>  @item c++20
>  @itemx c++2a
>  The 2020 ISO C++ standard plus amendments.
> @@ -2487,6 +2498,18 @@ change in incompatible ways in future releases.
>  GNU dialect of @option{-std=c++2b}.  Support is highly experimental,
>  and will almost certainly change in incompatible ways in future
>  releases.
> +
> +@item c++current
> +@itemx c++current
> +The current C++ standard, currently @option{-std=gnu++20}.
> +The C++ version selected by this option is a moving target.
> +
> +@item c++future
> +@itemx c++future
> +The next C++ standard, currently @option{-std=gnu++2b}.
> +The C++ version selected by this option is a moving target (as are the
> +semantics of that proposed version).
> +
>  @end table
>  
>  @item -aux-info @var{filename}
> diff --git a/gcc/testsuite/g++.dg/gnu-current.C b/gcc/testsuite/g++.dg/gnu-current.C
> new file mode 100644
> index 00000000000..c95c56d3ad8
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/gnu-current.C
> @@ -0,0 +1,7 @@
> +// { dg-do compile }
> +// { dg-options -std=gnu++current }
> +
> +static_assert (__cplusplus == 202002L, "time has moved on");
> +#if __STRICT_ANSI__
> +#error "__STRICT_ANSI__ surprisingly non-zero"
> +#endif
> diff --git a/gcc/testsuite/g++.dg/gnu-future.C b/gcc/testsuite/g++.dg/gnu-future.C
> new file mode 100644
> index 00000000000..366dcdeebc2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/gnu-future.C
> @@ -0,0 +1,7 @@
> +// { dg-do compile }
> +// { dg-options -std=gnu++future }
> +
> +static_assert (__cplusplus > 202002L, "time has moved on");
> +#if __STRICT_ANSI__
> +#error "__STRICT_ANSI__ surprisingly non-zero"
> +#endif
> diff --git a/gcc/testsuite/g++.dg/std-current.C b/gcc/testsuite/g++.dg/std-current.C
> new file mode 100644
> index 00000000000..334ffd1d2c4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/std-current.C
> @@ -0,0 +1,11 @@
> +// { dg-do compile }
> +// { dg-options -std=c++current }
> +
> +// Adust as tomorrow and tomorrow and tomorrow
> +// Creeps in this petty pace from day to day
> +// To the last syllable of recorded time.
> +
> +static_assert (__cplusplus == 202002L, "time has moved on");
> +#if !__STRICT_ANSI__
> +#error "__STRICT_ANSI__ surprisingly zero"
> +#endif
> diff --git a/gcc/testsuite/g++.dg/std-future.C b/gcc/testsuite/g++.dg/std-future.C
> new file mode 100644
> index 00000000000..dade97e6a71
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/std-future.C
> @@ -0,0 +1,8 @@
> +// { dg-do compile }
> +// { dg-options -std=c++future }
> +
> +static_assert (__cplusplus > 202002L, "time has moved on");
> +#if !__STRICT_ANSI__
> +#error "__STRICT_ANSI__ surprisingly zero"
> +#endif
> +
> -- 
> 2.30.2
> 

Marek