[libcamera-devel] [PATCH v1.1 1/5] meson: Switch to C++17

[Kieran Bingham]

On 22/08/2020 21:04, Laurent Pinchart wrote:
> Due to popular request, move from C++14 to C++17. This will allow
> dropping some custom constructs (such as a custom utils::clamp),
> benefiting from new language features, and dropping gcc 5 and 6 from the
> compilation tests.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
> Changes since v1:
> 
> - Update documentation
> - Print an error message when detecting a too old compiler

Ok, some useful additions... reading. ..


> ---
>  Documentation/coding-style.rst |  5 ++---
>  meson.build                    | 29 ++++++++++++++++++-----------
>  2 files changed, 20 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/coding-style.rst b/Documentation/coding-style.rst
> index 7acba37b8de8..7c56a1b70014 100644
> --- a/Documentation/coding-style.rst
> +++ b/Documentation/coding-style.rst
> @@ -88,13 +88,12 @@ headers, and with double quotes for other libcamera headers.
>  C++ Specific Rules
>  ------------------
>  
> -The code shall be implemented in C++14, with the following caveats:
> +The code shall be implemented in C++17, with the following caveats:
>  
>  * Type inference (auto and decltype) shall be used with caution, to avoid
>    drifting towards an untyped language.
>  * The explicit, override and final specifiers are to be used where applicable.
> -* General-purpose smart pointers (std::unique_ptr) deprecate std::auto_ptr.
> -  Smart pointers, as well as shared pointers and weak pointers, shall not be
> +* Smart pointers, as well as shared pointers and weak pointers, shall not be
>    overused.
>  * Classes are encouraged to define move constructors and assignment operators
>    where applicable, and generally make use of the features offered by rvalue
> diff --git a/meson.build b/meson.build
> index ec54e68f3635..cf2636d97100 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -6,7 +6,7 @@ project('libcamera', 'c', 'cpp',
>      default_options : [
>          'werror=true',
>          'warning_level=2',
> -        'cpp_std=c++14',
> +        'cpp_std=c++17',
>      ],
>      license : 'LGPL 2.1+')
>  
> @@ -62,6 +62,23 @@ if cc.get_id() == 'clang'
>      endif
>  endif
>  
> +if cc.get_id() == 'gcc'
> +    if cc.version().version_compare('<7')
> +        error('gcc version is too old, libcamera requires 7.0 or newer')
> +    endif


Clang v5 or greater is required for C++17. Do we need to catch that too?
or is that considered old enough that we're not going to hit it.

I think it looks like Clang 5 was released around September 2017, while
GCC 7.1 was released earlier in May 2017.

That said, wouldn't the compiler warn us quite verbosely if it didn't
support C++17 ?

I.e. .. do /we/ really need to do this check here in meson?

Anyway,

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

Still stands.


> +
> +    # gcc 7.1 introduced processor-specific ABI breakages related to parameter
> +    # passing on ARM platforms. This generates a large number of messages
> +    # during compilation with gcc >=7.1 until gcc 9. Silence them.
> +    if (host_machine.cpu_family() == 'arm' and
> +        cc.version().version_compare('>=7.1') and
> +        cc.version().version_compare('<9'))
> +        cpp_arguments += [
> +            '-Wno-psabi',
> +        ]
> +    endif
> +endif
> +
>  # We use C99 designated initializers for arrays as C++ has no equivalent
>  # feature. Both gcc and clang support this extension, but recent
>  # versions of clang generate a warning that needs to be disabled.
> @@ -71,16 +88,6 @@ if cc.has_argument('-Wno-c99-designator')
>      ]
>  endif
>  
> -# gcc 7.1 introduced processor-specific ABI breakages related to parameter
> -# passing on ARM platforms. This generates a large number of messages during
> -# compilation with gcc >=7.1 until gcc 9. Silence them.
> -if (host_machine.cpu_family() == 'arm' and cc.get_id() == 'gcc' and
> -    cc.version().version_compare('>=7.1') and cc.version().version_compare('<9'))
> -    cpp_arguments += [
> -        '-Wno-psabi',
> -    ]
> -endif
> -
>  c_arguments += common_arguments
>  cpp_arguments += common_arguments
>  
> 

-- 
Regards
--
Kieran