Re: [Qemu-devel] [PATCH v2 2/3] glib: enforce the minimum required version and warn about old APIs

[Thomas Huth]

On 06.06.2018 19:32, Daniel P. Berrangé wrote:
> There are two useful macros that can be defined before including
> glib.h that are related to the min required glib version
> 
>  - GLIB_VERSION_MIN_REQUIRED
> 
>    When this is defined, if code uses an API that was deprecated
>    in this version, or older, a compiler warning will be emitted.
>    This alerts maintainers to update their code to whatever new
>    replacement API is now recommended best practice.
> 
>  - GLIB_VERSION_MAX_ALLOWED
> 
>    When this is defined, if code uses an API that was introduced
>    in a version that is newer than the declared version, a compiler
>    warning will be emitted. This alerts maintainers if new code
>    accidentally uses functionality that won't be available on some
>    supported platforms.
> 
> The GLIB_VERSION_MAX_ALLOWED constant makes it a bit harder to opt
> in to using specific new APIs with a GLIB_CHECK_VERSION conditional.
> To workaround this Pragmas can be used to temporarily turn off the
> -Wdeprecated-declarations compiler warning, while a static inline
> compat function is implemented. This workaround is illustrated with the
> implementation of the g_strv_contains method to satisfy the test suite.

I wonder whether that's a little bit too much magic already. We could
also set GLIB_VERSION_MAX_ALLOWED to the version where we've already got
the work-arounds in place (i.e. to 2.44 here). If we introduce
additional code that uses other new functions from 2.41 - 2.44, this
should also be caught by the patchew CI builders?

> Signed-off-by: Daniel P. Berrangé <address@hidden>
> ---
>  include/glib-compat.h                    | 67 ++++++++++++++++++++++++
>  tests/docker/dockerfiles/centos6.docker  | 30 -----------
>  tests/docker/dockerfiles/min-glib.docker |  8 ---

The docker files are not directly related to this patch, are they? If
they are, please mention it in the patch description. If not, please
move this to a separate patch (or maybe into patch 1).

>  tests/test-qga.c                         |  2 -
>  4 files changed, 67 insertions(+), 40 deletions(-)
>  delete mode 100644 tests/docker/dockerfiles/centos6.docker
>  delete mode 100644 tests/docker/dockerfiles/min-glib.docker
> 
> diff --git a/include/glib-compat.h b/include/glib-compat.h
> index 3b340ab33c..cfc3cba751 100644
> --- a/include/glib-compat.h
> +++ b/include/glib-compat.h
> @@ -16,8 +16,73 @@
>  #ifndef QEMU_GLIB_COMPAT_H
>  #define QEMU_GLIB_COMPAT_H
>  
> +/* Ask for warnings for anything that was marked deprecated in
> + * the defined version, or before. It is a candidate for rewrite.
> + */
> +#define GLIB_VERSION_MIN_REQUIRED GLIB_VERSION_2_40
> +
> +/* Ask for warnings if code tries to use function that did not
> + * exist in the defined version. These risk breaking builds
> + */
> +#define GLIB_VERSION_MAX_ALLOWED GLIB_VERSION_2_40
> +
> +_Pragma("GCC diagnostic push")
> +_Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")

Why not "#pragma" ? I think that's a little bit more common?

 Thomas