Re: [libvirt PATCH] libxl: Fix build with recent Xen that introduces new disk backend type

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Aug 02, 2022 at 01:39:31PM +0200, Marek Marczykowski-Górecki wrote:
> On Mon, Aug 01, 2022 at 10:36:07AM +0100, Daniel P. Berrangé wrote:
> > Generally we want to see errors triggered from new enums arriving,
> > as it can be a sign that libvirt code needs a semantic change in
> > order to continue operating correctly.  It isn't always correct
> > to assume that the 'default' case gives the correct behaviour.
> 
> Isn't that the exact purpose of 'default' label? If use of 'default'
> means "any of the other 5 specific values, but lets save some characters
> to not name them explicitly", then IMHO better to name them
> explicitly...
> 
> I can see a value of -Werror=switch-enum when adding new (internal) enum
> value, to find all the cases where code needs to be adjusted, but even
> then a grep is probably sufficient enough. On the other hand, if there
> are cases where indeed all the values of (internal API) enum needs to be
> handled explicitly, maybe simply omit 'default' label and use
> -Werror=switch?
> 
> Anyway, if tracking all the enums values of all the used 3rd-party APIs
> is desirable (like, noticing when libxl adds new disk type), then it
> probably should be a separate CI job, not the default devel build.
> Otherwise breakages like this will happen from time to time, and will
> be annoyed for people on involved in specific code part at all.
> 
> As a short term fix, maybe Xen's CI can build libvirt with
> -Wno-error=switch-enum?

I think makes sense for a 3rd party CI todo that, since these warnings
are primarily targetted at libvirt upstream maintainers, so that we
catch problems before code is committed.

With regards,
Daniel
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