Re: [PATCH experiment 00/16] C++20 coroutine backend

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> writes:

> On Tue, Mar 15, 2022 at 03:50:26PM +0100, Kevin Wolf wrote:

[...]

>> ...using C++ in coroutine code means that all of the block layer would
>> suddenly become C++ and would be most affected by this effect. I'm not
>> sure if that's something I would like to see, at least until there is a
>> clear tree-wide policy (that preferably limits it to a subset that I
>> understand).
>
> Expecting maintainers to enforce a subset during code review feels
> like it would be a tedious burden, that will inevitably let stuff
> through because humans are fallible, especially when presented
> with uninspiring, tedious, repetitive tasks.
>
> Restricting ourselves to a subset is only viable if we have
> an automated tool that can reliably enforce that subset.

Concur.  We're talking about a complex subset of an even more complex
whole, where few to none of us will fully understand either.

>                                                          I'm not
> sure that any such tool exists, and not convinced our time is
> best served by trying to write & maintainer one either.
>
> IOW, I fear one we allow C++ in any level, it won't be practical
> to constrain it as much we desire. I fear us turning QEMU into
> even more of a monster like other big C++ apps I see which take
> all hours to compile while using all available RAM in Fedora RPM
> build hosts.

While I'm certainly concerned about the often poor ergonomics of
compiling C++ code, I'm even more concerned about the poor ergonomics of
*grokking* C++ code.

> My other question is whether adoption of C++ would complicate any
> desire to make more use of Rust in QEMU ? I know Rust came out of
> work by the Mozilla Firefox crew, and Firefox was C++, but I don't
> have any idea how they integrated use of Rust with Firefox, so
> whether there are any gotcha's for us or not ?

Good question.