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Re: [Qemu-block] [Qemu-devel] [PATCH v11 19/28] qapi: Change munging of

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v11 19/28] qapi: Change munging of CamelCase enum values
Date: Wed, 11 Nov 2015 09:03:23 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

[hmm, wonder why scripts/get-maintainer.pl didn't loop in Gerd to the
patch itself]

On 11/11/2015 07:50 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
>> When munging enum values, the fact that we were passing the entire
>> prefix + value through camel_to_upper() meant that enum values
>> spelled with CamelCase could be turned into CAMEL_CASE.  However,
>> this provides a potential collision (both OneTwo and One-Two would
>> munge into ONE_TWO).  By changing the generation of enum constants
>> to always be prefix + '_' + c_name(value).upper(), we can avoid
>> any risk of collisions (if we can also ensure no case collisions,
>> in the next patch) without having to think about what the
>> heuristics in camel_to_upper() will actually do to the value.
> This is the good part: the rules for clashes become much simpler.
> Bonus: the implementation for detecting them will be simple, too.
>> Thankfully, only two enums are affected: ErrorClass and InputButton.

Visiting just InputButton in this email.

> By convention (see CODING_STYLE), we use CamelCase for type names, and
> nothing else.
> Only enums violating this naming convention can be affected.  The bad
> part: they exist.
> InputButton has two camels: WheelUp and WheelDown.  The C enumeration
> constants change from INPUT_BUTTON_WHEEL_UP/WHEEL_DOWN to
> INPUT_BUTTON_WHEELUP/WHEELDOWN.  Not exactly an improvement, but one,
> there are just 21 occurences in 11 files, and two, I think we can still
> fix the enumeration to "lower case with dash", as it's only used by
> x-input-send-event.

The InputButton type has existed since 2.0; which is then part of the
'InputBtnEvent' struct, then the 'InputEvent' union, also since 2.0.  I
can't easily tell if it was only used internally at that point, or if we
exposed it through the command line (even if we didn't expose it through
QMP); but I concur with your reading that in QMP it is only used via
'x-input-send-event' (since 2.2, but the x- prefix gives us freedom).
[Oh, and I just spotted a typo; 'InputAxis' has a copy-and-paste doc
typo calling it 'InputButton']

If desired, I can prepare an alternate patch that adds the dash to the
qapi enum definition, to see what we think.

But meanwhile, look at some of the lines in the patch:

> diff --git a/ui/sdl.c b/ui/sdl.c
> index 570cb99..2678611 100644
> --- a/ui/sdl.c
> +++ b/ui/sdl.c
> @@ -469,8 +469,8 @@ static void sdl_send_mouse_event(int dx, int dy, int x, 
> int y, int state)

Since SDL already spells the names without space, it's not the end of
the world if we do likewise.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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