[cfe-dev] Overeager -Wswitch

[James Y Knight via cfe-dev]

If it was actually the last value, that wouldn't be an issue. But it's
actually set to 1L << 16 which is not any of the real values. I expect
they're using this as a trick to force the type of the enum to be a 32-bit
int, since before C++11, there was no way to specify the type of the enum
directly.

If that's so, they could switch to using "enum _Ios_Fmtflags : uint32_t"
now.

On Fri, Oct 16, 2015 at 9:00 AM, Yury Gribov via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On 10/11/2015 09:59 PM, Joerg Sonnenberger via cfe-dev wrote:
>
>> On Sun, Oct 11, 2015 at 07:58:32PM +0200, Kim Gräsman wrote:
>>
>>> Hi Joerg,
>>>
>>> On Sat, Oct 10, 2015 at 1:33 PM, Joerg Sonnenberger via cfe-dev
>>> <cfe-dev at lists.llvm.org> wrote:
>>>
>>>> On Sat, Oct 10, 2015 at 10:21:17AM +0200, Kim Gräsman via cfe-dev wrote:
>>>>
>>>>> Alternatively, if we could get a patch into Poco, is there something
>>>>> like MSVC's #pragma(warning:disable) for Clang, so they could
>>>>> selectively silence the warning around this function?
>>>>>
>>>>
>>>> add GCC diagnostic push
>>>> #pragma GCC diagnostic ignored "-Wswitch"
>>>> ... your function here...
>>>> #pragma GCC diagnostic pop
>>>>
>>>> I think it also works with clang as pragma group.
>>>>
>>>
>>> Thanks, that's what I was looking for in the way of disabling. To
>>> confirm, #pragma clang diagnostic also works.
>>>
>>> I think we've agreed to rewrite the function in Poco using if/else
>>> instead of switch, because it was hard to find a switch phrasing that
>>> worked with all -W combinations (-Weverything overrode the #pragma
>>> diagnostic and threw diagnostics for code that worked with -Wall).
>>>
>>> That said, it might be worth trying to make Clang aware of libstdc++'s
>>> enum convention, but I haven't thought of a way to do so yet.
>>>
>>
>> I don't think there is anything Clang can or should do here, but please
>> fill an upstream report against GCC if they still do it in the most
>> recent version.
>>
>
> Using the last enum value (often suffixed with "_end" or "_last") to track
> total number of values is a common coding practice so I'm not sure they are
> going to fix this.
>
> -Y
>
>
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