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Re: {PATCH] New C++ warning -Wcatch-value


On Mon, Jun 5, 2017 at 6:55 AM, Volker Reichelt
<v.reichelt@netcologne.de> wrote:
> On 15 May, Martin Sebor wrote:
>>> So how about the following then? I stayed with the catch part and added
>>> a parameter to the warning to let the user decide on the warnings she/he
>>> wants to get: -Wcatch-value=n.
>>> -Wcatch-value=1 only warns for polymorphic classes that are caught by
>>> value (to avoid slicing), -Wcatch-value=2 warns for all classes that
>>> are caught by value (to avoid copies). And finally -Wcatch-value=3
>>> warns for everything not caught by reference to find typos (like pointer
>>> instead of reference) and bad coding practices.
>>
>> It seems reasonable to me.  I'm not too fond of multi-level
>> warnings since few users take advantage of anything but the
>> default, but this case is simple and innocuous enough that
>> I don't think it can do harm.
>>
>>>
>>> Bootstrapped and regtested on x86_64-pc-linux-gnu.
>>> OK for trunk?
>>>
>>> If so, would it make sense to add -Wcatch-value=1 to -Wextra or even -Wall?
>>> I would do this in a seperate patch, becuase I haven't checked what that
>>> would mean for the testsuite.
>>
>> I can't think of a use case for polymorphic slicing that's not
>> harmful so unless there is a common one that escapes me, I'd say
>> -Wall.
>
> So that's what I committed after Jason's OK.
>
>> What are your thoughts on enhancing the warning to also handle
>> the rethrow case?
>>
>> Also, it seems that a similar warning would be useful even beyond
>> catch handlers, to help detect slicing when passing arguments to
>> functions by value.  Especially in code that mixes OOP with the
>> STL (or other template libraries).  Have you thought about tackling
>> that at some point as well?
>
> I don't have any plans to handle handle the rethrow case.
>
> A general slicing warning would be very nice to have. Actually
> clang-tidy has one (which is a little buggy, though).
> Implementing this is over my head, though.
> I'd rather stick with something less ambitious.

FWIW I think it would be pretty straightforward to do this in
convert_like_real, under the ck_base case.

Jason


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