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

[Volker Reichelt <v dot reichelt at netcologne dot de>]

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.

> Martin
> 
>>
>> Regards,
>> Volker