[PATCH] Restrict -Winconsistent-missing-override warnings on class templates with dependent bases

[jahanian]

> On Mar 6, 2015, at 3:15 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
> 
> 
> 
> On Fri, Mar 6, 2015 at 2:57 PM, jahanian <fjahanian at apple.com <mailto:fjahanian at apple.com>> wrote:
> 
>> On Mar 6, 2015, at 2:47 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>> 
>> 
>> 
>> On Fri, Mar 6, 2015 at 2:45 PM, jahanian <fjahanian at apple.com <mailto:fjahanian at apple.com>> wrote:
>> 
>>> On Mar 6, 2015, at 9:36 AM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>>> 
>>> Would it be plausible to check this on templates directly, rather than on their instantiations? This would be less work in the case of multiple instantiations, avoid redundant diagnostics, fail on templates without instantiations rather than creating a lurking failure, and we might even get all the "dependent" tests for free - because we wouldn't be able to look through the dependent types at all.
>> 
>> It could be plausible. But, in similar cases, checking is done on the instantiated templates and not on the templates directly. This adds another check in the
>> same code block. Providing a new iteration on templates for this one check is prohibitively expensive (and we normally don’t do much checking on templates).
>> 
>> It is? I'd be curious to see the numbers, as it sounds like you have some.
> 
> No I don’t have any. But iterating over templates looking for methods would add to cost.
> 
> Well, if we skipped template instantiations it wouldn't necessarily be a strict increase - we'd only visit the template pattern, and none of the instantiations.

We already visit template instantiations for issuing other diagnostics. New overhead is minimal comparing to iterating over template declarations looking for methods.

>  
> Are we iterating over templates for other diagnostics?
> If so, I can add this there.
> 
> I don't recall any particular cases for/against.
>  
> 
>>  
>> Do you see anything inherently wrong to adding this check where it is?
>> 
>> Just the issues I mentioned - duplicate diagnostics in the case of multiple instantiations (& no diagnostics in the case of no instantiations).
> 
> AFAIK, it is not common practice to add diagnostics on template declarations as this will break SDKs.
> 
> Not sure I follow - any type in a header/library could be violating this rule, whether it's a class template or a straight class.

By this I meant that we don’t issue diagnostics on template declarations in other situations. This will be the “first” and there
may be templates that no one is using and this will break SDKs for those (something template writers may not be used to).
>  
> Furthermore, if template is not used
> in practice, there is no point issuing this diagnostic.
> 
> Same would be true of non-template classes in headers, but we don't avoid those.

Templates are special in that for whatever reasons, we skip diagnostics on them.

>  
> Can you point to similar situations where templates are iterated over checking for method
> inconsistencies or other types of diagnostics?
> 
> Not that I recall/off-hand.

If we do none. This will be first and people may have strong opinion on the “firsts” :).

> 
> 
> I do recall Ted objecting to my desire to move unreachable-code warnings to act on template patterns rather than template instantiations  (& he didn't have numbers either, but the case is different - in that case there are many more function template definitions in headers that aren't necessarily instantiated (owing to the language need for the definitions to be available for instantiations) - unlike classes V class templates, which just appear in headers in a fairly similar way, not a particularly biased ratio one way or the other (except by library design preferences))

I think similar situation is applicable to class templates which may not be instantiated. I just don’t know enough about usages etc. to make a strong argument one way
or the other. So, other opinions are most welcome.
- Fariborz

> 
> - David
>  
> 
> - Fariborz
> 
>>  
>> 
>> - Fariborz
>> 
>>> 
>>> - David
>>> 
>>> On Wed, Feb 25, 2015 at 10:39 AM, jahanian <fjahanian at apple.com <mailto:fjahanian at apple.com>> wrote:
>>> 
>>> This patch restricts issuing -Winconsistent-missing-override when dealing with
>>> class template with dependent bases and dependent methods.
>>> Fixed pr22582 rdar://19917107 <>.
>>> Please review.
>>> 
>>> - Fariborz
>>> 
>>> 	
>>> 
>>> 
>>> _______________________________________________
>>> cfe-commits mailing list
>>> cfe-commits at cs.uiuc.edu <mailto:cfe-commits at cs.uiuc.edu>
>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits <http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits>
>>> 
>>> 
>> 
>> 
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20150306/a44e7b1e/attachment.html>