[PATCHv2] implement -Wold-style-cast

[Sean Silva]

On Tue, Nov 26, 2013 at 12:37 AM, Alp Toker <alp at nuanti.com> wrote:

>
> On 22/11/2013 15:54, Ondřej Hošek wrote:
>
>> I've been trying to implement the relevant fix-it, but apart from not
>> being able to find the end of the expression being cast (to insert the
>> closing paren), the pathological case
>>
>> On Fri, Nov 22, 2013 at 2:13 AM, Dmitri Gribenko <gribozavr at gmail.com>
>> wrote:
>>
>>> (for example, static cast of a const cast)
>>>
>> might pose even more of a challenge, because I have to find and print
>> the "halfway" type:
>>
>> int i = 42;
>> const int *cpi = &i;
>> float *fi = (float *)cpi;
>> // -> reinterpret_cast<float *>(const_cast<int *>(cpi));
>>
>> This already spells trouble with regard to code formatting, and it
>> gets worse if I have a multi-level pointer type where some of the
>> levels are const and some aren't.
>>
>
> Hi Ondřej,
>
> I suspect the complexity of converting complex / multi-level C-style casts
> to C++-style casts just isn't worth the effort.
>

Agreed. This almost borders on a stylistic choice better-suited for
clang-tidy.

-- Sean Silva


>
> Even if you get it to work, the results wouldn't be pretty. It's better to
> encourage the developer to find an idiomatic solution by restructuring
> their code. Thanks for investigating this though.
>
> I'd say it's fine just to provide FixIt replacements for the common cases
> like straight const_cast<> that are easy to determine using existing
> CastOperation machinery.
>
>
>
>> (Also, I have to move the warning from Parser to Sema because only
>> then do I have the type information to generate a fix-it, so I don't
>> know at all how well it will work with templates.)
>>
>
> It's also fine to work on this incrementally if you could prepare a patch
> similar to the original one but moving the check to the right place in
> Sema, along with a TODO about the FixIt. (It shouldn't be added to Parse
> because that's a clear dead-end.)
>
> I don't know what user expectations are for -Wold-style-cast, but it might
> be worth silently permitting the idiomatic C-style CK_ToVoid used to
> suppress unused variable warnings as a special case. Do you have an opinion
> on that?
>
> Alp.
>
>
>
>
>> Cheers,
>> ~~ Ondra
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