[cfe-dev] Doubt on a couple of warnings on deleted functions

[Richard Smith]

On Mon, Apr 21, 2014 at 7:47 AM, David Blaikie <dblaikie at gmail.com> wrote:

> Yep
> Both of these sound like bugs and should be able to be fixed just by
> checking for a non-deleted definition. I'm not sure if there's a particular
> function to test that.
>
I think the first warning is entirely appropriate. The point of this
warning is that every external linkage function should be declared in a
header file; it'd help if the warning suggested something like 'mark this
function 'static' if it's not intended to be used in other files' or
similar.

> The unused variable one might crop up in defaulted functions too, in which
> case we'll want to check for a user provided definition.
>
I agree on both counts. The same warning is visible here:

struct S { S(const S&s); }; S::S(const S&s) = default;


> On Apr 21, 2014 3:35 AM, "Nicola Gigante" <nicola.gigante at gmail.com>
> wrote:
>
>> Hello.
>>
>> Consider this:
>>
>> $ cat example.cpp
>> void func(int x) = delete;
>> $ clang++ -std=c++11 -fsyntax-only -Wunused-parameter
>> -Wmissing-prototypes example.cpp
>> example.cpp:1:6: warning: no previous prototype for function 'func'
>> [-Wmissing-prototypes]
>> void func(int x) = delete;
>>      ^
>> example.cpp:1:15: warning: unused parameter 'x' [-Wunused-parameter]
>> void func(int x) = delete;
>>               ^
>> 2 warnings generated.
>>
>> The two warnings seems false positives:
>>
>> 1) why does it warn about a missing prototype? One can't add a prototype
>> because
>> he'll get this error:
>>
>> error: deleted definition must be first declaration
>> void func(int x) = delete;
>>
>> So, the deleted definition is acting like a prototype itself, doesn't it?
>> I think the warning
>> is wrong.
>>
>> 2) Does it make sense to warn about an unused parameter on a deleted
>> definition?
>> Of course is unused, but it can't be used anyway.
>> This force the programmer to avoid parameters name, like:
>> void func(int) = delete;
>> but this can reduce readability and it seems to me there's no reason to
>> force it.
>>
>> Note that these warnings pop up only on free functions. Deleted member
>> functions
>> don't generate these warnings in these cases.
>>
>> Does it make sense to fix these issues?
>>
>> This mail is a part of a more general effort of mine to be able to
>> warning-less include
>> (with -Weverything, more or less) the LLVM headers that I use in my
>> project.
>> I think (and hope) more will follow.
>>
>> Thanks,
>> Nicola
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>>
>
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