[PATCH] D66919: Warn about zero-parameter K&R definitions in -Wstrict-prototypes

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D66919#1651108 <https://reviews.llvm.org/D66919#1651108>, @dexonsmith wrote:

> In D66919#1650775 <https://reviews.llvm.org/D66919#1650775>, @aaron.ballman wrote:
>
> > In D66919#1650174 <https://reviews.llvm.org/D66919#1650174>, @dexonsmith wrote:
> >
> > > This could cause a lot of churn in existing projects (especially with `static void foo()`), without giving Clang any new information.  I'm wary of this.
> >
> >
> > Those projects likely aren't aware they're using prototypeless functions, which are trivial to call incorrectly. I suspect this diagnostic will find real bugs in code.
>
>
> To be clear, my understanding is that `-Wstrict-prototypes` already warns on non-prototype declarations like this:
>
>   void foo();
>
>
> we just don't warn on non-prototype defining declarations, where the meaning is unambiguous:
>
>   void foo() {}
>


There are two different warnings, and perhaps we're speaking about different ones. We have a warning about not having a prototype (warning: this function declaration is not a prototype) and we have a warning about not seeing a preceding prototype (warning: this old-style function definition is not preceded by a prototype). I think this patch deals with the latter.

>> It's not incorrect to pass arguments to a function without a prototype, so that should not be an error. It is incorrect to pass the wrong number or types of arguments to a function without a prototype. It's not a bad idea to error in that circumstances, but there's no solution for `extern void foo()` where we don't see the actual definition.
> 
> Given my understanding, then the only corner case that's left is when we *do* see the definition.

Yeah, and we already handle that situation with an un-ignorable warning: https://godbolt.org/z/TPklNE

However, I think the inconsistency this patch is addressing is that we warn inconsistently here: https://godbolt.org/z/wvipEs I would expect the definition of `bar()` to warn similar to the definition of `foo()` for the same reasons that `foo()` is diagnosed.


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