[cfe-dev] Applicability of -Wunused-param

[Stephan Bergmann via cfe-dev]

On 18/09/2018 03:40, George Karpenkov via cfe-dev wrote:
> Many projects, including LLVM have to turn -Wunused-param off, as it has too many false positives.
> 
> Most false positives stem from the fact that often a function has to take a parameter not because it wants to, but because:
> 
> 1. It’s part of an interface, and has to be API/ABI compatible
> 2. It overrides another function which does need that parameter
> 
>   However, this warning is still very useful when the function is:
> 
>   - static
>   - private
>   - in an anonymous namespace
> 
> This asks for a warning on unused parameters which is restricted to “private" (static local / etc) functions.

But the criteria 1/2 whether a function needs to have unused parameters 
are orthogonal to whether the function is "private" (per your vague 
notion of what that would mean).  For example, a pointer to a static 
function can be passed to an API that expects a certain function type.

(At least for C++, an approach to suppress false -Wunused-param is to 
leave the parameters that are unused per criteria 1/2 unnamed in the 
function definition.  But which of course doesn't catch cases where the 
parameter has been left unnamed "maliciously" and a -Wunused-param would 
be warranted.)