[cfe-commits] PATCH: Generate more useful messages for out-of-line definition errors

[Douglas Gregor]

On Jul 22, 2011, at 4:19 PM, Kaelyn Uhrain wrote:

> Here's a patch to improve the messages for out-of-line definition errors by including the function's signature along with its name, and in the candidate function notes including the candidates name and signature as namespace qualifiers aren't always apparent at the line of code with the declaration.
> 
> The patch is also available for review at http://codereview.appspot.com/4817047
> 
> For example, given a file tmp.cpp containing:
> 
> namespace N2 {
>  struct S1;
> 
>   namespace N1 {
>    struct S2 {
>      void func(S1*);
>    };
> 
>    struct S1 {};
>   }
> }
> void N2::N1::S2::func(S1*) {}
> 
> Clang currently reports:
> 
> tmp.cpp:12:18: error: out-of-line definition of 'func' does not match any declaration in 'N2::N1::S2'
> void N2::N1::S2::func(S1*) {}
>      ~~~~~~~~~~~~^
> 
> Sadly, g++ (version 4.4.3) gives better messages:
> 
> tmp.cpp:12: error: prototype for 'void N2::N1::S2::func(N2::N1::S1*)' does not match any in class 'N2::N1::S2'
> tmp.cpp:6: error: candidate is: void N2::N1::S2::func(N2::S1*)
> 
> With this patch, clang yields:
> 
> tmp.cpp:12:18: error: out-of-line definition of 'void func(N2::N1::S1 *)' does not match any
>       declaration in 'N2::N1::S2'
> void N2::N1::S2::func(S1*) {}
>      ~~~~~~~~~~~~^
> tmp.cpp:6:11: note: member declaration 'void func(N2::S1 *)' nearly matches
>      void func(S1*);
>           ^


I'm not convinced we want to go in this direction. Or general principle for Clang diagnostics has been "show, don't tell", and we'd much rather point out specifically where the mismatch occurs than print out the entire type of the function and force the user to walk through the parameters to find the mismatch. This approach also allows us to add Fix-Its when the mismatch is due to something easily fixed (e.g., missing cv-qualifiers).

Overload-resolution diagnostics are a good model for what we want here. We don't just print out the types of the arguments and the types of the candidate functions; instead, we only point out the specific problem that caused us to reject each candidate, so users can focus on that parameter/argument pair.

	- Doug
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