[Bug c++/95725] Confusing error diagnostic in an invalid template

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95725

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Haoxin Tu from comment #6)
> Hi, there.
> 
> I hold the view that the compiler should have good fault tolerance, which
> means giving an input(even invalid), the compiler might emit appropriate
> error message diagnostics so that we can fix them into valid code according
> to the diagnostics. 

In an ideal world, yes. But this testcase is complete garbage. Nobody is going
to accidentally write that and be unable to see what's wrong with the code when
they get an error.

We could spend time giving perfect diagnostics for unrealistic garbage, or do
more useful things.

> I have tested in both GCC and Clang, the results show that GCC has lots of
> unrelated diagnostic messages than Clang. 

They're not unrelated, they're all directly related to the error in the code.

> In this report, GCC-trunk seems ok, but GCC-9 emits too many duplicated
> error messages. So I guess there might something not correct in FE.

So it's already fixed then.

> Finally, I am wondering if those cases are useful for the GCC community?

This particular case is not useful.