[cfe-dev] Weird diagnostic about non-type template argument

[Enea Zaffanella]

Chandler Carruth wrote:
> On Mon, Aug 16, 2010 at 12:31 AM, Abramo Bagnara 
> <abramo.bagnara at gmail.com <mailto:abramo.bagnara at gmail.com>> wrote:

[... snip ...]

>     3) that apart the diagnostic message is misleading: non-type template
>     argument might (and sometimes should, see the following line in source)
>     be surrounded by parentheses
> 
> 
> The second line is a completely different non-type template argument: an 
> integral constant-expression. There are no parentheses around the 
> template argument, there are parentheses as part of the 
> constant-expression, which allows parentheses among many other 
> constructs. It is certainly unfortunate that there is no way to write a 
> '>' in an ICE without parentheses, but I don't think that artifact 
> necessarily warrants allowing parentheses for all template arguments, or 
> even for all non-type template arguments...

I think that, in point 3, Abramo was just referring to the wording of 
the diagnostic, which maybe could be improved.

I don't think that usual C++ programmers can easily tell the difference 
(if any) from a non-type template argument and the constant expression 
that denotes a non-type template argument. So, it might be appropriate 
to change the message wording to something like:

non-type template argument having pointer type cannot be surrounded by 
paretheses
    or
pointer-type expression used as non-type template argument cannot be ...

or something similar.

Cheers,
Enea.