Add 'remark' diagnostic type in clang

[Tobias Grosser]

On 02/25/2014 11:20 AM, Tobias Grosser wrote:
> Hi,
>
> I would like to add the following patch. (I submitted a corresponding
> patch to LLVM).

Hi,

thanks to everybody for the comments. Here the conclusions I have taken.

1) We need a new severity level

The 'note' level is inherently attached to other diagnostics. We need a 
new severity level for informative remarks that are not attached to
any other diagnostic.

We have broad agreement here.

2) Adding the new severity level / the name of the diagnostic

Only small issues have been found in the patch. All of them have been 
addressed. The last open issues was the name of the diagnostic. Richard
proposed 'info' or 'remark'. Chris and Eric prefer to call the severity 
'info', in case there is no prior art. However, Alexander and Arthur 
mentioned prior art for 'remark' in both icc and edg. Also the comment 
from Arthur sounds right:

   I don't know of any compiler that uses the term "informative".
   Besides, that's redundant; *all* compiler diagnostics are purely
   "informative" by definition. The variable here is //severity//:
   fatal-error, recoverable-error, warning, remark, silent.

I personally preferred 'info' first, but now came to the conclusion
that 'remark' is the better option, except someone sees strong reasons 
to ignore the prior art.

I plan to resubmit this patch for review by itself to keep the in-flight 
patches small. It is mostly independent from the next step,
as 'remarks' are off by default.

3) How to enable 'remarks'

We need a way to enable 'remark' diagnostics. Quentin proposed to go
for an approach similar to the warning flags. Where we control remarks
with '-Rvector', '-Rloop-vector', ...

I will read a little bit through the existing option system to better 
understand what it is doing, possibly adding documentation / cleanups on 
my way. I will come back with a proposal here.

All the best,
Tobias