bug#62508: 28.2; vhdl-mode ModelSim compile warnings aren't highlighted

[Eli Zaretskii <eliz@gnu.org>]

> From: Cyril Arnould <cyril.arnould@outlook.com>
> Date: Tue, 28 Mar 2023 19:43:40 +0000
> 
> This bug is twofold. On one hand, the current configuration of the
> ModelSim compiler is not able to parse and highlight the Warnings as
> warnings when using vhdl-compile, they are listed as errors. With GHDL
> on the other hand, the *compile* buffer differentiates between
> warnings and errors when highlighting. I can't reproduce this at home
> since I don't have a ModelSim license there, but you can see the effect
> in a screenshot from the bugfix that introduced this:
> 
> https://lists.gnu.org/archive/html/bug-gnu-emacs/2014-10/msg01377.html
> 
> I have tried looking into modifying the regexp but for the life of me I
> couldn't figure out how compile.el differentiates between warnings and
> errors.
> 
> Now the second problem is that I believe the way bug#5768 was fixed is
> actually not compatible with ModelSim, but with ModelSim-Intel (formerly
> Altera). As the link above shows, the warnings are formatted as follows:
> 
> ** Warning: [3] counter_rtl.vhd(18): (vcom-1246) Range 5 downto 6 is null.
> 
> My ModelSim actually formats its Warnings differently, for example:
> 
> ** Warning: (vcom-1246) counter_rtl.vhd(18): Range 5 downto 6 is null.
> 
> You can look into the ModelSim documentation under the "Message Format"
> Section. I am not 100% certain if the number in brackets could also
> appear in my Installation but possibly the number is just optional. The
> regexp could be modified to allow both, this would avoid introducing a
> separate Modelsim-Intel compiler.
> 
> I can verify any fixes at work.

As I'm not an expert on vhdl, I CC people who might help us with this
issue.

Thanks.