[PATCH] Add --with-diagnostics-urls configuration option and GCC_URLS env var

[Jakub Jelinek]

On Thu, Dec 19, 2019 at 03:24:19PM -0500, David Malcolm wrote:
> Currently -fdiagnostics-urls defaults to "auto" and this works
> (e.g. for recent gnome-terminal, and is gracefully discarded by
> konsole5), but there have been reports of incompatibilities of the
> feature with various other terminals.
> 
> This patch adds a configuration option to change this default, based
> on Jakub's analogous change to -fdiagnostics-color (r217540).  One
> possible configure-time option is --with-diagnostics-urls=auto-if-env,
> which adds support for a GCC_URLS environment variable to control
> the default (again by analogy with the --with-diagnostics-color
> configure-time support for changing -fdiagnostics-color).

I think it would be better to have GCC_URLS env var to be be more consistent
with GCC_COLORS, so yes, have the never,auto,auto-if-env,always
configure possibilities like for colors and for auto-if-env don't print
URLS if the env var is not present, but on top of that, parse also the value
of the env var like parse_gcc_colors does, and have a way to disable urls
even with -fdiagnostics-urls=always (like GCC_COLORS= disables colors),
and perhaps use the env var to select between the ST and BEL terminator
as apparently some terminals like one or the other more.
So perhaps accept GCC_URLS= and GCC_URLS=no as disabling, GCC_URLS=bel
as the (default) case for BEL termination and GCC_URLS=st for the ST
termination?
E.g. have a way even for a compiler configured that it will work with new
terminals most of them time and thus --with-diagnostics-urls=always that
if somebody sshs to some machine from some old host, GCC_URLS=no (or none?)
can be still used to disable it, without the need to tweak build system to
inject there some flags.

> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu; I
> tested the --with-diagnostics-urls=auto-if-env and GCC_URLS behavior
> manually.
> 
> Jakub: does this look sane to you?  (given that this is heavily based
> on your 2014 patches for --with-diagnostics-color).

	Jakub