Re: [PATCH] binutils: experimental use of libdiagnostics in gas

[David Malcolm <dmalcolm@redhat.com>]

On Tue, 2023-11-07 at 16:57 +0100, Clément Chigot wrote:
> > > However, I'm not sure how you're planning to make the transition.
> > > But
> > > currently, it looks like libdiagnostics is either enabled and
> > > thus
> > > the
> > > new format being produced, either it's not and we do have the
> > > legacy
> > > format. I think the transition should be smoother than that,
> > > there
> > > are
> > > probably thousands of tests, scripts, whatever out in the wild
> > > expecting this legacy format. Allowing both formats within the
> > > same
> > > executable, basically chosen by a flag, would probably ease the
> > > transition.
> > 
> > Yes.  I'm assuming that consumers of libdiagnostics would have a
> > configure-time test for the availability of libdiagnostics.  In the
> > example I gave, it was just a compile-time "choice" (I'm not an
> > expert
> > at autotools, so I hacked all of that up for now)... but if the
> > feature
> > is available, it could be a run-time choice.
> > 
> > We've been adding new features to GCC's diagnostic output over the
> > years (adding column numbers, showing macro expansions, quoting
> > source
> > code with underlines, fix-it hints, etc), but each time we've added
> > a
> > flag to turn them off (e.g. -fno-diagnostics-show-line-numbers,  -
> > fno-
> > diagnostics-show-labels, etc).
> > 
> > As of GCC 11 we have a -fdiagnostics-plain-output which "requests
> > that
> > diagnostic output look as plain as possible, which may be useful
> > when
> > running dejagnu or other utilities that need to parse diagnostics
> > output and prefer that it remain more stable over time."
> 
> I guess starting by a configure-time choice before such flags like
> -fdiagnostics-plain-output are implemented is enough. I merely wish
> that there is a way to preserve the old output, giving people the
> time
> to experiment and then transitioning all their tools.
> 
> We can also introduce a flag like "-fdiagnostics-legacy-output`.
> Though, I'm fearing it will never be removed, meaning maintaining the
> previous code forever... 

One other consideration here may be bootstrapping a toolchain (e.g.
bringing up a new CPU architecture) and thus minimizing dependencies. 
binutils is such an important component that perhaps you'd want to
retain a minimal implementation of diagnostics that doesn't bring in an
external requirement? especially one based on GCC 14 (which itself
requires GCC 4.8 or later to build), e.g. configuring "--without-
libdiagnostics" or somesuch?

> A configure-time choice can be more easily
> enabled by default in a few versions and then removed completely
> after
> another bunch of versions.
> 
> 

[...snip...]

Dave