bug#41544: 26.3; Possible incorrect results from color-distance

[Eli Zaretskii <eliz@gnu.org>]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Sat, 6 Jun 2020 15:29:31 +0200
> Cc: 41544@debbugs.gnu.org
> 
> 6 juni 2020 kl. 13.59 skrev Eli Zaretskii <eliz@gnu.org>:
> 
> > I have already pointed out the negative consequences: the fix you
> > proposed changes the behavior and return values of a low-level API
> > that is used in many places, both directly and indirectly. Thus, it
> > runs a high risk of producing bugs and breaking code that works well
> > enough now.
> 
> This is very speculative and hypothetical. Forgive me for being sceptical, but can you come up with a concrete and realistic example of what you think will break?

None at this time.  But bitter experience has taught me that they will
almost certainly come.  They always do.

> > My assumption is that making changes for purely academic and/or
> > aesthetic reasons is something that we should avoid.
> 
> That is a rather disparaging way of referring to fixes intended to make code working as advertised. 

If the problem is that the documentation doesn't match the behavior,
it is much easier for me to agree to amend the documentation.  In this
case, I think a Lisp program that interprets the documentation too
literally is making a mistake, but I'm not opposed to make that
clearer in the docs.

> > I don't even understand what each paragraph above tries to say, and/or
> > with what argument of mine it attempts to argue.
> 
> You were saying that #ffffffffffff is as good an approximation as any other, and I was showing that it's not.

Then I'm not convinced, sorry.

> > Specifically, what is there that is the current state of affairs, what
> > is that _should_be_ the state of affairs
> 
> The current state of affairs is that 'color-values' returns an incorrect value in certain cases. This can be fixed by making the code simpler and more robust.

We've made a full circle: I was talking about the effects on the
callers of color-values and color-name-to-rgb, and explicitly asked
that we don't limit ourselves to these functions alone.  If there are
no problems caused to the callers of these functions, then I think we
should leave the code alone.