Re: when do we remove backward compatibility definitions?

[Paul Eggert]

On 11/21/2017 09:37 AM, Sam Steingold wrote:
> What is the policy on removing such declarations?
>
> R releases?
> M major releases?
> Y years?
>
> Where is it officially documented?

I don't think we have an official policy, so how about this as a first 
cut: If the oldest GNU/Linux or other GNU distribution still in 
reasonably widespread use has Emacs version N, then we don't need to 
continue to support features that were marked obsolete in version N or 
earlier.

One way to estimate what "reasonably widespread use" means is to look at 
commercial suppliers and see what they're supporting. If even (say) Red 
Hat doesn't support an old version of Emacs any more, I would say that 
the version is so old that we needn't worry about it. With that in mind, 
currently I would say that Emacs 23.1 is the oldest Emacs we currently 
need to worry about, since RHEL 6 uses 23.1 and Red Hat plans to keep 
RHEL 6 in production (which means they'll fix bugs) through 2020-11-30. 
In contrast, RHEL 5 reached end-of-production on 2017-03-17 so we no 
longer need to worry about Emacs 21.4, which is what RHEL 5 used.

According to this estimate, if a function was marked obsolete in Emacs 
23.1 or earlier, we should be able to remove it in the master branch. If 
not, we should keep it for now.

My source for the abovementioned dates is:

https://access.redhat.com/support/policy/updates/errata