Re: How to find when a feature was introduced

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 7 Jul 2016 21:28:06 -0700 (PDT)
> From: Rusi <rustompmody@gmail.com>
> 
> So now I need to tell my students gnu-apl-mode will not run in emacsen less than
> version X
> 
> How to find out X?

First, try the NEWS method that someone else pointed to.

If that doesn't work, and the symbol is a defcustom, it should have a
:version tag (if it isn't, report that as a bug).

If that doesn't work either, or is inapplicable, the most elaborate
method that _always_ works is this:

  . C-h f SOMETHING or C-h v SOMETHING
  . note the place in the sources where SOMETHING is defined
  . go to the nearest Emacs Git repository and use Git facilities to
    find out the date on which the code was added
  . consult etc/HISTORY to see which Emacs release the date
    corresponds to

Notes:
(1) The Git facilities are "git annotate" and "git log -L".
(2) Due to branching before the release, a date that is before a
release doesn't necessarily mean the feature was in that release, you
will have to see when the release branch was cut; there should be a
Git tag at the branch point.