Re: master 9ade7ea: Fix Eldoc problem when loading on Emacs 26.3

[João Távora]

João Távora <joaotavora@gmail.com> writes:

> Noam Postavsky <npostavs@gmail.com> writes:
>>> makunbound, as Noam suggested, doesn't work.
>>> Is there an easy way to "unlocalize" a symbol?
>> Oh, maybe kill-local-variable?
>
> No, that doesn't work either.  I was looking at data.c and alloc.c and

> Maybe come up with a better idea, or maybe, like Stefan suggests, don't
> make it an alias at all, just deprecate it and keep using it instead of
> eldoc-documentation-strategy when we find it to be bound.

That sort of works, but it forces extensions that do want to
"Package-Require" eldoc to remember to unbind
eldoc-documentation-function if they are loaded on older Emacs versions,
which is undesirable.

So I think a better plan is just to reverse the variable alias on older
Emacs versions.  Attaching the patch that does this:

commit b7019ed5e76dda40642db1b20d3dd1484b2536e6
Author: João Távora <joaotavora@gmail.com>
Date:   Fri Jul 10 20:49:54 2020 +0100

    Sort out Eldoc backward compatibility of eldoc-documentation-function
    
    Use eldoc--documentation-strategy-defcustom to decide in which
    direction to make the variable alias, depending on the Emacs version.
    
    * lisp/emacs-lisp/eldoc.el
    (eldoc--documentation-strategy-defcustom): Helper macro.
    (eldoc-documentation-strategy, eldoc-documentation-function): Use it.
    (Version): Bump to 1.5.0

diff --git a/lisp/emacs-lisp/eldoc.el b/lisp/emacs-lisp/eldoc.el
index 7964c4c45a..ccae09a906 100644
--- a/lisp/emacs-lisp/eldoc.el
+++ b/lisp/emacs-lisp/eldoc.el
@@ -5,7 +5,7 @@
 ;; Author: Noah Friedman <friedman@splode.com>
 ;; Keywords: extensions
 ;; Created: 1995-10-06
-;; Version: 1.4.0
+;; Version: 1.5.0
 ;; Package-Requires: ((emacs "26.3"))
 
 ;; This is a GNU ELPA :core package.  Avoid functionality that is not
@@ -535,10 +535,27 @@ eldoc-documentation-enthusiast
                         (if (stringp str) (funcall callback str))
                         nil))))
 
-(define-obsolete-variable-alias 'eldoc-documentation-function
-  'eldoc-documentation-strategy "eldoc-1.1.0")
-
-(defcustom eldoc-documentation-strategy #'eldoc-documentation-default
+;; JT@2020-07-10: Eldoc is pre-loaded, so in in Emacs < 28 we can't
+;; make the "old" `eldoc-documentation-function' point to the new
+;; `eldoc-documentation-strategy', so we do the reverse.  This allows
+;; for Eldoc to be loaded in those older Emacs versions and work with
+;; whomever (major-modes, extensions, ueser) sets one of the other
+;; variable.
+(defmacro eldoc--documentation-strategy-defcustom
+    (main secondary value docstring &rest more)
+  "Defcustom helper macro for sorting `eldoc-documentation-strategy'."
+  (declare (indent 2))
+  `(if (< emacs-major-version 28)
+       (progn
+         (defcustom ,secondary ,value ,docstring ,@more)
+         (defvaralias ',main ',secondary ,docstring))
+       (progn
+         (defcustom ,main ,value ,docstring  ,@more)
+         (defvaralias ',secondary ',main ,docstring))))
+
+(eldoc--documentation-strategy-defcustom eldoc-documentation-strategy
+    eldoc-documentation-function
+  #'eldoc-documentation-default
   "How to collect and organize results of `eldoc-documentation-functions'.
 
 This variable controls how `eldoc-documentation-functions', which