Expose ElDoc functions in a hook (Bug#28257)

* lisp/emacs-lisp/eldoc.el: Update commentary.
(eldoc--eval-expression-setup): Use new hook.
(eldoc--supported-p): Accomodate new hook.
(eldoc-documentation-functions): New hook.
(eldoc-documentation-default, eldoc-documentation-compose): New
functions.
(eldoc-documentation-function): Use 'eldoc-documentation-default' as new
default value.  Update documentation and custom attributes.
(eldoc-print-current-symbol-info): Accomodate possible null value for
'eldoc-documentation-function'.
* etc/NEWS: Mention them.
* doc/emacs/programs.texi (Emacs Lisp Documentation Lookup): Mention
new hook and changes to 'eldoc-documentation-function'.
* lisp/hexl.el (hexl-mode, hexl-revert-buffer-function):
* lisp/ielm.el (inferior-emacs-lisp-mode):
* lisp/progmodes/cfengine.el (cfengine3-mode):
* lisp/progmodes/elisp-mode.el (emacs-lisp-mode):
* lisp/progmodes/octave.el (octave-mode):
* lisp/progmodes/python.el (python-mode): Use new hook.

1 files changed, 12 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 54aab1a5b60..ee3a3c19e7c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -125,6 +125,18 @@ To revert to the previous behaviour,
 unconditionally aborts the current edebug instrumentation with the
 supplied error message.
 
++++
+** ElDoc
+
+*** New hook 'eldoc-documentation-functions' to be used for registering
+doc string functions.  This makes the results of all doc string
+functions accessible to the user through the existing single function hook
+'eldoc-documentation-function'.
+
+*** 'eldoc-documentation-function' is now a custom variable.
+Modes should use the new hook instead of this variable to register
+their backends.
+
 ** Tramp
 
 +++