bug#55096: Eldoc showing elisp variable value beside docs

["Štěpán Němec" <stepnem@gmail.com>]

On Mon, 25 Apr 2022 10:09:39 +0200
Lars Ingebrigtsen wrote:

> emacsq <laszlomail@protonmail.com> writes:
>
>> Eldoc showing the docs in the minibuffer is quite useful, but I often
>> check elisp variable values too in the code, and it can be quite handy
>> if eldoc shows that too simply by putting cursor on the variable.
>
> This would only work for global values, and in that case, you can just
> `C-x C-e' the variable if you're interested in the value.
>
> So it seems like this would be of marginal utility.  Anybody else got an
> opinion here?

FWIW, I've been running with some form of the following for many years,
and I find it extremely useful:

  ;; cf. `elisp-eldoc-var-docstring'
  (defun my-elisp-eldoc-var-docstring-with-value (callback &rest _)
    "Document variable at point.
  Intended for `eldoc-documentation-functions' (which see)."
    (when-let ((cs (elisp--current-symbol)))
      (when (and (boundp cs)
		 ;; nil and t are boundp!
		 (not (null cs))
		 (not (eq cs t)))
	(funcall callback
		 (format "%.1250S %s"
			 (symbol-value cs)
			 (let* ((doc (custom-variable-documentation cs))
				(more (- (length doc) 1000)))
			   (concat (propertize
				    (s-truncate 1000
						(if (string= doc "nil")
						    "Undocumented."
						  doc)
						"")
				    'face 'font-lock-doc-face)
				   (when (> more 0)
				     (format "[%sc more]" more)))))
		 :thing cs
		 :face 'font-lock-variable-name-face))))

It shows the current value, i.e. buffer-local for local variables, which
is what I want. (It also shows more of the doc string: I use multi-line
echo area.)

-- 
Štěpán