Adjust describe-char-eldoc to new eldoc-documentation-functions protocol

* lisp/descr-text.el (describe-char-eldoc): Adjust to new
eldoc-documentation-functions protocol.

diff --git a/lisp/descr-text.el b/lisp/descr-text.el
index 22cfccb1fb29df350f0350ee7ae75b5351041124..776ce7618d55a7f6eb249bc17aca130d344faea9 100644 (file)
--- a/lisp/descr-text.el
+++ b/lisp/descr-text.el
@@ -919,7 +919,7 @@ condition, the function may return string longer than WIDTH, see
            (t name)))))))
 
 ;;;###autoload
-(defun describe-char-eldoc ()
+(defun describe-char-eldoc (_callback &rest _)
   "Return a description of character at point for use by ElDoc mode.
 
 Return nil if character at point is a printable ASCII
@@ -934,7 +934,12 @@ This function can be used as a value of
   (let ((ch (following-char)))
     (when (and (not (zerop ch)) (or (< ch 32) (> ch 127)))
       ;; TODO: investigate if the new `eldoc-documentation-functions'
-      ;; API could significantly improve this.
+      ;; API could significantly improve this.  JT@2020-07-07: Indeed,
+      ;; instead of returning a string tailored here for the echo area
+      ;; exclusively, we could call the (now unused) argument
+      ;; _CALLBACK with hints on how to shorten the string if needed,
+      ;; or with multiple usable strings which Eldoc picks according
+      ;; to its space contraints.
       (describe-char-eldoc--format
        ch
        (unless (eq eldoc-echo-area-use-multiline-p t)