[Fix #2816] Update eldoc to work with Emacs 28.1

Author: bbatsov

CHANGELOG.md

@@ -28,6 +28,7 @@
 * [#2839](https://github.com/clojure-emacs/cider/pull/2839): Fix symbol-at-point on var-quoted symbols.
 * [#2807](https://github.com/clojure-emacs/cider/pull/2807): Fix require-repl-utils for shadow-cljs repls.
 * [#1971](https://github.com/clojure-emacs/cider/issues/1971), [#2628](https://github.com/clojure-emacs/cider/issues/2628): Don't try to font-lock multi-chunk results in the REPL.
+* [#2816](https://github.com/clojure-emacs/cider/issues/2816): Update eldoc to work with Emacs 28.1.
 
 ## 0.24.0 (2020-02-15)
 

cider-eldoc.el

@@ -473,7 +473,11 @@ Only useful for interop forms.  Clojure forms would be returned unchanged."
 (defun cider-eldoc-setup ()
   "Setup eldoc in the current buffer.
 eldoc mode has to be enabled for this to have any effect."
-  (setq-local eldoc-documentation-function #'cider-eldoc)
+  ;; Emacs 28.1 changes the way eldoc is setup.
+  ;; There you can have multiple eldoc functions.
+  (if (boundp 'eldoc-documentation-functions)
+      (add-hook 'eldoc-documentation-functions #'cider-eldoc nil t)
+    (setq-local eldoc-documentation-function #'cider-eldoc))
   (apply #'eldoc-add-command cider-extra-eldoc-commands))
 
 (provide 'cider-eldoc)