Add option to leave message in minibuffer when there's only one line

README.org

@@ -7,11 +7,11 @@ Get the file, add to load path, and
 #+END_SRC
 
 * Usage
-Show the documentation of the symbol at point: =eldoc-box-help-at-point=
-
-Show documentation upon hover: =eldoc-box-hover-mode=. Note that you need to enable ElDoc mode for this to work.
-
-Adjust =:background= of =eldoc-box-border= face for border color. Adjust =:background= of =eldoc-box-body= face for background color of childframe.
+-  =eldoc-box-help-at-point= :: Show the documentation of the symbol at point.
+- =eldoc-box-hover-mode= :: Show documentation upon hover. Note that you need to enable ElDoc mode for this to work.
+-  =eldoc-box-border= :: Adjust =:background= of this face for border color.
+- =eldoc-box-body= :: Adjust =:background= of  this face for background color of childframe.
+- =eldoc-box-only-multi-line= :: Set this to non-nil and eldoc-box only display multi-line message in childframe. One line messages are left in minibuffer.
 
 ** Use with eglot
 As of writing this README, eglot doesn't have a public mode hook, use this hook:

eldoc-box.el

@@ -39,6 +39,9 @@
 (defface eldoc-box-body '((t . (:background nil)))
   "Body face used in eglot doc childframe. Only :background is used.")
 
+(defvar eldoc-box-only-multi-line nil
+  "If non-nil, only use childframe when there are more than one line.")
+
 (defvar eldoc-box-frame-parameters
   '(
     ;; (left . -1)
@@ -169,7 +172,10 @@ Checkout `lsp-ui-doc--make-frame', `lsp-ui-doc--move-frame'."
   "Frontend for eldoc. Display STR in childframe and ARGS works like `message'."
   (when str
     (eldoc-box-quit-frame)
-    (eldoc-box--display (apply #'format str args))))
+    (let ((doc (apply #'format str args)))
+      (if (and eldoc-box-only-multi-line (eq (cl-count ?\n doc) 0))
+          (apply #'eldoc-minibuffer-message str args)
+        (eldoc-box--display (apply #'format str args))))))
 
 (define-minor-mode eldoc-box-hover-mode
   "Displays hover documentations in a childframe. This mode is buffer local."