Improve formatting for eldoc-box

We don't want visual-line-mode enabled.

We don't need the default markdown functions.

AFAICT the only way to handle this is with a somewhat ugly hack, as
discussed in the comment.

racket-xp.el

@@ -294,9 +294,7 @@ commands directly to whatever keys you prefer.
                      nil t)
            (add-hook 'eldoc-documentation-functions
                      #'racket-xp-eldoc-point
-                     nil t))
-         (when (boundp 'eldoc-box-buffer-hook)
-           (setq-local eldoc-box-buffer-hook nil)))
+                     nil t)))
         (t
          (racket-show nil)
          (racket--xp-clear)
@@ -324,6 +322,34 @@ commands directly to whatever keys you prefer.
                          hook
                          t))))))
 
+;; We do want to customize `eldoc-box-buffer-hook' because:
+;;
+;; - We don't want the default markdown adjustments (best case they do
+;; unnecessary work, worst case they might mis-format some things)
+;;
+;; - We want to disable `visual-line-mode'.
+;;
+;; Although a buffer-local hook is the usual way to handle something
+;; like this, it doesn't work for eldoc-box-buffer-hook, because the
+;; hook with /its/ buffer current, not ours. So we must resort to
+;; munging the global hook, and either doing something special for us,
+;; or doing the original default (so it keeps working when used by
+;; other modes that do use markdown docs). Sort of the moral
+;; equivalent of advising the hook.
+(defvar racket--orig-eldoc-box-buffer-hook nil)
+(defun racket-xp-eldoc-box-buffer-hook ()
+  (if (next-single-property-change (point-min) 'racket-xp-eldoc)
+      (visual-line-mode -1)
+    (run-hook-with-args 'racket--orig-eldoc-box-buffer-hook)))
+(eval-after-load 'eldoc-box
+  (when (boundp 'eldoc-box-buffer-hook)
+    (unless (member #'racket-xp-eldoc-box-buffer-hook
+                    eldoc-box-buffer-hook)
+      (setq racket--orig-eldoc-box-buffer-hook
+            eldoc-box-buffer-hook)
+      (setq eldoc-box-buffer-hook
+            (list #'racket-xp-eldoc-box-buffer-hook)))))
+
 ;;; Change hook and idle timer
 
 (defvar-local racket--xp-annotate-idle-timer nil)
@@ -666,12 +692,18 @@ racket-xp-doc and help-echo text properties added by
                 ('summary (racket--cmd/await nil `(bluebox ,tag)))
                 ('complete (racket--path+anchor->string path anchor)))))
          (when (or help-echo str)
-           (racket--eldoc-do-callback callback thing (concat help-echo str))))))
+           (racket--eldoc-do-callback callback thing
+                                      (propertize
+                                       (concat help-echo str)
+                                       'racket-xp-eldoc t))))))
     (_
      (pcase (racket--get-text-property/bounds pos 'help-echo)
        (`(,str ,beg ,end)
         (let ((thing (buffer-substring-no-properties beg end)))
-          (racket--eldoc-do-callback callback thing str)))))))
+          (racket--eldoc-do-callback callback thing
+                                     (propertize
+                                      str
+                                      'racket-xp-eldoc t))))))))
 
 (defun racket--get-text-property/bounds (pos prop)
   "Like `get-text-property' but also returning the bounds."