Fix frame size problem caused by markdown separators (issue#68)

* eldoc-box.el:
(eldoc-box--markdown-separator-display-props): New variable.
(eldoc-box--update-childframe-geometry): New workaround.
(eldoc-box--prettify-markdown-separator): Use the new variable.

eldoc-box.el

@@ -404,6 +404,8 @@ base on WIDTH and HEIGHT of childframe text window."
     (cons (or (eldoc-box--at-point-x-by-company) x)
           y)))
 
+(defvar eldoc-box--markdown-separator-display-props)
+
 (defun eldoc-box--update-childframe-geometry (frame window)
   "Update the size and the position of childframe.
 FRAME is the childframe, WINDOW is the primary window."
@@ -411,13 +413,18 @@ FRAME is the childframe, WINDOW is the primary window."
   ;; property of (space :width text) -- which is what we apply onto
   ;; markdown separators -- ‘window-text-pixel-size’ wouldn’t return
   ;; the correct value. Instead, it returns the current window width.
-  ;; So now the childram only grows in size and never shrinks. For
+  ;; So now the childram only grows in size and never shrinks.
-  ;; whatever reason, if we set the frame size very small before
+  ;;
-  ;; calculating window’s text size, it can return the right value.
   ;; (My guess is that the function takes (space :width text) at face
   ;; value, but that can’t be the whole picture because it works fine
   ;; when I manually evaluate the function in the childframe...)
-  (set-frame-size frame 1 1 t)
+  ;;
+  ;; The original workaround of setting the frame size to something
+  ;; small before calling ‘window-text-pixel-size’ works, but brings
+  ;; other problems. Now we just set the display property to nil
+  ;; before calling ‘window-text-pixel-size’, and set them back after.
+  (setcdr eldoc-box--markdown-separator-display-props nil)
+
   (let* ((size
           (window-text-pixel-size
            window nil nil
@@ -430,6 +437,11 @@ FRAME is the childframe, WINDOW is the primary window."
          (frame-resize-pixelwise t)
          (pos (funcall eldoc-box-position-function width height)))
     (set-frame-size frame width height t)
+
+    ;; Set the display property back.
+    (setcdr eldoc-box--markdown-separator-display-props
+            '(:width text))
+
     ;; move position
     (set-frame-position frame (car pos) (cdr pos))))
 
@@ -689,6 +701,13 @@ instead."
 
 ;;;; Markdown compatibility
 
+(defvar-local eldoc-box--markdown-separator-display-props
+    '(space :width text)
+  "Stores the display text property applied to markdown separators.
+
+Due to a bug, in ‘eldoc-box--update-childframe-geometry’, we
+modify the display property temporarily and then set it back.")
+
 (defun eldoc-box--prettify-markdown-separator ()
   "Prettify the markdown separator in doc returned by Eglot.
 Refontify the separator so they span exactly the width of the
@@ -697,11 +716,12 @@ childframe."
     (goto-char (point-min))
     (let (prop)
       (while (setq prop (text-property-search-forward 'markdown-hr))
-        (add-text-properties (prop-match-beginning prop)
+        (add-text-properties
-                             (prop-match-end prop)
+         (prop-match-beginning prop)
-                             '( display (space :width text)
+         (prop-match-end prop)
-                                face ( :strike-through t
+         `( display ,eldoc-box--markdown-separator-display-props
-                                       :height 0.4)))))))
+            face ( :strike-through t
+                   :height 0.4)))))))
 
 (defun eldoc-box--replace-en-space ()
   "Display the en spaces in documentation as regular spaces."