save excursion when formatting

close #392

Author: brotzeit

rust-rustfmt.el

@@ -331,9 +331,11 @@ Return the created process."
   ;; If emacs version >= 26.2, we can use replace-buffer-contents to
   ;; preserve location and markers in buffer, otherwise we can try to
   ;; save locations as best we can, though we still lose markers.
-  (if (version<= "26.2" emacs-version)
-      (rust--format-buffer-using-replace-buffer-contents)
-    (rust--format-buffer-saving-position-manually)))
+  (save-excursion
+    (save-window-excursion
+      (if (version<= "26.2" emacs-version)
+          (rust--format-buffer-using-replace-buffer-contents)
+        (rust--format-buffer-saving-position-manually)))))
 
 (defun rust-enable-format-on-save ()
   "Enable formatting using rustfmt when saving buffer."