[Fix #2126] Preserve the point position in cider-format-buffer

That's pretty important for people who want to apply the formatting
automatically on buffer save.

Unfortunately we can't use save-excursion here, because we're
deleting the location we want to preserve, so we have to get a bit
more creative.

Author: bbatsov

CHANGELOG.md

@@ -13,6 +13,7 @@
 * [cider-nrepl#438](https://github.com/clojure-emacs/cider-nrepl/pull/438): Improve startup time by deferring loading CIDER's middleware until the first usage.
 * [#2078](https://github.com/clojure-emacs/cider/pull/2078): Improve startup time by bundling together sync requests during startup.
 * `cider-rotate-default-connection` will warn if you use it with only a single active connection.
+* `cider-format-buffer` preserves the point position.
 
 ### Bugs Fixed
 

cider-interaction.el

@@ -1771,8 +1771,15 @@ of the buffer into a formatted string."
   (let* ((original (substring-no-properties (buffer-string)))
          (formatted (funcall formatter original)))
     (unless (equal original formatted)
-      (erase-buffer)
-      (insert formatted))))
+      (let ((current-line (line-number-at-pos))
+            (current-column (current-column)))
+        (erase-buffer)
+        (insert formatted)
+        ;; we have to preserve our point location in the buffer,
+        ;; but save-excursion doesn't work, because of erase-buffer
+        (goto-char (point-min))
+        (forward-line (1- current-line))
+        (forward-char current-column)))))
 
 (defun cider-format-buffer ()
   "Format the Clojure code in the current buffer."