From 9484735c0651a412ad6e2a4d6628c740feda1419 Mon Sep 17 00:00:00 2001
From: Nathaniel Nicandro <nathanielnicandro@gmail.com>
Date: Thu, 21 Feb 2019 22:54:30 -0600
Subject: [PATCH] Fix undo in the REPL

When inserting continuation prompts, extra text deletion entries where being
added in `buffer-undo-list` which caused yanked text to not be undone fully
since it would add in those entries before undoing the yank.
---
 jupyter-repl.el      | 16 +++++++++++-----
 test/jupyter-test.el | 14 ++++++++++++++
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/jupyter-repl.el b/jupyter-repl.el
index 927a664..9678b2c 100644
--- a/jupyter-repl.el
+++ b/jupyter-repl.el
@@ -359,7 +359,8 @@ interpreted as `in'."
        ;; The insertion of a new prompt starts a new cell, don't consider the
        ;; buffer modified anymore. This is also an indicator for when undo's
        ;; can be made in the buffer.
-       (set-buffer-modified-p nil))
+       (set-buffer-modified-p nil)
+       (setq buffer-undo-list '((t . 0))))
       ((eq type 'out)
        ;; Output is normally inserted by first going to the end of the output
        ;; for the request. The end of the ouput for a request is at the
@@ -1099,10 +1100,15 @@ Return the new BOUND since inserting continuation prompts may add
 more characters than were initially in the buffer."
   (setq bound (set-marker (make-marker) bound))
   (set-marker-insertion-type bound t)
-  (while (and (< (point) bound)
-              (search-forward "\n" bound 'noerror))
-    (delete-char -1)
-    (jupyter-repl-insert-prompt 'continuation))
+  ;; Don't record these changes as it adds unnecessary undo information which
+  ;; interferes with undo.
+  (let ((buffer-undo-list t))
+    (while (and (< (point) bound)
+                (search-forward "\n" bound 'noerror))
+      ;; Delete the newline that is re-added by prompt insertion
+      ;; FIXME: Why not just overlay the newline?
+      (delete-char -1)
+      (jupyter-repl-insert-prompt 'continuation)))
   (prog1 (marker-position bound)
     (set-marker bound nil)))
 
diff --git a/test/jupyter-test.el b/test/jupyter-test.el
index 9be3abd..a082e4b 100644
--- a/test/jupyter-test.el
+++ b/test/jupyter-test.el
@@ -1115,6 +1115,20 @@ last element being the newest element added to the history."
         (jupyter-repl-syntax-propertize-function #'ignore (point-min) (point-max))
         (jupyter-test-text-has-property 'syntax-table '(1 . ?.) '(5 9))))))
 
+(ert-deftest jupyter-repl-undo ()
+  :tags '(repl yank undo)
+  (jupyter-test-with-python-repl client
+    (jupyter-ert-info ("Undo after yank undoes all the yanked text")
+      (kill-new  "import IPython\ndef foo(x)\n\treturn x")
+      (undo-boundary)
+      (yank)
+      (should (equal (jupyter-repl-cell-code) "import IPython\ndef foo(x)\n\treturn x"))
+      (let ((beg (jupyter-repl-cell-beginning-position)))
+        (undo)
+        (should (get-text-property beg 'jupyter-cell))
+        (goto-char (point-max))
+        (should (equal (jupyter-repl-cell-code) ""))))))
+
 ;;; `org-mode'
 
 (defvar org-babel-jupyter-resource-directory nil)