Add duplicate-dwim (bug#56418)

Like duplicate-line but duplicates the region instead if active.
Rectangular regions are duplicated on the right-hand side.
The region remains active afterwards, to facilitate further
duplication or other operations on the same text.

* lisp/rect.el (rectangle--duplicate-right):
* lisp/misc.el (duplicate-dwim): New.
* test/lisp/misc-tests.el (misc--duplicate-dwim): New test.
* etc/NEWS: Announce.

2 files changed, 58 insertions, 0 deletions

diff --git a/lisp/misc.el b/lisp/misc.el
index 28c5d6e07f5..a53571f4639 100644
--- a/lisp/misc.el
+++ b/lisp/misc.el
@@ -79,6 +79,43 @@ Also see the `copy-from-above-command' command."
       (dotimes (_ n)
         (insert line "\n")))))
 
+(declare-function rectangle--duplicate-right "rect" (n))
+
+;; `duplicate-dwim' preserves an active region and changes the buffer
+;; outside of it: disregard the region when immediately undoing the
+;; actions of this command.
+(put 'duplicate-dwim 'undo-inhibit-region t)
+
+;;;###autoload
+(defun duplicate-dwim (&optional n)
+  "Duplicate the current line or region N times.
+If the region is inactive, duplicate the current line (like `duplicate-line').
+Otherwise, duplicate the region, which remains active afterwards.
+If the region is rectangular, duplicate on its right-hand side.
+Interactively, N is the prefix numeric argument, and defaults to 1."
+  (interactive "p")
+  (unless n
+    (setq n 1))
+  (cond
+   ;; Duplicate rectangle.
+   ((bound-and-true-p rectangle-mark-mode)
+    (rectangle--duplicate-right n)
+    (setq deactivate-mark nil))
+
+   ;; Duplicate (contiguous) region.
+   ((use-region-p)
+    (let* ((beg (region-beginning))
+           (end (region-end))
+           (text (buffer-substring beg end)))
+      (save-excursion
+        (goto-char end)
+        (dotimes (_ n)
+          (insert text))))
+    (setq deactivate-mark nil))
+
+   ;; Duplicate line.
+   (t (duplicate-line n))))
+
 ;; Variation of `zap-to-char'.
 
 ;;;###autoload
diff --git a/lisp/rect.el b/lisp/rect.el
index 47df95b04e4..eebbf999d40 100644
--- a/lisp/rect.el
+++ b/lisp/rect.el
@@ -930,6 +930,27 @@ Ignores `line-move-visual'."
     (mapc #'delete-overlay (nthcdr 5 rol))
     (setcar (cdr rol) nil)))
 
+(defun rectangle--duplicate-right (n)
+  "Duplicate the rectangular region N times on the right-hand side."
+  (let ((cols (rectangle--pos-cols (point) (mark))))
+    (apply-on-rectangle
+     (lambda (startcol endcol)
+       (let ((lines (list nil)))
+         (extract-rectangle-line startcol endcol lines)
+         (move-to-column endcol t)
+         (dotimes (_ n)
+           (insert (cadr lines)))))
+     (region-beginning) (region-end))
+    ;; Recompute the rectangle state; no crutches should be needed now.
+    (let ((p (point))
+          (m (mark)))
+      (rectangle--reset-crutches)
+      (goto-char m)
+      (move-to-column (cdr cols) t)
+      (set-mark (point))
+      (goto-char p)
+      (move-to-column (car cols) t))))
+
 (provide 'rect)
 
 ;;; rect.el ends here