Inhibit undo-in-region for mouse-drag-region (bug#37700)

'mouse-drag-region' leaves the region active around the dragged text,
so a straight undo did not revert the entire operation.  To remedy
this, inhibit undo-in-region when the last command was
mouse-drag-region.  (Method suggested by Stefan Monnier.)

* lisp/mouse.el (undo-drag-region): Set the undo-inhibit-region property.
* lisp/simple.el (undo): Inhibit undo-in-region if the last command
had the undo-inhibit-region property set.
* doc/lispref/symbols.texi (Standard Properties):
* doc/lispref/text.texi (Undo): Document undo-inhibit-region.
* etc/NEWS: Announce the property.

1 files changed, 6 insertions, 0 deletions

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index ac444f6afeb..9bc6213f3ac 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -1451,6 +1451,12 @@ continuing to undo.
 This function does not bind @code{undo-in-progress}.
 @end defun
 
+Some commands leave the region active after execution in such a way that
+it interferes with selective undo of that command.  To make @code{undo}
+ignore the active region when invoked immediately after such a command,
+set the property @code{undo-inhibit-region} of the command's function
+symbol to a non-nil value.  @xref{Standard Properties}.
+
 @node Maintaining Undo
 @section Maintaining Undo Lists