Add user options to move point and scroll window during DND

* doc/emacs/frames.texi (Drag and Drop):
* etc/NEWS: Document new options 'dnd-scroll-margin' and
'dnd-indicate-insertion-point'.
* lisp/dnd.el (dnd-protocol-alist):
(dnd-open-remote-file-function):
(dnd-open-file-other-window): Add right group to defcustoms.
(dnd-scroll-margin, dnd-indicate-insertion-point): New user
options.
(dnd-handle-movement): New function.
* lisp/x-dnd.el (x-dnd-handle-xdnd):
(x-dnd-handle-motif): Call `dnd-handle-movement' when
appropriate.

doc/emacs/frames.texi

@@ -1196,6 +1196,18 @@ the variable @code{dnd-open-file-other-window}.
   The XDND and Motif drag and drop protocols, and the old KDE 1.x
 protocol, are currently supported.
 
+@vindex dnd-indicate-insertion-point
+@vindex dnd-scroll-margin
+
+  It can be difficult to scroll a window or determine where dropped
+text will be inserted while dragging text onto an Emacs window.
+Setting the option @var{dnd-indicate-insertion-point} to a
+non-@code{nil} value makes point move to the location any dropped text
+will be inserted when the mouse moves in a window during drag, and
+setting @code{dnd-scroll-margin} to an integer value causes a window
+to be scrolled if the mouse moves within that many lines of the top
+or bottom of the window during drag.
+
 @vindex mouse-drag-and-drop-region
   Emacs can also optionally drag the region with the mouse into
 another portion of this or another buffer.  To enable that, customize

etc/NEWS

@@ -195,6 +195,11 @@ to another program.
 If non-nil, this option allows scrolling a window while dragging text
 around without a scroll wheel.
 
++++
+** New user options 'dnd-indicate-insertion-point' and 'dnd-scroll-margin'.
+These options allow adjusting point and scrolling a window when
+dragging items from another program.
+
 +++
 ** New function 'command-query'.
 This function makes its argument command prompt the user for

lisp/dnd.el

@@ -42,8 +42,7 @@
   `((,(purecopy "^file:///")  . dnd-open-local-file)	; XDND format.
     (,(purecopy "^file://")   . dnd-open-file)		; URL with host
     (,(purecopy "^file:")     . dnd-open-local-file)	; Old KDE, Motif, Sun
-    (,(purecopy "^\\(https?\\|ftp\\|file\\|nfs\\)://") . dnd-open-file)
-   )
+    (,(purecopy "^\\(https?\\|ftp\\|file\\|nfs\\)://") . dnd-open-file))
 
   "The functions to call for different protocols when a drop is made.
 This variable is used by `dnd-handle-one-url' and `dnd-handle-file-name'.
@@ -57,7 +56,8 @@ If no match is found, the URL is inserted as text by calling `dnd-insert-text'.
 The function shall return the action done (move, copy, link or private)
 if some action was made, or nil if the URL is ignored."
   :version "22.1"
-  :type '(repeat (cons (regexp) (function))))
+  :type '(repeat (cons (regexp) (function)))
+  :group 'dnd)
 
 
 (defcustom dnd-open-remote-file-function
@@ -73,17 +73,66 @@ Predefined functions are `dnd-open-local-file' and `dnd-open-remote-url'.
 is the default on MS-Windows.  `dnd-open-remote-url' uses `url-handler-mode'
 and is the default except for MS-Windows."
   :version "22.1"
-  :type 'function)
+  :type 'function
+  :group 'dnd)
 
 
 (defcustom dnd-open-file-other-window nil
   "If non-nil, always use `find-file-other-window' to open dropped files."
   :version "22.1"
-  :type 'boolean)
+  :type 'boolean
+  :group 'dnd)
 
+(defcustom dnd-scroll-margin nil
+  "The scroll margin inside a window underneath the cursor during drag-and-drop.
+If the mouse moves this many lines close to the top or bottom of
+a window while dragging text, then that window will be scrolled
+down and up respectively."
+  :type '(choice (const :tag "Don't scroll during mouse movement")
+                 (integer :tag "This many lines from window top or bottom"))
+  :version "29.1"
+  :group 'dnd)
+
+(defcustom dnd-indicate-insertion-point nil
+  "Whether or not point should follow the position of the mouse.
+If non-nil, the point of the window underneath the mouse will be
+adjusted to reflect where any text will be inserted upon drop
+when the mouse moves while receiving a drop from another
+program."
+  :type 'boolean
+  :version "29.1"
+  :group 'dnd)
 
 ;; Functions
 
+(defun dnd-handle-movement (posn)
+  "Handle mouse movement to POSN when receiving a drop from another program."
+  (when dnd-scroll-margin
+    (ignore-errors
+      (let* ((row (cdr (posn-col-row posn)))
+             (window (when (windowp (posn-window posn))
+                       (posn-window posn)))
+             (text-height (window-text-height window))
+             ;; Make sure it's possible to scroll both up
+             ;; and down if the margin is too large for the
+             ;; window.
+             (margin (min (/ text-height 3) dnd-scroll-margin)))
+        ;; At 2 lines, the window becomes too small for any
+        ;; meaningful scrolling.
+        (unless (<= text-height 2)
+          (cond
+           ;; Inside the bottom scroll margin, scroll up.
+           ((> row (- text-height margin))
+            (with-selected-window window
+              (scroll-up 1)))
+           ;; Inside the top scroll margin, scroll down.
+           ((< row margin)
+            (with-selected-window window
+              (scroll-down 1))))))))
+  (when dnd-indicate-insertion-point
+    (ignore-errors
+      (goto-char (posn-point posn)))))
+
 (defun dnd-handle-one-url (window action url)
   "Handle one dropped url by calling the appropriate handler.
 The handler is first located by looking at `dnd-protocol-alist'.

lisp/x-dnd.el

@@ -499,7 +499,7 @@ FORMAT is 32 (not used).  MESSAGE is the data part of an XClientMessageEvent."
 		       )))
 	   (x-send-client-message
 	    frame dnd-source frame "XdndStatus" 32 list-to-send)
-	   ))
+           (dnd-handle-movement (event-start event))))
 
 	((equal "XdndLeave" message)
 	 (x-dnd-forget-drop window))
@@ -676,7 +676,8 @@ FORMAT is 32 (not used).  MESSAGE is the data part of an XClientMessageEvent."
 				      frame
 				      "_MOTIF_DRAG_AND_DROP_MESSAGE"
 				      8
-				      reply)))
+				      reply)
+               (dnd-handle-movement (event-start event))))
 
 	    ((eq message-type 'XmOPERATION_CHANGED)
 	     (let* ((state (x-dnd-get-state-for-frame frame))