Add file dragging support to NS port

* lisp/dired.el (dired-mouse-drag-files): Document that
`dired-mouse-drag-files' now works on NS.

* lisp/term/ns-win.el (x-begin-drag): Handle FILE_NAME.
* src/nsselect.m (ns_decode_data_to_pasteboard): Handle file URL
type.
(ns_lisp_to_pasteboard, Fns_begin_drag): Handle new type `file'.

lisp/dired.el

@@ -254,7 +254,7 @@ The target is used in the prompt for file copy, rename etc."
 Dragging the mouse and then releasing it over the window of
 another program will result in that program opening the file, or
 creating a copy of it.  This feature is supported only on X
-Windows and Haiku.
+Windows, Haiku, and Nextstep (macOS or GNUstep).
 
 If the value is `link', then a symbolic link will be created to
 the file instead by the other program (usually a file manager)."

lisp/term/ns-win.el

@@ -903,6 +903,13 @@ See the documentation of `create-fontset-from-fontset-spec' for the format.")
     (when (and (member "STRING" targets)
                (stringp ns-dnd-selection-value))
       (push (cons 'string ns-dnd-selection-value) pasteboard))
+    (when (and (member "FILE_NAME" targets)
+               (file-exists-p ns-dnd-selection-value))
+      (push (cons 'file
+                  (url-encode-url (concat "file://"
+                                          (expand-file-name
+                                           ns-dnd-selection-value))))
+            pasteboard))
     (ns-begin-drag frame pasteboard action)))
 
 (provide 'ns-win)

src/nsselect.m

@@ -561,17 +561,34 @@ Updated by Christian Limpach (chris@nice.ch)
 ns_decode_data_to_pasteboard (Lisp_Object type, Lisp_Object data,
 			      NSPasteboard *pasteboard)
 {
+  NSArray *types, *new;
+
+  types = [pasteboard types];
+
   CHECK_SYMBOL (type);
 
   if (EQ (type, Qstring))
     {
       CHECK_STRING (data);
 
-      [pasteboard declareTypes: [NSArray arrayWithObject: NSPasteboardTypeString]
+      new = [types arrayByAddingObject: NSPasteboardTypeString];
+
+      [pasteboard declareTypes: new
 			 owner: nil];
       [pasteboard setString: [NSString stringWithLispString: data]
 		    forType: NSPasteboardTypeString];
     }
+  else if (EQ (type, Qfile))
+    {
+      CHECK_STRING (data);
+
+      new = [types arrayByAddingObject: NSPasteboardTypeFileURL];
+
+      [pasteboard declareTypes: new
+			 owner: nil];
+      [pasteboard setString: [NSString stringWithLispString: data]
+		    forType: NSPasteboardTypeFileURL];
+    }
   else
     signal_error ("Unknown pasteboard type", type);
 }
@@ -582,6 +599,9 @@ Updated by Christian Limpach (chris@nice.ch)
 {
   Lisp_Object tem, type, data;
 
+  [pasteboard declareTypes: [NSArray array]
+		     owner: nil];
+
   CHECK_LIST (object);
   for (tem = object; CONSP (tem); tem = XCDR (tem))
     {
@@ -642,6 +662,9 @@ Updated by Christian Limpach (chris@nice.ch)
   - `string' means DATA should be a string describing text that will
     be dragged to another program.
 
+  - `file' means DATA should be a file URL that will be dragged to
+    another program.
+
 ACTION is the action that will be taken by the drop target towards the
 data inside PBOARD.