nemo-window.c: Remember the second pane's location until the

remaining pane's location changes.

If the user is working in the split view, and toggles split pane
off (from either side), remember the location of the closed
pane and restore it if the split view is toggled again.

If the remaining pane's location changes, the stored location is
cleared, and traditional behavior will prevail (opening the second
pane in the same location as the first).

If a pane had multiple tabs open, only the active tab's location
is remembered and re-opened.

ref:
https://blog.linuxmint.com/?p=4850#comment-499214

Author: mtwebster

src/nemo-window-manage-views.c

@@ -1520,6 +1520,7 @@ update_for_new_location (NemoWindowSlot *slot)
 	}
 
 	if (location_really_changed) {
+        nemo_window_clear_secondary_pane_location (window);
 		nemo_window_slot_remove_extra_location_widgets (slot);
 
 		directory = nemo_directory_get (slot->location);

src/nemo-window-private.h

@@ -95,6 +95,10 @@ struct NemoWindowDetails
         /* split view */
         GtkWidget *split_view_hpane;
 
+        // A closed pane's location, valid until the remaining pane
+        // location changes.
+        GFile *secondary_pane_last_location;
+
         gboolean disable_chrome;
 
         guint sidebar_width_handler_id;

src/nemo-window.c

@@ -873,6 +873,7 @@ nemo_window_finalize (GObject *object)
 	nemo_window_finalize_menus (window);
 
 	g_clear_object (&window->details->nav_state);
+    g_clear_object (&window->details->secondary_pane_last_location);
 
 	g_clear_object (&window->details->ui_manager);
 
@@ -2195,8 +2196,9 @@ nemo_window_split_view_on (NemoWindow *window)
 	old_active_slot = nemo_window_get_active_slot (window);
 	slot = create_extra_pane (window);
 
-	location = NULL;
-	if (old_active_slot != NULL) {
+    location = window->details->secondary_pane_last_location;
+
+	if (location == NULL && old_active_slot != NULL) {
 		location = nemo_window_slot_get_location (old_active_slot);
 		if (location != NULL) {
 			if (g_file_has_uri_scheme (location, "x-nemo-search")) {
@@ -2228,6 +2230,8 @@ nemo_window_split_view_off (NemoWindow *window)
 		next = l->next;
 		pane = l->data;
 		if (pane != active_pane) {
+            g_clear_object (&window->details->secondary_pane_last_location);
+            window->details->secondary_pane_last_location = nemo_window_slot_get_location (pane->active_slot);
 			nemo_window_close_pane (window, pane);
 		}
 	}
@@ -2252,6 +2256,13 @@ nemo_window_split_view_showing (NemoWindow *window)
 	return g_list_length (NEMO_WINDOW (window)->details->panes) > 1;
 }
 
+void
+nemo_window_clear_secondary_pane_location (NemoWindow *window)
+{
+    g_return_if_fail (NEMO_IS_WINDOW (window));
+    g_clear_object (&window->details->secondary_pane_last_location);
+}
+
 void
 nemo_window_set_sidebar_id (NemoWindow *window,
                             const gchar *id)

src/nemo-window.h

@@ -184,6 +184,7 @@ void         nemo_window_set_ignore_meta_sort_column (NemoWindow *window, const
 gint         nemo_window_get_ignore_meta_sort_direction (NemoWindow *window);
 void         nemo_window_set_ignore_meta_sort_direction (NemoWindow *window, gint direction);
 
+void         nemo_window_clear_secondary_pane_location (NemoWindow *window);
 NemoWindowOpenFlags nemo_event_get_window_open_flags   (void);
 
 void nemo_window_slot_added (NemoWindow *window,  NemoWindowSlot *slot);