patch 8.0.1211: cannot reorder tab pages with drag & drop

Problem:    Cannot reorder tab pages with drag & drop.
Solution:   Support drag & drop for GTK and MS-Windows. (Ken Takata, Masamichi
            Abe)

src/gui_gtk_x11.c

@@ -3567,8 +3567,29 @@ on_select_tab(
 	gpointer	data UNUSED)
 {
     if (!ignore_tabline_evt)
-    {
 	send_tabline_event(idx + 1);
+}
+
+/*
+ * Handle reordering the tabs (using D&D).
+ */
+    static void
+on_tab_reordered(
+	GtkNotebook	*notebook UNUSED,
+# if GTK_CHECK_VERSION(3,0,0)
+	gpointer	*page UNUSED,
+# else
+	GtkNotebookPage *page UNUSED,
+# endif
+	gint		idx,
+	gpointer	data UNUSED)
+{
+    if (!ignore_tabline_evt)
+    {
+	if ((tabpage_index(curtab) - 1) < idx)
+	    tabpage_move(idx + 1);
+	else
+	    tabpage_move(idx);
     }
 }
 
@@ -3658,6 +3679,9 @@ gui_mch_update_tabline(void)
 		    page,
 		    event_box,
 		    nr++);
+	    gtk_notebook_set_tab_reorderable(GTK_NOTEBOOK(gui.tabline),
+		    page,
+		    TRUE);
 	}
 
 	event_box = gtk_notebook_get_tab_label(GTK_NOTEBOOK(gui.tabline), page);
@@ -4093,14 +4117,19 @@ gui_mch_init(void)
 # endif
 	gtk_container_add(GTK_CONTAINER(event_box), label);
 	gtk_notebook_set_tab_label(GTK_NOTEBOOK(gui.tabline), page, event_box);
+	gtk_notebook_set_tab_reorderable(GTK_NOTEBOOK(gui.tabline), page, TRUE);
     }
 
 # if GTK_CHECK_VERSION(3,0,0)
     g_signal_connect(G_OBJECT(gui.tabline), "switch-page",
 		     G_CALLBACK(on_select_tab), NULL);
+    g_signal_connect(G_OBJECT(gui.tabline), "page-reordered",
+		     G_CALLBACK(on_tab_reordered), NULL);
 # else
     gtk_signal_connect(GTK_OBJECT(gui.tabline), "switch_page",
 		       GTK_SIGNAL_FUNC(on_select_tab), NULL);
+    gtk_signal_connect(GTK_OBJECT(gui.tabline), "page-reordered",
+		       GTK_SIGNAL_FUNC(on_tab_reordered), NULL);
 # endif
 
     /* Create a popup menu for the tab line and connect it. */

src/gui_w32.c

@@ -8151,6 +8151,34 @@ initialise_tabline(void)
 # endif
 }
 
+/*
+ * Get tabpage_T from POINT.
+ */
+    static tabpage_T *
+GetTabFromPoint(
+    HWND    hWnd,
+    POINT   pt)
+{
+    tabpage_T	*ptp = NULL;
+
+    if (gui_mch_showing_tabline())
+    {
+	TCHITTESTINFO htinfo;
+	htinfo.pt = pt;
+	/* ignore if a window under cusor is not tabcontrol. */
+	if (s_tabhwnd == hWnd)
+	{
+	    int idx = TabCtrl_HitTest(s_tabhwnd, &htinfo);
+	    if (idx != -1)
+		ptp = find_tabpage(idx + 1);
+	}
+    }
+    return ptp;
+}
+
+static POINT	    s_pt = {0, 0};
+static HCURSOR      s_hCursor = NULL;
+
     static LRESULT CALLBACK
 tabline_wndproc(
     HWND hwnd,
@@ -8158,7 +8186,73 @@ tabline_wndproc(
     WPARAM wParam,
     LPARAM lParam)
 {
+    POINT	pt;
+    tabpage_T	*tp;
+    RECT	rect;
+    int		nCenter;
+    int		idx0;
+    int		idx1;
+
     HandleMouseHide(uMsg, lParam);
+
+    switch (uMsg)
+    {
+	case WM_LBUTTONDOWN:
+	    {
+		s_pt.x = GET_X_LPARAM(lParam);
+		s_pt.y = GET_Y_LPARAM(lParam);
+		SetCapture(hwnd);
+		s_hCursor = GetCursor(); /* backup default cursor */
+		break;
+	    }
+	case WM_MOUSEMOVE:
+	    if (GetCapture() == hwnd
+		    && ((wParam & MK_LBUTTON)) != 0)
+	    {
+		pt.x = GET_X_LPARAM(lParam);
+		pt.y = s_pt.y;
+		if (abs(pt.x - s_pt.x) > GetSystemMetrics(SM_CXDRAG))
+		{
+		    SetCursor(LoadCursor(NULL, IDC_SIZEWE));
+
+		    tp = GetTabFromPoint(hwnd, pt);
+		    if (tp != NULL)
+		    {
+			idx0 = tabpage_index(curtab) - 1;
+			idx1 = tabpage_index(tp) - 1;
+
+			TabCtrl_GetItemRect(hwnd, idx1, &rect);
+			nCenter = rect.left + (rect.right - rect.left) / 2;
+
+			/* Check if the mouse cursor goes over the center of
+			 * the next tab to prevent "flickering". */
+			if ((idx0 < idx1) && (nCenter < pt.x))
+			{
+			    tabpage_move(idx1 + 1);
+			    update_screen(0);
+			}
+			else if ((idx1 < idx0) && (pt.x < nCenter))
+			{
+			    tabpage_move(idx1);
+			    update_screen(0);
+			}
+		    }
+		}
+	    }
+	    break;
+	case WM_LBUTTONUP:
+	    {
+		if (GetCapture() == hwnd)
+		{
+		    SetCursor(s_hCursor);
+		    ReleaseCapture();
+		}
+		break;
+	    }
+	default:
+	    break;
+    }
+
     return CallWindowProc(s_tabline_wndproc, hwnd, uMsg, wParam, lParam);
 }
 #endif

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1211,
 /**/
     1210,
 /**/