[fix, UX] Allow modal widget on top of modal widget (#3170)

Fixes #2653.

frontend/ui/screensaver.lua

@@ -1,9 +1,9 @@
-local DocumentRegistry = require("document/documentregistry")
-local UIManager = require("ui/uimanager")
 local Device = require("device")
-local Screen = Device.screen
 local DocSettings = require("docsettings")
+local DocumentRegistry = require("document/documentregistry")
+local UIManager = require("ui/uimanager")
 local logger = require("logger")
+local Screen = Device.screen
 
 local Screensaver = {
 }
@@ -28,13 +28,13 @@ local function createWidgetFromFile(file)
     if lfs.attributes(file, "mode") == "file" then
         local ImageWidget = require("ui/widget/imagewidget")
         return createWidgetFromImage(
-                   ImageWidget:new{
-                       file = file,
-                       file_do_cache = false,
-                       height = Screen:getHeight(),
-                       width = Screen:getWidth(),
-                       scale_factor = 0, -- scale to fit height/width
-                   })
+            ImageWidget:new{
+                file = file,
+                file_do_cache = false,
+                height = Screen:getHeight(),
+                width = Screen:getWidth(),
+                scale_factor = 0, -- scale to fit height/width
+            })
     end
 end
 
@@ -134,6 +134,9 @@ function Screensaver:show(kind, default_msg)
             UIManager:show(self.left_msg)
         end
     else
+        -- set modal to put screensaver on top of everything else
+        -- NB InfoMessage (in case of no image) defaults to modal
+        self.left_msg.modal = true
         -- refresh whole screen for other types
         UIManager:show(self.left_msg, "full")
     end

frontend/ui/uimanager.lua

@@ -191,7 +191,7 @@ function UIManager:show(widget, refreshtype, refreshregion, x, y)
     for i = #self._window_stack, 0, -1 do
         local top_window = self._window_stack[i]
         -- skip modal window
-        if not top_window or not top_window.widget.modal then
+        if widget.modal or not top_window or not top_window.widget.modal then
             table.insert(self._window_stack, i + 1, window)
             break
         end

spec/unit/uimanager_spec.lua

@@ -162,6 +162,43 @@ describe("UIManager spec", function()
         assert.is_true(UIManager._task_queue_dirty)
     end)
 
+    describe("modal widgets", function()
+        it("should insert modal widget on top", function()
+            -- first modal widget
+            UIManager:show({
+                x_prefix_test_number = 1,
+                modal = true,
+                handleEvent = function()
+                    return true
+                end
+            })
+            -- regular widget, should go under modal widget
+            UIManager:show({
+                x_prefix_test_number = 2,
+                modal = nil,
+                handleEvent = function()
+                    return true
+                end
+            })
+
+            assert.equals(UIManager._window_stack[1].widget.x_prefix_test_number, 2)
+            assert.equals(UIManager._window_stack[2].widget.x_prefix_test_number, 1)
+        end)
+        it("should insert second modal widget on top of first modal widget", function()
+            UIManager:show({
+                x_prefix_test_number = 3,
+                modal = true,
+                handleEvent = function()
+                    return true
+                end
+            })
+
+            assert.equals(UIManager._window_stack[1].widget.x_prefix_test_number, 2)
+            assert.equals(UIManager._window_stack[2].widget.x_prefix_test_number, 1)
+            assert.equals(UIManager._window_stack[3].widget.x_prefix_test_number, 3)
+        end)
+    end)
+
     it("should check active widgets in order", function()
         local call_signals = {false, false, false}
         UIManager._window_stack = {