Properly initialize the default binding of a state to its materialized value

Fixes #1237

internal/compiler/passes/lower_states.rs

@@ -201,7 +201,9 @@ fn expression_for_property(element: &ElementRc, name: &str) -> ExpressionForProp
             None
         };
     }
-    ExpressionForProperty::Expression(Expression::default_value_for_type(
-        &element.borrow().lookup_property(name).property_type,
-    ))
+    let expr = super::materialize_fake_properties::initialize(element, name).unwrap_or_else(|| {
+        Expression::default_value_for_type(&element.borrow().lookup_property(name).property_type)
+    });
+
+    ExpressionForProperty::Expression(expr)
 }

internal/compiler/passes/materialize_fake_properties.rs

@@ -121,7 +121,7 @@ fn has_declared_property(elem: &Element, prop: &str) -> bool {
 }
 
 /// Initialize a sensible default binding for the now materialized property
-fn initialize(elem: &ElementRc, name: &str) -> Option<Expression> {
+pub fn initialize(elem: &ElementRc, name: &str) -> Option<Expression> {
     let expr = match name {
         "min-height" => layout_constraint_prop(elem, "min", Orientation::Vertical),
         "min-width" => layout_constraint_prop(elem, "min", Orientation::Horizontal),

tests/cases/properties/issue1237_states_visible.slint

@@ -0,0 +1,53 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+TestCase := Window {
+   width: 100px;
+   height: 100px;
+   property<int> niceness: 33;
+   greeting := TouchArea {
+       clicked => { root.niceness += 1; }
+       t:= Text {
+           text: "Hello world";
+       }
+
+       states [
+            rude when root.niceness <= 0: {visible: false;}
+            mannered when root.niceness > 100: {t.text: "Hello, dearest world"; t.font-size: 32px;}
+       ]
+   }
+
+   property <bool> test: greeting.visible;
+}
+
+
+/*
+```cpp
+auto handle = TestCase::create();
+const TestCase &instance = *handle;
+assert(instance.get_test());
+slint::testing::send_mouse_click(&instance, 50., 50.);
+assert_eq(instance.get_niceness(), 34);
+
+instance.set_niceness(-1);
+assert(!instance.get_test());
+slint::testing::send_mouse_click(&instance, 50., 50.);
+assert_eq(instance.get_niceness(), -1);
+
+```
+
+
+```rust
+let instance = TestCase::new();
+assert!(instance.get_test());
+slint::testing::send_mouse_click(&instance, 50., 50.);
+assert_eq!(instance.get_niceness(), 34);
+
+instance.set_niceness(-1);
+assert!(!instance.get_test());
+slint::testing::send_mouse_click(&instance, 50., 50.);
+assert_eq!(instance.get_niceness(), -1);
+```
+
+
+*/