Fix generated setter and getter of public property alias in globals

We need to skip the generation of the local property so it directly
forward to the alias in the public property

Fixes #5855
ChangeLog: Fixed generated getter and setter of alias properties in globals

internal/compiler/llr/lower_to_item_tree.rs

@@ -709,6 +709,9 @@ fn lower_global(
     let mut functions = vec![];
 
     for (p, x) in &global.root_element.borrow().property_declarations {
+        if x.is_alias.is_some() {
+            continue;
+        }
         let property_index = properties.len();
         let nr = NamedReference::new(&global.root_element, p);
 

internal/compiler/llr/pretty_print.rs

@@ -68,6 +68,15 @@ impl<'a> PrettyPrinter<'a> {
                 DisplayExpression(&f.code, &ctx)
             )?;
         }
+        for (p1, p2) in &sc.two_way_bindings {
+            self.indent()?;
+            writeln!(
+                self.writer,
+                "{} <=> {};",
+                DisplayPropertyRef(p1, &ctx),
+                DisplayPropertyRef(p2, &ctx)
+            )?
+        }
         for (p, init) in &sc.property_init {
             self.indent()?;
             writeln!(

tests/cases/bindings/two_way_global.slint

@@ -0,0 +1,81 @@
+// Copyright © SixtyFPS GmbH <info@slint.dev>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
+
+export global G1 {
+    in-out property <int> data: 42;
+}
+
+export global G2 {
+    in-out property <int> data <=> G1.data;
+}
+
+export component TestCase inherits Window {
+
+    out property <int> d1: G1.data;
+    out property <int> d2: G2.data;
+    out property <bool> test: G2.data == 42;
+}
+
+
+/*
+
+```rust
+let instance = TestCase::new().unwrap();
+assert!(instance.get_test());
+assert_eq!(G1::get(&instance).get_data(), 42);
+assert_eq!(G2::get(&instance).get_data(), 42);
+assert_eq!(instance.get_d1(), 42);
+assert_eq!(instance.get_d2(), 42);
+instance.global::<G1<'_>>().set_data(100);
+assert_eq!(G1::get(&instance).get_data(), 100);
+assert_eq!(G2::get(&instance).get_data(), 100);
+assert_eq!(instance.get_d1(), 100);
+assert_eq!(instance.get_d2(), 100);
+instance.global::<G2<'_>>().set_data(-1);
+assert_eq!(G1::get(&instance).get_data(), -1);
+assert_eq!(G2::get(&instance).get_data(), -1);
+assert_eq!(instance.get_d1(), -1);
+assert_eq!(instance.get_d2(), -1);
+
+```
+
+```cpp
+auto handle = TestCase::create();
+const TestCase &instance = *handle;
+assert(instance.get_test());
+assert_eq(instance.global<G1>().get_data(), 42);
+assert_eq(instance.global<G2>().get_data(), 42);
+assert_eq(instance.get_d1(), 42);
+assert_eq(instance.get_d2(), 42);
+instance.global<G1>().set_data(100);
+assert_eq(instance.global<G1>().get_data(), 100);
+assert_eq(instance.global<G2>().get_data(), 100);
+assert_eq(instance.get_d1(), 100);
+assert_eq(instance.get_d2(), 100);
+instance.global<G2>().set_data(-1);
+assert_eq(instance.global<G1>().get_data(), -1);
+assert_eq(instance.global<G2>().get_data(), -1);
+assert_eq(instance.get_d1(), -1);
+assert_eq(instance.get_d2(), -1);
+```
+
+```js
+let instance = new slint.TestCase({});
+assert(instance.test);
+assert.equal(instance.G1.data, 42);
+assert.equal(instance.G2.data, 42);
+assert.equal(instance.d1, 42);
+assert.equal(instance.d2, 42);
+instance.G1.data = 100;
+assert.equal(instance.G1.data, 100);
+assert.equal(instance.G2.data, 100);
+assert.equal(instance.d1, 100);
+assert.equal(instance.d2, 100);
+instance.G2.data = -1;
+assert.equal(instance.G1.data, -1);
+assert.equal(instance.G2.data, -1);
+assert.equal(instance.d1, -1);
+assert.equal(instance.d2, -1);
+```
+
+*/