C++: fix including the generated file in several translation units

api/cpp/tests/CMakeLists.txt

@@ -49,6 +49,8 @@ target_link_libraries(test_eventloop PRIVATE Threads::Threads)
 slint_test(models)
 slint_test(window)
 
+add_subdirectory(multiple-includes)
+
 if(SLINT_FEATURE_EXPERIMENTAL)
     if(Qt6_FOUND)
         add_subdirectory(manual/platform_qt)

api/cpp/tests/multiple-includes/CMakeLists.txt

@@ -0,0 +1,7 @@
+# Copyright © SixtyFPS GmbH <info@slint-ui.com>
+# SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+add_executable(multiple-includes main.cpp logic.cpp)
+target_link_libraries(multiple-includes PRIVATE Slint::Slint)
+slint_target_sources(multiple-includes appwindow.slint)
+

api/cpp/tests/multiple-includes/README.md

@@ -0,0 +1 @@
+This is a test making sure that the header can be included in several file without causing multiple definitions

api/cpp/tests/multiple-includes/appwindow.slint

@@ -0,0 +1,35 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+import {Button, AboutSlint} from "std-widgets.slint";
+
+export global Logic {
+    callback increment(int) -> int;
+}
+
+export struct FooBar {
+    abc: int, def: string
+}
+
+component R {
+    property <FooBar> foo;
+    Rectangle {
+        TouchArea {}
+    }
+}
+
+export component App inherits Window {
+    preferred-width: 800px;
+    preferred-height: 600px;
+    property <int> count;
+
+    VerticalLayout {
+        AboutSlint {  }
+        Button {
+            text: "Hello";
+            clicked => { count = Logic.increment(count); }
+        }
+        Text { text: count; }
+        R {  }
+    }
+}

api/cpp/tests/multiple-includes/logic.cpp

@@ -0,0 +1,10 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+#include "logic.h"
+#include "appwindow.h"
+
+void setup_logic(const Logic &logic)
+{
+    logic.on_increment([](int x) { return x + 1; });
+}

api/cpp/tests/multiple-includes/logic.h

@@ -0,0 +1,8 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+#pragma once
+
+struct Logic;
+
+void setup_logic(const Logic &);

api/cpp/tests/multiple-includes/main.cpp

@@ -0,0 +1,12 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+#include "logic.h"
+#include "appwindow.h"
+
+int main(int argc, char **argv)
+{
+    auto my_ui = App::create();
+    setup_logic(my_ui->global<Logic>());
+    my_ui->run();
+}

internal/compiler/generator/cpp.rs

@@ -1136,7 +1136,7 @@ fn generate_item_tree(
     ));
 
     file.definitions.push(Declaration::Var(Var {
-        ty: "const slint::private_api::ComponentVTable".to_owned(),
+        ty: "inline const slint::private_api::ComponentVTable".to_owned(),
         name: format!("{}::static_vtable", item_tree_class_name),
         init: Some(format!(
             "{{ visit_children, get_item_ref, get_subtree_range, get_subtree_component, \