Bridge module without QObject type

[SanderVocke]

Hi there,

I'm finding that cxx-qt does not seem to allow defining a bridge module that does not have a #[qobject]-type in it. The reason seems to be that automoc is run on the resulting C++ files, and they error out when there are no Q_OBJECT types in the headers. For this reason, I am having to add dummy QObject types to all the bridge modules that I am making with e.g. some trivial types in them.

Am I missing something?

Example:

#[cxx_qt::bridge(cxx_file_stem = "shoop_rust_callable")]
pub mod ffi {
    unsafe extern "C++" {
        include!("cxx-qt-lib/qvariant.h");
        type QVariant = cxx_qt_lib::QVariant;
    }

    unsafe extern "C++" {
        include!("cxx-qt-shoop/shoop_rust_callable.h");
        type ShoopRustCallable = type_shoop_rust_callable::ShoopRustCallableRust;

        #[rust_name = "qvariant_can_convert_shoop_rust_callable"]
        fn qvariantCanConvertShoopRustCallable(variant: &QVariant) -> bool;

        #[rust_name = "register_metatype_shoop_rust_callable"]
        fn registerMetatypeShoopRustCallable(name : &mut String);
    }

    #[namespace = "rust::cxxqtlib1::qvariant"]
    unsafe extern "C++" {
        include!("cxx-qt-lib/qvariant.h");

        #[rust_name = "qvariant_construct_shoop_rust_callable"]
        fn qvariantConstruct(value: &ShoopRustCallable) -> QVariant;

        #[rust_name = "qvariant_value_or_default_shoop_rust_callable"]
        fn qvariantValueOrDefault(variant: &QVariant) -> ShoopRustCallable;
    }

    extern "RustQt" {
        #[qobject]
        type Dummy= super::DummyRust;
    }
}

use ffi::*;
#[derive(Default)]
pub struct DummyRust {}


(...)

This works, but fails as soon as the Dummy and DummyRust types are removed.

[ahayzen-kdab]

This sounds like a bug :-) we probably assume that any rust file that is given to CxxQtBuilder than has a cxx_qt::bridge would need to have moc run on generated code. When in your case there is no QObject being generated into the C++ code, we would need to detect this case and run when required.

As a workaround note you can use cxx::bridge instead of cxx_qt::bridge if you are only using extern "Rust" and extern "C++" blocks and no RustQt / C++Qt ones (but also note you may end up with a different file stem.

Lets convert this to an issue to investigate the original issue though.

[ahayzen-kdab]

Created #1033

[SanderVocke]

I will try out changing to a regular cxx bridge as a workaround. Thanks for opening an issue - I'll mark the discussion closed so any details can be discussed there.