Defining C++ methods and Q_INVOKABLES from Rust

[ahayzen-kdab]

Current situation

We currently have only one option for declaring C++ context methods available on the C++ object, that is to use the qinvokable macro attribute. However this then means that all methods exposed on the C++ object are marked as Q_INVOKABLE

impl qobject::T {
  #[qinvokable] 
  fn my_invokable() ... // exposed on C++ object

  fn cpp_context() ... // not exposed on C++ object but has C++ context
}

Possible solutions

Instead we should have the ability to expose a C++ context method on the C++ object but not as a Q_INVOKABLE. Note that we still need to be able to mark the C++ specifiers on these methods.

Some possible options:

impl qobject::MyObject {
  #[cxx_override]
  pub fn cpp_method()  // C++ and Rust, this is already on the C++ context, why not make it on the C++ side already if it's `pub` ?

  #[qinvokable] 
  #[cxx_override]
  pub fn invokable() // QML, C++, Rust

  fn private() // Rust
}

Or

#[cxx_method(qinvokable, override)]  // where does return_cxx_type go here? #[cxx_method(qinvokable(return_cxx_type = "T"), override)]  ?
fn test() // callable from C++, Rust and QML

#[cxx_method(override)] 
fn test2() // callable from C++ and Rust

fn test3() // callable from Rust on a qobject::MyObject

Or

#[cxx_qt::method(qinvokable, override)]  // where does return_cxx_type go here? #[cxx_method(qinvokable(return_cxx_type = "T"), override)]  ?
fn test() // callable from C++, Rust and QML

#[cxx_qt::method(override)] 
fn test2() // callable from C++ and Rust

fn test3() // callable from Rust on a qobject::MyObject