Support lifetime parameters on the Q_OBJECT macro

[paulolieuthier]

Problem:

struct PG
{
    engine: &mut Engine, -- lifetime error here
    names: Vec<String>
}

Q_OBJECT! { PG:
    slot fn parse(String);
}

To fix the code, I use a lifetime parameter for PG:

struct PG<'a>
{
    engine: &'a mut Engine, // works :)
    names: Vec<String>
}

Q_OBJECT! { PG<'a>: // but now this is broken :(
    slot fn parse(String);
}

This is what the compiler says:

src/main.rs:52:16: 52:18 error: use of undeclared lifetime name `'a` [E0261]
src/main.rs:52 Q_OBJECT! { PG<'a>:
                              ^~

And if I don't use the lifetime parameter in the macro:

src/main.rs:52:13: 52:15 error: wrong number of lifetime parameters: expected 1, found 0 [E0107]
src/main.rs:52 Q_OBJECT! { PG:
                           ^~

Apparently, the macro understands the type just fine, but can't find the definition of 'a. It should be as in impl, where the parameter is defined before used:

impl<'a> PG<'a>

I'm trying to find how to fix this, or how to improve Q_OBJECT, but no success so far.

[florianjacob]

It's currently not possible to capture a lifetime parameter with a macro, but there's a rust issue for that.

I think the best current solution to this would be to have smaller macros which would help to implement something like this by hand:

impl<'a> qmlrs::Object for PG<'a> {
    fn qt_metaobject(…) => qmlrs::MetaObject {…}
    fn qt_metacall(…) {…}
}