Unable to use generic argument/return type with lifetime bound

[lilymara-onesignal]

When trying to mock a method that has a generic argument or return type that is bound by a generic lifetime, automock can't seem to generate the correct code:

use mockall::automock;

trait Foo<'a> {}

#[automock]
trait Bar {
    fn bar<'a, F>(&self, foo: F)
    where
        F: Foo<'a>;
}

This fails to compile with these errors:

    Checking mock-test v0.1.0 (/Users/nate/projects/hacks/mock-test)
error[E0601]: `main` function not found in crate `mock_test`
  --> src/main.rs:1:1
   |
1  | / use mockall::automock;
2  | |
3  | | trait Foo<'a> {}
4  | |
...  |
9  | |         F: Foo<'a>;
10 | | }
   | |_^ consider adding a `main` function to `src/main.rs`

error[E0261]: use of undeclared lifetime name `'a`
 --> src/main.rs:9:16
  |
7 |     fn bar<'a, F>(&self, foo: F)
  |                - help: consider introducing lifetime `'a` here: `'a,`
8 |     where
9 |         F: Foo<'a>;
  |                ^^ undeclared lifetime

error[E0261]: use of undeclared lifetime name `'a`
 --> src/main.rs:9:16
  |
9 |         F: Foo<'a>;
  |                ^^ undeclared lifetime
  |
help: consider introducing lifetime `'a` here
  |
5 | #[automock]<'a>
  |            ^^^^
help: consider introducing lifetime `'a` here
  |
7 |     fn bar<'a, 'a, F>(&self, foo: F)
  |                ^^^

error[E0310]: the parameter type `F` may not live long enough
 --> src/main.rs:5:1
  |
5 | #[automock]
  | ^^^^^^^^^^^ ...so that the type `__mock_MockBar_Bar::__bar::Expectations<F>` will meet its required lifetime bounds
6 | trait Bar {
7 |     fn bar<'a, F>(&self, foo: F)
  |                - help: consider adding an explicit lifetime bound...: `F: 'static`
  |
  = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0310]: the parameter type `F` may not live long enough
 --> src/main.rs:5:1
  |
5 | #[automock]
  | ^^^^^^^^^^^ ...so that the type `F` will meet its required lifetime bounds
6 | trait Bar {
7 |     fn bar<'a, F>(&self, foo: F)
  |                - help: consider adding an explicit lifetime bound...: `F: 'static`
  |
  = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 5 previous errors

Some errors have detailed explanations: E0261, E0310, E0601.
For more information about an error, try `rustc --explain E0261`.
error: could not compile `mock-test`.

[asomers-ax]

Unsurprising. Lifetime arguments are a real viper's nest. What happens if you write it like this?

use mockall::automock;

trait Foo<'a> {}

#[automock]
trait Bar {
    fn bar<'a, F: Foo<'a>>(&self, foo: F);
}

[lilymara-onesignal]

That code appears to fail with the same errors

[asomers]

This is harder than I expected, thanks to that Generic. Mockall uses downcasting to handle generic methods, and Rust's Any type requires 'static. That means that Mockall can't handle any non-'static type generics. I don't think I'm going to be able to implement this. The best workaround I can suggest would be to manually implement your function in terms of a mock function that has no non-'static type generics, like this:

trait Bar {
    fn bar<'a, F: Foo<'a>>(&self, foo: F);
}
mock! {
    Boo { }
    Bar {
        pub fn bean<'a>(&self, foo: &dyn Foo<'a>);
    }
}
impl Bar for MockBoo {
    fn bar<'a, F: Foo<'a>>(&self, foo: F) {
        self.bean(&foo)
    }
}

[asomers]

Closing this issue in favor of the more general #217 .