Cannot use lifetime in `impl` blocks

[ClementNerma]

When writing an impl block with the #[graphql_object] attribute, declared lifetimes cannot be used in the return type. Example:

pub struct IndexGraph;

#[graphql_object(context = GraphQLContext)]
impl IndexGraph {
    async fn fingerprint<'c>(&self, context: &'c GraphQLContext) -> &'c str {
        context.index.fingerprint.as_str()
    }
}

I get the following error: use of undeclared lifetime name 'c in the return type.

The document states to use this syntax for lifetimes so I wonder if it's a bug or if there is another way to do this?

Using Juniper 0.15.9.

[tyranron]

@ClementNerma this is not possible in juniper 0.15 due to how #[graphql_object] is desugared. This, however, is fixed in the current master (see #971) and will be released in 0.16, once we complete all the necessities for the release (no ETAs can be given, though).