Function definition 

pub(super) fn definition(
    db: &RootDatabase,
    def: Definition,
    famous_defs: Option<&FamousDefs<'_, '_>>,
    notable_traits: &[(Trait, Vec<(Option<Type<'_>>, Name)>)],
    macro_arm: Option<u32>,
    render_extras: bool,
    subst_types: Option<&Vec<(Symbol, Type<'_>)>>,
    config: &HoverConfig<'_>,
    edition: Edition,
    display_target: DisplayTarget,
) -> (Markup, Option<Docs>)