Function chalk_solve::clauses::builtin_traits::fn_family::add_fn_trait_program_clauses

pub fn add_fn_trait_program_clauses<I: Interner>(
    db: &dyn RustIrDatabase<I>,
    builder: &mut ClauseBuilder<'_, I>,
    well_known: WellKnownTrait,
    self_ty: Ty<I>
)

Handles clauses for FnOnce/FnMut/Fn. If self_ty is a function, we push a clause of the form fn(A1, A2, ..., AN) -> O: FnTrait<(A1, A2, ..., AN)>, where FnTrait is the trait corresponding to trait_id (FnOnce/FnMut/Fn)

If trait_id is FnOnce, we also push a clause for the output type of the form: Normalize(<fn(A) -> B as FnOnce<(A,)>>::Output -> B) We do not add the usual Implemented(fn(A) -> b as FnOnce<(A,)> clause as a condition, since we already called push_fact with it