1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
use crate::infer::InferCtxt;
use crate::traits::Obligation;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::{self, ToPredicate, Ty};

use super::FulfillmentError;
use super::{ObligationCause, PredicateObligation};

pub trait TraitEngine<'tcx>: 'tcx {
    /// Requires that `ty` must implement the trait with `def_id` in
    /// the given environment. This trait must not have any type
    /// parameters (except for `Self`).
    fn register_bound(
        &mut self,
        infcx: &InferCtxt<'tcx>,
        param_env: ty::ParamEnv<'tcx>,
        ty: Ty<'tcx>,
        def_id: DefId,
        cause: ObligationCause<'tcx>,
    ) {
        let trait_ref = ty::TraitRef::new(infcx.tcx, def_id, [ty]);
        self.register_predicate_obligation(
            infcx,
            Obligation {
                cause,
                recursion_depth: 0,
                param_env,
                predicate: ty::Binder::dummy(trait_ref).to_predicate(infcx.tcx),
            },
        );
    }

    fn register_predicate_obligation(
        &mut self,
        infcx: &InferCtxt<'tcx>,
        obligation: PredicateObligation<'tcx>,
    );

    #[must_use]
    fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>>;

    fn collect_remaining_errors(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>>;

    fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>>;

    /// Among all pending obligations, collect those are stalled on a inference variable which has
    /// changed since the last call to `select_where_possible`. Those obligations are marked as
    /// successful and returned.
    fn drain_unstalled_obligations(
        &mut self,
        infcx: &InferCtxt<'tcx>,
    ) -> Vec<PredicateObligation<'tcx>>;
}

pub trait TraitEngineExt<'tcx> {
    fn register_predicate_obligations(
        &mut self,
        infcx: &InferCtxt<'tcx>,
        obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
    );

    #[must_use]
    fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>>;
}

impl<'tcx, T: ?Sized + TraitEngine<'tcx>> TraitEngineExt<'tcx> for T {
    fn register_predicate_obligations(
        &mut self,
        infcx: &InferCtxt<'tcx>,
        obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
    ) {
        for obligation in obligations {
            self.register_predicate_obligation(infcx, obligation);
        }
    }

    fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
        let errors = self.select_where_possible(infcx);
        if !errors.is_empty() {
            return errors;
        }

        self.collect_remaining_errors(infcx)
    }
}