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
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170

use rustc_infer::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelatingDelegate};
use rustc_infer::infer::NllRegionVariableOrigin;
use rustc_infer::traits::ObligationCause;
use rustc_middle::mir::ConstraintCategory;
use rustc_middle::ty::error::TypeError;
use rustc_middle::ty::relate::TypeRelation;
use rustc_middle::ty::{self, Const, Ty};
use rustc_span::Span;
use rustc_trait_selection::traits::query::Fallible;

use crate::constraints::OutlivesConstraint;
use crate::diagnostics::UniverseInfo;
use crate::type_check::{InstantiateOpaqueType, Locations, TypeChecker};

impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
    /// Adds sufficient constraints to ensure that `a R b` where `R` depends on `v`:
    ///
    /// - "Covariant" `a <: b`
    /// - "Invariant" `a == b`
    /// - "Contravariant" `a :> b`
    ///
    /// N.B., the type `a` is permitted to have unresolved inference
    /// variables, but not the type `b`.
    #[instrument(skip(self), level = "debug")]
    pub(super) fn relate_types(
        &mut self,
        a: Ty<'tcx>,
        v: ty::Variance,
        b: Ty<'tcx>,
        locations: Locations,
        category: ConstraintCategory<'tcx>,
    ) -> Fallible<()> {
        TypeRelating::new(
            self.infcx,
            NllTypeRelatingDelegate::new(self, locations, category, UniverseInfo::relate(a, b)),
            v,
        )
        .relate(a, b)?;
        Ok(())
    }
}

struct NllTypeRelatingDelegate<'me, 'bccx, 'tcx> {
    type_checker: &'me mut TypeChecker<'bccx, 'tcx>,

    /// Where (and why) is this relation taking place?
    locations: Locations,

    /// What category do we assign the resulting `'a: 'b` relationships?
    category: ConstraintCategory<'tcx>,

    /// Information so that error reporting knows what types we are relating
    /// when reporting a bound region error.
    universe_info: UniverseInfo<'tcx>,
}

impl<'me, 'bccx, 'tcx> NllTypeRelatingDelegate<'me, 'bccx, 'tcx> {
    fn new(
        type_checker: &'me mut TypeChecker<'bccx, 'tcx>,
        locations: Locations,
        category: ConstraintCategory<'tcx>,
        universe_info: UniverseInfo<'tcx>,
    ) -> Self {
        Self { type_checker, locations, category, universe_info }
    }
}

impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx> {
    fn span(&self) -> Span {
        self.locations.span(self.type_checker.body)
    }

    fn param_env(&self) -> ty::ParamEnv<'tcx> {
        self.type_checker.param_env
    }

    fn create_next_universe(&mut self) -> ty::UniverseIndex {
        let universe = self.type_checker.infcx.create_next_universe();
        self.type_checker
            .borrowck_context
            .constraints
            .universe_causes
            .insert(universe, self.universe_info.clone());
        universe
    }

    fn next_existential_region_var(&mut self, from_forall: bool) -> ty::Region<'tcx> {
        let origin = NllRegionVariableOrigin::Existential { from_forall };
        self.type_checker.infcx.next_nll_region_var(origin)
    }

    fn next_placeholder_region(&mut self, placeholder: ty::PlaceholderRegion) -> ty::Region<'tcx> {
        self.type_checker
            .borrowck_context
            .constraints
            .placeholder_region(self.type_checker.infcx, placeholder)
    }

    fn generalize_existential(&mut self, universe: ty::UniverseIndex) -> ty::Region<'tcx> {
        self.type_checker.infcx.next_nll_region_var_in_universe(
            NllRegionVariableOrigin::Existential { from_forall: false },
            universe,
        )
    }

    fn push_outlives(
        &mut self,
        sup: ty::Region<'tcx>,
        sub: ty::Region<'tcx>,
        info: ty::VarianceDiagInfo<'tcx>,
    ) {
        let sub = self.type_checker.borrowck_context.universal_regions.to_region_vid(sub);
        let sup = self.type_checker.borrowck_context.universal_regions.to_region_vid(sup);
        self.type_checker.borrowck_context.constraints.outlives_constraints.push(
            OutlivesConstraint {
                sup,
                sub,
                locations: self.locations,
                span: self.locations.span(self.type_checker.body),
                category: self.category,
                variance_info: info,
            },
        );
    }

    // We don't have to worry about the equality of consts during borrow checking
    // as consts always have a static lifetime.
    // FIXME(oli-obk): is this really true? We can at least have HKL and with
    // inline consts we may have further lifetimes that may be unsound to treat as
    // 'static.
    fn const_equate(&mut self, _a: Const<'tcx>, _b: Const<'tcx>) {}

    fn normalization() -> NormalizationStrategy {
        NormalizationStrategy::Eager
    }

    fn forbid_inference_vars() -> bool {
        true
    }

    fn register_opaque_type(
        &mut self,
        a: Ty<'tcx>,
        b: Ty<'tcx>,
        a_is_expected: bool,
    ) -> Result<(), TypeError<'tcx>> {
        let param_env = self.param_env();
        let span = self.span();
        let def_id = self.type_checker.body.source.def_id().expect_local();
        let body_id = self.type_checker.tcx().hir().local_def_id_to_hir_id(def_id);
        let cause = ObligationCause::misc(span, body_id);
        self.type_checker
            .fully_perform_op(
                self.locations,
                self.category,
                InstantiateOpaqueType {
                    obligations: self
                        .type_checker
                        .infcx
                        .handle_opaque_type(a, b, a_is_expected, &cause, param_env)?
                        .obligations,
                    // These fields are filled in during execution of the operation
                    base_universe: None,
                    region_constraints: None,
                },
            )
            .unwrap();
        Ok(())
    }
}