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
171
172
173
174
175
176
177
178
179
use rustc_middle::bug;
use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::visit::TypeVisitableExt;
use rustc_middle::ty::{self, Const, InferConst, Ty, TyCtxt, TypeFoldable};

use super::{FixupError, FixupResult, InferCtxt};

///////////////////////////////////////////////////////////////////////////
// OPPORTUNISTIC VAR RESOLVER

/// The opportunistic resolver can be used at any time. It simply replaces
/// type/const variables that have been unified with the things they have
/// been unified with (similar to `shallow_resolve`, but deep). This is
/// useful for printing messages etc but also required at various
/// points for correctness.
pub struct OpportunisticVarResolver<'a, 'tcx> {
    infcx: &'a InferCtxt<'tcx>,
}

impl<'a, 'tcx> OpportunisticVarResolver<'a, 'tcx> {
    #[inline]
    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
        OpportunisticVarResolver { infcx }
    }
}

impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for OpportunisticVarResolver<'a, 'tcx> {
    fn cx(&self) -> TyCtxt<'tcx> {
        self.infcx.tcx
    }

    #[inline]
    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
        if !t.has_non_region_infer() {
            t // micro-optimize -- if there is nothing in this type that this fold affects...
        } else {
            let t = self.infcx.shallow_resolve(t);
            t.super_fold_with(self)
        }
    }

    fn fold_const(&mut self, ct: Const<'tcx>) -> Const<'tcx> {
        if !ct.has_non_region_infer() {
            ct // micro-optimize -- if there is nothing in this const that this fold affects...
        } else {
            let ct = self.infcx.shallow_resolve_const(ct);
            ct.super_fold_with(self)
        }
    }
}

/// The opportunistic region resolver opportunistically resolves regions
/// variables to the variable with the least variable id. It is used when
/// normalizing projections to avoid hitting the recursion limit by creating
/// many versions of a predicate for types that in the end have to unify.
///
/// If you want to resolve type and const variables as well, call
/// [InferCtxt::resolve_vars_if_possible] first.
pub struct OpportunisticRegionResolver<'a, 'tcx> {
    infcx: &'a InferCtxt<'tcx>,
}

impl<'a, 'tcx> OpportunisticRegionResolver<'a, 'tcx> {
    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
        OpportunisticRegionResolver { infcx }
    }
}

impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for OpportunisticRegionResolver<'a, 'tcx> {
    fn cx(&self) -> TyCtxt<'tcx> {
        self.infcx.tcx
    }

    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
        if !t.has_infer_regions() {
            t // micro-optimize -- if there is nothing in this type that this fold affects...
        } else {
            t.super_fold_with(self)
        }
    }

    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
        match *r {
            ty::ReVar(vid) => self
                .infcx
                .inner
                .borrow_mut()
                .unwrap_region_constraints()
                .opportunistic_resolve_var(TypeFolder::cx(self), vid),
            _ => r,
        }
    }

    fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
        if !ct.has_infer_regions() {
            ct // micro-optimize -- if there is nothing in this const that this fold affects...
        } else {
            ct.super_fold_with(self)
        }
    }
}

///////////////////////////////////////////////////////////////////////////
// FULL TYPE RESOLUTION

/// Full type resolution replaces all type and region variables with
/// their concrete results. If any variable cannot be replaced (never unified, etc)
/// then an `Err` result is returned.
pub fn fully_resolve<'tcx, T>(infcx: &InferCtxt<'tcx>, value: T) -> FixupResult<T>
where
    T: TypeFoldable<TyCtxt<'tcx>>,
{
    value.try_fold_with(&mut FullTypeResolver { infcx })
}

// N.B. This type is not public because the protocol around checking the
// `err` field is not enforceable otherwise.
struct FullTypeResolver<'a, 'tcx> {
    infcx: &'a InferCtxt<'tcx>,
}

impl<'a, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for FullTypeResolver<'a, 'tcx> {
    type Error = FixupError;

    fn cx(&self) -> TyCtxt<'tcx> {
        self.infcx.tcx
    }

    fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
        if !t.has_infer() {
            Ok(t) // micro-optimize -- if there is nothing in this type that this fold affects...
        } else {
            let t = self.infcx.shallow_resolve(t);
            match *t.kind() {
                ty::Infer(ty::TyVar(vid)) => Err(FixupError::UnresolvedTy(vid)),
                ty::Infer(ty::IntVar(vid)) => Err(FixupError::UnresolvedIntTy(vid)),
                ty::Infer(ty::FloatVar(vid)) => Err(FixupError::UnresolvedFloatTy(vid)),
                ty::Infer(_) => {
                    bug!("Unexpected type in full type resolver: {:?}", t);
                }
                _ => t.try_super_fold_with(self),
            }
        }
    }

    fn try_fold_region(&mut self, r: ty::Region<'tcx>) -> Result<ty::Region<'tcx>, Self::Error> {
        match *r {
            ty::ReVar(_) => Ok(self
                .infcx
                .lexical_region_resolutions
                .borrow()
                .as_ref()
                .expect("region resolution not performed")
                .resolve_region(self.infcx.tcx, r)),
            _ => Ok(r),
        }
    }

    fn try_fold_const(&mut self, c: ty::Const<'tcx>) -> Result<ty::Const<'tcx>, Self::Error> {
        if !c.has_infer() {
            Ok(c) // micro-optimize -- if there is nothing in this const that this fold affects...
        } else {
            let c = self.infcx.shallow_resolve_const(c);
            match c.kind() {
                ty::ConstKind::Infer(InferConst::Var(vid)) => {
                    return Err(FixupError::UnresolvedConst(vid));
                }
                ty::ConstKind::Infer(InferConst::Fresh(_)) => {
                    bug!("Unexpected const in full const resolver: {:?}", c);
                }
                ty::ConstKind::Infer(InferConst::EffectVar(evid)) => {
                    return Err(FixupError::UnresolvedEffect(evid));
                }
                _ => {}
            }
            c.try_super_fold_with(self)
        }
    }
}