rustc_middle/infer/
unify_key.rs

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
use std::cmp;
use std::marker::PhantomData;

use rustc_data_structures::unify::{NoError, UnifyKey, UnifyValue};
use rustc_span::Span;
use rustc_span::def_id::DefId;

use crate::ty::{self, Ty, TyCtxt};

pub trait ToType {
    fn to_type<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
}

#[derive(Copy, Clone, Debug)]
pub enum RegionVariableValue<'tcx> {
    Known { value: ty::Region<'tcx> },
    Unknown { universe: ty::UniverseIndex },
}

#[derive(PartialEq, Copy, Clone, Debug)]
pub struct RegionVidKey<'tcx> {
    pub vid: ty::RegionVid,
    pub phantom: PhantomData<RegionVariableValue<'tcx>>,
}

impl<'tcx> From<ty::RegionVid> for RegionVidKey<'tcx> {
    fn from(vid: ty::RegionVid) -> Self {
        RegionVidKey { vid, phantom: PhantomData }
    }
}

impl<'tcx> UnifyKey for RegionVidKey<'tcx> {
    type Value = RegionVariableValue<'tcx>;
    #[inline]
    fn index(&self) -> u32 {
        self.vid.as_u32()
    }
    #[inline]
    fn from_index(i: u32) -> Self {
        RegionVidKey::from(ty::RegionVid::from_u32(i))
    }
    fn tag() -> &'static str {
        "RegionVidKey"
    }
}

pub struct RegionUnificationError;
impl<'tcx> UnifyValue for RegionVariableValue<'tcx> {
    type Error = RegionUnificationError;

    fn unify_values(value1: &Self, value2: &Self) -> Result<Self, Self::Error> {
        match (*value1, *value2) {
            (RegionVariableValue::Known { .. }, RegionVariableValue::Known { .. }) => {
                Err(RegionUnificationError)
            }

            (RegionVariableValue::Known { value }, RegionVariableValue::Unknown { universe })
            | (RegionVariableValue::Unknown { universe }, RegionVariableValue::Known { value }) => {
                let universe_of_value = match value.kind() {
                    ty::ReStatic
                    | ty::ReErased
                    | ty::ReLateParam(..)
                    | ty::ReEarlyParam(..)
                    | ty::ReError(_) => ty::UniverseIndex::ROOT,
                    ty::RePlaceholder(placeholder) => placeholder.universe,
                    ty::ReVar(..) | ty::ReBound(..) => bug!("not a universal region"),
                };

                if universe.can_name(universe_of_value) {
                    Ok(RegionVariableValue::Known { value })
                } else {
                    Err(RegionUnificationError)
                }
            }

            (
                RegionVariableValue::Unknown { universe: a },
                RegionVariableValue::Unknown { universe: b },
            ) => {
                // If we unify two unconstrained regions then whatever
                // value they wind up taking (which must be the same value) must
                // be nameable by both universes. Therefore, the resulting
                // universe is the minimum of the two universes, because that is
                // the one which contains the fewest names in scope.
                Ok(RegionVariableValue::Unknown { universe: a.min(b) })
            }
        }
    }
}

// Generic consts.

#[derive(Copy, Clone, Debug)]
pub struct ConstVariableOrigin {
    pub span: Span,
    /// `DefId` of the const parameter this was instantiated for, if any.
    ///
    /// This should only be used for diagnostics.
    pub param_def_id: Option<DefId>,
}

#[derive(Copy, Clone, Debug)]
pub enum ConstVariableValue<'tcx> {
    Known { value: ty::Const<'tcx> },
    Unknown { origin: ConstVariableOrigin, universe: ty::UniverseIndex },
}

impl<'tcx> ConstVariableValue<'tcx> {
    /// If this value is known, returns the const it is known to be.
    /// Otherwise, `None`.
    pub fn known(&self) -> Option<ty::Const<'tcx>> {
        match *self {
            ConstVariableValue::Unknown { .. } => None,
            ConstVariableValue::Known { value } => Some(value),
        }
    }
}

#[derive(PartialEq, Copy, Clone, Debug)]
pub struct ConstVidKey<'tcx> {
    pub vid: ty::ConstVid,
    pub phantom: PhantomData<ty::Const<'tcx>>,
}

impl<'tcx> From<ty::ConstVid> for ConstVidKey<'tcx> {
    fn from(vid: ty::ConstVid) -> Self {
        ConstVidKey { vid, phantom: PhantomData }
    }
}

impl<'tcx> UnifyKey for ConstVidKey<'tcx> {
    type Value = ConstVariableValue<'tcx>;
    #[inline]
    fn index(&self) -> u32 {
        self.vid.as_u32()
    }
    #[inline]
    fn from_index(i: u32) -> Self {
        ConstVidKey::from(ty::ConstVid::from_u32(i))
    }
    fn tag() -> &'static str {
        "ConstVidKey"
    }
}

impl<'tcx> UnifyValue for ConstVariableValue<'tcx> {
    type Error = NoError;

    fn unify_values(&value1: &Self, &value2: &Self) -> Result<Self, Self::Error> {
        match (value1, value2) {
            (ConstVariableValue::Known { .. }, ConstVariableValue::Known { .. }) => {
                bug!("equating two const variables, both of which have known values")
            }

            // If one side is known, prefer that one.
            (ConstVariableValue::Known { .. }, ConstVariableValue::Unknown { .. }) => Ok(value1),
            (ConstVariableValue::Unknown { .. }, ConstVariableValue::Known { .. }) => Ok(value2),

            // If both sides are *unknown*, it hardly matters, does it?
            (
                ConstVariableValue::Unknown { origin, universe: universe1 },
                ConstVariableValue::Unknown { origin: _, universe: universe2 },
            ) => {
                // If we unify two unbound variables, ?T and ?U, then whatever
                // value they wind up taking (which must be the same value) must
                // be nameable by both universes. Therefore, the resulting
                // universe is the minimum of the two universes, because that is
                // the one which contains the fewest names in scope.
                let universe = cmp::min(universe1, universe2);
                Ok(ConstVariableValue::Unknown { origin, universe })
            }
        }
    }
}