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
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
//! **Canonicalization** is the key to constructing a query in the
//! middle of type inference. Ordinarily, it is not possible to store
//! types from type inference in query keys, because they contain
//! references to inference variables whose lifetimes are too short
//! and so forth. Canonicalizing a value T1 using `canonicalize_query`
//! produces two things:
//!
//! - a value T2 where each unbound inference variable has been
//!   replaced with a **canonical variable**;
//! - a map M (of type `CanonicalVarValues`) from those canonical
//!   variables back to the original.
//!
//! We can then do queries using T2. These will give back constraints
//! on the canonical variables which can be translated, using the map
//! M, into constraints in our source context. This process of
//! translating the results back is done by the
//! `instantiate_query_result` method.
//!
//! For a more detailed look at what is happening here, check
//! out the [chapter in the rustc dev guide][c].
//!
//! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html

use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::Lock;
use rustc_macros::HashStable;
use rustc_type_ir::Canonical as IrCanonical;
use rustc_type_ir::CanonicalVarInfo as IrCanonicalVarInfo;
pub use rustc_type_ir::{CanonicalTyVarKind, CanonicalVarKind};
use smallvec::SmallVec;
use std::collections::hash_map::Entry;
use std::ops::Index;

use crate::infer::MemberConstraint;
use crate::mir::ConstraintCategory;
use crate::ty::GenericArg;
use crate::ty::{self, BoundVar, List, Region, Ty, TyCtxt, TypeFlags, TypeVisitableExt};

pub type Canonical<'tcx, V> = IrCanonical<TyCtxt<'tcx>, V>;

pub type CanonicalVarInfo<'tcx> = IrCanonicalVarInfo<TyCtxt<'tcx>>;

pub type CanonicalVarInfos<'tcx> = &'tcx List<CanonicalVarInfo<'tcx>>;

impl<'tcx> ty::TypeFoldable<TyCtxt<'tcx>> for CanonicalVarInfos<'tcx> {
    fn try_fold_with<F: ty::FallibleTypeFolder<TyCtxt<'tcx>>>(
        self,
        folder: &mut F,
    ) -> Result<Self, F::Error> {
        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_canonical_var_infos(v))
    }
}

/// A set of values corresponding to the canonical variables from some
/// `Canonical`. You can give these values to
/// `canonical_value.instantiate` to instantiate them into the canonical
/// value at the right places.
///
/// When you canonicalize a value `V`, you get back one of these
/// vectors with the original values that were replaced by canonical
/// variables. You will need to supply it later to instantiate the
/// canonicalized query response.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyDecodable, TyEncodable)]
#[derive(HashStable, TypeFoldable, TypeVisitable)]
pub struct CanonicalVarValues<'tcx> {
    pub var_values: ty::GenericArgsRef<'tcx>,
}

impl CanonicalVarValues<'_> {
    pub fn is_identity(&self) -> bool {
        self.var_values.iter().enumerate().all(|(bv, arg)| match arg.unpack() {
            ty::GenericArgKind::Lifetime(r) => {
                matches!(*r, ty::ReBound(ty::INNERMOST, br) if br.var.as_usize() == bv)
            }
            ty::GenericArgKind::Type(ty) => {
                matches!(*ty.kind(), ty::Bound(ty::INNERMOST, bt) if bt.var.as_usize() == bv)
            }
            ty::GenericArgKind::Const(ct) => {
                matches!(ct.kind(), ty::ConstKind::Bound(ty::INNERMOST, bc) if bc.as_usize() == bv)
            }
        })
    }

    pub fn is_identity_modulo_regions(&self) -> bool {
        let mut var = ty::BoundVar::ZERO;
        for arg in self.var_values {
            match arg.unpack() {
                ty::GenericArgKind::Lifetime(r) => {
                    if let ty::ReBound(ty::INNERMOST, br) = *r
                        && var == br.var
                    {
                        var = var + 1;
                    } else {
                        // It's ok if this region var isn't unique
                    }
                }
                ty::GenericArgKind::Type(ty) => {
                    if let ty::Bound(ty::INNERMOST, bt) = *ty.kind()
                        && var == bt.var
                    {
                        var = var + 1;
                    } else {
                        return false;
                    }
                }
                ty::GenericArgKind::Const(ct) => {
                    if let ty::ConstKind::Bound(ty::INNERMOST, bc) = ct.kind()
                        && var == bc
                    {
                        var = var + 1;
                    } else {
                        return false;
                    }
                }
            }
        }

        true
    }
}

/// When we canonicalize a value to form a query, we wind up replacing
/// various parts of it with canonical variables. This struct stores
/// those replaced bits to remember for when we process the query
/// result.
#[derive(Clone, Debug)]
pub struct OriginalQueryValues<'tcx> {
    /// Map from the universes that appear in the query to the universes in the
    /// caller context. For all queries except `evaluate_goal` (used by Chalk),
    /// we only ever put ROOT values into the query, so this map is very
    /// simple.
    pub universe_map: SmallVec<[ty::UniverseIndex; 4]>,

    /// This is equivalent to `CanonicalVarValues`, but using a
    /// `SmallVec` yields a significant performance win.
    pub var_values: SmallVec<[GenericArg<'tcx>; 8]>,
}

impl<'tcx> Default for OriginalQueryValues<'tcx> {
    fn default() -> Self {
        let mut universe_map = SmallVec::default();
        universe_map.push(ty::UniverseIndex::ROOT);

        Self { universe_map, var_values: SmallVec::default() }
    }
}

/// After we execute a query with a canonicalized key, we get back a
/// `Canonical<QueryResponse<..>>`. You can use
/// `instantiate_query_result` to access the data in this result.
#[derive(Clone, Debug, HashStable, TypeFoldable, TypeVisitable)]
pub struct QueryResponse<'tcx, R> {
    pub var_values: CanonicalVarValues<'tcx>,
    pub region_constraints: QueryRegionConstraints<'tcx>,
    pub certainty: Certainty,
    pub opaque_types: Vec<(ty::OpaqueTypeKey<'tcx>, Ty<'tcx>)>,
    pub value: R,
}

#[derive(Clone, Debug, Default, PartialEq, Eq, Hash)]
#[derive(HashStable, TypeFoldable, TypeVisitable)]
pub struct QueryRegionConstraints<'tcx> {
    pub outlives: Vec<QueryOutlivesConstraint<'tcx>>,
    pub member_constraints: Vec<MemberConstraint<'tcx>>,
}

impl QueryRegionConstraints<'_> {
    /// Represents an empty (trivially true) set of region
    /// constraints.
    pub fn is_empty(&self) -> bool {
        self.outlives.is_empty() && self.member_constraints.is_empty()
    }
}

pub type CanonicalQueryResponse<'tcx, T> = &'tcx Canonical<'tcx, QueryResponse<'tcx, T>>;

/// Indicates whether or not we were able to prove the query to be
/// true.
#[derive(Copy, Clone, Debug, HashStable)]
pub enum Certainty {
    /// The query is known to be true, presuming that you apply the
    /// given `var_values` and the region-constraints are satisfied.
    Proven,

    /// The query is not known to be true, but also not known to be
    /// false. The `var_values` represent *either* values that must
    /// hold in order for the query to be true, or helpful tips that
    /// *might* make it true. Currently rustc's trait solver cannot
    /// distinguish the two (e.g., due to our preference for where
    /// clauses over impls).
    ///
    /// After some unification and things have been done, it makes
    /// sense to try and prove again -- of course, at that point, the
    /// canonical form will be different, making this a distinct
    /// query.
    Ambiguous,
}

impl Certainty {
    pub fn is_proven(&self) -> bool {
        match self {
            Certainty::Proven => true,
            Certainty::Ambiguous => false,
        }
    }
}

impl<'tcx, R> QueryResponse<'tcx, R> {
    pub fn is_proven(&self) -> bool {
        self.certainty.is_proven()
    }
}

pub type QueryOutlivesConstraint<'tcx> =
    (ty::OutlivesPredicate<GenericArg<'tcx>, Region<'tcx>>, ConstraintCategory<'tcx>);

TrivialTypeTraversalImpls! {
    crate::infer::canonical::Certainty,
}

impl<'tcx> CanonicalVarValues<'tcx> {
    // Given a list of canonical variables, construct a set of values which are
    // the identity response.
    pub fn make_identity(
        tcx: TyCtxt<'tcx>,
        infos: CanonicalVarInfos<'tcx>,
    ) -> CanonicalVarValues<'tcx> {
        CanonicalVarValues {
            var_values: tcx.mk_args_from_iter(infos.iter().enumerate().map(
                |(i, info)| -> ty::GenericArg<'tcx> {
                    match info.kind {
                        CanonicalVarKind::Ty(_) | CanonicalVarKind::PlaceholderTy(_) => {
                            Ty::new_bound(tcx, ty::INNERMOST, ty::BoundVar::from_usize(i).into())
                                .into()
                        }
                        CanonicalVarKind::Region(_) | CanonicalVarKind::PlaceholderRegion(_) => {
                            let br = ty::BoundRegion {
                                var: ty::BoundVar::from_usize(i),
                                kind: ty::BrAnon,
                            };
                            ty::Region::new_bound(tcx, ty::INNERMOST, br).into()
                        }
                        CanonicalVarKind::Effect => ty::Const::new_bound(
                            tcx,
                            ty::INNERMOST,
                            ty::BoundVar::from_usize(i),
                            tcx.types.bool,
                        )
                        .into(),
                        CanonicalVarKind::Const(_, ty)
                        | CanonicalVarKind::PlaceholderConst(_, ty) => ty::Const::new_bound(
                            tcx,
                            ty::INNERMOST,
                            ty::BoundVar::from_usize(i),
                            ty,
                        )
                        .into(),
                    }
                },
            )),
        }
    }

    /// Creates dummy var values which should not be used in a
    /// canonical response.
    pub fn dummy() -> CanonicalVarValues<'tcx> {
        CanonicalVarValues { var_values: ty::List::empty() }
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.var_values.len()
    }
}

impl<'a, 'tcx> IntoIterator for &'a CanonicalVarValues<'tcx> {
    type Item = GenericArg<'tcx>;
    type IntoIter = ::std::iter::Copied<::std::slice::Iter<'a, GenericArg<'tcx>>>;

    fn into_iter(self) -> Self::IntoIter {
        self.var_values.iter()
    }
}

impl<'tcx> Index<BoundVar> for CanonicalVarValues<'tcx> {
    type Output = GenericArg<'tcx>;

    fn index(&self, value: BoundVar) -> &GenericArg<'tcx> {
        &self.var_values[value.as_usize()]
    }
}

#[derive(Default)]
pub struct CanonicalParamEnvCache<'tcx> {
    map: Lock<
        FxHashMap<
            ty::ParamEnv<'tcx>,
            (Canonical<'tcx, ty::ParamEnv<'tcx>>, &'tcx [GenericArg<'tcx>]),
        >,
    >,
}

impl<'tcx> CanonicalParamEnvCache<'tcx> {
    /// Gets the cached canonical form of `key` or executes
    /// `canonicalize_op` and caches the result if not present.
    ///
    /// `canonicalize_op` is intentionally not allowed to be a closure to
    /// statically prevent it from capturing `InferCtxt` and resolving
    /// inference variables, which invalidates the cache.
    pub fn get_or_insert(
        &self,
        tcx: TyCtxt<'tcx>,
        key: ty::ParamEnv<'tcx>,
        state: &mut OriginalQueryValues<'tcx>,
        canonicalize_op: fn(
            TyCtxt<'tcx>,
            ty::ParamEnv<'tcx>,
            &mut OriginalQueryValues<'tcx>,
        ) -> Canonical<'tcx, ty::ParamEnv<'tcx>>,
    ) -> Canonical<'tcx, ty::ParamEnv<'tcx>> {
        if !key.has_type_flags(
            TypeFlags::HAS_INFER | TypeFlags::HAS_PLACEHOLDER | TypeFlags::HAS_FREE_REGIONS,
        ) {
            return Canonical {
                max_universe: ty::UniverseIndex::ROOT,
                variables: List::empty(),
                value: key,
                defining_opaque_types: ty::List::empty(),
            };
        }

        assert_eq!(state.var_values.len(), 0);
        assert_eq!(state.universe_map.len(), 1);
        debug_assert_eq!(&*state.universe_map, &[ty::UniverseIndex::ROOT]);

        match self.map.borrow().entry(key) {
            Entry::Occupied(e) => {
                let (canonical, var_values) = e.get();
                if cfg!(debug_assertions) {
                    let mut state = state.clone();
                    let rerun_canonical = canonicalize_op(tcx, key, &mut state);
                    assert_eq!(rerun_canonical, *canonical);
                    let OriginalQueryValues { var_values: rerun_var_values, universe_map } = state;
                    assert_eq!(universe_map.len(), 1);
                    assert_eq!(**var_values, *rerun_var_values);
                }
                state.var_values.extend_from_slice(var_values);
                *canonical
            }
            Entry::Vacant(e) => {
                let canonical = canonicalize_op(tcx, key, state);
                let OriginalQueryValues { var_values, universe_map } = state;
                assert_eq!(universe_map.len(), 1);
                e.insert((canonical, tcx.arena.alloc_slice(var_values)));
                canonical
            }
        }
    }
}