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
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
//! There are four type combiners: [TypeRelating], [Lub], and [Glb],
//! and `NllTypeRelating` in rustc_borrowck, which is only used for NLL.
//!
//! Each implements the trait [TypeRelation] and contains methods for
//! combining two instances of various things and yielding a new instance.
//! These combiner methods always yield a `Result<T>`. To relate two
//! types, you can use `infcx.at(cause, param_env)` which then allows
//! you to use the relevant methods of [At](crate::infer::at::At).
//!
//! Combiners mostly do their specific behavior and then hand off the
//! bulk of the work to [InferCtxt::super_combine_tys] and
//! [InferCtxt::super_combine_consts].
//!
//! Combining two types may have side-effects on the inference contexts
//! which can be undone by using snapshots. You probably want to use
//! either [InferCtxt::commit_if_ok] or [InferCtxt::probe].
//!
//! On success, the  LUB/GLB operations return the appropriate bound. The
//! return value of `Equate` or `Sub` shouldn't really be used.

use super::glb::Glb;
use super::lub::Lub;
use super::type_relating::TypeRelating;
use super::StructurallyRelateAliases;
use crate::infer::{DefineOpaqueTypes, InferCtxt, TypeTrace};
use crate::traits::{Obligation, PredicateObligations};
use rustc_middle::infer::canonical::OriginalQueryValues;
use rustc_middle::infer::unify_key::EffectVarValue;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::relate::{RelateResult, TypeRelation};
use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{IntType, UintType};
use rustc_span::Span;

#[derive(Clone)]
pub struct CombineFields<'infcx, 'tcx> {
    pub infcx: &'infcx InferCtxt<'tcx>,
    pub trace: TypeTrace<'tcx>,
    pub param_env: ty::ParamEnv<'tcx>,
    pub obligations: PredicateObligations<'tcx>,
    pub define_opaque_types: DefineOpaqueTypes,
}

impl<'tcx> InferCtxt<'tcx> {
    pub fn super_combine_tys<R>(
        &self,
        relation: &mut R,
        a: Ty<'tcx>,
        b: Ty<'tcx>,
    ) -> RelateResult<'tcx, Ty<'tcx>>
    where
        R: ObligationEmittingRelation<'tcx>,
    {
        debug_assert!(!a.has_escaping_bound_vars());
        debug_assert!(!b.has_escaping_bound_vars());

        match (a.kind(), b.kind()) {
            // Relate integral variables to other types
            (&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => {
                self.inner
                    .borrow_mut()
                    .int_unification_table()
                    .unify_var_var(a_id, b_id)
                    .map_err(|e| int_unification_error(true, e))?;
                Ok(a)
            }
            (&ty::Infer(ty::IntVar(v_id)), &ty::Int(v)) => {
                self.unify_integral_variable(true, v_id, IntType(v))
            }
            (&ty::Int(v), &ty::Infer(ty::IntVar(v_id))) => {
                self.unify_integral_variable(false, v_id, IntType(v))
            }
            (&ty::Infer(ty::IntVar(v_id)), &ty::Uint(v)) => {
                self.unify_integral_variable(true, v_id, UintType(v))
            }
            (&ty::Uint(v), &ty::Infer(ty::IntVar(v_id))) => {
                self.unify_integral_variable(false, v_id, UintType(v))
            }

            // Relate floating-point variables to other types
            (&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => {
                self.inner
                    .borrow_mut()
                    .float_unification_table()
                    .unify_var_var(a_id, b_id)
                    .map_err(|e| float_unification_error(true, e))?;
                Ok(a)
            }
            (&ty::Infer(ty::FloatVar(v_id)), &ty::Float(v)) => {
                self.unify_float_variable(true, v_id, v)
            }
            (&ty::Float(v), &ty::Infer(ty::FloatVar(v_id))) => {
                self.unify_float_variable(false, v_id, v)
            }

            // We don't expect `TyVar` or `Fresh*` vars at this point with lazy norm.
            (ty::Alias(..), ty::Infer(ty::TyVar(_))) | (ty::Infer(ty::TyVar(_)), ty::Alias(..))
                if self.next_trait_solver() =>
            {
                bug!(
                    "We do not expect to encounter `TyVar` this late in combine \
                    -- they should have been handled earlier"
                )
            }
            (_, ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)))
            | (ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)), _)
                if self.next_trait_solver() =>
            {
                bug!("We do not expect to encounter `Fresh` variables in the new solver")
            }

            (_, ty::Alias(..)) | (ty::Alias(..), _) if self.next_trait_solver() => {
                match relation.structurally_relate_aliases() {
                    StructurallyRelateAliases::Yes => {
                        ty::relate::structurally_relate_tys(relation, a, b)
                    }
                    StructurallyRelateAliases::No => {
                        relation.register_type_relate_obligation(a, b);
                        Ok(a)
                    }
                }
            }

            // All other cases of inference are errors
            (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
                Err(TypeError::Sorts(ty::relate::expected_found(a, b)))
            }

            // During coherence, opaque types should be treated as *possibly*
            // equal to any other type (except for possibly itself). This is an
            // extremely heavy hammer, but can be relaxed in a fowards-compatible
            // way later.
            (&ty::Alias(ty::Opaque, _), _) | (_, &ty::Alias(ty::Opaque, _)) if self.intercrate => {
                relation.register_predicates([ty::Binder::dummy(ty::PredicateKind::Ambiguous)]);
                Ok(a)
            }

            _ => ty::relate::structurally_relate_tys(relation, a, b),
        }
    }

    pub fn super_combine_consts<R>(
        &self,
        relation: &mut R,
        a: ty::Const<'tcx>,
        b: ty::Const<'tcx>,
    ) -> RelateResult<'tcx, ty::Const<'tcx>>
    where
        R: ObligationEmittingRelation<'tcx>,
    {
        debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
        debug_assert!(!a.has_escaping_bound_vars());
        debug_assert!(!b.has_escaping_bound_vars());
        if a == b {
            return Ok(a);
        }

        let a = self.shallow_resolve(a);
        let b = self.shallow_resolve(b);

        // We should never have to relate the `ty` field on `Const` as it is checked elsewhere that consts have the
        // correct type for the generic param they are an argument for. However there have been a number of cases
        // historically where asserting that the types are equal has found bugs in the compiler so this is valuable
        // to check even if it is a bit nasty impl wise :(
        //
        // This probe is probably not strictly necessary but it seems better to be safe and not accidentally find
        // ourselves with a check to find bugs being required for code to compile because it made inference progress.
        self.probe(|_| {
            if a.ty() == b.ty() {
                return;
            }

            // We don't have access to trait solving machinery in `rustc_infer` so the logic for determining if the
            // two const param's types are able to be equal has to go through a canonical query with the actual logic
            // in `rustc_trait_selection`.
            let canonical = self.canonicalize_query(
                relation.param_env().and((a.ty(), b.ty())),
                &mut OriginalQueryValues::default(),
            );
            self.tcx.check_tys_might_be_eq(canonical).unwrap_or_else(|_| {
                // The error will only be reported later. If we emit an ErrorGuaranteed
                // here, then we will never get to the code that actually emits the error.
                self.tcx.dcx().delayed_bug(format!(
                    "cannot relate consts of different types (a={a:?}, b={b:?})",
                ));
                // We treat these constants as if they were of the same type, so that any
                // such constants being used in impls make these impls match barring other mismatches.
                // This helps with diagnostics down the road.
            });
        });

        match (a.kind(), b.kind()) {
            (
                ty::ConstKind::Infer(InferConst::Var(a_vid)),
                ty::ConstKind::Infer(InferConst::Var(b_vid)),
            ) => {
                self.inner.borrow_mut().const_unification_table().union(a_vid, b_vid);
                Ok(a)
            }

            (
                ty::ConstKind::Infer(InferConst::EffectVar(a_vid)),
                ty::ConstKind::Infer(InferConst::EffectVar(b_vid)),
            ) => {
                self.inner.borrow_mut().effect_unification_table().union(a_vid, b_vid);
                Ok(a)
            }

            // All other cases of inference with other variables are errors.
            (
                ty::ConstKind::Infer(InferConst::Var(_) | InferConst::EffectVar(_)),
                ty::ConstKind::Infer(_),
            )
            | (
                ty::ConstKind::Infer(_),
                ty::ConstKind::Infer(InferConst::Var(_) | InferConst::EffectVar(_)),
            ) => {
                bug!(
                    "tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var): {a:?} and {b:?}"
                )
            }

            (ty::ConstKind::Infer(InferConst::Var(vid)), _) => {
                self.instantiate_const_var(relation, true, vid, b)?;
                Ok(b)
            }

            (_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
                self.instantiate_const_var(relation, false, vid, a)?;
                Ok(a)
            }

            (ty::ConstKind::Infer(InferConst::EffectVar(vid)), _) => {
                Ok(self.unify_effect_variable(vid, b))
            }

            (_, ty::ConstKind::Infer(InferConst::EffectVar(vid))) => {
                Ok(self.unify_effect_variable(vid, a))
            }

            (ty::ConstKind::Unevaluated(..), _) | (_, ty::ConstKind::Unevaluated(..))
                if self.tcx.features().generic_const_exprs || self.next_trait_solver() =>
            {
                match relation.structurally_relate_aliases() {
                    StructurallyRelateAliases::No => {
                        relation.register_predicates([if self.next_trait_solver() {
                            ty::PredicateKind::AliasRelate(
                                a.into(),
                                b.into(),
                                ty::AliasRelationDirection::Equate,
                            )
                        } else {
                            ty::PredicateKind::ConstEquate(a, b)
                        }]);

                        Ok(b)
                    }
                    StructurallyRelateAliases::Yes => {
                        ty::relate::structurally_relate_consts(relation, a, b)
                    }
                }
            }
            _ => ty::relate::structurally_relate_consts(relation, a, b),
        }
    }

    fn unify_integral_variable(
        &self,
        vid_is_expected: bool,
        vid: ty::IntVid,
        val: ty::IntVarValue,
    ) -> RelateResult<'tcx, Ty<'tcx>> {
        self.inner
            .borrow_mut()
            .int_unification_table()
            .unify_var_value(vid, Some(val))
            .map_err(|e| int_unification_error(vid_is_expected, e))?;
        match val {
            IntType(v) => Ok(Ty::new_int(self.tcx, v)),
            UintType(v) => Ok(Ty::new_uint(self.tcx, v)),
        }
    }

    fn unify_float_variable(
        &self,
        vid_is_expected: bool,
        vid: ty::FloatVid,
        val: ty::FloatTy,
    ) -> RelateResult<'tcx, Ty<'tcx>> {
        self.inner
            .borrow_mut()
            .float_unification_table()
            .unify_var_value(vid, Some(ty::FloatVarValue(val)))
            .map_err(|e| float_unification_error(vid_is_expected, e))?;
        Ok(Ty::new_float(self.tcx, val))
    }

    fn unify_effect_variable(&self, vid: ty::EffectVid, val: ty::Const<'tcx>) -> ty::Const<'tcx> {
        self.inner
            .borrow_mut()
            .effect_unification_table()
            .union_value(vid, EffectVarValue::Known(val));
        val
    }
}

impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
    pub fn tcx(&self) -> TyCtxt<'tcx> {
        self.infcx.tcx
    }

    pub fn equate<'a>(
        &'a mut self,
        structurally_relate_aliases: StructurallyRelateAliases,
    ) -> TypeRelating<'a, 'infcx, 'tcx> {
        TypeRelating::new(self, structurally_relate_aliases, ty::Invariant)
    }

    pub fn sub<'a>(&'a mut self) -> TypeRelating<'a, 'infcx, 'tcx> {
        TypeRelating::new(self, StructurallyRelateAliases::No, ty::Covariant)
    }

    pub fn sup<'a>(&'a mut self) -> TypeRelating<'a, 'infcx, 'tcx> {
        TypeRelating::new(self, StructurallyRelateAliases::No, ty::Contravariant)
    }

    pub fn lub<'a>(&'a mut self) -> Lub<'a, 'infcx, 'tcx> {
        Lub::new(self)
    }

    pub fn glb<'a>(&'a mut self) -> Glb<'a, 'infcx, 'tcx> {
        Glb::new(self)
    }

    pub fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) {
        self.obligations.extend(obligations);
    }

    pub fn register_predicates(&mut self, obligations: impl IntoIterator<Item: ToPredicate<'tcx>>) {
        self.obligations.extend(obligations.into_iter().map(|to_pred| {
            Obligation::new(self.infcx.tcx, self.trace.cause.clone(), self.param_env, to_pred)
        }))
    }
}

pub trait ObligationEmittingRelation<'tcx>: TypeRelation<'tcx> {
    fn span(&self) -> Span;

    fn param_env(&self) -> ty::ParamEnv<'tcx>;

    /// Whether aliases should be related structurally. This is pretty much
    /// always `No` unless you're equating in some specific locations of the
    /// new solver. See the comments in these use-cases for more details.
    fn structurally_relate_aliases(&self) -> StructurallyRelateAliases;

    /// Register obligations that must hold in order for this relation to hold
    fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>);

    /// Register predicates that must hold in order for this relation to hold. Uses
    /// a default obligation cause, [`ObligationEmittingRelation::register_obligations`] should
    /// be used if control over the obligation causes is required.
    fn register_predicates(&mut self, obligations: impl IntoIterator<Item: ToPredicate<'tcx>>);

    /// Register `AliasRelate` obligation(s) that both types must be related to each other.
    fn register_type_relate_obligation(&mut self, a: Ty<'tcx>, b: Ty<'tcx>);
}

fn int_unification_error<'tcx>(
    a_is_expected: bool,
    v: (ty::IntVarValue, ty::IntVarValue),
) -> TypeError<'tcx> {
    let (a, b) = v;
    TypeError::IntMismatch(ExpectedFound::new(a_is_expected, a, b))
}

fn float_unification_error<'tcx>(
    a_is_expected: bool,
    v: (ty::FloatVarValue, ty::FloatVarValue),
) -> TypeError<'tcx> {
    let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
    TypeError::FloatMismatch(ExpectedFound::new(a_is_expected, a, b))
}