rustc_next_trait_solver/canonical/
canonicalizer.rs

1use rustc_type_ir::data_structures::{HashMap, ensure_sufficient_stack};
2use rustc_type_ir::inherent::*;
3use rustc_type_ir::solve::{Goal, QueryInput};
4use rustc_type_ir::{
5    self as ty, Canonical, CanonicalParamEnvCacheEntry, CanonicalVarKind, Flags, InferCtxtLike,
6    Interner, TypeFlags, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
7};
8
9use crate::delegate::SolverDelegate;
10
11/// Does this have infer/placeholder/param, free regions or ReErased?
12const NEEDS_CANONICAL: TypeFlags = TypeFlags::from_bits(
13    TypeFlags::HAS_INFER.bits()
14        | TypeFlags::HAS_PLACEHOLDER.bits()
15        | TypeFlags::HAS_PARAM.bits()
16        | TypeFlags::HAS_FREE_REGIONS.bits()
17        | TypeFlags::HAS_RE_ERASED.bits(),
18)
19.unwrap();
20
21#[derive(Debug, Clone, Copy)]
22enum CanonicalizeInputKind {
23    /// When canonicalizing the `param_env`, we keep `'static` as merging
24    /// trait candidates relies on it when deciding whether a where-bound
25    /// is trivial.
26    ParamEnv,
27    /// When canonicalizing predicates, we don't keep `'static`.
28    Predicate,
29}
30
31/// Whether we're canonicalizing a query input or the query response.
32///
33/// When canonicalizing an input we're in the context of the caller
34/// while canonicalizing the response happens in the context of the
35/// query.
36#[derive(Debug, Clone, Copy)]
37enum CanonicalizeMode {
38    Input(CanonicalizeInputKind),
39    /// FIXME: We currently return region constraints referring to
40    /// placeholders and inference variables from a binder instantiated
41    /// inside of the query.
42    ///
43    /// In the long term we should eagerly deal with these constraints
44    /// inside of the query and only propagate constraints which are
45    /// actually nameable by the caller.
46    Response {
47        /// The highest universe nameable by the caller.
48        ///
49        /// All variables in a universe nameable by the caller get mapped
50        /// to the root universe in the response and then mapped back to
51        /// their correct universe when applying the query response in the
52        /// context of the caller.
53        ///
54        /// This doesn't work for universes created inside of the query so
55        /// we do remember their universe in the response.
56        max_input_universe: ty::UniverseIndex,
57    },
58}
59
60pub(super) struct Canonicalizer<'a, D: SolverDelegate<Interner = I>, I: Interner> {
61    delegate: &'a D,
62
63    // Immutable field.
64    canonicalize_mode: CanonicalizeMode,
65
66    // Mutable fields.
67    variables: &'a mut Vec<I::GenericArg>,
68    var_kinds: Vec<CanonicalVarKind<I>>,
69    variable_lookup_table: HashMap<I::GenericArg, usize>,
70    /// Maps each `sub_unification_table_root_var` to the index of the first
71    /// variable which used it.
72    ///
73    /// This means in case two type variables have the same sub relations root,
74    /// we set the `sub_root` of the second variable to the position of the first.
75    /// Otherwise the `sub_root` of each type variable is just its own position.
76    sub_root_lookup_table: HashMap<ty::TyVid, usize>,
77
78    /// We can simply cache based on the ty itself, because we use
79    /// `ty::BoundVarIndexKind::Canonical`.
80    cache: HashMap<I::Ty, I::Ty>,
81}
82
83impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
84    pub(super) fn canonicalize_response<T: TypeFoldable<I>>(
85        delegate: &'a D,
86        max_input_universe: ty::UniverseIndex,
87        variables: &'a mut Vec<I::GenericArg>,
88        value: T,
89    ) -> ty::Canonical<I, T> {
90        let mut canonicalizer = Canonicalizer {
91            delegate,
92            canonicalize_mode: CanonicalizeMode::Response { max_input_universe },
93
94            variables,
95            variable_lookup_table: Default::default(),
96            sub_root_lookup_table: Default::default(),
97            var_kinds: Vec::new(),
98
99            cache: Default::default(),
100        };
101
102        let value = if value.has_type_flags(NEEDS_CANONICAL) {
103            value.fold_with(&mut canonicalizer)
104        } else {
105            value
106        };
107        debug_assert!(!value.has_infer(), "unexpected infer in {value:?}");
108        debug_assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
109        let (max_universe, variables) = canonicalizer.finalize();
110        Canonical { max_universe, variables, value }
111    }
112    fn canonicalize_param_env(
113        delegate: &'a D,
114        variables: &'a mut Vec<I::GenericArg>,
115        param_env: I::ParamEnv,
116    ) -> (I::ParamEnv, HashMap<I::GenericArg, usize>, Vec<CanonicalVarKind<I>>) {
117        if !param_env.has_type_flags(NEEDS_CANONICAL) {
118            return (param_env, Default::default(), Vec::new());
119        }
120
121        // Check whether we can use the global cache for this param_env. As we only use
122        // the `param_env` itself as the cache key, considering any additional information
123        // durnig its canonicalization would be incorrect. We always canonicalize region
124        // inference variables in a separate universe, so these are fine. However, we do
125        // track the universe of type and const inference variables so these must not be
126        // globally cached. We don't rely on any additional information when canonicalizing
127        // placeholders.
128        if !param_env.has_non_region_infer() {
129            delegate.cx().canonical_param_env_cache_get_or_insert(
130                param_env,
131                || {
132                    let mut variables = Vec::new();
133                    let mut env_canonicalizer = Canonicalizer {
134                        delegate,
135                        canonicalize_mode: CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv),
136
137                        variables: &mut variables,
138                        variable_lookup_table: Default::default(),
139                        sub_root_lookup_table: Default::default(),
140                        var_kinds: Vec::new(),
141
142                        cache: Default::default(),
143                    };
144                    let param_env = param_env.fold_with(&mut env_canonicalizer);
145                    debug_assert!(env_canonicalizer.sub_root_lookup_table.is_empty());
146                    CanonicalParamEnvCacheEntry {
147                        param_env,
148                        variable_lookup_table: env_canonicalizer.variable_lookup_table,
149                        var_kinds: env_canonicalizer.var_kinds,
150                        variables,
151                    }
152                },
153                |&CanonicalParamEnvCacheEntry {
154                     param_env,
155                     variables: ref cache_variables,
156                     ref variable_lookup_table,
157                     ref var_kinds,
158                 }| {
159                    debug_assert!(variables.is_empty());
160                    variables.extend(cache_variables.iter().copied());
161                    (param_env, variable_lookup_table.clone(), var_kinds.clone())
162                },
163            )
164        } else {
165            let mut env_canonicalizer = Canonicalizer {
166                delegate,
167                canonicalize_mode: CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv),
168
169                variables,
170                variable_lookup_table: Default::default(),
171                sub_root_lookup_table: Default::default(),
172                var_kinds: Vec::new(),
173
174                cache: Default::default(),
175            };
176            let param_env = param_env.fold_with(&mut env_canonicalizer);
177            debug_assert!(env_canonicalizer.sub_root_lookup_table.is_empty());
178            (param_env, env_canonicalizer.variable_lookup_table, env_canonicalizer.var_kinds)
179        }
180    }
181
182    /// When canonicalizing query inputs, we keep `'static` in the `param_env`
183    /// but erase it everywhere else. We generally don't want to depend on region
184    /// identity, so while it should not matter whether `'static` is kept in the
185    /// value or opaque type storage as well, this prevents us from accidentally
186    /// relying on it in the future.
187    ///
188    /// We want to keep the option of canonicalizing `'static` to an existential
189    /// variable in the future by changing the way we detect global where-bounds.
190    pub(super) fn canonicalize_input<P: TypeFoldable<I>>(
191        delegate: &'a D,
192        variables: &'a mut Vec<I::GenericArg>,
193        input: QueryInput<I, P>,
194    ) -> ty::Canonical<I, QueryInput<I, P>> {
195        // First canonicalize the `param_env` while keeping `'static`
196        let (param_env, variable_lookup_table, var_kinds) =
197            Canonicalizer::canonicalize_param_env(delegate, variables, input.goal.param_env);
198        // Then canonicalize the rest of the input without keeping `'static`
199        // while *mostly* reusing the canonicalizer from above.
200        let mut rest_canonicalizer = Canonicalizer {
201            delegate,
202            canonicalize_mode: CanonicalizeMode::Input(CanonicalizeInputKind::Predicate),
203
204            variables,
205            variable_lookup_table,
206            sub_root_lookup_table: Default::default(),
207            var_kinds,
208
209            // We do not reuse the cache as it may contain entries whose canonicalized
210            // value contains `'static`. While we could alternatively handle this by
211            // checking for `'static` when using cached entries, this does not
212            // feel worth the effort. I do not expect that a `ParamEnv` will ever
213            // contain large enough types for caching to be necessary.
214            cache: Default::default(),
215        };
216
217        let predicate = input.goal.predicate;
218        let predicate = if predicate.has_type_flags(NEEDS_CANONICAL) {
219            predicate.fold_with(&mut rest_canonicalizer)
220        } else {
221            predicate
222        };
223        let goal = Goal { param_env, predicate };
224
225        let predefined_opaques_in_body = input.predefined_opaques_in_body;
226        let predefined_opaques_in_body =
227            if input.predefined_opaques_in_body.has_type_flags(NEEDS_CANONICAL) {
228                predefined_opaques_in_body.fold_with(&mut rest_canonicalizer)
229            } else {
230                predefined_opaques_in_body
231            };
232
233        let value = QueryInput { goal, predefined_opaques_in_body };
234
235        debug_assert!(!value.has_infer(), "unexpected infer in {value:?}");
236        debug_assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
237        let (max_universe, variables) = rest_canonicalizer.finalize();
238        Canonical { max_universe, variables, value }
239    }
240
241    fn get_or_insert_bound_var(
242        &mut self,
243        arg: impl Into<I::GenericArg>,
244        kind: CanonicalVarKind<I>,
245    ) -> ty::BoundVar {
246        // FIXME: 16 is made up and arbitrary. We should look at some
247        // perf data here.
248        let arg = arg.into();
249        let idx = if self.variables.len() > 16 {
250            if self.variable_lookup_table.is_empty() {
251                self.variable_lookup_table.extend(self.variables.iter().copied().zip(0..));
252            }
253
254            *self.variable_lookup_table.entry(arg).or_insert_with(|| {
255                let var = self.variables.len();
256                self.variables.push(arg);
257                self.var_kinds.push(kind);
258                var
259            })
260        } else {
261            self.variables.iter().position(|&v| v == arg).unwrap_or_else(|| {
262                let var = self.variables.len();
263                self.variables.push(arg);
264                self.var_kinds.push(kind);
265                var
266            })
267        };
268
269        ty::BoundVar::from(idx)
270    }
271
272    fn get_or_insert_sub_root(&mut self, vid: ty::TyVid) -> ty::BoundVar {
273        let root_vid = self.delegate.sub_unification_table_root_var(vid);
274        let idx =
275            *self.sub_root_lookup_table.entry(root_vid).or_insert_with(|| self.variables.len());
276        ty::BoundVar::from(idx)
277    }
278
279    fn finalize(self) -> (ty::UniverseIndex, I::CanonicalVarKinds) {
280        let mut var_kinds = self.var_kinds;
281        // See the rustc-dev-guide section about how we deal with universes
282        // during canonicalization in the new solver.
283        match self.canonicalize_mode {
284            // All placeholders and vars are canonicalized in the root universe.
285            CanonicalizeMode::Input { .. } => {
286                debug_assert!(
287                    var_kinds.iter().all(|var| var.universe() == ty::UniverseIndex::ROOT),
288                    "expected all vars to be canonicalized in root universe: {var_kinds:#?}"
289                );
290                let var_kinds = self.delegate.cx().mk_canonical_var_kinds(&var_kinds);
291                (ty::UniverseIndex::ROOT, var_kinds)
292            }
293            // When canonicalizing a response we map a universes already entered
294            // by the caller to the root universe and only return useful universe
295            // information for placeholders and inference variables created inside
296            // of the query.
297            CanonicalizeMode::Response { max_input_universe } => {
298                for var in var_kinds.iter_mut() {
299                    let uv = var.universe();
300                    let new_uv = ty::UniverseIndex::from(
301                        uv.index().saturating_sub(max_input_universe.index()),
302                    );
303                    *var = var.with_updated_universe(new_uv);
304                }
305                let max_universe = var_kinds
306                    .iter()
307                    .map(|kind| kind.universe())
308                    .max()
309                    .unwrap_or(ty::UniverseIndex::ROOT);
310                let var_kinds = self.delegate.cx().mk_canonical_var_kinds(&var_kinds);
311                (max_universe, var_kinds)
312            }
313        }
314    }
315
316    fn inner_fold_ty(&mut self, t: I::Ty) -> I::Ty {
317        let kind = match t.kind() {
318            ty::Infer(i) => match i {
319                ty::TyVar(vid) => {
320                    debug_assert_eq!(
321                        self.delegate.opportunistic_resolve_ty_var(vid),
322                        t,
323                        "ty vid should have been resolved fully before canonicalization"
324                    );
325
326                    let sub_root = self.get_or_insert_sub_root(vid);
327                    let ui = match self.canonicalize_mode {
328                        CanonicalizeMode::Input { .. } => ty::UniverseIndex::ROOT,
329                        CanonicalizeMode::Response { .. } => self
330                            .delegate
331                            .universe_of_ty(vid)
332                            .unwrap_or_else(|| panic!("ty var should have been resolved: {t:?}")),
333                    };
334                    CanonicalVarKind::Ty { ui, sub_root }
335                }
336                ty::IntVar(vid) => {
337                    debug_assert_eq!(
338                        self.delegate.opportunistic_resolve_int_var(vid),
339                        t,
340                        "ty vid should have been resolved fully before canonicalization"
341                    );
342                    CanonicalVarKind::Int
343                }
344                ty::FloatVar(vid) => {
345                    debug_assert_eq!(
346                        self.delegate.opportunistic_resolve_float_var(vid),
347                        t,
348                        "ty vid should have been resolved fully before canonicalization"
349                    );
350                    CanonicalVarKind::Float
351                }
352                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
353                    panic!("fresh vars not expected in canonicalization")
354                }
355            },
356            ty::Placeholder(placeholder) => match self.canonicalize_mode {
357                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderTy(
358                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
359                ),
360                CanonicalizeMode::Response { .. } => CanonicalVarKind::PlaceholderTy(placeholder),
361            },
362            ty::Param(_) => match self.canonicalize_mode {
363                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderTy(
364                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
365                ),
366                CanonicalizeMode::Response { .. } => panic!("param ty in response: {t:?}"),
367            },
368            ty::Bool
369            | ty::Char
370            | ty::Int(_)
371            | ty::Uint(_)
372            | ty::Float(_)
373            | ty::Adt(_, _)
374            | ty::Foreign(_)
375            | ty::Str
376            | ty::Array(_, _)
377            | ty::Slice(_)
378            | ty::RawPtr(_, _)
379            | ty::Ref(_, _, _)
380            | ty::Pat(_, _)
381            | ty::FnDef(_, _)
382            | ty::FnPtr(..)
383            | ty::UnsafeBinder(_)
384            | ty::Dynamic(_, _)
385            | ty::Closure(..)
386            | ty::CoroutineClosure(..)
387            | ty::Coroutine(_, _)
388            | ty::CoroutineWitness(..)
389            | ty::Never
390            | ty::Tuple(_)
391            | ty::Alias(_, _)
392            | ty::Bound(_, _)
393            | ty::Error(_) => {
394                return if t.has_type_flags(NEEDS_CANONICAL) {
395                    ensure_sufficient_stack(|| t.super_fold_with(self))
396                } else {
397                    t
398                };
399            }
400        };
401
402        let var = self.get_or_insert_bound_var(t, kind);
403
404        Ty::new_canonical_bound(self.cx(), var)
405    }
406}
407
408impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicalizer<'_, D, I> {
409    fn cx(&self) -> I {
410        self.delegate.cx()
411    }
412
413    fn fold_region(&mut self, r: I::Region) -> I::Region {
414        let kind = match r.kind() {
415            ty::ReBound(..) => return r,
416
417            // We don't canonicalize `ReStatic` in the `param_env` as we use it
418            // when checking whether a `ParamEnv` candidate is global.
419            ty::ReStatic => match self.canonicalize_mode {
420                CanonicalizeMode::Input(CanonicalizeInputKind::Predicate { .. }) => {
421                    CanonicalVarKind::Region(ty::UniverseIndex::ROOT)
422                }
423                CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv)
424                | CanonicalizeMode::Response { .. } => return r,
425            },
426
427            // `ReErased` should only be encountered in the hidden
428            // type of an opaque for regions that are ignored for the purposes of
429            // captures.
430            //
431            // FIXME: We should investigate the perf implications of not uniquifying
432            // `ReErased`. We may be able to short-circuit registering region
433            // obligations if we encounter a `ReErased` on one side, for example.
434            ty::ReErased | ty::ReError(_) => match self.canonicalize_mode {
435                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
436                CanonicalizeMode::Response { .. } => return r,
437            },
438
439            ty::ReEarlyParam(_) | ty::ReLateParam(_) => match self.canonicalize_mode {
440                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
441                CanonicalizeMode::Response { .. } => {
442                    panic!("unexpected region in response: {r:?}")
443                }
444            },
445
446            ty::RePlaceholder(placeholder) => match self.canonicalize_mode {
447                // We canonicalize placeholder regions as existentials in query inputs.
448                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
449                CanonicalizeMode::Response { max_input_universe } => {
450                    // If we have a placeholder region inside of a query, it must be from
451                    // a new universe.
452                    if max_input_universe.can_name(placeholder.universe()) {
453                        panic!("new placeholder in universe {max_input_universe:?}: {r:?}");
454                    }
455                    CanonicalVarKind::PlaceholderRegion(placeholder)
456                }
457            },
458
459            ty::ReVar(vid) => {
460                debug_assert_eq!(
461                    self.delegate.opportunistic_resolve_lt_var(vid),
462                    r,
463                    "region vid should have been resolved fully before canonicalization"
464                );
465                match self.canonicalize_mode {
466                    CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
467                    CanonicalizeMode::Response { .. } => {
468                        CanonicalVarKind::Region(self.delegate.universe_of_lt(vid).unwrap())
469                    }
470                }
471            }
472        };
473
474        let var = self.get_or_insert_bound_var(r, kind);
475
476        Region::new_canonical_bound(self.cx(), var)
477    }
478
479    fn fold_ty(&mut self, t: I::Ty) -> I::Ty {
480        if let Some(&ty) = self.cache.get(&t) {
481            ty
482        } else {
483            let res = self.inner_fold_ty(t);
484            let old = self.cache.insert(t, res);
485            assert_eq!(old, None);
486            res
487        }
488    }
489
490    fn fold_const(&mut self, c: I::Const) -> I::Const {
491        let kind = match c.kind() {
492            ty::ConstKind::Infer(i) => match i {
493                ty::InferConst::Var(vid) => {
494                    debug_assert_eq!(
495                        self.delegate.opportunistic_resolve_ct_var(vid),
496                        c,
497                        "const vid should have been resolved fully before canonicalization"
498                    );
499
500                    match self.canonicalize_mode {
501                        CanonicalizeMode::Input { .. } => {
502                            CanonicalVarKind::Const(ty::UniverseIndex::ROOT)
503                        }
504                        CanonicalizeMode::Response { .. } => {
505                            CanonicalVarKind::Const(self.delegate.universe_of_ct(vid).unwrap())
506                        }
507                    }
508                }
509                ty::InferConst::Fresh(_) => todo!(),
510            },
511            ty::ConstKind::Placeholder(placeholder) => match self.canonicalize_mode {
512                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderConst(
513                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
514                ),
515                CanonicalizeMode::Response { .. } => {
516                    CanonicalVarKind::PlaceholderConst(placeholder)
517                }
518            },
519            ty::ConstKind::Param(_) => match self.canonicalize_mode {
520                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderConst(
521                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
522                ),
523                CanonicalizeMode::Response { .. } => panic!("param ty in response: {c:?}"),
524            },
525            // FIXME: See comment above -- we could fold the region separately or something.
526            ty::ConstKind::Bound(_, _)
527            | ty::ConstKind::Unevaluated(_)
528            | ty::ConstKind::Value(_)
529            | ty::ConstKind::Error(_)
530            | ty::ConstKind::Expr(_) => {
531                return if c.has_type_flags(NEEDS_CANONICAL) { c.super_fold_with(self) } else { c };
532            }
533        };
534
535        let var = self.get_or_insert_bound_var(c, kind);
536
537        Const::new_canonical_bound(self.cx(), var)
538    }
539
540    fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate {
541        if p.flags().intersects(NEEDS_CANONICAL) { p.super_fold_with(self) } else { p }
542    }
543
544    fn fold_clauses(&mut self, c: I::Clauses) -> I::Clauses {
545        match self.canonicalize_mode {
546            CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv)
547            | CanonicalizeMode::Response { max_input_universe: _ } => {}
548            CanonicalizeMode::Input(CanonicalizeInputKind::Predicate { .. }) => {
549                panic!("erasing 'static in env")
550            }
551        }
552        if c.flags().intersects(NEEDS_CANONICAL) { c.super_fold_with(self) } else { c }
553    }
554}
rustc_next_trait_solver/canonical/canonicalizer.rs

rustc_next_trait_solver/canonical/
canonicalizer.rs
