rustc_next_trait_solver/
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 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    binder_index: ty::DebruijnIndex,
78
79    /// We only use the debruijn index during lookup. We don't need to
80    /// track the `variables` as each generic arg only results in a single
81    /// bound variable regardless of how many times it is encountered.
82    cache: HashMap<(ty::DebruijnIndex, I::Ty), I::Ty>,
83}
84
85impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
86    pub fn canonicalize_response<T: TypeFoldable<I>>(
87        delegate: &'a D,
88        max_input_universe: ty::UniverseIndex,
89        variables: &'a mut Vec<I::GenericArg>,
90        value: T,
91    ) -> ty::Canonical<I, T> {
92        let mut canonicalizer = Canonicalizer {
93            delegate,
94            canonicalize_mode: CanonicalizeMode::Response { max_input_universe },
95
96            variables,
97            variable_lookup_table: Default::default(),
98            sub_root_lookup_table: Default::default(),
99            var_kinds: Vec::new(),
100            binder_index: ty::INNERMOST,
101
102            cache: Default::default(),
103        };
104
105        let value = if value.has_type_flags(NEEDS_CANONICAL) {
106            value.fold_with(&mut canonicalizer)
107        } else {
108            value
109        };
110        debug_assert!(!value.has_infer(), "unexpected infer in {value:?}");
111        debug_assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
112        let (max_universe, variables) = canonicalizer.finalize();
113        Canonical { max_universe, variables, value }
114    }
115
116    fn canonicalize_param_env(
117        delegate: &'a D,
118        variables: &'a mut Vec<I::GenericArg>,
119        param_env: I::ParamEnv,
120    ) -> (I::ParamEnv, HashMap<I::GenericArg, usize>, Vec<CanonicalVarKind<I>>) {
121        if !param_env.has_type_flags(NEEDS_CANONICAL) {
122            return (param_env, Default::default(), Vec::new());
123        }
124
125        // Check whether we can use the global cache for this param_env. As we only use
126        // the `param_env` itself as the cache key, considering any additional information
127        // durnig its canonicalization would be incorrect. We always canonicalize region
128        // inference variables in a separate universe, so these are fine. However, we do
129        // track the universe of type and const inference variables so these must not be
130        // globally cached. We don't rely on any additional information when canonicalizing
131        // placeholders.
132        if !param_env.has_non_region_infer() {
133            delegate.cx().canonical_param_env_cache_get_or_insert(
134                param_env,
135                || {
136                    let mut variables = Vec::new();
137                    let mut env_canonicalizer = Canonicalizer {
138                        delegate,
139                        canonicalize_mode: CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv),
140
141                        variables: &mut variables,
142                        variable_lookup_table: Default::default(),
143                        sub_root_lookup_table: Default::default(),
144                        var_kinds: Vec::new(),
145                        binder_index: ty::INNERMOST,
146
147                        cache: Default::default(),
148                    };
149                    let param_env = param_env.fold_with(&mut env_canonicalizer);
150                    debug_assert_eq!(env_canonicalizer.binder_index, ty::INNERMOST);
151                    debug_assert!(env_canonicalizer.sub_root_lookup_table.is_empty());
152                    CanonicalParamEnvCacheEntry {
153                        param_env,
154                        variable_lookup_table: env_canonicalizer.variable_lookup_table,
155                        var_kinds: env_canonicalizer.var_kinds,
156                        variables,
157                    }
158                },
159                |&CanonicalParamEnvCacheEntry {
160                     param_env,
161                     variables: ref cache_variables,
162                     ref variable_lookup_table,
163                     ref var_kinds,
164                 }| {
165                    debug_assert!(variables.is_empty());
166                    variables.extend(cache_variables.iter().copied());
167                    (param_env, variable_lookup_table.clone(), var_kinds.clone())
168                },
169            )
170        } else {
171            let mut env_canonicalizer = Canonicalizer {
172                delegate,
173                canonicalize_mode: CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv),
174
175                variables,
176                variable_lookup_table: Default::default(),
177                sub_root_lookup_table: Default::default(),
178                var_kinds: Vec::new(),
179                binder_index: ty::INNERMOST,
180
181                cache: Default::default(),
182            };
183            let param_env = param_env.fold_with(&mut env_canonicalizer);
184            debug_assert_eq!(env_canonicalizer.binder_index, ty::INNERMOST);
185            debug_assert!(env_canonicalizer.sub_root_lookup_table.is_empty());
186            (param_env, env_canonicalizer.variable_lookup_table, env_canonicalizer.var_kinds)
187        }
188    }
189
190    /// When canonicalizing query inputs, we keep `'static` in the `param_env`
191    /// but erase it everywhere else. We generally don't want to depend on region
192    /// identity, so while it should not matter whether `'static` is kept in the
193    /// value or opaque type storage as well, this prevents us from accidentally
194    /// relying on it in the future.
195    ///
196    /// We want to keep the option of canonicalizing `'static` to an existential
197    /// variable in the future by changing the way we detect global where-bounds.
198    pub fn canonicalize_input<P: TypeFoldable<I>>(
199        delegate: &'a D,
200        variables: &'a mut Vec<I::GenericArg>,
201        input: QueryInput<I, P>,
202    ) -> ty::Canonical<I, QueryInput<I, P>> {
203        // First canonicalize the `param_env` while keeping `'static`
204        let (param_env, variable_lookup_table, var_kinds) =
205            Canonicalizer::canonicalize_param_env(delegate, variables, input.goal.param_env);
206        // Then canonicalize the rest of the input without keeping `'static`
207        // while *mostly* reusing the canonicalizer from above.
208        let mut rest_canonicalizer = Canonicalizer {
209            delegate,
210            canonicalize_mode: CanonicalizeMode::Input(CanonicalizeInputKind::Predicate),
211
212            variables,
213            variable_lookup_table,
214            sub_root_lookup_table: Default::default(),
215            var_kinds,
216            binder_index: ty::INNERMOST,
217
218            // We do not reuse the cache as it may contain entries whose canonicalized
219            // value contains `'static`. While we could alternatively handle this by
220            // checking for `'static` when using cached entries, this does not
221            // feel worth the effort. I do not expect that a `ParamEnv` will ever
222            // contain large enough types for caching to be necessary.
223            cache: Default::default(),
224        };
225
226        let predicate = input.goal.predicate;
227        let predicate = if predicate.has_type_flags(NEEDS_CANONICAL) {
228            predicate.fold_with(&mut rest_canonicalizer)
229        } else {
230            predicate
231        };
232        let goal = Goal { param_env, predicate };
233
234        let predefined_opaques_in_body = input.predefined_opaques_in_body;
235        let predefined_opaques_in_body =
236            if input.predefined_opaques_in_body.has_type_flags(NEEDS_CANONICAL) {
237                predefined_opaques_in_body.fold_with(&mut rest_canonicalizer)
238            } else {
239                predefined_opaques_in_body
240            };
241
242        let value = QueryInput { goal, predefined_opaques_in_body };
243
244        debug_assert!(!value.has_infer(), "unexpected infer in {value:?}");
245        debug_assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
246        let (max_universe, variables) = rest_canonicalizer.finalize();
247        Canonical { max_universe, variables, value }
248    }
249
250    fn get_or_insert_bound_var(
251        &mut self,
252        arg: impl Into<I::GenericArg>,
253        kind: CanonicalVarKind<I>,
254    ) -> ty::BoundVar {
255        // FIXME: 16 is made up and arbitrary. We should look at some
256        // perf data here.
257        let arg = arg.into();
258        let idx = if self.variables.len() > 16 {
259            if self.variable_lookup_table.is_empty() {
260                self.variable_lookup_table.extend(self.variables.iter().copied().zip(0..));
261            }
262
263            *self.variable_lookup_table.entry(arg).or_insert_with(|| {
264                let var = self.variables.len();
265                self.variables.push(arg);
266                self.var_kinds.push(kind);
267                var
268            })
269        } else {
270            self.variables.iter().position(|&v| v == arg).unwrap_or_else(|| {
271                let var = self.variables.len();
272                self.variables.push(arg);
273                self.var_kinds.push(kind);
274                var
275            })
276        };
277
278        ty::BoundVar::from(idx)
279    }
280
281    fn get_or_insert_sub_root(&mut self, vid: ty::TyVid) -> ty::BoundVar {
282        let root_vid = self.delegate.sub_unification_table_root_var(vid);
283        let idx =
284            *self.sub_root_lookup_table.entry(root_vid).or_insert_with(|| self.variables.len());
285        ty::BoundVar::from(idx)
286    }
287
288    fn finalize(self) -> (ty::UniverseIndex, I::CanonicalVarKinds) {
289        let mut var_kinds = self.var_kinds;
290        // See the rustc-dev-guide section about how we deal with universes
291        // during canonicalization in the new solver.
292        match self.canonicalize_mode {
293            // All placeholders and vars are canonicalized in the root universe.
294            CanonicalizeMode::Input { .. } => {
295                debug_assert!(
296                    var_kinds.iter().all(|var| var.universe() == ty::UniverseIndex::ROOT),
297                    "expected all vars to be canonicalized in root universe: {var_kinds:#?}"
298                );
299                let var_kinds = self.delegate.cx().mk_canonical_var_kinds(&var_kinds);
300                (ty::UniverseIndex::ROOT, var_kinds)
301            }
302            // When canonicalizing a response we map a universes already entered
303            // by the caller to the root universe and only return useful universe
304            // information for placeholders and inference variables created inside
305            // of the query.
306            CanonicalizeMode::Response { max_input_universe } => {
307                for var in var_kinds.iter_mut() {
308                    let uv = var.universe();
309                    let new_uv = ty::UniverseIndex::from(
310                        uv.index().saturating_sub(max_input_universe.index()),
311                    );
312                    *var = var.with_updated_universe(new_uv);
313                }
314                let max_universe = var_kinds
315                    .iter()
316                    .map(|kind| kind.universe())
317                    .max()
318                    .unwrap_or(ty::UniverseIndex::ROOT);
319                let var_kinds = self.delegate.cx().mk_canonical_var_kinds(&var_kinds);
320                (max_universe, var_kinds)
321            }
322        }
323    }
324
325    fn inner_fold_ty(&mut self, t: I::Ty) -> I::Ty {
326        let kind = match t.kind() {
327            ty::Infer(i) => match i {
328                ty::TyVar(vid) => {
329                    debug_assert_eq!(
330                        self.delegate.opportunistic_resolve_ty_var(vid),
331                        t,
332                        "ty vid should have been resolved fully before canonicalization"
333                    );
334
335                    let sub_root = self.get_or_insert_sub_root(vid);
336                    let ui = match self.canonicalize_mode {
337                        CanonicalizeMode::Input { .. } => ty::UniverseIndex::ROOT,
338                        CanonicalizeMode::Response { .. } => self
339                            .delegate
340                            .universe_of_ty(vid)
341                            .unwrap_or_else(|| panic!("ty var should have been resolved: {t:?}")),
342                    };
343                    CanonicalVarKind::Ty { ui, sub_root }
344                }
345                ty::IntVar(vid) => {
346                    debug_assert_eq!(
347                        self.delegate.opportunistic_resolve_int_var(vid),
348                        t,
349                        "ty vid should have been resolved fully before canonicalization"
350                    );
351                    CanonicalVarKind::Int
352                }
353                ty::FloatVar(vid) => {
354                    debug_assert_eq!(
355                        self.delegate.opportunistic_resolve_float_var(vid),
356                        t,
357                        "ty vid should have been resolved fully before canonicalization"
358                    );
359                    CanonicalVarKind::Float
360                }
361                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
362                    panic!("fresh vars not expected in canonicalization")
363                }
364            },
365            ty::Placeholder(placeholder) => match self.canonicalize_mode {
366                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderTy(
367                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
368                ),
369                CanonicalizeMode::Response { .. } => CanonicalVarKind::PlaceholderTy(placeholder),
370            },
371            ty::Param(_) => match self.canonicalize_mode {
372                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderTy(
373                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
374                ),
375                CanonicalizeMode::Response { .. } => panic!("param ty in response: {t:?}"),
376            },
377            ty::Bool
378            | ty::Char
379            | ty::Int(_)
380            | ty::Uint(_)
381            | ty::Float(_)
382            | ty::Adt(_, _)
383            | ty::Foreign(_)
384            | ty::Str
385            | ty::Array(_, _)
386            | ty::Slice(_)
387            | ty::RawPtr(_, _)
388            | ty::Ref(_, _, _)
389            | ty::Pat(_, _)
390            | ty::FnDef(_, _)
391            | ty::FnPtr(..)
392            | ty::UnsafeBinder(_)
393            | ty::Dynamic(_, _, _)
394            | ty::Closure(..)
395            | ty::CoroutineClosure(..)
396            | ty::Coroutine(_, _)
397            | ty::CoroutineWitness(..)
398            | ty::Never
399            | ty::Tuple(_)
400            | ty::Alias(_, _)
401            | ty::Bound(_, _)
402            | ty::Error(_) => {
403                return if t.has_type_flags(NEEDS_CANONICAL) {
404                    ensure_sufficient_stack(|| t.super_fold_with(self))
405                } else {
406                    t
407                };
408            }
409        };
410
411        let var = self.get_or_insert_bound_var(t, kind);
412
413        Ty::new_anon_bound(self.cx(), self.binder_index, var)
414    }
415}
416
417impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicalizer<'_, D, I> {
418    fn cx(&self) -> I {
419        self.delegate.cx()
420    }
421
422    fn fold_binder<T>(&mut self, t: ty::Binder<I, T>) -> ty::Binder<I, T>
423    where
424        T: TypeFoldable<I>,
425    {
426        self.binder_index.shift_in(1);
427        let t = t.super_fold_with(self);
428        self.binder_index.shift_out(1);
429        t
430    }
431
432    fn fold_region(&mut self, r: I::Region) -> I::Region {
433        let kind = match r.kind() {
434            ty::ReBound(..) => return r,
435
436            // We don't canonicalize `ReStatic` in the `param_env` as we use it
437            // when checking whether a `ParamEnv` candidate is global.
438            ty::ReStatic => match self.canonicalize_mode {
439                CanonicalizeMode::Input(CanonicalizeInputKind::Predicate { .. }) => {
440                    CanonicalVarKind::Region(ty::UniverseIndex::ROOT)
441                }
442                CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv)
443                | CanonicalizeMode::Response { .. } => return r,
444            },
445
446            // `ReErased` should only be encountered in the hidden
447            // type of an opaque for regions that are ignored for the purposes of
448            // captures.
449            //
450            // FIXME: We should investigate the perf implications of not uniquifying
451            // `ReErased`. We may be able to short-circuit registering region
452            // obligations if we encounter a `ReErased` on one side, for example.
453            ty::ReErased | ty::ReError(_) => match self.canonicalize_mode {
454                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
455                CanonicalizeMode::Response { .. } => return r,
456            },
457
458            ty::ReEarlyParam(_) | ty::ReLateParam(_) => match self.canonicalize_mode {
459                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
460                CanonicalizeMode::Response { .. } => {
461                    panic!("unexpected region in response: {r:?}")
462                }
463            },
464
465            ty::RePlaceholder(placeholder) => match self.canonicalize_mode {
466                // We canonicalize placeholder regions as existentials in query inputs.
467                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
468                CanonicalizeMode::Response { max_input_universe } => {
469                    // If we have a placeholder region inside of a query, it must be from
470                    // a new universe.
471                    if max_input_universe.can_name(placeholder.universe()) {
472                        panic!("new placeholder in universe {max_input_universe:?}: {r:?}");
473                    }
474                    CanonicalVarKind::PlaceholderRegion(placeholder)
475                }
476            },
477
478            ty::ReVar(vid) => {
479                debug_assert_eq!(
480                    self.delegate.opportunistic_resolve_lt_var(vid),
481                    r,
482                    "region vid should have been resolved fully before canonicalization"
483                );
484                match self.canonicalize_mode {
485                    CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
486                    CanonicalizeMode::Response { .. } => {
487                        CanonicalVarKind::Region(self.delegate.universe_of_lt(vid).unwrap())
488                    }
489                }
490            }
491        };
492
493        let var = self.get_or_insert_bound_var(r, kind);
494
495        Region::new_anon_bound(self.cx(), self.binder_index, var)
496    }
497
498    fn fold_ty(&mut self, t: I::Ty) -> I::Ty {
499        if let Some(&ty) = self.cache.get(&(self.binder_index, t)) {
500            ty
501        } else {
502            let res = self.inner_fold_ty(t);
503            let old = self.cache.insert((self.binder_index, t), res);
504            assert_eq!(old, None);
505            res
506        }
507    }
508
509    fn fold_const(&mut self, c: I::Const) -> I::Const {
510        let kind = match c.kind() {
511            ty::ConstKind::Infer(i) => match i {
512                ty::InferConst::Var(vid) => {
513                    debug_assert_eq!(
514                        self.delegate.opportunistic_resolve_ct_var(vid),
515                        c,
516                        "const vid should have been resolved fully before canonicalization"
517                    );
518
519                    match self.canonicalize_mode {
520                        CanonicalizeMode::Input { .. } => {
521                            CanonicalVarKind::Const(ty::UniverseIndex::ROOT)
522                        }
523                        CanonicalizeMode::Response { .. } => {
524                            CanonicalVarKind::Const(self.delegate.universe_of_ct(vid).unwrap())
525                        }
526                    }
527                }
528                ty::InferConst::Fresh(_) => todo!(),
529            },
530            ty::ConstKind::Placeholder(placeholder) => match self.canonicalize_mode {
531                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderConst(
532                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
533                ),
534                CanonicalizeMode::Response { .. } => {
535                    CanonicalVarKind::PlaceholderConst(placeholder)
536                }
537            },
538            ty::ConstKind::Param(_) => match self.canonicalize_mode {
539                CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderConst(
540                    PlaceholderLike::new_anon(ty::UniverseIndex::ROOT, self.variables.len().into()),
541                ),
542                CanonicalizeMode::Response { .. } => panic!("param ty in response: {c:?}"),
543            },
544            // FIXME: See comment above -- we could fold the region separately or something.
545            ty::ConstKind::Bound(_, _)
546            | ty::ConstKind::Unevaluated(_)
547            | ty::ConstKind::Value(_)
548            | ty::ConstKind::Error(_)
549            | ty::ConstKind::Expr(_) => {
550                return if c.has_type_flags(NEEDS_CANONICAL) { c.super_fold_with(self) } else { c };
551            }
552        };
553
554        let var = self.get_or_insert_bound_var(c, kind);
555
556        Const::new_anon_bound(self.cx(), self.binder_index, var)
557    }
558
559    fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate {
560        if p.flags().intersects(NEEDS_CANONICAL) { p.super_fold_with(self) } else { p }
561    }
562
563    fn fold_clauses(&mut self, c: I::Clauses) -> I::Clauses {
564        match self.canonicalize_mode {
565            CanonicalizeMode::Input(CanonicalizeInputKind::ParamEnv)
566            | CanonicalizeMode::Response { max_input_universe: _ } => {}
567            CanonicalizeMode::Input(CanonicalizeInputKind::Predicate { .. }) => {
568                panic!("erasing 'static in env")
569            }
570        }
571        if c.flags().intersects(NEEDS_CANONICAL) { c.super_fold_with(self) } else { c }
572    }
573}
rustc_next_trait_solver/canonicalizer.rs

rustc_next_trait_solver/
canonicalizer.rs
