rustc_next_trait_solver/solve/assembly/mod.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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802
//! Code shared by trait and projection goals for candidate assembly.
pub(super) mod structural_traits;
use derive_where::derive_where;
use rustc_type_ir::fold::TypeFoldable;
use rustc_type_ir::inherent::*;
use rustc_type_ir::lang_items::TraitSolverLangItem;
use rustc_type_ir::solve::inspect;
use rustc_type_ir::visit::TypeVisitableExt as _;
use rustc_type_ir::{self as ty, Interner, TypingMode, Upcast as _, elaborate};
use tracing::{debug, instrument};
use crate::delegate::SolverDelegate;
use crate::solve::inspect::ProbeKind;
use crate::solve::{
BuiltinImplSource, CandidateSource, CanonicalResponse, Certainty, EvalCtxt, Goal, GoalSource,
MaybeCause, NoSolution, QueryResult,
};
/// A candidate is a possible way to prove a goal.
///
/// It consists of both the `source`, which describes how that goal would be proven,
/// and the `result` when using the given `source`.
#[derive_where(Clone, Debug; I: Interner)]
pub(super) struct Candidate<I: Interner> {
pub(super) source: CandidateSource<I>,
pub(super) result: CanonicalResponse<I>,
}
/// Methods used to assemble candidates for either trait or projection goals.
pub(super) trait GoalKind<D, I = <D as SolverDelegate>::Interner>:
TypeFoldable<I> + Copy + Eq + std::fmt::Display
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
fn self_ty(self) -> I::Ty;
fn trait_ref(self, cx: I) -> ty::TraitRef<I>;
fn with_self_ty(self, cx: I, self_ty: I::Ty) -> Self;
fn trait_def_id(self, cx: I) -> I::DefId;
/// Try equating an assumption predicate against a goal's predicate. If it
/// holds, then execute the `then` callback, which should do any additional
/// work, then produce a response (typically by executing
/// [`EvalCtxt::evaluate_added_goals_and_make_canonical_response`]).
fn probe_and_match_goal_against_assumption(
ecx: &mut EvalCtxt<'_, D>,
source: CandidateSource<I>,
goal: Goal<I, Self>,
assumption: I::Clause,
then: impl FnOnce(&mut EvalCtxt<'_, D>) -> QueryResult<I>,
) -> Result<Candidate<I>, NoSolution>;
/// Consider a clause, which consists of a "assumption" and some "requirements",
/// to satisfy a goal. If the requirements hold, then attempt to satisfy our
/// goal by equating it with the assumption.
fn probe_and_consider_implied_clause(
ecx: &mut EvalCtxt<'_, D>,
parent_source: CandidateSource<I>,
goal: Goal<I, Self>,
assumption: I::Clause,
requirements: impl IntoIterator<Item = (GoalSource, Goal<I, I::Predicate>)>,
) -> Result<Candidate<I>, NoSolution> {
Self::probe_and_match_goal_against_assumption(ecx, parent_source, goal, assumption, |ecx| {
for (nested_source, goal) in requirements {
ecx.add_goal(nested_source, goal);
}
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
/// Consider a clause specifically for a `dyn Trait` self type. This requires
/// additionally checking all of the supertraits and object bounds to hold,
/// since they're not implied by the well-formedness of the object type.
fn probe_and_consider_object_bound_candidate(
ecx: &mut EvalCtxt<'_, D>,
source: CandidateSource<I>,
goal: Goal<I, Self>,
assumption: I::Clause,
) -> Result<Candidate<I>, NoSolution> {
Self::probe_and_match_goal_against_assumption(ecx, source, goal, assumption, |ecx| {
let cx = ecx.cx();
let ty::Dynamic(bounds, _, _) = goal.predicate.self_ty().kind() else {
panic!("expected object type in `probe_and_consider_object_bound_candidate`");
};
ecx.add_goals(
GoalSource::ImplWhereBound,
structural_traits::predicates_for_object_candidate(
ecx,
goal.param_env,
goal.predicate.trait_ref(cx),
bounds,
),
);
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
/// Assemble additional assumptions for an alias that are not included
/// in the item bounds of the alias. For now, this is limited to the
/// `explicit_implied_const_bounds` for an associated type.
fn consider_additional_alias_assumptions(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
alias_ty: ty::AliasTy<I>,
) -> Vec<Candidate<I>>;
fn consider_impl_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
impl_def_id: I::DefId,
) -> Result<Candidate<I>, NoSolution>;
/// If the predicate contained an error, we want to avoid emitting unnecessary trait
/// errors but still want to emit errors for other trait goals. We have some special
/// handling for this case.
///
/// Trait goals always hold while projection goals never do. This is a bit arbitrary
/// but prevents incorrect normalization while hiding any trait errors.
fn consider_error_guaranteed_candidate(
ecx: &mut EvalCtxt<'_, D>,
guar: I::ErrorGuaranteed,
) -> Result<Candidate<I>, NoSolution>;
/// A type implements an `auto trait` if its components do as well.
///
/// These components are given by built-in rules from
/// [`structural_traits::instantiate_constituent_tys_for_auto_trait`].
fn consider_auto_trait_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A trait alias holds if the RHS traits and `where` clauses hold.
fn consider_trait_alias_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A type is `Sized` if its tail component is `Sized`.
///
/// These components are given by built-in rules from
/// [`structural_traits::instantiate_constituent_tys_for_sized_trait`].
fn consider_builtin_sized_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A type is `Copy` or `Clone` if its components are `Copy` or `Clone`.
///
/// These components are given by built-in rules from
/// [`structural_traits::instantiate_constituent_tys_for_copy_clone_trait`].
fn consider_builtin_copy_clone_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A type is a `FnPtr` if it is of `FnPtr` type.
fn consider_builtin_fn_ptr_trait_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A callable type (a closure, fn def, or fn ptr) is known to implement the `Fn<A>`
/// family of traits where `A` is given by the signature of the type.
fn consider_builtin_fn_trait_candidates(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
kind: ty::ClosureKind,
) -> Result<Candidate<I>, NoSolution>;
/// An async closure is known to implement the `AsyncFn<A>` family of traits
/// where `A` is given by the signature of the type.
fn consider_builtin_async_fn_trait_candidates(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
kind: ty::ClosureKind,
) -> Result<Candidate<I>, NoSolution>;
/// Compute the built-in logic of the `AsyncFnKindHelper` helper trait, which
/// is used internally to delay computation for async closures until after
/// upvar analysis is performed in HIR typeck.
fn consider_builtin_async_fn_kind_helper_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// `Tuple` is implemented if the `Self` type is a tuple.
fn consider_builtin_tuple_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// `Pointee` is always implemented.
///
/// See the projection implementation for the `Metadata` types for all of
/// the built-in types. For structs, the metadata type is given by the struct
/// tail.
fn consider_builtin_pointee_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A coroutine (that comes from an `async` desugaring) is known to implement
/// `Future<Output = O>`, where `O` is given by the coroutine's return type
/// that was computed during type-checking.
fn consider_builtin_future_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A coroutine (that comes from a `gen` desugaring) is known to implement
/// `Iterator<Item = O>`, where `O` is given by the generator's yield type
/// that was computed during type-checking.
fn consider_builtin_iterator_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A coroutine (that comes from a `gen` desugaring) is known to implement
/// `FusedIterator`
fn consider_builtin_fused_iterator_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
fn consider_builtin_async_iterator_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// A coroutine (that doesn't come from an `async` or `gen` desugaring) is known to
/// implement `Coroutine<R, Yield = Y, Return = O>`, given the resume, yield,
/// and return types of the coroutine computed during type-checking.
fn consider_builtin_coroutine_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
fn consider_builtin_discriminant_kind_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
fn consider_builtin_async_destruct_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
fn consider_builtin_destruct_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
fn consider_builtin_transmute_candidate(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Result<Candidate<I>, NoSolution>;
/// Consider (possibly several) candidates to upcast or unsize a type to another
/// type, excluding the coercion of a sized type into a `dyn Trait`.
///
/// We return the `BuiltinImplSource` for each candidate as it is needed
/// for unsize coercion in hir typeck and because it is difficult to
/// otherwise recompute this for codegen. This is a bit of a mess but the
/// easiest way to maintain the existing behavior for now.
fn consider_structural_builtin_unsize_candidates(
ecx: &mut EvalCtxt<'_, D>,
goal: Goal<I, Self>,
) -> Vec<Candidate<I>>;
}
impl<D, I> EvalCtxt<'_, D>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
pub(super) fn assemble_and_evaluate_candidates<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
) -> Vec<Candidate<I>> {
let Ok(normalized_self_ty) =
self.structurally_normalize_ty(goal.param_env, goal.predicate.self_ty())
else {
// FIXME: We register a fake candidate when normalization fails so that
// we can point at the reason for *why*. I'm tempted to say that this
// is the wrong way to do this, though.
let result =
self.probe(|&result| inspect::ProbeKind::RigidAlias { result }).enter(|this| {
let normalized_ty = this.next_ty_infer();
let alias_relate_goal = Goal::new(
this.cx(),
goal.param_env,
ty::PredicateKind::AliasRelate(
goal.predicate.self_ty().into(),
normalized_ty.into(),
ty::AliasRelationDirection::Equate,
),
);
this.add_goal(GoalSource::AliasWellFormed, alias_relate_goal);
this.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
});
assert_eq!(result, Err(NoSolution));
return vec![];
};
if normalized_self_ty.is_ty_var() {
debug!("self type has been normalized to infer");
return self.forced_ambiguity(MaybeCause::Ambiguity).into_iter().collect();
}
let goal: Goal<I, G> =
goal.with(self.cx(), goal.predicate.with_self_ty(self.cx(), normalized_self_ty));
// Vars that show up in the rest of the goal substs may have been constrained by
// normalizing the self type as well, since type variables are not uniquified.
let goal = self.resolve_vars_if_possible(goal);
let mut candidates = vec![];
if let TypingMode::Coherence = self.typing_mode(goal.param_env) {
if let Ok(candidate) = self.consider_coherence_unknowable_candidate(goal) {
return vec![candidate];
}
}
self.assemble_impl_candidates(goal, &mut candidates);
self.assemble_builtin_impl_candidates(goal, &mut candidates);
self.assemble_alias_bound_candidates(goal, &mut candidates);
self.assemble_object_bound_candidates(goal, &mut candidates);
self.assemble_param_env_candidates(goal, &mut candidates);
match self.typing_mode(goal.param_env) {
TypingMode::Coherence => {}
TypingMode::Analysis { .. } | TypingMode::PostAnalysis => {
self.discard_impls_shadowed_by_env(goal, &mut candidates);
}
}
candidates
}
pub(super) fn forced_ambiguity(
&mut self,
cause: MaybeCause,
) -> Result<Candidate<I>, NoSolution> {
// This may fail if `try_evaluate_added_goals` overflows because it
// fails to reach a fixpoint but ends up getting an error after
// running for some additional step.
//
// cc trait-system-refactor-initiative#105
let source = CandidateSource::BuiltinImpl(BuiltinImplSource::Misc);
let certainty = Certainty::Maybe(cause);
self.probe_trait_candidate(source)
.enter(|this| this.evaluate_added_goals_and_make_canonical_response(certainty))
}
#[instrument(level = "trace", skip_all)]
fn assemble_impl_candidates<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let cx = self.cx();
cx.for_each_relevant_impl(
goal.predicate.trait_def_id(cx),
goal.predicate.self_ty(),
|impl_def_id| {
// For every `default impl`, there's always a non-default `impl`
// that will *also* apply. There's no reason to register a candidate
// for this impl, since it is *not* proof that the trait goal holds.
if cx.impl_is_default(impl_def_id) {
return;
}
match G::consider_impl_candidate(self, goal, impl_def_id) {
Ok(candidate) => candidates.push(candidate),
Err(NoSolution) => (),
}
},
);
}
#[instrument(level = "trace", skip_all)]
fn assemble_builtin_impl_candidates<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let cx = self.cx();
let trait_def_id = goal.predicate.trait_def_id(cx);
// N.B. When assembling built-in candidates for lang items that are also
// `auto` traits, then the auto trait candidate that is assembled in
// `consider_auto_trait_candidate` MUST be disqualified to remain sound.
//
// Instead of adding the logic here, it's a better idea to add it in
// `EvalCtxt::disqualify_auto_trait_candidate_due_to_possible_impl` in
// `solve::trait_goals` instead.
let result = if let Err(guar) = goal.predicate.error_reported() {
G::consider_error_guaranteed_candidate(self, guar)
} else if cx.trait_is_auto(trait_def_id) {
G::consider_auto_trait_candidate(self, goal)
} else if cx.trait_is_alias(trait_def_id) {
G::consider_trait_alias_candidate(self, goal)
} else {
match cx.as_lang_item(trait_def_id) {
Some(TraitSolverLangItem::Sized) => G::consider_builtin_sized_candidate(self, goal),
Some(TraitSolverLangItem::Copy | TraitSolverLangItem::Clone) => {
G::consider_builtin_copy_clone_candidate(self, goal)
}
Some(TraitSolverLangItem::Fn) => {
G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
}
Some(TraitSolverLangItem::FnMut) => {
G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::FnMut)
}
Some(TraitSolverLangItem::FnOnce) => {
G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::FnOnce)
}
Some(TraitSolverLangItem::AsyncFn) => {
G::consider_builtin_async_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
}
Some(TraitSolverLangItem::AsyncFnMut) => {
G::consider_builtin_async_fn_trait_candidates(
self,
goal,
ty::ClosureKind::FnMut,
)
}
Some(TraitSolverLangItem::AsyncFnOnce) => {
G::consider_builtin_async_fn_trait_candidates(
self,
goal,
ty::ClosureKind::FnOnce,
)
}
Some(TraitSolverLangItem::FnPtrTrait) => {
G::consider_builtin_fn_ptr_trait_candidate(self, goal)
}
Some(TraitSolverLangItem::AsyncFnKindHelper) => {
G::consider_builtin_async_fn_kind_helper_candidate(self, goal)
}
Some(TraitSolverLangItem::Tuple) => G::consider_builtin_tuple_candidate(self, goal),
Some(TraitSolverLangItem::PointeeTrait) => {
G::consider_builtin_pointee_candidate(self, goal)
}
Some(TraitSolverLangItem::Future) => {
G::consider_builtin_future_candidate(self, goal)
}
Some(TraitSolverLangItem::Iterator) => {
G::consider_builtin_iterator_candidate(self, goal)
}
Some(TraitSolverLangItem::FusedIterator) => {
G::consider_builtin_fused_iterator_candidate(self, goal)
}
Some(TraitSolverLangItem::AsyncIterator) => {
G::consider_builtin_async_iterator_candidate(self, goal)
}
Some(TraitSolverLangItem::Coroutine) => {
G::consider_builtin_coroutine_candidate(self, goal)
}
Some(TraitSolverLangItem::DiscriminantKind) => {
G::consider_builtin_discriminant_kind_candidate(self, goal)
}
Some(TraitSolverLangItem::AsyncDestruct) => {
G::consider_builtin_async_destruct_candidate(self, goal)
}
Some(TraitSolverLangItem::Destruct) => {
G::consider_builtin_destruct_candidate(self, goal)
}
Some(TraitSolverLangItem::TransmuteTrait) => {
G::consider_builtin_transmute_candidate(self, goal)
}
_ => Err(NoSolution),
}
};
candidates.extend(result);
// There may be multiple unsize candidates for a trait with several supertraits:
// `trait Foo: Bar<A> + Bar<B>` and `dyn Foo: Unsize<dyn Bar<_>>`
if cx.is_lang_item(trait_def_id, TraitSolverLangItem::Unsize) {
candidates.extend(G::consider_structural_builtin_unsize_candidates(self, goal));
}
}
#[instrument(level = "trace", skip_all)]
fn assemble_param_env_candidates<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
for (i, assumption) in goal.param_env.caller_bounds().into_iter().enumerate() {
candidates.extend(G::probe_and_consider_implied_clause(
self,
CandidateSource::ParamEnv(i),
goal,
assumption,
[],
));
}
}
#[instrument(level = "trace", skip_all)]
fn assemble_alias_bound_candidates<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let () = self.probe(|_| ProbeKind::NormalizedSelfTyAssembly).enter(|ecx| {
ecx.assemble_alias_bound_candidates_recur(goal.predicate.self_ty(), goal, candidates);
});
}
/// For some deeply nested `<T>::A::B::C::D` rigid associated type,
/// we should explore the item bounds for all levels, since the
/// `associated_type_bounds` feature means that a parent associated
/// type may carry bounds for a nested associated type.
///
/// If we have a projection, check that its self type is a rigid projection.
/// If so, continue searching by recursively calling after normalization.
// FIXME: This may recurse infinitely, but I can't seem to trigger it without
// hitting another overflow error something. Add a depth parameter needed later.
fn assemble_alias_bound_candidates_recur<G: GoalKind<D>>(
&mut self,
self_ty: I::Ty,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let (kind, alias_ty) = match self_ty.kind() {
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(_, _)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Pat(_, _)
| ty::Slice(_)
| ty::RawPtr(_, _)
| ty::Ref(_, _, _)
| ty::FnDef(_, _)
| ty::FnPtr(..)
| ty::Dynamic(..)
| ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::Param(_)
| ty::Placeholder(..)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Error(_) => return,
ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) | ty::Bound(..) => {
panic!("unexpected self type for `{goal:?}`")
}
ty::Infer(ty::TyVar(_)) => {
// If we hit infer when normalizing the self type of an alias,
// then bail with ambiguity. We should never encounter this on
// the *first* iteration of this recursive function.
if let Ok(result) =
self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
{
candidates.push(Candidate { source: CandidateSource::AliasBound, result });
}
return;
}
ty::Alias(kind @ (ty::Projection | ty::Opaque), alias_ty) => (kind, alias_ty),
ty::Alias(ty::Inherent | ty::Weak, _) => {
self.cx().delay_bug(format!("could not normalize {self_ty:?}, it is not WF"));
return;
}
};
for assumption in
self.cx().item_bounds(alias_ty.def_id).iter_instantiated(self.cx(), alias_ty.args)
{
candidates.extend(G::probe_and_consider_implied_clause(
self,
CandidateSource::AliasBound,
goal,
assumption,
[],
));
}
candidates.extend(G::consider_additional_alias_assumptions(self, goal, alias_ty));
if kind != ty::Projection {
return;
}
// Recurse on the self type of the projection.
match self.structurally_normalize_ty(goal.param_env, alias_ty.self_ty()) {
Ok(next_self_ty) => {
self.assemble_alias_bound_candidates_recur(next_self_ty, goal, candidates)
}
Err(NoSolution) => {}
}
}
#[instrument(level = "trace", skip_all)]
fn assemble_object_bound_candidates<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let cx = self.cx();
if !cx.trait_may_be_implemented_via_object(goal.predicate.trait_def_id(cx)) {
return;
}
let self_ty = goal.predicate.self_ty();
let bounds = match self_ty.kind() {
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(_, _)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Pat(_, _)
| ty::Slice(_)
| ty::RawPtr(_, _)
| ty::Ref(_, _, _)
| ty::FnDef(_, _)
| ty::FnPtr(..)
| ty::Alias(..)
| ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::Param(_)
| ty::Placeholder(..)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Error(_) => return,
ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_))
| ty::Bound(..) => panic!("unexpected self type for `{goal:?}`"),
ty::Dynamic(bounds, ..) => bounds,
};
// Do not consider built-in object impls for dyn-incompatible types.
if bounds.principal_def_id().is_some_and(|def_id| !cx.trait_is_dyn_compatible(def_id)) {
return;
}
// Consider all of the auto-trait and projection bounds, which don't
// need to be recorded as a `BuiltinImplSource::Object` since they don't
// really have a vtable base...
for bound in bounds.iter() {
match bound.skip_binder() {
ty::ExistentialPredicate::Trait(_) => {
// Skip principal
}
ty::ExistentialPredicate::Projection(_)
| ty::ExistentialPredicate::AutoTrait(_) => {
candidates.extend(G::probe_and_consider_object_bound_candidate(
self,
CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
goal,
bound.with_self_ty(cx, self_ty),
));
}
}
}
// FIXME: We only need to do *any* of this if we're considering a trait goal,
// since we don't need to look at any supertrait or anything if we are doing
// a projection goal.
if let Some(principal) = bounds.principal() {
let principal_trait_ref = principal.with_self_ty(cx, self_ty);
for (idx, assumption) in elaborate::supertraits(cx, principal_trait_ref).enumerate() {
candidates.extend(G::probe_and_consider_object_bound_candidate(
self,
CandidateSource::BuiltinImpl(BuiltinImplSource::Object(idx)),
goal,
assumption.upcast(cx),
));
}
}
}
/// In coherence we have to not only care about all impls we know about, but
/// also consider impls which may get added in a downstream or sibling crate
/// or which an upstream impl may add in a minor release.
///
/// To do so we return a single ambiguous candidate in case such an unknown
/// impl could apply to the current goal.
#[instrument(level = "trace", skip_all)]
fn consider_coherence_unknowable_candidate<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
) -> Result<Candidate<I>, NoSolution> {
self.probe_trait_candidate(CandidateSource::CoherenceUnknowable).enter(|ecx| {
let cx = ecx.cx();
let trait_ref = goal.predicate.trait_ref(cx);
if ecx.trait_ref_is_knowable(goal.param_env, trait_ref)? {
Err(NoSolution)
} else {
// While the trait bound itself may be unknowable, we may be able to
// prove that a super trait is not implemented. For this, we recursively
// prove the super trait bounds of the current goal.
//
// We skip the goal itself as that one would cycle.
let predicate: I::Predicate = trait_ref.upcast(cx);
ecx.add_goals(
GoalSource::Misc,
elaborate::elaborate(cx, [predicate])
.skip(1)
.map(|predicate| goal.with(cx, predicate)),
);
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
}
})
}
/// If there's a where-bound for the current goal, do not use any impl candidates
/// to prove the current goal. Most importantly, if there is a where-bound which does
/// not specify any associated types, we do not allow normalizing the associated type
/// by using an impl, even if it would apply.
///
/// <https://github.com/rust-lang/trait-system-refactor-initiative/issues/76>
// FIXME(@lcnr): The current structure here makes me unhappy and feels ugly. idk how
// to improve this however. However, this should make it fairly straightforward to refine
// the filtering going forward, so it seems alright-ish for now.
#[instrument(level = "debug", skip(self, goal))]
fn discard_impls_shadowed_by_env<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let cx = self.cx();
let trait_goal: Goal<I, ty::TraitPredicate<I>> =
goal.with(cx, goal.predicate.trait_ref(cx));
let mut trait_candidates_from_env = vec![];
self.probe(|_| ProbeKind::ShadowedEnvProbing).enter(|ecx| {
ecx.assemble_param_env_candidates(trait_goal, &mut trait_candidates_from_env);
ecx.assemble_alias_bound_candidates(trait_goal, &mut trait_candidates_from_env);
});
if !trait_candidates_from_env.is_empty() {
let trait_env_result = self.merge_candidates(trait_candidates_from_env);
match trait_env_result.unwrap().value.certainty {
// If proving the trait goal succeeds by using the env,
// we freely drop all impl candidates.
//
// FIXME(@lcnr): It feels like this could easily hide
// a forced ambiguity candidate added earlier.
// This feels dangerous.
Certainty::Yes => {
candidates.retain(|c| match c.source {
CandidateSource::Impl(_) | CandidateSource::BuiltinImpl(_) => {
debug!(?c, "discard impl candidate");
false
}
CandidateSource::ParamEnv(_) | CandidateSource::AliasBound => true,
CandidateSource::CoherenceUnknowable => panic!("uh oh"),
});
}
// If it is still ambiguous we instead just force the whole goal
// to be ambig and wait for inference constraints. See
// tests/ui/traits/next-solver/env-shadows-impls/ambig-env-no-shadow.rs
Certainty::Maybe(cause) => {
debug!(?cause, "force ambiguity");
*candidates = self.forced_ambiguity(cause).into_iter().collect();
}
}
}
}
/// If there are multiple ways to prove a trait or projection goal, we have
/// to somehow try to merge the candidates into one. If that fails, we return
/// ambiguity.
#[instrument(level = "debug", skip(self), ret)]
pub(super) fn merge_candidates(&mut self, candidates: Vec<Candidate<I>>) -> QueryResult<I> {
// First try merging all candidates. This is complete and fully sound.
let responses = candidates.iter().map(|c| c.result).collect::<Vec<_>>();
if let Some(result) = self.try_merge_responses(&responses) {
return Ok(result);
} else {
self.flounder(&responses)
}
}
}