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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947
//! Trait Resolution. See the [rustc dev guide] for more information on how this works.
//!
//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
pub mod query;
pub mod select;
pub mod solve;
pub mod specialization_graph;
mod structural_impls;
pub mod util;
use crate::infer::canonical::Canonical;
use crate::mir::ConstraintCategory;
use crate::ty::abstract_const::NotConstEvaluatable;
use crate::ty::GenericArgsRef;
use crate::ty::{self, AdtKind, Ty};
use rustc_data_structures::sync::Lrc;
use rustc_errors::{Applicability, Diagnostic};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_span::def_id::{LocalDefId, CRATE_DEF_ID};
use rustc_span::symbol::Symbol;
use rustc_span::{Span, DUMMY_SP};
use smallvec::SmallVec;
use std::borrow::Cow;
use std::hash::{Hash, Hasher};
pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
pub use self::ObligationCauseCode::*;
/// Depending on the stage of compilation, we want projection to be
/// more or less conservative.
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable, Encodable, Decodable)]
pub enum Reveal {
/// At type-checking time, we refuse to project any associated
/// type that is marked `default`. Non-`default` ("final") types
/// are always projected. This is necessary in general for
/// soundness of specialization. However, we *could* allow
/// projections in fully-monomorphic cases. We choose not to,
/// because we prefer for `default type` to force the type
/// definition to be treated abstractly by any consumers of the
/// impl. Concretely, that means that the following example will
/// fail to compile:
///
/// ```compile_fail,E0308
/// #![feature(specialization)]
/// trait Assoc {
/// type Output;
/// }
///
/// impl<T> Assoc for T {
/// default type Output = bool;
/// }
///
/// fn main() {
/// let x: <() as Assoc>::Output = true;
/// }
/// ```
///
/// We also do not reveal the hidden type of opaque types during
/// type-checking.
UserFacing,
/// At codegen time, all monomorphic projections will succeed.
/// Also, `impl Trait` is normalized to the concrete type,
/// which has to be already collected by type-checking.
///
/// NOTE: as `impl Trait`'s concrete type should *never*
/// be observable directly by the user, `Reveal::All`
/// should not be used by checks which may expose
/// type equality or type contents to the user.
/// There are some exceptions, e.g., around auto traits and
/// transmute-checking, which expose some details, but
/// not the whole concrete type of the `impl Trait`.
All,
}
/// The reason why we incurred this obligation; used for error reporting.
///
/// Non-misc `ObligationCauseCode`s are stored on the heap. This gives the
/// best trade-off between keeping the type small (which makes copies cheaper)
/// while not doing too many heap allocations.
///
/// We do not want to intern this as there are a lot of obligation causes which
/// only live for a short period of time.
#[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub struct ObligationCause<'tcx> {
pub span: Span,
/// The ID of the fn body that triggered this obligation. This is
/// used for region obligations to determine the precise
/// environment in which the region obligation should be evaluated
/// (in particular, closures can add new assumptions). See the
/// field `region_obligations` of the `FulfillmentContext` for more
/// information.
pub body_id: LocalDefId,
code: InternedObligationCauseCode<'tcx>,
}
// This custom hash function speeds up hashing for `Obligation` deduplication
// greatly by skipping the `code` field, which can be large and complex. That
// shouldn't affect hash quality much since there are several other fields in
// `Obligation` which should be unique enough, especially the predicate itself
// which is hashed as an interned pointer. See #90996.
impl Hash for ObligationCause<'_> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.body_id.hash(state);
self.span.hash(state);
}
}
impl<'tcx> ObligationCause<'tcx> {
#[inline]
pub fn new(
span: Span,
body_id: LocalDefId,
code: ObligationCauseCode<'tcx>,
) -> ObligationCause<'tcx> {
ObligationCause { span, body_id, code: code.into() }
}
pub fn misc(span: Span, body_id: LocalDefId) -> ObligationCause<'tcx> {
ObligationCause::new(span, body_id, MiscObligation)
}
#[inline(always)]
pub fn dummy() -> ObligationCause<'tcx> {
ObligationCause::dummy_with_span(DUMMY_SP)
}
#[inline(always)]
pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
ObligationCause { span, body_id: CRATE_DEF_ID, code: Default::default() }
}
pub fn span(&self) -> Span {
match *self.code() {
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
arm_span,
..
}) => arm_span,
_ => self.span,
}
}
#[inline]
pub fn code(&self) -> &ObligationCauseCode<'tcx> {
&self.code
}
pub fn map_code(
&mut self,
f: impl FnOnce(InternedObligationCauseCode<'tcx>) -> ObligationCauseCode<'tcx>,
) {
self.code = f(std::mem::take(&mut self.code)).into();
}
pub fn derived_cause(
mut self,
parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
variant: impl FnOnce(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>,
) -> ObligationCause<'tcx> {
/*!
* Creates a cause for obligations that are derived from
* `obligation` by a recursive search (e.g., for a builtin
* bound, or eventually a `auto trait Foo`). If `obligation`
* is itself a derived obligation, this is just a clone, but
* otherwise we create a "derived obligation" cause so as to
* keep track of the original root obligation for error
* reporting.
*/
// NOTE(flaper87): As of now, it keeps track of the whole error
// chain. Ideally, we should have a way to configure this either
// by using -Z verbose or just a CLI argument.
self.code =
variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into();
self
}
pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> {
match self.code() {
MatchImpl(cause, _) => cause.to_constraint_category(),
AscribeUserTypeProvePredicate(predicate_span) => {
ConstraintCategory::Predicate(*predicate_span)
}
_ => ConstraintCategory::BoringNoLocation,
}
}
}
#[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub struct UnifyReceiverContext<'tcx> {
pub assoc_item: ty::AssocItem,
pub param_env: ty::ParamEnv<'tcx>,
pub args: GenericArgsRef<'tcx>,
}
#[derive(Clone, PartialEq, Eq, Default, HashStable)]
#[derive(TypeVisitable, TypeFoldable, TyEncodable, TyDecodable)]
pub struct InternedObligationCauseCode<'tcx> {
/// `None` for `ObligationCauseCode::MiscObligation` (a common case, occurs ~60% of
/// the time). `Some` otherwise.
code: Option<Lrc<ObligationCauseCode<'tcx>>>,
}
impl<'tcx> std::fmt::Debug for InternedObligationCauseCode<'tcx> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let cause: &ObligationCauseCode<'_> = self;
cause.fmt(f)
}
}
impl<'tcx> ObligationCauseCode<'tcx> {
#[inline(always)]
fn into(self) -> InternedObligationCauseCode<'tcx> {
InternedObligationCauseCode {
code: if let ObligationCauseCode::MiscObligation = self {
None
} else {
Some(Lrc::new(self))
},
}
}
}
impl<'tcx> std::ops::Deref for InternedObligationCauseCode<'tcx> {
type Target = ObligationCauseCode<'tcx>;
fn deref(&self) -> &Self::Target {
self.code.as_deref().unwrap_or(&ObligationCauseCode::MiscObligation)
}
}
#[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub enum ObligationCauseCode<'tcx> {
/// Not well classified or should be obvious from the span.
MiscObligation,
/// A slice or array is WF only if `T: Sized`.
SliceOrArrayElem,
/// A tuple is WF only if its middle elements are `Sized`.
TupleElem,
/// This is the trait reference from the given projection.
ProjectionWf(ty::AliasTy<'tcx>),
/// Must satisfy all of the where-clause predicates of the
/// given item.
ItemObligation(DefId),
/// Like `ItemObligation`, but carries the span of the
/// predicate when it can be identified.
BindingObligation(DefId, Span),
/// Like `ItemObligation`, but carries the `HirId` of the
/// expression that caused the obligation, and the `usize`
/// indicates exactly which predicate it is in the list of
/// instantiated predicates.
ExprItemObligation(DefId, rustc_hir::HirId, usize),
/// Combines `ExprItemObligation` and `BindingObligation`.
ExprBindingObligation(DefId, Span, rustc_hir::HirId, usize),
/// A type like `&'a T` is WF only if `T: 'a`.
ReferenceOutlivesReferent(Ty<'tcx>),
/// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
/// Obligation incurred due to a coercion.
Coercion {
source: Ty<'tcx>,
target: Ty<'tcx>,
},
/// Various cases where expressions must be `Sized` / `Copy` / etc.
/// `L = X` implies that `L` is `Sized`.
AssignmentLhsSized,
/// `(x1, .., xn)` must be `Sized`.
TupleInitializerSized,
/// `S { ... }` must be `Sized`.
StructInitializerSized,
/// Type of each variable must be `Sized`.
VariableType(hir::HirId),
/// Argument type must be `Sized`.
SizedArgumentType(Option<Span>),
/// Return type must be `Sized`.
SizedReturnType,
/// Yield type must be `Sized`.
SizedYieldType,
/// Inline asm operand type must be `Sized`.
InlineAsmSized,
/// Captured closure type must be `Sized`.
SizedClosureCapture(LocalDefId),
/// Types live across generator yields must be `Sized`.
SizedGeneratorInterior(LocalDefId),
/// `[expr; N]` requires `type_of(expr): Copy`.
RepeatElementCopy {
/// If element is a `const fn` we display a help message suggesting to move the
/// function call to a new `const` item while saying that `T` doesn't implement `Copy`.
is_const_fn: bool,
},
/// Types of fields (other than the last, except for packed structs) in a struct must be sized.
FieldSized {
adt_kind: AdtKind,
span: Span,
last: bool,
},
/// Constant expressions must be sized.
ConstSized,
/// `static` items must have `Sync` type.
SharedStatic,
BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>),
DerivedObligation(DerivedObligationCause<'tcx>),
FunctionArgumentObligation {
/// The node of the relevant argument in the function call.
arg_hir_id: hir::HirId,
/// The node of the function call.
call_hir_id: hir::HirId,
/// The obligation introduced by this argument.
parent_code: InternedObligationCauseCode<'tcx>,
},
/// Error derived when matching traits/impls; see ObligationCause for more details
CompareImplItemObligation {
impl_item_def_id: LocalDefId,
trait_item_def_id: DefId,
kind: ty::AssocKind,
},
/// Checking that the bounds of a trait's associated type hold for a given impl
CheckAssociatedTypeBounds {
impl_item_def_id: LocalDefId,
trait_item_def_id: DefId,
},
/// Checking that this expression can be assigned to its target.
ExprAssignable,
/// Computing common supertype in the arms of a match expression
MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
/// Type error arising from type checking a pattern against an expected type.
Pattern {
/// The span of the scrutinee or type expression which caused the `root_ty` type.
span: Option<Span>,
/// The root expected type induced by a scrutinee or type expression.
root_ty: Ty<'tcx>,
/// Whether the `Span` came from an expression or a type expression.
origin_expr: bool,
},
/// Constants in patterns must have `Structural` type.
ConstPatternStructural,
/// Computing common supertype in an if expression
IfExpression(Box<IfExpressionCause<'tcx>>),
/// Computing common supertype of an if expression with no else counter-part
IfExpressionWithNoElse,
/// `main` has wrong type
MainFunctionType,
/// `start` has wrong type
StartFunctionType,
/// language function has wrong type
LangFunctionType(Symbol),
/// Intrinsic has wrong type
IntrinsicType,
/// A let else block does not diverge
LetElse,
/// Method receiver
MethodReceiver,
UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
/// `return` with no expression
ReturnNoExpression,
/// `return` with an expression
ReturnValue(hir::HirId),
/// Return type of this function
ReturnType,
/// Opaque return type of this function
OpaqueReturnType(Option<(Ty<'tcx>, Span)>),
/// Block implicit return
BlockTailExpression(hir::HirId, hir::MatchSource),
/// #[feature(trivial_bounds)] is not enabled
TrivialBound,
/// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
OpaqueType,
AwaitableExpr(Option<hir::HirId>),
ForLoopIterator,
QuestionMark,
/// Well-formed checking. If a `WellFormedLoc` is provided,
/// then it will be used to perform HIR-based wf checking
/// after an error occurs, in order to generate a more precise error span.
/// This is purely for diagnostic purposes - it is always
/// correct to use `MiscObligation` instead, or to specify
/// `WellFormed(None)`
WellFormed(Option<WellFormedLoc>),
/// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against.
MatchImpl(ObligationCause<'tcx>, DefId),
BinOp {
rhs_span: Option<Span>,
is_lit: bool,
output_ty: Option<Ty<'tcx>>,
},
AscribeUserTypeProvePredicate(Span),
RustCall,
/// Obligations to prove that a `std::ops::Drop` impl is not stronger than
/// the ADT it's being implemented for.
DropImpl,
/// Requirement for a `const N: Ty` to implement `Ty: ConstParamTy`
ConstParam(Ty<'tcx>),
/// Obligations emitted during the normalization of a weak type alias.
TypeAlias(InternedObligationCauseCode<'tcx>, Span, DefId),
}
/// The 'location' at which we try to perform HIR-based wf checking.
/// This information is used to obtain an `hir::Ty`, which
/// we can walk in order to obtain precise spans for any
/// 'nested' types (e.g. `Foo` in `Option<Foo>`).
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, Encodable, Decodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub enum WellFormedLoc {
/// Use the type of the provided definition.
Ty(LocalDefId),
/// Use the type of the parameter of the provided function.
/// We cannot use `hir::Param`, since the function may
/// not have a body (e.g. a trait method definition)
Param {
/// The function to lookup the parameter in
function: LocalDefId,
/// The index of the parameter to use.
/// Parameters are indexed from 0, with the return type
/// being the last 'parameter'
param_idx: u16,
},
}
#[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub struct ImplDerivedObligationCause<'tcx> {
pub derived: DerivedObligationCause<'tcx>,
/// The `DefId` of the `impl` that gave rise to the `derived` obligation.
/// If the `derived` obligation arose from a trait alias, which conceptually has a synthetic impl,
/// then this will be the `DefId` of that trait alias. Care should therefore be taken to handle
/// that exceptional case where appropriate.
pub impl_or_alias_def_id: DefId,
/// The index of the derived predicate in the parent impl's predicates.
pub impl_def_predicate_index: Option<usize>,
pub span: Span,
}
impl<'tcx> ObligationCauseCode<'tcx> {
/// Returns the base obligation, ignoring derived obligations.
pub fn peel_derives(&self) -> &Self {
let mut base_cause = self;
while let Some((parent_code, _)) = base_cause.parent() {
base_cause = parent_code;
}
base_cause
}
pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> {
match self {
FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)),
BuiltinDerivedObligation(derived)
| DerivedObligation(derived)
| ImplDerivedObligation(box ImplDerivedObligationCause { derived, .. }) => {
Some((&derived.parent_code, Some(derived.parent_trait_pred)))
}
_ => None,
}
}
pub fn peel_match_impls(&self) -> &Self {
match self {
MatchImpl(cause, _) => cause.code(),
_ => self,
}
}
}
// `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
static_assert_size!(ObligationCauseCode<'_>, 48);
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
pub enum StatementAsExpression {
CorrectType,
NeedsBoxing,
}
#[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub struct MatchExpressionArmCause<'tcx> {
pub arm_block_id: Option<hir::HirId>,
pub arm_ty: Ty<'tcx>,
pub arm_span: Span,
pub prior_arm_block_id: Option<hir::HirId>,
pub prior_arm_ty: Ty<'tcx>,
pub prior_arm_span: Span,
pub scrut_span: Span,
pub source: hir::MatchSource,
pub prior_arms: Vec<Span>,
pub opt_suggest_box_span: Option<Span>,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[derive(TypeFoldable, TypeVisitable, HashStable, TyEncodable, TyDecodable)]
pub struct IfExpressionCause<'tcx> {
pub then_id: hir::HirId,
pub else_id: hir::HirId,
pub then_ty: Ty<'tcx>,
pub else_ty: Ty<'tcx>,
pub outer_span: Option<Span>,
pub opt_suggest_box_span: Option<Span>,
}
#[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
#[derive(TypeVisitable, TypeFoldable)]
pub struct DerivedObligationCause<'tcx> {
/// The trait predicate of the parent obligation that led to the
/// current obligation. Note that only trait obligations lead to
/// derived obligations, so we just store the trait predicate here
/// directly.
pub parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
/// The parent trait had this cause.
pub parent_code: InternedObligationCauseCode<'tcx>,
}
#[derive(Clone, Debug, TypeVisitable)]
pub enum SelectionError<'tcx> {
/// The trait is not implemented.
Unimplemented,
/// After a closure impl has selected, its "outputs" were evaluated
/// (which for closures includes the "input" type params) and they
/// didn't resolve. See `confirm_poly_trait_refs` for more.
OutputTypeParameterMismatch(Box<SelectionOutputTypeParameterMismatch<'tcx>>),
/// The trait pointed by `DefId` is not object safe.
TraitNotObjectSafe(DefId),
/// A given constant couldn't be evaluated.
NotConstEvaluatable(NotConstEvaluatable),
/// Exceeded the recursion depth during type projection.
Overflow(OverflowError),
/// Signaling that an error has already been emitted, to avoid
/// multiple errors being shown.
ErrorReporting,
/// Computing an opaque type's hidden type caused an error (e.g. a cycle error).
/// We can thus not know whether the hidden type implements an auto trait, so
/// we should not presume anything about it.
OpaqueTypeAutoTraitLeakageUnknown(DefId),
}
#[derive(Clone, Debug, TypeVisitable)]
pub struct SelectionOutputTypeParameterMismatch<'tcx> {
pub found_trait_ref: ty::PolyTraitRef<'tcx>,
pub expected_trait_ref: ty::PolyTraitRef<'tcx>,
pub terr: ty::error::TypeError<'tcx>,
}
/// When performing resolution, it is typically the case that there
/// can be one of three outcomes:
///
/// - `Ok(Some(r))`: success occurred with result `r`
/// - `Ok(None)`: could not definitely determine anything, usually due
/// to inconclusive type inference.
/// - `Err(e)`: error `e` occurred
pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
/// Given the successful resolution of an obligation, the `ImplSource`
/// indicates where the impl comes from.
///
/// For example, the obligation may be satisfied by a specific impl (case A),
/// or it may be relative to some bound that is in scope (case B).
///
/// ```ignore (illustrative)
/// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
/// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
/// impl Clone for i32 { ... } // Impl_3
///
/// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
/// // Case A: ImplSource points at a specific impl. Only possible when
/// // type is concretely known. If the impl itself has bounded
/// // type parameters, ImplSource will carry resolutions for those as well:
/// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
///
/// // Case B: ImplSource must be provided by caller. This applies when
/// // type is a type parameter.
/// param.clone(); // ImplSource::Param
///
/// // Case C: A mix of cases A and B.
/// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param])
/// }
/// ```
///
/// ### The type parameter `N`
///
/// See explanation on `ImplSourceUserDefinedData`.
#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum ImplSource<'tcx, N> {
/// ImplSource identifying a particular impl.
UserDefined(ImplSourceUserDefinedData<'tcx, N>),
/// Successful resolution to an obligation provided by the caller
/// for some type parameter. The `Vec<N>` represents the
/// obligations incurred from normalizing the where-clause (if
/// any).
Param(Vec<N>),
/// Successful resolution for a builtin impl.
Builtin(BuiltinImplSource, Vec<N>),
}
impl<'tcx, N> ImplSource<'tcx, N> {
pub fn nested_obligations(self) -> Vec<N> {
match self {
ImplSource::UserDefined(i) => i.nested,
ImplSource::Param(n) | ImplSource::Builtin(_, n) => n,
}
}
pub fn borrow_nested_obligations(&self) -> &[N] {
match self {
ImplSource::UserDefined(i) => &i.nested,
ImplSource::Param(n) | ImplSource::Builtin(_, n) => &n,
}
}
pub fn borrow_nested_obligations_mut(&mut self) -> &mut [N] {
match self {
ImplSource::UserDefined(i) => &mut i.nested,
ImplSource::Param(n) | ImplSource::Builtin(_, n) => n,
}
}
pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
where
F: FnMut(N) -> M,
{
match self {
ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
impl_def_id: i.impl_def_id,
args: i.args,
nested: i.nested.into_iter().map(f).collect(),
}),
ImplSource::Param(n) => ImplSource::Param(n.into_iter().map(f).collect()),
ImplSource::Builtin(source, n) => {
ImplSource::Builtin(source, n.into_iter().map(f).collect())
}
}
}
}
/// Identifies a particular impl in the source, along with a set of
/// substitutions from the impl's type/lifetime parameters. The
/// `nested` vector corresponds to the nested obligations attached to
/// the impl's type parameters.
///
/// The type parameter `N` indicates the type used for "nested
/// obligations" that are required by the impl. During type-check, this
/// is `Obligation`, as one might expect. During codegen, however, this
/// is `()`, because codegen only requires a shallow resolution of an
/// impl, and nested obligations are satisfied later.
#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub struct ImplSourceUserDefinedData<'tcx, N> {
pub impl_def_id: DefId,
pub args: GenericArgsRef<'tcx>,
pub nested: Vec<N>,
}
#[derive(Copy, Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Debug)]
pub enum BuiltinImplSource {
/// Some builtin impl we don't need to differentiate. This should be used
/// unless more specific information is necessary.
Misc,
/// A builtin impl for trait objects.
///
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits, pointers to supertrait vtable will
/// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
/// in that vtable.
Object { vtable_base: usize },
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits, pointers to supertrait vtable will
/// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
/// within that vtable.
TraitUpcasting { vtable_vptr_slot: Option<usize> },
/// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
///
/// This needs to be a separate variant as it is still unstable and we need to emit
/// a feature error when using it on stable.
TupleUnsizing,
}
TrivialTypeTraversalImpls! { BuiltinImplSource }
#[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
pub enum ObjectSafetyViolation {
/// `Self: Sized` declared on the trait.
SizedSelf(SmallVec<[Span; 1]>),
/// Supertrait reference references `Self` an in illegal location
/// (e.g., `trait Foo : Bar<Self>`).
SupertraitSelf(SmallVec<[Span; 1]>),
// Supertrait has a non-lifetime `for<T>` binder.
SupertraitNonLifetimeBinder(SmallVec<[Span; 1]>),
/// Method has something illegal.
Method(Symbol, MethodViolationCode, Span),
/// Associated const.
AssocConst(Symbol, Span),
/// GAT
GAT(Symbol, Span),
}
impl ObjectSafetyViolation {
pub fn error_msg(&self) -> Cow<'static, str> {
match self {
ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
ObjectSafetyViolation::SupertraitSelf(ref spans) => {
if spans.iter().any(|sp| *sp != DUMMY_SP) {
"it uses `Self` as a type parameter".into()
} else {
"it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
.into()
}
}
ObjectSafetyViolation::SupertraitNonLifetimeBinder(_) => {
"where clause cannot reference non-lifetime `for<...>` variables".into()
}
ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
format!("associated function `{name}` has no `self` parameter").into()
}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::ReferencesSelfInput(_),
DUMMY_SP,
) => format!("method `{name}` references the `Self` type in its parameters").into(),
ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
format!("method `{name}` references the `Self` type in this parameter").into()
}
ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
format!("method `{name}` references the `Self` type in its return type").into()
}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::ReferencesImplTraitInTrait(_),
_,
) => {
format!("method `{name}` references an `impl Trait` type in its return type").into()
}
ObjectSafetyViolation::Method(name, MethodViolationCode::AsyncFn, _) => {
format!("method `{name}` is `async`").into()
}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::WhereClauseReferencesSelf,
_,
) => format!("method `{name}` references the `Self` type in its `where` clause").into(),
ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
format!("method `{name}` has generic type parameters").into()
}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::UndispatchableReceiver(_),
_,
) => format!("method `{name}`'s `self` parameter cannot be dispatched on").into(),
ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
format!("it contains associated `const` `{name}`").into()
}
ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
ObjectSafetyViolation::GAT(name, _) => {
format!("it contains the generic associated type `{name}`").into()
}
}
}
pub fn solution(&self, err: &mut Diagnostic) {
match self {
ObjectSafetyViolation::SizedSelf(_)
| ObjectSafetyViolation::SupertraitSelf(_)
| ObjectSafetyViolation::SupertraitNonLifetimeBinder(..) => {}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))),
_,
) => {
err.span_suggestion(
add_self_sugg.1,
format!(
"consider turning `{name}` into a method by giving it a `&self` argument"
),
add_self_sugg.0.to_string(),
Applicability::MaybeIncorrect,
);
err.span_suggestion(
make_sized_sugg.1,
format!(
"alternatively, consider constraining `{name}` so it does not apply to \
trait objects"
),
make_sized_sugg.0.to_string(),
Applicability::MaybeIncorrect,
);
}
ObjectSafetyViolation::Method(
name,
MethodViolationCode::UndispatchableReceiver(Some(span)),
_,
) => {
err.span_suggestion(
*span,
format!("consider changing method `{name}`'s `self` parameter to be `&self`"),
"&Self",
Applicability::MachineApplicable,
);
}
ObjectSafetyViolation::AssocConst(name, _)
| ObjectSafetyViolation::GAT(name, _)
| ObjectSafetyViolation::Method(name, ..) => {
err.help(format!("consider moving `{name}` to another trait"));
}
}
}
pub fn spans(&self) -> SmallVec<[Span; 1]> {
// When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
// diagnostics use a `note` instead of a `span_label`.
match self {
ObjectSafetyViolation::SupertraitSelf(spans)
| ObjectSafetyViolation::SizedSelf(spans)
| ObjectSafetyViolation::SupertraitNonLifetimeBinder(spans) => spans.clone(),
ObjectSafetyViolation::AssocConst(_, span)
| ObjectSafetyViolation::GAT(_, span)
| ObjectSafetyViolation::Method(_, _, span)
if *span != DUMMY_SP =>
{
smallvec![*span]
}
_ => smallvec![],
}
}
}
/// Reasons a method might not be object-safe.
#[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
pub enum MethodViolationCode {
/// e.g., `fn foo()`
StaticMethod(Option<(/* add &self */ (String, Span), /* add Self: Sized */ (String, Span))>),
/// e.g., `fn foo(&self, x: Self)`
ReferencesSelfInput(Option<Span>),
/// e.g., `fn foo(&self) -> Self`
ReferencesSelfOutput,
/// e.g., `fn foo(&self) -> impl Sized`
ReferencesImplTraitInTrait(Span),
/// e.g., `async fn foo(&self)`
AsyncFn,
/// e.g., `fn foo(&self) where Self: Clone`
WhereClauseReferencesSelf,
/// e.g., `fn foo<A>()`
Generic,
/// the method's receiver (`self` argument) can't be dispatched on
UndispatchableReceiver(Option<Span>),
}
/// These are the error cases for `codegen_select_candidate`.
#[derive(Copy, Clone, Debug, Hash, HashStable, Encodable, Decodable)]
pub enum CodegenObligationError {
/// Ambiguity can happen when monomorphizing during trans
/// expands to some humongous type that never occurred
/// statically -- this humongous type can then overflow,
/// leading to an ambiguous result. So report this as an
/// overflow bug, since I believe this is the only case
/// where ambiguity can result.
Ambiguity,
/// This can trigger when we probe for the source of a `'static` lifetime requirement
/// on a trait object: `impl Foo for dyn Trait {}` has an implicit `'static` bound.
/// This can also trigger when we have a global bound that is not actually satisfied,
/// but was included during typeck due to the trivial_bounds feature.
Unimplemented,
FulfillmentError,
}
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
pub enum DefiningAnchor {
/// `DefId` of the item.
Bind(LocalDefId),
/// When opaque types are not resolved, we `Bubble` up, meaning
/// return the opaque/hidden type pair from query, for caller of query to handle it.
Bubble,
/// Used to catch type mismatch errors when handling opaque types.
Error,
}