1 //! Trait Resolution. See the [rustc dev guide] for more information on how this works. 2 //! 3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html 4 5 mod chalk; 6 pub mod query; 7 pub mod select; 8 pub mod specialization_graph; 9 mod structural_impls; 10 pub mod util; 11 12 use crate::infer::canonical::Canonical; 13 use crate::thir::abstract_const::NotConstEvaluatable; 14 use crate::ty::subst::SubstsRef; 15 use crate::ty::{self, AdtKind, Ty, TyCtxt}; 16 17 use rustc_data_structures::sync::Lrc; 18 use rustc_errors::{Applicability, DiagnosticBuilder}; 19 use rustc_hir as hir; 20 use rustc_hir::def_id::{DefId, LocalDefId}; 21 use rustc_span::symbol::Symbol; 22 use rustc_span::{Span, DUMMY_SP}; 23 use smallvec::SmallVec; 24 25 use std::borrow::Cow; 26 use std::fmt; 27 use std::hash::{Hash, Hasher}; 28 use std::ops::Deref; 29 30 pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache}; 31 32 pub type CanonicalChalkEnvironmentAndGoal<'tcx> = Canonical<'tcx, ChalkEnvironmentAndGoal<'tcx>>; 33 34 pub use self::ObligationCauseCode::*; 35 36 pub use self::chalk::{ChalkEnvironmentAndGoal, RustInterner as ChalkRustInterner}; 37 38 /// Depending on the stage of compilation, we want projection to be 39 /// more or less conservative. 40 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)] 41 pub enum Reveal { 42 /// At type-checking time, we refuse to project any associated 43 /// type that is marked `default`. Non-`default` ("final") types 44 /// are always projected. This is necessary in general for 45 /// soundness of specialization. However, we *could* allow 46 /// projections in fully-monomorphic cases. We choose not to, 47 /// because we prefer for `default type` to force the type 48 /// definition to be treated abstractly by any consumers of the 49 /// impl. Concretely, that means that the following example will 50 /// fail to compile: 51 /// 52 /// ``` 53 /// trait Assoc { 54 /// type Output; 55 /// } 56 /// 57 /// impl<T> Assoc for T { 58 /// default type Output = bool; 59 /// } 60 /// 61 /// fn main() { 62 /// let <() as Assoc>::Output = true; 63 /// } 64 /// ``` 65 UserFacing, 66 67 /// At codegen time, all monomorphic projections will succeed. 68 /// Also, `impl Trait` is normalized to the concrete type, 69 /// which has to be already collected by type-checking. 70 /// 71 /// NOTE: as `impl Trait`'s concrete type should *never* 72 /// be observable directly by the user, `Reveal::All` 73 /// should not be used by checks which may expose 74 /// type equality or type contents to the user. 75 /// There are some exceptions, e.g., around auto traits and 76 /// transmute-checking, which expose some details, but 77 /// not the whole concrete type of the `impl Trait`. 78 All, 79 } 80 81 /// The reason why we incurred this obligation; used for error reporting. 82 /// 83 /// As the happy path does not care about this struct, storing this on the heap 84 /// ends up increasing performance. 85 /// 86 /// We do not want to intern this as there are a lot of obligation causes which 87 /// only live for a short period of time. 88 #[derive(Clone, PartialEq, Eq, Hash, Lift)] 89 pub struct ObligationCause<'tcx> { 90 /// `None` for `ObligationCause::dummy`, `Some` otherwise. 91 data: Option<Lrc<ObligationCauseData<'tcx>>>, 92 } 93 94 const DUMMY_OBLIGATION_CAUSE_DATA: ObligationCauseData<'static> = 95 ObligationCauseData { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }; 96 97 // Correctly format `ObligationCause::dummy`. 98 impl<'tcx> fmt::Debug for ObligationCause<'tcx> { fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result99 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 100 ObligationCauseData::fmt(self, f) 101 } 102 } 103 104 impl Deref for ObligationCause<'tcx> { 105 type Target = ObligationCauseData<'tcx>; 106 107 #[inline(always)] deref(&self) -> &Self::Target108 fn deref(&self) -> &Self::Target { 109 self.data.as_deref().unwrap_or(&DUMMY_OBLIGATION_CAUSE_DATA) 110 } 111 } 112 113 #[derive(Clone, Debug, PartialEq, Eq, Lift)] 114 pub struct ObligationCauseData<'tcx> { 115 pub span: Span, 116 117 /// The ID of the fn body that triggered this obligation. This is 118 /// used for region obligations to determine the precise 119 /// environment in which the region obligation should be evaluated 120 /// (in particular, closures can add new assumptions). See the 121 /// field `region_obligations` of the `FulfillmentContext` for more 122 /// information. 123 pub body_id: hir::HirId, 124 125 pub code: ObligationCauseCode<'tcx>, 126 } 127 128 impl Hash for ObligationCauseData<'_> { hash<H: Hasher>(&self, state: &mut H)129 fn hash<H: Hasher>(&self, state: &mut H) { 130 self.body_id.hash(state); 131 self.span.hash(state); 132 std::mem::discriminant(&self.code).hash(state); 133 } 134 } 135 136 impl<'tcx> ObligationCause<'tcx> { 137 #[inline] new( span: Span, body_id: hir::HirId, code: ObligationCauseCode<'tcx>, ) -> ObligationCause<'tcx>138 pub fn new( 139 span: Span, 140 body_id: hir::HirId, 141 code: ObligationCauseCode<'tcx>, 142 ) -> ObligationCause<'tcx> { 143 ObligationCause { data: Some(Lrc::new(ObligationCauseData { span, body_id, code })) } 144 } 145 misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx>146 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> { 147 ObligationCause::new(span, body_id, MiscObligation) 148 } 149 dummy_with_span(span: Span) -> ObligationCause<'tcx>150 pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> { 151 ObligationCause::new(span, hir::CRATE_HIR_ID, MiscObligation) 152 } 153 154 #[inline(always)] dummy() -> ObligationCause<'tcx>155 pub fn dummy() -> ObligationCause<'tcx> { 156 ObligationCause { data: None } 157 } 158 make_mut(&mut self) -> &mut ObligationCauseData<'tcx>159 pub fn make_mut(&mut self) -> &mut ObligationCauseData<'tcx> { 160 Lrc::make_mut(self.data.get_or_insert_with(|| Lrc::new(DUMMY_OBLIGATION_CAUSE_DATA))) 161 } 162 span(&self, tcx: TyCtxt<'tcx>) -> Span163 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span { 164 match self.code { 165 ObligationCauseCode::CompareImplMethodObligation { .. } 166 | ObligationCauseCode::MainFunctionType 167 | ObligationCauseCode::StartFunctionType => { 168 tcx.sess.source_map().guess_head_span(self.span) 169 } 170 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause { 171 arm_span, 172 .. 173 }) => arm_span, 174 _ => self.span, 175 } 176 } 177 } 178 179 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] 180 pub struct UnifyReceiverContext<'tcx> { 181 pub assoc_item: ty::AssocItem, 182 pub param_env: ty::ParamEnv<'tcx>, 183 pub substs: SubstsRef<'tcx>, 184 } 185 186 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] 187 pub enum ObligationCauseCode<'tcx> { 188 /// Not well classified or should be obvious from the span. 189 MiscObligation, 190 191 /// A slice or array is WF only if `T: Sized`. 192 SliceOrArrayElem, 193 194 /// A tuple is WF only if its middle elements are `Sized`. 195 TupleElem, 196 197 /// This is the trait reference from the given projection. 198 ProjectionWf(ty::ProjectionTy<'tcx>), 199 200 /// In an impl of trait `X` for type `Y`, type `Y` must 201 /// also implement all supertraits of `X`. 202 ItemObligation(DefId), 203 204 /// Like `ItemObligation`, but with extra detail on the source of the obligation. 205 BindingObligation(DefId, Span), 206 207 /// A type like `&'a T` is WF only if `T: 'a`. 208 ReferenceOutlivesReferent(Ty<'tcx>), 209 210 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`. 211 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>), 212 213 /// Obligation incurred due to an object cast. 214 ObjectCastObligation(/* Object type */ Ty<'tcx>), 215 216 /// Obligation incurred due to a coercion. 217 Coercion { 218 source: Ty<'tcx>, 219 target: Ty<'tcx>, 220 }, 221 222 /// Various cases where expressions must be `Sized` / `Copy` / etc. 223 /// `L = X` implies that `L` is `Sized`. 224 AssignmentLhsSized, 225 /// `(x1, .., xn)` must be `Sized`. 226 TupleInitializerSized, 227 /// `S { ... }` must be `Sized`. 228 StructInitializerSized, 229 /// Type of each variable must be `Sized`. 230 VariableType(hir::HirId), 231 /// Argument type must be `Sized`. 232 SizedArgumentType(Option<Span>), 233 /// Return type must be `Sized`. 234 SizedReturnType, 235 /// Yield type must be `Sized`. 236 SizedYieldType, 237 /// Box expression result type must be `Sized`. 238 SizedBoxType, 239 /// Inline asm operand type must be `Sized`. 240 InlineAsmSized, 241 /// `[T, ..n]` implies that `T` must be `Copy`. 242 /// If the function in the array repeat expression is a `const fn`, 243 /// display a help message suggesting to move the function call to a 244 /// new `const` item while saying that `T` doesn't implement `Copy`. 245 RepeatVec(bool), 246 247 /// Types of fields (other than the last, except for packed structs) in a struct must be sized. 248 FieldSized { 249 adt_kind: AdtKind, 250 span: Span, 251 last: bool, 252 }, 253 254 /// Constant expressions must be sized. 255 ConstSized, 256 257 /// `static` items must have `Sync` type. 258 SharedStatic, 259 260 BuiltinDerivedObligation(DerivedObligationCause<'tcx>), 261 262 ImplDerivedObligation(DerivedObligationCause<'tcx>), 263 264 DerivedObligation(DerivedObligationCause<'tcx>), 265 266 FunctionArgumentObligation { 267 /// The node of the relevant argument in the function call. 268 arg_hir_id: hir::HirId, 269 /// The node of the function call. 270 call_hir_id: hir::HirId, 271 /// The obligation introduced by this argument. 272 parent_code: Lrc<ObligationCauseCode<'tcx>>, 273 }, 274 275 /// Error derived when matching traits/impls; see ObligationCause for more details 276 CompareImplConstObligation, 277 278 /// Error derived when matching traits/impls; see ObligationCause for more details 279 CompareImplMethodObligation { 280 impl_item_def_id: DefId, 281 trait_item_def_id: DefId, 282 }, 283 284 /// Error derived when matching traits/impls; see ObligationCause for more details 285 CompareImplTypeObligation { 286 impl_item_def_id: DefId, 287 trait_item_def_id: DefId, 288 }, 289 290 /// Checking that this expression can be assigned where it needs to be 291 // FIXME(eddyb) #11161 is the original Expr required? 292 ExprAssignable, 293 294 /// Computing common supertype in the arms of a match expression 295 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>), 296 297 /// Type error arising from type checking a pattern against an expected type. 298 Pattern { 299 /// The span of the scrutinee or type expression which caused the `root_ty` type. 300 span: Option<Span>, 301 /// The root expected type induced by a scrutinee or type expression. 302 root_ty: Ty<'tcx>, 303 /// Whether the `Span` came from an expression or a type expression. 304 origin_expr: bool, 305 }, 306 307 /// Constants in patterns must have `Structural` type. 308 ConstPatternStructural, 309 310 /// Computing common supertype in an if expression 311 IfExpression(Box<IfExpressionCause>), 312 313 /// Computing common supertype of an if expression with no else counter-part 314 IfExpressionWithNoElse, 315 316 /// `main` has wrong type 317 MainFunctionType, 318 319 /// `start` has wrong type 320 StartFunctionType, 321 322 /// Intrinsic has wrong type 323 IntrinsicType, 324 325 /// A let else block does not diverge 326 LetElse, 327 328 /// Method receiver 329 MethodReceiver, 330 331 UnifyReceiver(Box<UnifyReceiverContext<'tcx>>), 332 333 /// `return` with no expression 334 ReturnNoExpression, 335 336 /// `return` with an expression 337 ReturnValue(hir::HirId), 338 339 /// Return type of this function 340 ReturnType, 341 342 /// Block implicit return 343 BlockTailExpression(hir::HirId), 344 345 /// #[feature(trivial_bounds)] is not enabled 346 TrivialBound, 347 348 /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y` 349 OpaqueType, 350 351 /// Well-formed checking. If a `WellFormedLoc` is provided, 352 /// then it will be used to eprform HIR-based wf checking 353 /// after an error occurs, in order to generate a more precise error span. 354 /// This is purely for diagnostic purposes - it is always 355 /// correct to use `MiscObligation` instead, or to specify 356 /// `WellFormed(None)` 357 WellFormed(Option<WellFormedLoc>), 358 359 /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against. 360 MatchImpl(ObligationCause<'tcx>, DefId), 361 } 362 363 /// The 'location' at which we try to perform HIR-based wf checking. 364 /// This information is used to obtain an `hir::Ty`, which 365 /// we can walk in order to obtain precise spans for any 366 /// 'nested' types (e.g. `Foo` in `Option<Foo>`). 367 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)] 368 pub enum WellFormedLoc { 369 /// Use the type of the provided definition. 370 Ty(LocalDefId), 371 /// Use the type of the parameter of the provided function. 372 /// We cannot use `hir::Param`, since the function may 373 /// not have a body (e.g. a trait method definition) 374 Param { 375 /// The function to lookup the parameter in 376 function: LocalDefId, 377 /// The index of the parameter to use. 378 /// Parameters are indexed from 0, with the return type 379 /// being the last 'parameter' 380 param_idx: u16, 381 }, 382 } 383 384 impl ObligationCauseCode<'_> { 385 // Return the base obligation, ignoring derived obligations. peel_derives(&self) -> &Self386 pub fn peel_derives(&self) -> &Self { 387 let mut base_cause = self; 388 while let BuiltinDerivedObligation(DerivedObligationCause { parent_code, .. }) 389 | ImplDerivedObligation(DerivedObligationCause { parent_code, .. }) 390 | DerivedObligation(DerivedObligationCause { parent_code, .. }) 391 | FunctionArgumentObligation { parent_code, .. } = base_cause 392 { 393 base_cause = &parent_code; 394 } 395 base_cause 396 } 397 } 398 399 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger. 400 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))] 401 static_assert_size!(ObligationCauseCode<'_>, 40); 402 403 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] 404 pub enum StatementAsExpression { 405 CorrectType, 406 NeedsBoxing, 407 } 408 409 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression { 410 type Lifted = StatementAsExpression; lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression>411 fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> { 412 Some(self) 413 } 414 } 415 416 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] 417 pub struct MatchExpressionArmCause<'tcx> { 418 pub arm_span: Span, 419 pub scrut_span: Span, 420 pub semi_span: Option<(Span, StatementAsExpression)>, 421 pub source: hir::MatchSource, 422 pub prior_arms: Vec<Span>, 423 pub last_ty: Ty<'tcx>, 424 pub scrut_hir_id: hir::HirId, 425 pub opt_suggest_box_span: Option<Span>, 426 } 427 428 #[derive(Clone, Debug, PartialEq, Eq, Hash)] 429 pub struct IfExpressionCause { 430 pub then: Span, 431 pub else_sp: Span, 432 pub outer: Option<Span>, 433 pub semicolon: Option<(Span, StatementAsExpression)>, 434 pub opt_suggest_box_span: Option<Span>, 435 } 436 437 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] 438 pub struct DerivedObligationCause<'tcx> { 439 /// The trait reference of the parent obligation that led to the 440 /// current obligation. Note that only trait obligations lead to 441 /// derived obligations, so we just store the trait reference here 442 /// directly. 443 pub parent_trait_ref: ty::PolyTraitRef<'tcx>, 444 445 /// The parent trait had this cause. 446 pub parent_code: Lrc<ObligationCauseCode<'tcx>>, 447 } 448 449 #[derive(Clone, Debug, TypeFoldable, Lift)] 450 pub enum SelectionError<'tcx> { 451 /// The trait is not implemented. 452 Unimplemented, 453 /// After a closure impl has selected, its "outputs" were evaluated 454 /// (which for closures includes the "input" type params) and they 455 /// didn't resolve. See `confirm_poly_trait_refs` for more. 456 OutputTypeParameterMismatch( 457 ty::PolyTraitRef<'tcx>, 458 ty::PolyTraitRef<'tcx>, 459 ty::error::TypeError<'tcx>, 460 ), 461 /// The trait pointed by `DefId` is not object safe. 462 TraitNotObjectSafe(DefId), 463 /// A given constant couldn't be evaluated. 464 NotConstEvaluatable(NotConstEvaluatable), 465 /// Exceeded the recursion depth during type projection. 466 Overflow, 467 /// Signaling that an error has already been emitted, to avoid 468 /// multiple errors being shown. 469 ErrorReporting, 470 /// Multiple applicable `impl`s where found. The `DefId`s correspond to 471 /// all the `impl`s' Items. 472 Ambiguous(Vec<DefId>), 473 } 474 475 /// When performing resolution, it is typically the case that there 476 /// can be one of three outcomes: 477 /// 478 /// - `Ok(Some(r))`: success occurred with result `r` 479 /// - `Ok(None)`: could not definitely determine anything, usually due 480 /// to inconclusive type inference. 481 /// - `Err(e)`: error `e` occurred 482 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>; 483 484 /// Given the successful resolution of an obligation, the `ImplSource` 485 /// indicates where the impl comes from. 486 /// 487 /// For example, the obligation may be satisfied by a specific impl (case A), 488 /// or it may be relative to some bound that is in scope (case B). 489 /// 490 /// ``` 491 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1 492 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2 493 /// impl Clone for i32 { ... } // Impl_3 494 /// 495 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) { 496 /// // Case A: ImplSource points at a specific impl. Only possible when 497 /// // type is concretely known. If the impl itself has bounded 498 /// // type parameters, ImplSource will carry resolutions for those as well: 499 /// concrete.clone(); // ImpleSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])]) 500 /// 501 /// // Case A: ImplSource points at a specific impl. Only possible when 502 /// // type is concretely known. If the impl itself has bounded 503 /// // type parameters, ImplSource will carry resolutions for those as well: 504 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])]) 505 /// 506 /// // Case B: ImplSource must be provided by caller. This applies when 507 /// // type is a type parameter. 508 /// param.clone(); // ImplSource::Param 509 /// 510 /// // Case C: A mix of cases A and B. 511 /// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param]) 512 /// } 513 /// ``` 514 /// 515 /// ### The type parameter `N` 516 /// 517 /// See explanation on `ImplSourceUserDefinedData`. 518 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 519 pub enum ImplSource<'tcx, N> { 520 /// ImplSource identifying a particular impl. 521 UserDefined(ImplSourceUserDefinedData<'tcx, N>), 522 523 /// ImplSource for auto trait implementations. 524 /// This carries the information and nested obligations with regards 525 /// to an auto implementation for a trait `Trait`. The nested obligations 526 /// ensure the trait implementation holds for all the constituent types. 527 AutoImpl(ImplSourceAutoImplData<N>), 528 529 /// Successful resolution to an obligation provided by the caller 530 /// for some type parameter. The `Vec<N>` represents the 531 /// obligations incurred from normalizing the where-clause (if 532 /// any). 533 Param(Vec<N>, ty::BoundConstness), 534 535 /// Virtual calls through an object. 536 Object(ImplSourceObjectData<'tcx, N>), 537 538 /// Successful resolution for a builtin trait. 539 Builtin(ImplSourceBuiltinData<N>), 540 541 /// ImplSource for trait upcasting coercion 542 TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>), 543 544 /// ImplSource automatically generated for a closure. The `DefId` is the ID 545 /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the 546 /// impl is generated by the compiler and does not appear in the source. 547 Closure(ImplSourceClosureData<'tcx, N>), 548 549 /// Same as above, but for a function pointer type with the given signature. 550 FnPointer(ImplSourceFnPointerData<'tcx, N>), 551 552 /// ImplSource for a builtin `DeterminantKind` trait implementation. 553 DiscriminantKind(ImplSourceDiscriminantKindData), 554 555 /// ImplSource for a builtin `Pointee` trait implementation. 556 Pointee(ImplSourcePointeeData), 557 558 /// ImplSource automatically generated for a generator. 559 Generator(ImplSourceGeneratorData<'tcx, N>), 560 561 /// ImplSource for a trait alias. 562 TraitAlias(ImplSourceTraitAliasData<'tcx, N>), 563 564 /// ImplSource for a `const Drop` implementation. 565 ConstDrop(ImplSourceConstDropData), 566 } 567 568 impl<'tcx, N> ImplSource<'tcx, N> { nested_obligations(self) -> Vec<N>569 pub fn nested_obligations(self) -> Vec<N> { 570 match self { 571 ImplSource::UserDefined(i) => i.nested, 572 ImplSource::Param(n, _) => n, 573 ImplSource::Builtin(i) => i.nested, 574 ImplSource::AutoImpl(d) => d.nested, 575 ImplSource::Closure(c) => c.nested, 576 ImplSource::Generator(c) => c.nested, 577 ImplSource::Object(d) => d.nested, 578 ImplSource::FnPointer(d) => d.nested, 579 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) 580 | ImplSource::Pointee(ImplSourcePointeeData) 581 | ImplSource::ConstDrop(ImplSourceConstDropData) => Vec::new(), 582 ImplSource::TraitAlias(d) => d.nested, 583 ImplSource::TraitUpcasting(d) => d.nested, 584 } 585 } 586 borrow_nested_obligations(&self) -> &[N]587 pub fn borrow_nested_obligations(&self) -> &[N] { 588 match &self { 589 ImplSource::UserDefined(i) => &i.nested[..], 590 ImplSource::Param(n, _) => &n[..], 591 ImplSource::Builtin(i) => &i.nested[..], 592 ImplSource::AutoImpl(d) => &d.nested[..], 593 ImplSource::Closure(c) => &c.nested[..], 594 ImplSource::Generator(c) => &c.nested[..], 595 ImplSource::Object(d) => &d.nested[..], 596 ImplSource::FnPointer(d) => &d.nested[..], 597 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) 598 | ImplSource::Pointee(ImplSourcePointeeData) 599 | ImplSource::ConstDrop(ImplSourceConstDropData) => &[], 600 ImplSource::TraitAlias(d) => &d.nested[..], 601 ImplSource::TraitUpcasting(d) => &d.nested[..], 602 } 603 } 604 map<M, F>(self, f: F) -> ImplSource<'tcx, M> where F: FnMut(N) -> M,605 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M> 606 where 607 F: FnMut(N) -> M, 608 { 609 match self { 610 ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData { 611 impl_def_id: i.impl_def_id, 612 substs: i.substs, 613 nested: i.nested.into_iter().map(f).collect(), 614 }), 615 ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct), 616 ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData { 617 nested: i.nested.into_iter().map(f).collect(), 618 }), 619 ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData { 620 upcast_trait_ref: o.upcast_trait_ref, 621 vtable_base: o.vtable_base, 622 nested: o.nested.into_iter().map(f).collect(), 623 }), 624 ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData { 625 trait_def_id: d.trait_def_id, 626 nested: d.nested.into_iter().map(f).collect(), 627 }), 628 ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData { 629 closure_def_id: c.closure_def_id, 630 substs: c.substs, 631 nested: c.nested.into_iter().map(f).collect(), 632 }), 633 ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData { 634 generator_def_id: c.generator_def_id, 635 substs: c.substs, 636 nested: c.nested.into_iter().map(f).collect(), 637 }), 638 ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData { 639 fn_ty: p.fn_ty, 640 nested: p.nested.into_iter().map(f).collect(), 641 }), 642 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => { 643 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) 644 } 645 ImplSource::Pointee(ImplSourcePointeeData) => { 646 ImplSource::Pointee(ImplSourcePointeeData) 647 } 648 ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData { 649 alias_def_id: d.alias_def_id, 650 substs: d.substs, 651 nested: d.nested.into_iter().map(f).collect(), 652 }), 653 ImplSource::TraitUpcasting(d) => { 654 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData { 655 upcast_trait_ref: d.upcast_trait_ref, 656 vtable_vptr_slot: d.vtable_vptr_slot, 657 nested: d.nested.into_iter().map(f).collect(), 658 }) 659 } 660 ImplSource::ConstDrop(ImplSourceConstDropData) => { 661 ImplSource::ConstDrop(ImplSourceConstDropData) 662 } 663 } 664 } 665 } 666 667 /// Identifies a particular impl in the source, along with a set of 668 /// substitutions from the impl's type/lifetime parameters. The 669 /// `nested` vector corresponds to the nested obligations attached to 670 /// the impl's type parameters. 671 /// 672 /// The type parameter `N` indicates the type used for "nested 673 /// obligations" that are required by the impl. During type-check, this 674 /// is `Obligation`, as one might expect. During codegen, however, this 675 /// is `()`, because codegen only requires a shallow resolution of an 676 /// impl, and nested obligations are satisfied later. 677 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 678 pub struct ImplSourceUserDefinedData<'tcx, N> { 679 pub impl_def_id: DefId, 680 pub substs: SubstsRef<'tcx>, 681 pub nested: Vec<N>, 682 } 683 684 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 685 pub struct ImplSourceGeneratorData<'tcx, N> { 686 pub generator_def_id: DefId, 687 pub substs: SubstsRef<'tcx>, 688 /// Nested obligations. This can be non-empty if the generator 689 /// signature contains associated types. 690 pub nested: Vec<N>, 691 } 692 693 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 694 pub struct ImplSourceClosureData<'tcx, N> { 695 pub closure_def_id: DefId, 696 pub substs: SubstsRef<'tcx>, 697 /// Nested obligations. This can be non-empty if the closure 698 /// signature contains associated types. 699 pub nested: Vec<N>, 700 } 701 702 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 703 pub struct ImplSourceAutoImplData<N> { 704 pub trait_def_id: DefId, 705 pub nested: Vec<N>, 706 } 707 708 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 709 pub struct ImplSourceTraitUpcastingData<'tcx, N> { 710 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`. 711 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>, 712 713 /// The vtable is formed by concatenating together the method lists of 714 /// the base object trait and all supertraits, pointers to supertrait vtable will 715 /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable 716 /// within that vtable. 717 pub vtable_vptr_slot: Option<usize>, 718 719 pub nested: Vec<N>, 720 } 721 722 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 723 pub struct ImplSourceBuiltinData<N> { 724 pub nested: Vec<N>, 725 } 726 727 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 728 pub struct ImplSourceObjectData<'tcx, N> { 729 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`. 730 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>, 731 732 /// The vtable is formed by concatenating together the method lists of 733 /// the base object trait and all supertraits, pointers to supertrait vtable will 734 /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods 735 /// in that vtable. 736 pub vtable_base: usize, 737 738 pub nested: Vec<N>, 739 } 740 741 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 742 pub struct ImplSourceFnPointerData<'tcx, N> { 743 pub fn_ty: Ty<'tcx>, 744 pub nested: Vec<N>, 745 } 746 747 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables. 748 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] 749 pub struct ImplSourceDiscriminantKindData; 750 751 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] 752 pub struct ImplSourcePointeeData; 753 754 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] 755 pub struct ImplSourceConstDropData; 756 757 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)] 758 pub struct ImplSourceTraitAliasData<'tcx, N> { 759 pub alias_def_id: DefId, 760 pub substs: SubstsRef<'tcx>, 761 pub nested: Vec<N>, 762 } 763 764 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)] 765 pub enum ObjectSafetyViolation { 766 /// `Self: Sized` declared on the trait. 767 SizedSelf(SmallVec<[Span; 1]>), 768 769 /// Supertrait reference references `Self` an in illegal location 770 /// (e.g., `trait Foo : Bar<Self>`). 771 SupertraitSelf(SmallVec<[Span; 1]>), 772 773 /// Method has something illegal. 774 Method(Symbol, MethodViolationCode, Span), 775 776 /// Associated const. 777 AssocConst(Symbol, Span), 778 779 /// GAT 780 GAT(Symbol, Span), 781 } 782 783 impl ObjectSafetyViolation { error_msg(&self) -> Cow<'static, str>784 pub fn error_msg(&self) -> Cow<'static, str> { 785 match *self { 786 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(), 787 ObjectSafetyViolation::SupertraitSelf(ref spans) => { 788 if spans.iter().any(|sp| *sp != DUMMY_SP) { 789 "it uses `Self` as a type parameter".into() 790 } else { 791 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause" 792 .into() 793 } 794 } 795 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => { 796 format!("associated function `{}` has no `self` parameter", name).into() 797 } 798 ObjectSafetyViolation::Method( 799 name, 800 MethodViolationCode::ReferencesSelfInput(_), 801 DUMMY_SP, 802 ) => format!("method `{}` references the `Self` type in its parameters", name).into(), 803 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => { 804 format!("method `{}` references the `Self` type in this parameter", name).into() 805 } 806 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => { 807 format!("method `{}` references the `Self` type in its return type", name).into() 808 } 809 ObjectSafetyViolation::Method( 810 name, 811 MethodViolationCode::WhereClauseReferencesSelf, 812 _, 813 ) => { 814 format!("method `{}` references the `Self` type in its `where` clause", name).into() 815 } 816 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => { 817 format!("method `{}` has generic type parameters", name).into() 818 } 819 ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => { 820 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into() 821 } 822 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => { 823 format!("it contains associated `const` `{}`", name).into() 824 } 825 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(), 826 ObjectSafetyViolation::GAT(name, _) => { 827 format!("it contains the generic associated type `{}`", name).into() 828 } 829 } 830 } 831 solution(&self, err: &mut DiagnosticBuilder<'_>)832 pub fn solution(&self, err: &mut DiagnosticBuilder<'_>) { 833 match *self { 834 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {} 835 ObjectSafetyViolation::Method( 836 name, 837 MethodViolationCode::StaticMethod(sugg, self_span, has_args), 838 _, 839 ) => { 840 err.span_suggestion( 841 self_span, 842 &format!( 843 "consider turning `{}` into a method by giving it a `&self` argument", 844 name 845 ), 846 format!("&self{}", if has_args { ", " } else { "" }), 847 Applicability::MaybeIncorrect, 848 ); 849 match sugg { 850 Some((sugg, span)) => { 851 err.span_suggestion( 852 span, 853 &format!( 854 "alternatively, consider constraining `{}` so it does not apply to \ 855 trait objects", 856 name 857 ), 858 sugg.to_string(), 859 Applicability::MaybeIncorrect, 860 ); 861 } 862 None => { 863 err.help(&format!( 864 "consider turning `{}` into a method by giving it a `&self` \ 865 argument or constraining it so it does not apply to trait objects", 866 name 867 )); 868 } 869 } 870 } 871 ObjectSafetyViolation::Method( 872 name, 873 MethodViolationCode::UndispatchableReceiver, 874 span, 875 ) => { 876 err.span_suggestion( 877 span, 878 &format!( 879 "consider changing method `{}`'s `self` parameter to be `&self`", 880 name 881 ), 882 "&Self".to_string(), 883 Applicability::MachineApplicable, 884 ); 885 } 886 ObjectSafetyViolation::AssocConst(name, _) 887 | ObjectSafetyViolation::GAT(name, _) 888 | ObjectSafetyViolation::Method(name, ..) => { 889 err.help(&format!("consider moving `{}` to another trait", name)); 890 } 891 } 892 } 893 spans(&self) -> SmallVec<[Span; 1]>894 pub fn spans(&self) -> SmallVec<[Span; 1]> { 895 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so 896 // diagnostics use a `note` instead of a `span_label`. 897 match self { 898 ObjectSafetyViolation::SupertraitSelf(spans) 899 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(), 900 ObjectSafetyViolation::AssocConst(_, span) 901 | ObjectSafetyViolation::GAT(_, span) 902 | ObjectSafetyViolation::Method(_, _, span) 903 if *span != DUMMY_SP => 904 { 905 smallvec![*span] 906 } 907 _ => smallvec![], 908 } 909 } 910 } 911 912 /// Reasons a method might not be object-safe. 913 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)] 914 pub enum MethodViolationCode { 915 /// e.g., `fn foo()` 916 StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */), 917 918 /// e.g., `fn foo(&self, x: Self)` 919 ReferencesSelfInput(usize), 920 921 /// e.g., `fn foo(&self) -> Self` 922 ReferencesSelfOutput, 923 924 /// e.g., `fn foo(&self) where Self: Clone` 925 WhereClauseReferencesSelf, 926 927 /// e.g., `fn foo<A>()` 928 Generic, 929 930 /// the method's receiver (`self` argument) can't be dispatched on 931 UndispatchableReceiver, 932 } 933