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Diffstat (limited to 'compiler/rustc_infer/src/infer/mod.rs')
| -rw-r--r-- | compiler/rustc_infer/src/infer/mod.rs | 2066 |
1 files changed, 2066 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs new file mode 100644 index 000000000..d7d1b5fa2 --- /dev/null +++ b/compiler/rustc_infer/src/infer/mod.rs @@ -0,0 +1,2066 @@ +pub use self::freshen::TypeFreshener; +pub use self::lexical_region_resolve::RegionResolutionError; +pub use self::LateBoundRegionConversionTime::*; +pub use self::RegionVariableOrigin::*; +pub use self::SubregionOrigin::*; +pub use self::ValuePairs::*; + +use self::opaque_types::OpaqueTypeStorage; +pub(crate) use self::undo_log::{InferCtxtUndoLogs, Snapshot, UndoLog}; + +use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine, TraitEngineExt}; + +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; +use rustc_data_structures::sync::Lrc; +use rustc_data_structures::undo_log::Rollback; +use rustc_data_structures::unify as ut; +use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed}; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues}; +use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue}; +use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType}; +use rustc_middle::mir::interpret::{ErrorHandled, EvalToValTreeResult}; +use rustc_middle::traits::select; +use rustc_middle::ty::abstract_const::{AbstractConst, FailureKind}; +use rustc_middle::ty::error::{ExpectedFound, TypeError}; +use rustc_middle::ty::fold::BoundVarReplacerDelegate; +use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable}; +use rustc_middle::ty::relate::RelateResult; +use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef}; +use rustc_middle::ty::visit::TypeVisitable; +pub use rustc_middle::ty::IntVarValue; +use rustc_middle::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt}; +use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid}; +use rustc_span::symbol::Symbol; +use rustc_span::Span; + +use std::cell::{Cell, Ref, RefCell}; +use std::fmt; + +use self::combine::CombineFields; +use self::free_regions::RegionRelations; +use self::lexical_region_resolve::LexicalRegionResolutions; +use self::outlives::env::OutlivesEnvironment; +use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound}; +use self::region_constraints::{ + RegionConstraintCollector, RegionConstraintStorage, RegionSnapshot, +}; +use self::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; + +pub mod at; +pub mod canonical; +mod combine; +mod equate; +pub mod error_reporting; +pub mod free_regions; +mod freshen; +mod fudge; +mod glb; +mod higher_ranked; +pub mod lattice; +mod lexical_region_resolve; +mod lub; +pub mod nll_relate; +pub mod opaque_types; +pub mod outlives; +mod projection; +pub mod region_constraints; +pub mod resolve; +mod sub; +pub mod type_variable; +mod undo_log; + +#[must_use] +#[derive(Debug)] +pub struct InferOk<'tcx, T> { + pub value: T, + pub obligations: PredicateObligations<'tcx>, +} +pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>; + +pub type Bound<T> = Option<T>; +pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result" +pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result" + +pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable< + ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>, +>; + +/// This type contains all the things within `InferCtxt` that sit within a +/// `RefCell` and are involved with taking/rolling back snapshots. Snapshot +/// operations are hot enough that we want only one call to `borrow_mut` per +/// call to `start_snapshot` and `rollback_to`. +#[derive(Clone)] +pub struct InferCtxtInner<'tcx> { + /// Cache for projections. This cache is snapshotted along with the infcx. + /// + /// Public so that `traits::project` can use it. + pub projection_cache: traits::ProjectionCacheStorage<'tcx>, + + /// We instantiate `UnificationTable` with `bounds<Ty>` because the types + /// that might instantiate a general type variable have an order, + /// represented by its upper and lower bounds. + type_variable_storage: type_variable::TypeVariableStorage<'tcx>, + + /// Map from const parameter variable to the kind of const it represents. + const_unification_storage: ut::UnificationTableStorage<ty::ConstVid<'tcx>>, + + /// Map from integral variable to the kind of integer it represents. + int_unification_storage: ut::UnificationTableStorage<ty::IntVid>, + + /// Map from floating variable to the kind of float it represents. + float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>, + + /// Tracks the set of region variables and the constraints between them. + /// This is initially `Some(_)` but when + /// `resolve_regions_and_report_errors` is invoked, this gets set to `None` + /// -- further attempts to perform unification, etc., may fail if new + /// region constraints would've been added. + region_constraint_storage: Option<RegionConstraintStorage<'tcx>>, + + /// A set of constraints that regionck must validate. Each + /// constraint has the form `T:'a`, meaning "some type `T` must + /// outlive the lifetime 'a". These constraints derive from + /// instantiated type parameters. So if you had a struct defined + /// like + /// ```ignore (illustrative) + /// struct Foo<T:'static> { ... } + /// ``` + /// then in some expression `let x = Foo { ... }` it will + /// instantiate the type parameter `T` with a fresh type `$0`. At + /// the same time, it will record a region obligation of + /// `$0:'static`. This will get checked later by regionck. (We + /// can't generally check these things right away because we have + /// to wait until types are resolved.) + /// + /// These are stored in a map keyed to the id of the innermost + /// enclosing fn body / static initializer expression. This is + /// because the location where the obligation was incurred can be + /// relevant with respect to which sublifetime assumptions are in + /// place. The reason that we store under the fn-id, and not + /// something more fine-grained, is so that it is easier for + /// regionck to be sure that it has found *all* the region + /// obligations (otherwise, it's easy to fail to walk to a + /// particular node-id). + /// + /// Before running `resolve_regions_and_report_errors`, the creator + /// of the inference context is expected to invoke + /// [`InferCtxt::process_registered_region_obligations`] + /// for each body-id in this map, which will process the + /// obligations within. This is expected to be done 'late enough' + /// that all type inference variables have been bound and so forth. + region_obligations: Vec<RegionObligation<'tcx>>, + + undo_log: InferCtxtUndoLogs<'tcx>, + + /// Caches for opaque type inference. + pub opaque_type_storage: OpaqueTypeStorage<'tcx>, +} + +impl<'tcx> InferCtxtInner<'tcx> { + fn new() -> InferCtxtInner<'tcx> { + InferCtxtInner { + projection_cache: Default::default(), + type_variable_storage: type_variable::TypeVariableStorage::new(), + undo_log: InferCtxtUndoLogs::default(), + const_unification_storage: ut::UnificationTableStorage::new(), + int_unification_storage: ut::UnificationTableStorage::new(), + float_unification_storage: ut::UnificationTableStorage::new(), + region_constraint_storage: Some(RegionConstraintStorage::new()), + region_obligations: vec![], + opaque_type_storage: Default::default(), + } + } + + #[inline] + pub fn region_obligations(&self) -> &[RegionObligation<'tcx>] { + &self.region_obligations + } + + #[inline] + pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> { + self.projection_cache.with_log(&mut self.undo_log) + } + + #[inline] + fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> { + self.type_variable_storage.with_log(&mut self.undo_log) + } + + #[inline] + pub fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> { + self.opaque_type_storage.with_log(&mut self.undo_log) + } + + #[inline] + fn int_unification_table( + &mut self, + ) -> ut::UnificationTable< + ut::InPlace< + ty::IntVid, + &mut ut::UnificationStorage<ty::IntVid>, + &mut InferCtxtUndoLogs<'tcx>, + >, + > { + self.int_unification_storage.with_log(&mut self.undo_log) + } + + #[inline] + fn float_unification_table( + &mut self, + ) -> ut::UnificationTable< + ut::InPlace< + ty::FloatVid, + &mut ut::UnificationStorage<ty::FloatVid>, + &mut InferCtxtUndoLogs<'tcx>, + >, + > { + self.float_unification_storage.with_log(&mut self.undo_log) + } + + #[inline] + fn const_unification_table( + &mut self, + ) -> ut::UnificationTable< + ut::InPlace< + ty::ConstVid<'tcx>, + &mut ut::UnificationStorage<ty::ConstVid<'tcx>>, + &mut InferCtxtUndoLogs<'tcx>, + >, + > { + self.const_unification_storage.with_log(&mut self.undo_log) + } + + #[inline] + pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> { + self.region_constraint_storage + .as_mut() + .expect("region constraints already solved") + .with_log(&mut self.undo_log) + } +} + +#[derive(Clone, Copy, Debug, PartialEq, Eq)] +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, +} + +pub struct InferCtxt<'a, 'tcx> { + pub tcx: TyCtxt<'tcx>, + + /// The `DefId` of the item in whose context we are performing inference or typeck. + /// It is used to check whether an opaque type use is a defining use. + /// + /// If it is `DefiningAnchor::Bubble`, we can't resolve opaque types here and need to bubble up + /// the obligation. This frequently happens for + /// short lived InferCtxt within queries. The opaque type obligations are forwarded + /// to the outside until the end up in an `InferCtxt` for typeck or borrowck. + /// + /// It is default value is `DefiningAnchor::Error`, this way it is easier to catch errors that + /// might come up during inference or typeck. + pub defining_use_anchor: DefiningAnchor, + + /// Whether this inference context should care about region obligations in + /// the root universe. Most notably, this is used during hir typeck as region + /// solving is left to borrowck instead. + pub considering_regions: bool, + + /// During type-checking/inference of a body, `in_progress_typeck_results` + /// contains a reference to the typeck results being built up, which are + /// used for reading closure kinds/signatures as they are inferred, + /// and for error reporting logic to read arbitrary node types. + pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>, + + pub inner: RefCell<InferCtxtInner<'tcx>>, + + /// If set, this flag causes us to skip the 'leak check' during + /// higher-ranked subtyping operations. This flag is a temporary one used + /// to manage the removal of the leak-check: for the time being, we still run the + /// leak-check, but we issue warnings. This flag can only be set to true + /// when entering a snapshot. + skip_leak_check: Cell<bool>, + + /// Once region inference is done, the values for each variable. + lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>, + + /// Caches the results of trait selection. This cache is used + /// for things that have to do with the parameters in scope. + pub selection_cache: select::SelectionCache<'tcx>, + + /// Caches the results of trait evaluation. + pub evaluation_cache: select::EvaluationCache<'tcx>, + + /// the set of predicates on which errors have been reported, to + /// avoid reporting the same error twice. + pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>, + + pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>, + + /// When an error occurs, we want to avoid reporting "derived" + /// errors that are due to this original failure. Normally, we + /// handle this with the `err_count_on_creation` count, which + /// basically just tracks how many errors were reported when we + /// started type-checking a fn and checks to see if any new errors + /// have been reported since then. Not great, but it works. + /// + /// However, when errors originated in other passes -- notably + /// resolve -- this heuristic breaks down. Therefore, we have this + /// auxiliary flag that one can set whenever one creates a + /// type-error that is due to an error in a prior pass. + /// + /// Don't read this flag directly, call `is_tainted_by_errors()` + /// and `set_tainted_by_errors()`. + tainted_by_errors_flag: Cell<bool>, + + /// Track how many errors were reported when this infcx is created. + /// If the number of errors increases, that's also a sign (line + /// `tainted_by_errors`) to avoid reporting certain kinds of errors. + // FIXME(matthewjasper) Merge into `tainted_by_errors_flag` + err_count_on_creation: usize, + + /// This flag is true while there is an active snapshot. + in_snapshot: Cell<bool>, + + /// What is the innermost universe we have created? Starts out as + /// `UniverseIndex::root()` but grows from there as we enter + /// universal quantifiers. + /// + /// N.B., at present, we exclude the universal quantifiers on the + /// item we are type-checking, and just consider those names as + /// part of the root universe. So this would only get incremented + /// when we enter into a higher-ranked (`for<..>`) type or trait + /// bound. + universe: Cell<ty::UniverseIndex>, +} + +/// See the `error_reporting` module for more details. +#[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable)] +pub enum ValuePairs<'tcx> { + Regions(ExpectedFound<ty::Region<'tcx>>), + Terms(ExpectedFound<ty::Term<'tcx>>), + TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>), + PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>), +} + +impl<'tcx> ValuePairs<'tcx> { + pub fn ty(&self) -> Option<(Ty<'tcx>, Ty<'tcx>)> { + if let ValuePairs::Terms(ExpectedFound { + expected: ty::Term::Ty(expected), + found: ty::Term::Ty(found), + }) = self + { + Some((*expected, *found)) + } else { + None + } + } +} + +/// The trace designates the path through inference that we took to +/// encounter an error or subtyping constraint. +/// +/// See the `error_reporting` module for more details. +#[derive(Clone, Debug)] +pub struct TypeTrace<'tcx> { + pub cause: ObligationCause<'tcx>, + pub values: ValuePairs<'tcx>, +} + +/// The origin of a `r1 <= r2` constraint. +/// +/// See `error_reporting` module for more details +#[derive(Clone, Debug)] +pub enum SubregionOrigin<'tcx> { + /// Arose from a subtyping relation + Subtype(Box<TypeTrace<'tcx>>), + + /// When casting `&'a T` to an `&'b Trait` object, + /// relating `'a` to `'b` + RelateObjectBound(Span), + + /// Some type parameter was instantiated with the given type, + /// and that type must outlive some region. + RelateParamBound(Span, Ty<'tcx>, Option<Span>), + + /// The given region parameter was instantiated with a region + /// that must outlive some other region. + RelateRegionParamBound(Span), + + /// Creating a pointer `b` to contents of another reference + Reborrow(Span), + + /// Creating a pointer `b` to contents of an upvar + ReborrowUpvar(Span, ty::UpvarId), + + /// Data with type `Ty<'tcx>` was borrowed + DataBorrowed(Ty<'tcx>, Span), + + /// (&'a &'b T) where a >= b + ReferenceOutlivesReferent(Ty<'tcx>, Span), + + /// Comparing the signature and requirements of an impl method against + /// the containing trait. + CompareImplItemObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId }, + + /// Checking that the bounds of a trait's associated type hold for a given impl + CheckAssociatedTypeBounds { + parent: Box<SubregionOrigin<'tcx>>, + impl_item_def_id: LocalDefId, + trait_item_def_id: DefId, + }, +} + +// `SubregionOrigin` 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!(SubregionOrigin<'_>, 32); + +/// Times when we replace late-bound regions with variables: +#[derive(Clone, Copy, Debug)] +pub enum LateBoundRegionConversionTime { + /// when a fn is called + FnCall, + + /// when two higher-ranked types are compared + HigherRankedType, + + /// when projecting an associated type + AssocTypeProjection(DefId), +} + +/// Reasons to create a region inference variable +/// +/// See `error_reporting` module for more details +#[derive(Copy, Clone, Debug)] +pub enum RegionVariableOrigin { + /// Region variables created for ill-categorized reasons, + /// mostly indicates places in need of refactoring + MiscVariable(Span), + + /// Regions created by a `&P` or `[...]` pattern + PatternRegion(Span), + + /// Regions created by `&` operator + AddrOfRegion(Span), + + /// Regions created as part of an autoref of a method receiver + Autoref(Span), + + /// Regions created as part of an automatic coercion + Coercion(Span), + + /// Region variables created as the values for early-bound regions + EarlyBoundRegion(Span, Symbol), + + /// Region variables created for bound regions + /// in a function or method that is called + LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime), + + UpvarRegion(ty::UpvarId, Span), + + /// This origin is used for the inference variables that we create + /// during NLL region processing. + Nll(NllRegionVariableOrigin), +} + +#[derive(Copy, Clone, Debug)] +pub enum NllRegionVariableOrigin { + /// During NLL region processing, we create variables for free + /// regions that we encounter in the function signature and + /// elsewhere. This origin indices we've got one of those. + FreeRegion, + + /// "Universal" instantiation of a higher-ranked region (e.g., + /// from a `for<'a> T` binder). Meant to represent "any region". + Placeholder(ty::PlaceholderRegion), + + Existential { + /// If this is true, then this variable was created to represent a lifetime + /// bound in a `for` binder. For example, it might have been created to + /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`. + /// Such variables are created when we are trying to figure out if there + /// is any valid instantiation of `'a` that could fit into some scenario. + /// + /// This is used to inform error reporting: in the case that we are trying to + /// determine whether there is any valid instantiation of a `'a` variable that meets + /// some constraint C, we want to blame the "source" of that `for` type, + /// rather than blaming the source of the constraint C. + from_forall: bool, + }, +} + +// FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`. +#[derive(Copy, Clone, Debug)] +pub enum FixupError<'tcx> { + UnresolvedIntTy(IntVid), + UnresolvedFloatTy(FloatVid), + UnresolvedTy(TyVid), + UnresolvedConst(ConstVid<'tcx>), +} + +/// See the `region_obligations` field for more information. +#[derive(Clone)] +pub struct RegionObligation<'tcx> { + pub sub_region: ty::Region<'tcx>, + pub sup_type: Ty<'tcx>, + pub origin: SubregionOrigin<'tcx>, +} + +impl<'tcx> fmt::Display for FixupError<'tcx> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + use self::FixupError::*; + + match *self { + UnresolvedIntTy(_) => write!( + f, + "cannot determine the type of this integer; \ + add a suffix to specify the type explicitly" + ), + UnresolvedFloatTy(_) => write!( + f, + "cannot determine the type of this number; \ + add a suffix to specify the type explicitly" + ), + UnresolvedTy(_) => write!(f, "unconstrained type"), + UnresolvedConst(_) => write!(f, "unconstrained const value"), + } + } +} + +/// A temporary returned by `tcx.infer_ctxt()`. This is necessary +/// for multiple `InferCtxt` to share the same `in_progress_typeck_results` +/// without using `Rc` or something similar. +pub struct InferCtxtBuilder<'tcx> { + tcx: TyCtxt<'tcx>, + defining_use_anchor: DefiningAnchor, + considering_regions: bool, + fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>, +} + +pub trait TyCtxtInferExt<'tcx> { + fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>; +} + +impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> { + fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> { + InferCtxtBuilder { + tcx: self, + defining_use_anchor: DefiningAnchor::Error, + considering_regions: true, + fresh_typeck_results: None, + } + } +} + +impl<'tcx> InferCtxtBuilder<'tcx> { + /// Used only by `rustc_typeck` during body type-checking/inference, + /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`. + /// Will also change the scope for opaque type defining use checks to the given owner. + pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self { + self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner))); + self.with_opaque_type_inference(DefiningAnchor::Bind(table_owner)) + } + + /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types, + /// you need to call this function. Otherwise the opaque type will be treated opaquely. + /// + /// It is only meant to be called in two places, for typeck + /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used + /// in mir borrowck. + pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor) -> Self { + self.defining_use_anchor = defining_use_anchor; + self + } + + pub fn ignoring_regions(mut self) -> Self { + self.considering_regions = false; + self + } + + /// Given a canonical value `C` as a starting point, create an + /// inference context that contains each of the bound values + /// within instantiated as a fresh variable. The `f` closure is + /// invoked with the new infcx, along with the instantiated value + /// `V` and a substitution `S`. This substitution `S` maps from + /// the bound values in `C` to their instantiated values in `V` + /// (in other words, `S(C) = V`). + pub fn enter_with_canonical<T, R>( + &mut self, + span: Span, + canonical: &Canonical<'tcx, T>, + f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R, + ) -> R + where + T: TypeFoldable<'tcx>, + { + self.enter(|infcx| { + let (value, subst) = + infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical); + f(infcx, value, subst) + }) + } + + pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R { + let InferCtxtBuilder { + tcx, + defining_use_anchor, + considering_regions, + ref fresh_typeck_results, + } = *self; + let in_progress_typeck_results = fresh_typeck_results.as_ref(); + f(InferCtxt { + tcx, + defining_use_anchor, + considering_regions, + in_progress_typeck_results, + inner: RefCell::new(InferCtxtInner::new()), + lexical_region_resolutions: RefCell::new(None), + selection_cache: Default::default(), + evaluation_cache: Default::default(), + reported_trait_errors: Default::default(), + reported_closure_mismatch: Default::default(), + tainted_by_errors_flag: Cell::new(false), + err_count_on_creation: tcx.sess.err_count(), + in_snapshot: Cell::new(false), + skip_leak_check: Cell::new(false), + universe: Cell::new(ty::UniverseIndex::ROOT), + }) + } +} + +impl<'tcx, T> InferOk<'tcx, T> { + pub fn unit(self) -> InferOk<'tcx, ()> { + InferOk { value: (), obligations: self.obligations } + } + + /// Extracts `value`, registering any obligations into `fulfill_cx`. + pub fn into_value_registering_obligations( + self, + infcx: &InferCtxt<'_, 'tcx>, + fulfill_cx: &mut dyn TraitEngine<'tcx>, + ) -> T { + let InferOk { value, obligations } = self; + fulfill_cx.register_predicate_obligations(infcx, obligations); + value + } +} + +impl<'tcx> InferOk<'tcx, ()> { + pub fn into_obligations(self) -> PredicateObligations<'tcx> { + self.obligations + } +} + +#[must_use = "once you start a snapshot, you should always consume it"] +pub struct CombinedSnapshot<'a, 'tcx> { + undo_snapshot: Snapshot<'tcx>, + region_constraints_snapshot: RegionSnapshot, + universe: ty::UniverseIndex, + was_in_snapshot: bool, + _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>, +} + +impl<'a, 'tcx> InferCtxt<'a, 'tcx> { + /// calls `tcx.try_unify_abstract_consts` after + /// canonicalizing the consts. + #[instrument(skip(self), level = "debug")] + pub fn try_unify_abstract_consts( + &self, + a: ty::Unevaluated<'tcx, ()>, + b: ty::Unevaluated<'tcx, ()>, + param_env: ty::ParamEnv<'tcx>, + ) -> bool { + // Reject any attempt to unify two unevaluated constants that contain inference + // variables, since inference variables in queries lead to ICEs. + if a.substs.has_infer_types_or_consts() + || b.substs.has_infer_types_or_consts() + || param_env.has_infer_types_or_consts() + { + debug!("a or b or param_env contain infer vars in its substs -> cannot unify"); + return false; + } + + let param_env_and = param_env.and((a, b)); + let erased = self.tcx.erase_regions(param_env_and); + debug!("after erase_regions: {:?}", erased); + + self.tcx.try_unify_abstract_consts(erased) + } + + pub fn is_in_snapshot(&self) -> bool { + self.in_snapshot.get() + } + + pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T { + t.fold_with(&mut self.freshener()) + } + + /// Returns the origin of the type variable identified by `vid`, or `None` + /// if this is not a type variable. + /// + /// No attempt is made to resolve `ty`. + pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> { + match *ty.kind() { + ty::Infer(ty::TyVar(vid)) => { + Some(*self.inner.borrow_mut().type_variables().var_origin(vid)) + } + _ => None, + } + } + + pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> { + freshen::TypeFreshener::new(self, false) + } + + /// Like `freshener`, but does not replace `'static` regions. + pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> { + freshen::TypeFreshener::new(self, true) + } + + pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> { + let mut inner = self.inner.borrow_mut(); + let mut vars: Vec<Ty<'_>> = inner + .type_variables() + .unsolved_variables() + .into_iter() + .map(|t| self.tcx.mk_ty_var(t)) + .collect(); + vars.extend( + (0..inner.int_unification_table().len()) + .map(|i| ty::IntVid { index: i as u32 }) + .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none()) + .map(|v| self.tcx.mk_int_var(v)), + ); + vars.extend( + (0..inner.float_unification_table().len()) + .map(|i| ty::FloatVid { index: i as u32 }) + .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none()) + .map(|v| self.tcx.mk_float_var(v)), + ); + vars + } + + fn combine_fields( + &'a self, + trace: TypeTrace<'tcx>, + param_env: ty::ParamEnv<'tcx>, + define_opaque_types: bool, + ) -> CombineFields<'a, 'tcx> { + CombineFields { + infcx: self, + trace, + cause: None, + param_env, + obligations: PredicateObligations::new(), + define_opaque_types, + } + } + + /// Clear the "currently in a snapshot" flag, invoke the closure, + /// then restore the flag to its original value. This flag is a + /// debugging measure designed to detect cases where we start a + /// snapshot, create type variables, and register obligations + /// which may involve those type variables in the fulfillment cx, + /// potentially leaving "dangling type variables" behind. + /// In such cases, an assertion will fail when attempting to + /// register obligations, within a snapshot. Very useful, much + /// better than grovelling through megabytes of `RUSTC_LOG` output. + /// + /// HOWEVER, in some cases the flag is unhelpful. In particular, we + /// sometimes create a "mini-fulfilment-cx" in which we enroll + /// obligations. As long as this fulfillment cx is fully drained + /// before we return, this is not a problem, as there won't be any + /// escaping obligations in the main cx. In those cases, you can + /// use this function. + pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R + where + F: FnOnce(&Self) -> R, + { + let flag = self.in_snapshot.replace(false); + let result = func(self); + self.in_snapshot.set(flag); + result + } + + fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> { + debug!("start_snapshot()"); + + let in_snapshot = self.in_snapshot.replace(true); + + let mut inner = self.inner.borrow_mut(); + + CombinedSnapshot { + undo_snapshot: inner.undo_log.start_snapshot(), + region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(), + universe: self.universe(), + was_in_snapshot: in_snapshot, + // Borrow typeck results "in progress" (i.e., during typeck) + // to ban writes from within a snapshot to them. + _in_progress_typeck_results: self + .in_progress_typeck_results + .map(|typeck_results| typeck_results.borrow()), + } + } + + #[instrument(skip(self, snapshot), level = "debug")] + fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) { + let CombinedSnapshot { + undo_snapshot, + region_constraints_snapshot, + universe, + was_in_snapshot, + _in_progress_typeck_results, + } = snapshot; + + self.in_snapshot.set(was_in_snapshot); + self.universe.set(universe); + + let mut inner = self.inner.borrow_mut(); + inner.rollback_to(undo_snapshot); + inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot); + } + + #[instrument(skip(self, snapshot), level = "debug")] + fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) { + let CombinedSnapshot { + undo_snapshot, + region_constraints_snapshot: _, + universe: _, + was_in_snapshot, + _in_progress_typeck_results, + } = snapshot; + + self.in_snapshot.set(was_in_snapshot); + + self.inner.borrow_mut().commit(undo_snapshot); + } + + /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`. + #[instrument(skip(self, f), level = "debug")] + pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E> + where + F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>, + { + let snapshot = self.start_snapshot(); + let r = f(&snapshot); + debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok()); + match r { + Ok(_) => { + self.commit_from(snapshot); + } + Err(_) => { + self.rollback_to("commit_if_ok -- error", snapshot); + } + } + r + } + + /// Execute `f` then unroll any bindings it creates. + #[instrument(skip(self, f), level = "debug")] + pub fn probe<R, F>(&self, f: F) -> R + where + F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R, + { + let snapshot = self.start_snapshot(); + let r = f(&snapshot); + self.rollback_to("probe", snapshot); + r + } + + /// If `should_skip` is true, then execute `f` then unroll any bindings it creates. + #[instrument(skip(self, f), level = "debug")] + pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R + where + F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R, + { + let snapshot = self.start_snapshot(); + let was_skip_leak_check = self.skip_leak_check.get(); + if should_skip { + self.skip_leak_check.set(true); + } + let r = f(&snapshot); + self.rollback_to("probe", snapshot); + self.skip_leak_check.set(was_skip_leak_check); + r + } + + /// Scan the constraints produced since `snapshot` began and returns: + /// + /// - `None` -- if none of them involve "region outlives" constraints + /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder + /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders + pub fn region_constraints_added_in_snapshot( + &self, + snapshot: &CombinedSnapshot<'a, 'tcx>, + ) -> Option<bool> { + self.inner + .borrow_mut() + .unwrap_region_constraints() + .region_constraints_added_in_snapshot(&snapshot.undo_snapshot) + } + + pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'a, 'tcx>) -> bool { + self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot) + } + + pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) { + self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup); + } + + pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx> + where + T: at::ToTrace<'tcx>, + { + let origin = &ObligationCause::dummy(); + self.probe(|_| { + self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| { + // Ignore obligations, since we are unrolling + // everything anyway. + }) + }) + } + + pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx> + where + T: at::ToTrace<'tcx>, + { + let origin = &ObligationCause::dummy(); + self.probe(|_| { + self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| { + // Ignore obligations, since we are unrolling + // everything anyway. + }) + }) + } + + #[instrument(skip(self), level = "debug")] + pub fn sub_regions( + &self, + origin: SubregionOrigin<'tcx>, + a: ty::Region<'tcx>, + b: ty::Region<'tcx>, + ) { + self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b); + } + + /// Require that the region `r` be equal to one of the regions in + /// the set `regions`. + #[instrument(skip(self), level = "debug")] + pub fn member_constraint( + &self, + key: ty::OpaqueTypeKey<'tcx>, + definition_span: Span, + hidden_ty: Ty<'tcx>, + region: ty::Region<'tcx>, + in_regions: &Lrc<Vec<ty::Region<'tcx>>>, + ) { + self.inner.borrow_mut().unwrap_region_constraints().member_constraint( + key, + definition_span, + hidden_ty, + region, + in_regions, + ); + } + + /// Processes a `Coerce` predicate from the fulfillment context. + /// This is NOT the preferred way to handle coercion, which is to + /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`). + /// + /// This method here is actually a fallback that winds up being + /// invoked when `FnCtxt::coerce` encounters unresolved type variables + /// and records a coercion predicate. Presently, this method is equivalent + /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up + /// actually requiring `a <: b`. This is of course a valid coercion, + /// but it's not as flexible as `FnCtxt::coerce` would be. + /// + /// (We may refactor this in the future, but there are a number of + /// practical obstacles. Among other things, `FnCtxt::coerce` presently + /// records adjustments that are required on the HIR in order to perform + /// the coercion, and we don't currently have a way to manage that.) + pub fn coerce_predicate( + &self, + cause: &ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + predicate: ty::PolyCoercePredicate<'tcx>, + ) -> Option<InferResult<'tcx, ()>> { + let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate { + a_is_expected: false, // when coercing from `a` to `b`, `b` is expected + a: p.a, + b: p.b, + }); + self.subtype_predicate(cause, param_env, subtype_predicate) + } + + pub fn subtype_predicate( + &self, + cause: &ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + predicate: ty::PolySubtypePredicate<'tcx>, + ) -> Option<InferResult<'tcx, ()>> { + // Check for two unresolved inference variables, in which case we can + // make no progress. This is partly a micro-optimization, but it's + // also an opportunity to "sub-unify" the variables. This isn't + // *necessary* to prevent cycles, because they would eventually be sub-unified + // anyhow during generalization, but it helps with diagnostics (we can detect + // earlier that they are sub-unified). + // + // Note that we can just skip the binders here because + // type variables can't (at present, at + // least) capture any of the things bound by this binder. + // + // Note that this sub here is not just for diagnostics - it has semantic + // effects as well. + let r_a = self.shallow_resolve(predicate.skip_binder().a); + let r_b = self.shallow_resolve(predicate.skip_binder().b); + match (r_a.kind(), r_b.kind()) { + (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => { + self.inner.borrow_mut().type_variables().sub(a_vid, b_vid); + return None; + } + _ => {} + } + + Some(self.commit_if_ok(|_snapshot| { + let ty::SubtypePredicate { a_is_expected, a, b } = + self.replace_bound_vars_with_placeholders(predicate); + + let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?; + + Ok(ok.unit()) + })) + } + + pub fn region_outlives_predicate( + &self, + cause: &traits::ObligationCause<'tcx>, + predicate: ty::PolyRegionOutlivesPredicate<'tcx>, + ) { + let ty::OutlivesPredicate(r_a, r_b) = self.replace_bound_vars_with_placeholders(predicate); + let origin = + SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span)); + self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b` + } + + /// Number of type variables created so far. + pub fn num_ty_vars(&self) -> usize { + self.inner.borrow_mut().type_variables().num_vars() + } + + pub fn next_ty_var_id(&self, origin: TypeVariableOrigin) -> TyVid { + self.inner.borrow_mut().type_variables().new_var(self.universe(), origin) + } + + pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> { + self.tcx.mk_ty_var(self.next_ty_var_id(origin)) + } + + pub fn next_ty_var_id_in_universe( + &self, + origin: TypeVariableOrigin, + universe: ty::UniverseIndex, + ) -> TyVid { + self.inner.borrow_mut().type_variables().new_var(universe, origin) + } + + pub fn next_ty_var_in_universe( + &self, + origin: TypeVariableOrigin, + universe: ty::UniverseIndex, + ) -> Ty<'tcx> { + let vid = self.next_ty_var_id_in_universe(origin, universe); + self.tcx.mk_ty_var(vid) + } + + pub fn next_const_var(&self, ty: Ty<'tcx>, origin: ConstVariableOrigin) -> ty::Const<'tcx> { + self.tcx.mk_const_var(self.next_const_var_id(origin), ty) + } + + pub fn next_const_var_in_universe( + &self, + ty: Ty<'tcx>, + origin: ConstVariableOrigin, + universe: ty::UniverseIndex, + ) -> ty::Const<'tcx> { + let vid = self + .inner + .borrow_mut() + .const_unification_table() + .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } }); + self.tcx.mk_const_var(vid, ty) + } + + pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> { + self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue { + origin, + val: ConstVariableValue::Unknown { universe: self.universe() }, + }) + } + + fn next_int_var_id(&self) -> IntVid { + self.inner.borrow_mut().int_unification_table().new_key(None) + } + + pub fn next_int_var(&self) -> Ty<'tcx> { + self.tcx.mk_int_var(self.next_int_var_id()) + } + + fn next_float_var_id(&self) -> FloatVid { + self.inner.borrow_mut().float_unification_table().new_key(None) + } + + pub fn next_float_var(&self) -> Ty<'tcx> { + self.tcx.mk_float_var(self.next_float_var_id()) + } + + /// Creates a fresh region variable with the next available index. + /// The variable will be created in the maximum universe created + /// thus far, allowing it to name any region created thus far. + pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> { + self.next_region_var_in_universe(origin, self.universe()) + } + + /// Creates a fresh region variable with the next available index + /// in the given universe; typically, you can use + /// `next_region_var` and just use the maximal universe. + pub fn next_region_var_in_universe( + &self, + origin: RegionVariableOrigin, + universe: ty::UniverseIndex, + ) -> ty::Region<'tcx> { + let region_var = + self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin); + self.tcx.mk_region(ty::ReVar(region_var)) + } + + /// Return the universe that the region `r` was created in. For + /// most regions (e.g., `'static`, named regions from the user, + /// etc) this is the root universe U0. For inference variables or + /// placeholders, however, it will return the universe which which + /// they are associated. + pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex { + self.inner.borrow_mut().unwrap_region_constraints().universe(r) + } + + /// Number of region variables created so far. + pub fn num_region_vars(&self) -> usize { + self.inner.borrow_mut().unwrap_region_constraints().num_region_vars() + } + + /// Just a convenient wrapper of `next_region_var` for using during NLL. + pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> { + self.next_region_var(RegionVariableOrigin::Nll(origin)) + } + + /// Just a convenient wrapper of `next_region_var` for using during NLL. + pub fn next_nll_region_var_in_universe( + &self, + origin: NllRegionVariableOrigin, + universe: ty::UniverseIndex, + ) -> ty::Region<'tcx> { + self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe) + } + + pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> { + match param.kind { + GenericParamDefKind::Lifetime => { + // Create a region inference variable for the given + // region parameter definition. + self.next_region_var(EarlyBoundRegion(span, param.name)).into() + } + GenericParamDefKind::Type { .. } => { + // Create a type inference variable for the given + // type parameter definition. The substitutions are + // for actual parameters that may be referred to by + // the default of this type parameter, if it exists. + // e.g., `struct Foo<A, B, C = (A, B)>(...);` when + // used in a path such as `Foo::<T, U>::new()` will + // use an inference variable for `C` with `[T, U]` + // as the substitutions for the default, `(T, U)`. + let ty_var_id = self.inner.borrow_mut().type_variables().new_var( + self.universe(), + TypeVariableOrigin { + kind: TypeVariableOriginKind::TypeParameterDefinition( + param.name, + Some(param.def_id), + ), + span, + }, + ); + + self.tcx.mk_ty_var(ty_var_id).into() + } + GenericParamDefKind::Const { .. } => { + let origin = ConstVariableOrigin { + kind: ConstVariableOriginKind::ConstParameterDefinition( + param.name, + param.def_id, + ), + span, + }; + let const_var_id = + self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue { + origin, + val: ConstVariableValue::Unknown { universe: self.universe() }, + }); + self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into() + } + } + } + + /// Given a set of generics defined on a type or impl, returns a substitution mapping each + /// type/region parameter to a fresh inference variable. + pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> { + InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param)) + } + + /// Returns `true` if errors have been reported since this infcx was + /// created. This is sometimes used as a heuristic to skip + /// reporting errors that often occur as a result of earlier + /// errors, but where it's hard to be 100% sure (e.g., unresolved + /// inference variables, regionck errors). + pub fn is_tainted_by_errors(&self) -> bool { + debug!( + "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \ + tainted_by_errors_flag={})", + self.tcx.sess.err_count(), + self.err_count_on_creation, + self.tainted_by_errors_flag.get() + ); + + if self.tcx.sess.err_count() > self.err_count_on_creation { + return true; // errors reported since this infcx was made + } + self.tainted_by_errors_flag.get() + } + + /// Set the "tainted by errors" flag to true. We call this when we + /// observe an error from a prior pass. + pub fn set_tainted_by_errors(&self) { + debug!("set_tainted_by_errors()"); + self.tainted_by_errors_flag.set(true) + } + + pub fn skip_region_resolution(&self) { + let (var_infos, _) = { + let mut inner = self.inner.borrow_mut(); + let inner = &mut *inner; + // Note: `inner.region_obligations` may not be empty, because we + // didn't necessarily call `process_registered_region_obligations`. + // This is okay, because that doesn't introduce new vars. + inner + .region_constraint_storage + .take() + .expect("regions already resolved") + .with_log(&mut inner.undo_log) + .into_infos_and_data() + }; + + let lexical_region_resolutions = LexicalRegionResolutions { + values: rustc_index::vec::IndexVec::from_elem_n( + crate::infer::lexical_region_resolve::VarValue::Value(self.tcx.lifetimes.re_erased), + var_infos.len(), + ), + }; + + let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions)); + assert!(old_value.is_none()); + } + + /// Process the region constraints and return any any errors that + /// result. After this, no more unification operations should be + /// done -- or the compiler will panic -- but it is legal to use + /// `resolve_vars_if_possible` as well as `fully_resolve`. + pub fn resolve_regions( + &self, + outlives_env: &OutlivesEnvironment<'tcx>, + ) -> Vec<RegionResolutionError<'tcx>> { + let (var_infos, data) = { + let mut inner = self.inner.borrow_mut(); + let inner = &mut *inner; + assert!( + self.is_tainted_by_errors() || inner.region_obligations.is_empty(), + "region_obligations not empty: {:#?}", + inner.region_obligations + ); + inner + .region_constraint_storage + .take() + .expect("regions already resolved") + .with_log(&mut inner.undo_log) + .into_infos_and_data() + }; + + let region_rels = &RegionRelations::new(self.tcx, outlives_env.free_region_map()); + + let (lexical_region_resolutions, errors) = + lexical_region_resolve::resolve(outlives_env.param_env, region_rels, var_infos, data); + + let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions)); + assert!(old_value.is_none()); + + errors + } + + /// Process the region constraints and report any errors that + /// result. After this, no more unification operations should be + /// done -- or the compiler will panic -- but it is legal to use + /// `resolve_vars_if_possible` as well as `fully_resolve`. + /// + /// Make sure to call [`InferCtxt::process_registered_region_obligations`] + /// first, or preferrably use [`InferCtxt::check_region_obligations_and_report_errors`] + /// to do both of these operations together. + pub fn resolve_regions_and_report_errors( + &self, + generic_param_scope: LocalDefId, + outlives_env: &OutlivesEnvironment<'tcx>, + ) { + let errors = self.resolve_regions(outlives_env); + + if !self.is_tainted_by_errors() { + // As a heuristic, just skip reporting region errors + // altogether if other errors have been reported while + // this infcx was in use. This is totally hokey but + // otherwise we have a hard time separating legit region + // errors from silly ones. + self.report_region_errors(generic_param_scope, &errors); + } + } + + /// Obtains (and clears) the current set of region + /// constraints. The inference context is still usable: further + /// unifications will simply add new constraints. + /// + /// This method is not meant to be used with normal lexical region + /// resolution. Rather, it is used in the NLL mode as a kind of + /// interim hack: basically we run normal type-check and generate + /// region constraints as normal, but then we take them and + /// translate them into the form that the NLL solver + /// understands. See the NLL module for mode details. + pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> { + assert!( + self.inner.borrow().region_obligations.is_empty(), + "region_obligations not empty: {:#?}", + self.inner.borrow().region_obligations + ); + + self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data() + } + + /// Gives temporary access to the region constraint data. + pub fn with_region_constraints<R>( + &self, + op: impl FnOnce(&RegionConstraintData<'tcx>) -> R, + ) -> R { + let mut inner = self.inner.borrow_mut(); + op(inner.unwrap_region_constraints().data()) + } + + pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin { + let mut inner = self.inner.borrow_mut(); + let inner = &mut *inner; + inner + .region_constraint_storage + .as_mut() + .expect("regions already resolved") + .with_log(&mut inner.undo_log) + .var_origin(vid) + } + + /// Takes ownership of the list of variable regions. This implies + /// that all the region constraints have already been taken, and + /// hence that `resolve_regions_and_report_errors` can never be + /// called. This is used only during NLL processing to "hand off" ownership + /// of the set of region variables into the NLL region context. + pub fn take_region_var_origins(&self) -> VarInfos { + let mut inner = self.inner.borrow_mut(); + let (var_infos, data) = inner + .region_constraint_storage + .take() + .expect("regions already resolved") + .with_log(&mut inner.undo_log) + .into_infos_and_data(); + assert!(data.is_empty()); + var_infos + } + + pub fn ty_to_string(&self, t: Ty<'tcx>) -> String { + self.resolve_vars_if_possible(t).to_string() + } + + /// If `TyVar(vid)` resolves to a type, return that type. Else, return the + /// universe index of `TyVar(vid)`. + pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> { + use self::type_variable::TypeVariableValue; + + match self.inner.borrow_mut().type_variables().probe(vid) { + TypeVariableValue::Known { value } => Ok(value), + TypeVariableValue::Unknown { universe } => Err(universe), + } + } + + /// Resolve any type variables found in `value` -- but only one + /// level. So, if the variable `?X` is bound to some type + /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may + /// itself be bound to a type). + /// + /// Useful when you only need to inspect the outermost level of + /// the type and don't care about nested types (or perhaps you + /// will be resolving them as well, e.g. in a loop). + pub fn shallow_resolve<T>(&self, value: T) -> T + where + T: TypeFoldable<'tcx>, + { + value.fold_with(&mut ShallowResolver { infcx: self }) + } + + pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid { + self.inner.borrow_mut().type_variables().root_var(var) + } + + /// Where possible, replaces type/const variables in + /// `value` with their final value. Note that region variables + /// are unaffected. If a type/const variable has not been unified, it + /// is left as is. This is an idempotent operation that does + /// not affect inference state in any way and so you can do it + /// at will. + pub fn resolve_vars_if_possible<T>(&self, value: T) -> T + where + T: TypeFoldable<'tcx>, + { + if !value.needs_infer() { + return value; // Avoid duplicated subst-folding. + } + let mut r = resolve::OpportunisticVarResolver::new(self); + value.fold_with(&mut r) + } + + pub fn resolve_numeric_literals_with_default<T>(&self, value: T) -> T + where + T: TypeFoldable<'tcx>, + { + if !value.needs_infer() { + return value; // Avoid duplicated subst-folding. + } + let mut r = InferenceLiteralEraser { tcx: self.tcx }; + value.fold_with(&mut r) + } + + /// Returns the first unresolved variable contained in `T`. In the + /// process of visiting `T`, this will resolve (where possible) + /// type variables in `T`, but it never constructs the final, + /// resolved type, so it's more efficient than + /// `resolve_vars_if_possible()`. + pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)> + where + T: TypeVisitable<'tcx>, + { + value.visit_with(&mut resolve::UnresolvedTypeFinder::new(self)).break_value() + } + + pub fn probe_const_var( + &self, + vid: ty::ConstVid<'tcx>, + ) -> Result<ty::Const<'tcx>, ty::UniverseIndex> { + match self.inner.borrow_mut().const_unification_table().probe_value(vid).val { + ConstVariableValue::Known { value } => Ok(value), + ConstVariableValue::Unknown { universe } => Err(universe), + } + } + + pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: T) -> FixupResult<'tcx, T> { + /*! + * Attempts to resolve all type/region/const variables in + * `value`. Region inference must have been run already (e.g., + * by calling `resolve_regions_and_report_errors`). If some + * variable was never unified, an `Err` results. + * + * This method is idempotent, but it not typically not invoked + * except during the writeback phase. + */ + + resolve::fully_resolve(self, value) + } + + // [Note-Type-error-reporting] + // An invariant is that anytime the expected or actual type is Error (the special + // error type, meaning that an error occurred when typechecking this expression), + // this is a derived error. The error cascaded from another error (that was already + // reported), so it's not useful to display it to the user. + // The following methods implement this logic. + // They check if either the actual or expected type is Error, and don't print the error + // in this case. The typechecker should only ever report type errors involving mismatched + // types using one of these methods, and should not call span_err directly for such + // errors. + + pub fn type_error_struct_with_diag<M>( + &self, + sp: Span, + mk_diag: M, + actual_ty: Ty<'tcx>, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> + where + M: FnOnce(String) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>, + { + let actual_ty = self.resolve_vars_if_possible(actual_ty); + debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty); + + let mut err = mk_diag(self.ty_to_string(actual_ty)); + + // Don't report an error if actual type is `Error`. + if actual_ty.references_error() { + err.downgrade_to_delayed_bug(); + } + + err + } + + pub fn report_mismatched_types( + &self, + cause: &ObligationCause<'tcx>, + expected: Ty<'tcx>, + actual: Ty<'tcx>, + err: TypeError<'tcx>, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + let trace = TypeTrace::types(cause, true, expected, actual); + self.report_and_explain_type_error(trace, &err) + } + + pub fn report_mismatched_consts( + &self, + cause: &ObligationCause<'tcx>, + expected: ty::Const<'tcx>, + actual: ty::Const<'tcx>, + err: TypeError<'tcx>, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + let trace = TypeTrace::consts(cause, true, expected, actual); + self.report_and_explain_type_error(trace, &err) + } + + pub fn replace_bound_vars_with_fresh_vars<T>( + &self, + span: Span, + lbrct: LateBoundRegionConversionTime, + value: ty::Binder<'tcx, T>, + ) -> T + where + T: TypeFoldable<'tcx> + Copy, + { + if let Some(inner) = value.no_bound_vars() { + return inner; + } + + struct ToFreshVars<'a, 'tcx> { + infcx: &'a InferCtxt<'a, 'tcx>, + span: Span, + lbrct: LateBoundRegionConversionTime, + map: FxHashMap<ty::BoundVar, ty::GenericArg<'tcx>>, + } + + impl<'tcx> BoundVarReplacerDelegate<'tcx> for ToFreshVars<'_, 'tcx> { + fn replace_region(&mut self, br: ty::BoundRegion) -> ty::Region<'tcx> { + self.map + .entry(br.var) + .or_insert_with(|| { + self.infcx + .next_region_var(LateBoundRegion(self.span, br.kind, self.lbrct)) + .into() + }) + .expect_region() + } + fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> { + self.map + .entry(bt.var) + .or_insert_with(|| { + self.infcx + .next_ty_var(TypeVariableOrigin { + kind: TypeVariableOriginKind::MiscVariable, + span: self.span, + }) + .into() + }) + .expect_ty() + } + fn replace_const(&mut self, bv: ty::BoundVar, ty: Ty<'tcx>) -> ty::Const<'tcx> { + self.map + .entry(bv) + .or_insert_with(|| { + self.infcx + .next_const_var( + ty, + ConstVariableOrigin { + kind: ConstVariableOriginKind::MiscVariable, + span: self.span, + }, + ) + .into() + }) + .expect_const() + } + } + let delegate = ToFreshVars { infcx: self, span, lbrct, map: Default::default() }; + self.tcx.replace_bound_vars_uncached(value, delegate) + } + + /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method. + pub fn verify_generic_bound( + &self, + origin: SubregionOrigin<'tcx>, + kind: GenericKind<'tcx>, + a: ty::Region<'tcx>, + bound: VerifyBound<'tcx>, + ) { + debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound); + + self.inner + .borrow_mut() + .unwrap_region_constraints() + .verify_generic_bound(origin, kind, a, bound); + } + + /// Obtains the latest type of the given closure; this may be a + /// closure in the current function, in which case its + /// `ClosureKind` may not yet be known. + pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> { + let closure_kind_ty = closure_substs.as_closure().kind_ty(); + let closure_kind_ty = self.shallow_resolve(closure_kind_ty); + closure_kind_ty.to_opt_closure_kind() + } + + /// Clears the selection, evaluation, and projection caches. This is useful when + /// repeatedly attempting to select an `Obligation` while changing only + /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing. + pub fn clear_caches(&self) { + self.selection_cache.clear(); + self.evaluation_cache.clear(); + self.inner.borrow_mut().projection_cache().clear(); + } + + pub fn universe(&self) -> ty::UniverseIndex { + self.universe.get() + } + + /// Creates and return a fresh universe that extends all previous + /// universes. Updates `self.universe` to that new universe. + pub fn create_next_universe(&self) -> ty::UniverseIndex { + let u = self.universe.get().next_universe(); + self.universe.set(u); + u + } + + pub fn try_const_eval_resolve( + &self, + param_env: ty::ParamEnv<'tcx>, + unevaluated: ty::Unevaluated<'tcx>, + ty: Ty<'tcx>, + span: Option<Span>, + ) -> Result<ty::Const<'tcx>, ErrorHandled> { + match self.const_eval_resolve(param_env, unevaluated, span) { + Ok(Some(val)) => Ok(ty::Const::from_value(self.tcx, val, ty)), + Ok(None) => { + let tcx = self.tcx; + let def_id = unevaluated.def.did; + span_bug!( + tcx.def_span(def_id), + "unable to construct a constant value for the unevaluated constant {:?}", + unevaluated + ); + } + Err(err) => Err(err), + } + } + + /// Resolves and evaluates a constant. + /// + /// The constant can be located on a trait like `<A as B>::C`, in which case the given + /// substitutions and environment are used to resolve the constant. Alternatively if the + /// constant has generic parameters in scope the substitutions are used to evaluate the value of + /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count + /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still + /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is + /// returned. + /// + /// This handles inferences variables within both `param_env` and `substs` by + /// performing the operation on their respective canonical forms. + #[instrument(skip(self), level = "debug")] + pub fn const_eval_resolve( + &self, + mut param_env: ty::ParamEnv<'tcx>, + unevaluated: ty::Unevaluated<'tcx>, + span: Option<Span>, + ) -> EvalToValTreeResult<'tcx> { + let mut substs = self.resolve_vars_if_possible(unevaluated.substs); + debug!(?substs); + + // Postpone the evaluation of constants whose substs depend on inference + // variables + if substs.has_infer_types_or_consts() { + let ac = AbstractConst::new(self.tcx, unevaluated.shrink()); + match ac { + Ok(None) => { + substs = InternalSubsts::identity_for_item(self.tcx, unevaluated.def.did); + param_env = self.tcx.param_env(unevaluated.def.did); + } + Ok(Some(ct)) => { + if ct.unify_failure_kind(self.tcx) == FailureKind::Concrete { + substs = replace_param_and_infer_substs_with_placeholder(self.tcx, substs); + } else { + return Err(ErrorHandled::TooGeneric); + } + } + Err(guar) => return Err(ErrorHandled::Reported(guar)), + } + } + + let param_env_erased = self.tcx.erase_regions(param_env); + let substs_erased = self.tcx.erase_regions(substs); + debug!(?param_env_erased); + debug!(?substs_erased); + + let unevaluated = ty::Unevaluated { + def: unevaluated.def, + substs: substs_erased, + promoted: unevaluated.promoted, + }; + + // The return value is the evaluated value which doesn't contain any reference to inference + // variables, thus we don't need to substitute back the original values. + self.tcx.const_eval_resolve_for_typeck(param_env_erased, unevaluated, span) + } + + /// `ty_or_const_infer_var_changed` is equivalent to one of these two: + /// * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`) + /// * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`) + /// + /// However, `ty_or_const_infer_var_changed` is more efficient. It's always + /// inlined, despite being large, because it has only two call sites that + /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on` + /// inference variables), and it handles both `Ty` and `ty::Const` without + /// having to resort to storing full `GenericArg`s in `stalled_on`. + #[inline(always)] + pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool { + match infer_var { + TyOrConstInferVar::Ty(v) => { + use self::type_variable::TypeVariableValue; + + // If `inlined_probe` returns a `Known` value, it never equals + // `ty::Infer(ty::TyVar(v))`. + match self.inner.borrow_mut().type_variables().inlined_probe(v) { + TypeVariableValue::Unknown { .. } => false, + TypeVariableValue::Known { .. } => true, + } + } + + TyOrConstInferVar::TyInt(v) => { + // If `inlined_probe_value` returns a value it's always a + // `ty::Int(_)` or `ty::UInt(_)`, which never matches a + // `ty::Infer(_)`. + self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some() + } + + TyOrConstInferVar::TyFloat(v) => { + // If `probe_value` returns a value it's always a + // `ty::Float(_)`, which never matches a `ty::Infer(_)`. + // + // Not `inlined_probe_value(v)` because this call site is colder. + self.inner.borrow_mut().float_unification_table().probe_value(v).is_some() + } + + TyOrConstInferVar::Const(v) => { + // If `probe_value` returns a `Known` value, it never equals + // `ty::ConstKind::Infer(ty::InferConst::Var(v))`. + // + // Not `inlined_probe_value(v)` because this call site is colder. + match self.inner.borrow_mut().const_unification_table().probe_value(v).val { + ConstVariableValue::Unknown { .. } => false, + ConstVariableValue::Known { .. } => true, + } + } + } + } +} + +/// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently +/// used only for `traits::fulfill`'s list of `stalled_on` inference variables. +#[derive(Copy, Clone, Debug)] +pub enum TyOrConstInferVar<'tcx> { + /// Equivalent to `ty::Infer(ty::TyVar(_))`. + Ty(TyVid), + /// Equivalent to `ty::Infer(ty::IntVar(_))`. + TyInt(IntVid), + /// Equivalent to `ty::Infer(ty::FloatVar(_))`. + TyFloat(FloatVid), + + /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`. + Const(ConstVid<'tcx>), +} + +impl<'tcx> TyOrConstInferVar<'tcx> { + /// Tries to extract an inference variable from a type or a constant, returns `None` + /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and + /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`). + pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> { + match arg.unpack() { + GenericArgKind::Type(ty) => Self::maybe_from_ty(ty), + GenericArgKind::Const(ct) => Self::maybe_from_const(ct), + GenericArgKind::Lifetime(_) => None, + } + } + + /// Tries to extract an inference variable from a type, returns `None` + /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`). + pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> { + match *ty.kind() { + ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)), + ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)), + ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)), + _ => None, + } + } + + /// Tries to extract an inference variable from a constant, returns `None` + /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`). + pub fn maybe_from_const(ct: ty::Const<'tcx>) -> Option<Self> { + match ct.kind() { + ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)), + _ => None, + } + } +} + +/// Replace `{integer}` with `i32` and `{float}` with `f64`. +/// Used only for diagnostics. +struct InferenceLiteralEraser<'tcx> { + tcx: TyCtxt<'tcx>, +} + +impl<'tcx> TypeFolder<'tcx> for InferenceLiteralEraser<'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + match ty.kind() { + ty::Infer(ty::IntVar(_) | ty::FreshIntTy(_)) => self.tcx.types.i32, + ty::Infer(ty::FloatVar(_) | ty::FreshFloatTy(_)) => self.tcx.types.f64, + _ => ty.super_fold_with(self), + } + } +} + +struct ShallowResolver<'a, 'tcx> { + infcx: &'a InferCtxt<'a, 'tcx>, +} + +impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> { + fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { + self.infcx.tcx + } + + /// If `ty` is a type variable of some kind, resolve it one level + /// (but do not resolve types found in the result). If `typ` is + /// not a type variable, just return it unmodified. + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + match *ty.kind() { + ty::Infer(ty::TyVar(v)) => { + // Not entirely obvious: if `typ` is a type variable, + // it can be resolved to an int/float variable, which + // can then be recursively resolved, hence the + // recursion. Note though that we prevent type + // variables from unifying to other type variables + // directly (though they may be embedded + // structurally), and we prevent cycles in any case, + // so this recursion should always be of very limited + // depth. + // + // Note: if these two lines are combined into one we get + // dynamic borrow errors on `self.inner`. + let known = self.infcx.inner.borrow_mut().type_variables().probe(v).known(); + known.map_or(ty, |t| self.fold_ty(t)) + } + + ty::Infer(ty::IntVar(v)) => self + .infcx + .inner + .borrow_mut() + .int_unification_table() + .probe_value(v) + .map_or(ty, |v| v.to_type(self.infcx.tcx)), + + ty::Infer(ty::FloatVar(v)) => self + .infcx + .inner + .borrow_mut() + .float_unification_table() + .probe_value(v) + .map_or(ty, |v| v.to_type(self.infcx.tcx)), + + _ => ty, + } + } + + fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> { + if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.kind() { + self.infcx + .inner + .borrow_mut() + .const_unification_table() + .probe_value(vid) + .val + .known() + .unwrap_or(ct) + } else { + ct + } + } +} + +impl<'tcx> TypeTrace<'tcx> { + pub fn span(&self) -> Span { + self.cause.span + } + + pub fn types( + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Ty<'tcx>, + b: Ty<'tcx>, + ) -> TypeTrace<'tcx> { + TypeTrace { + cause: cause.clone(), + values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())), + } + } + + pub fn consts( + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: ty::Const<'tcx>, + b: ty::Const<'tcx>, + ) -> TypeTrace<'tcx> { + TypeTrace { + cause: cause.clone(), + values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())), + } + } +} + +impl<'tcx> SubregionOrigin<'tcx> { + pub fn span(&self) -> Span { + match *self { + Subtype(ref a) => a.span(), + RelateObjectBound(a) => a, + RelateParamBound(a, ..) => a, + RelateRegionParamBound(a) => a, + Reborrow(a) => a, + ReborrowUpvar(a, _) => a, + DataBorrowed(_, a) => a, + ReferenceOutlivesReferent(_, a) => a, + CompareImplItemObligation { span, .. } => span, + CheckAssociatedTypeBounds { ref parent, .. } => parent.span(), + } + } + + pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self + where + F: FnOnce() -> Self, + { + match *cause.code() { + traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => { + SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span) + } + + traits::ObligationCauseCode::CompareImplItemObligation { + impl_item_def_id, + trait_item_def_id, + kind: _, + } => SubregionOrigin::CompareImplItemObligation { + span: cause.span, + impl_item_def_id, + trait_item_def_id, + }, + + traits::ObligationCauseCode::CheckAssociatedTypeBounds { + impl_item_def_id, + trait_item_def_id, + } => SubregionOrigin::CheckAssociatedTypeBounds { + impl_item_def_id, + trait_item_def_id, + parent: Box::new(default()), + }, + + _ => default(), + } + } +} + +impl RegionVariableOrigin { + pub fn span(&self) -> Span { + match *self { + MiscVariable(a) + | PatternRegion(a) + | AddrOfRegion(a) + | Autoref(a) + | Coercion(a) + | EarlyBoundRegion(a, ..) + | LateBoundRegion(a, ..) + | UpvarRegion(_, a) => a, + Nll(..) => bug!("NLL variable used with `span`"), + } + } +} + +impl<'tcx> fmt::Debug for RegionObligation<'tcx> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + write!( + f, + "RegionObligation(sub_region={:?}, sup_type={:?})", + self.sub_region, self.sup_type + ) + } +} + +/// Replaces substs that reference param or infer variables with suitable +/// placeholders. This function is meant to remove these param and infer +/// substs when they're not actually needed to evaluate a constant. +fn replace_param_and_infer_substs_with_placeholder<'tcx>( + tcx: TyCtxt<'tcx>, + substs: SubstsRef<'tcx>, +) -> SubstsRef<'tcx> { + tcx.mk_substs(substs.iter().enumerate().map(|(idx, arg)| { + match arg.unpack() { + GenericArgKind::Type(_) + if arg.has_param_types_or_consts() || arg.has_infer_types_or_consts() => + { + tcx.mk_ty(ty::Placeholder(ty::PlaceholderType { + universe: ty::UniverseIndex::ROOT, + name: ty::BoundVar::from_usize(idx), + })) + .into() + } + GenericArgKind::Const(ct) + if ct.has_infer_types_or_consts() || ct.has_param_types_or_consts() => + { + let ty = ct.ty(); + // If the type references param or infer, replace that too... + if ty.has_param_types_or_consts() || ty.has_infer_types_or_consts() { + bug!("const `{ct}`'s type should not reference params or types"); + } + tcx.mk_const(ty::ConstS { + ty, + kind: ty::ConstKind::Placeholder(ty::PlaceholderConst { + universe: ty::UniverseIndex::ROOT, + name: ty::BoundVar::from_usize(idx), + }), + }) + .into() + } + _ => arg, + } + })) +} |