// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! See the Book for more information. pub use self::LateBoundRegionConversionTime::*; pub use self::RegionVariableOrigin::*; pub use self::SubregionOrigin::*; pub use self::ValuePairs::*; pub use ty::IntVarValue; pub use self::freshen::TypeFreshener; use hir::def_id::DefId; use middle::free_region::RegionRelations; use middle::region; use middle::lang_items; use ty::subst::Substs; use ty::{TyVid, IntVid, FloatVid}; use ty::{self, Ty, TyCtxt}; use ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric}; use ty::fold::TypeFoldable; use ty::relate::RelateResult; use traits::{self, ObligationCause, PredicateObligations}; use rustc_data_structures::lazy_btree_map::LazyBTreeMap; use rustc_data_structures::unify as ut; use std::cell::{Cell, RefCell, Ref, RefMut}; use std::fmt; use syntax::ast; use errors::DiagnosticBuilder; use syntax_pos::{self, Span}; use syntax_pos::symbol::InternedString; use util::nodemap::FxHashMap; use arena::SyncDroplessArena; use self::combine::CombineFields; use self::higher_ranked::HrMatchResult; use self::region_constraints::{RegionConstraintCollector, RegionSnapshot}; use self::region_constraints::{GenericKind, VerifyBound, RegionConstraintData, VarInfos}; use self::lexical_region_resolve::LexicalRegionResolutions; use self::outlives::env::OutlivesEnvironment; use self::type_variable::TypeVariableOrigin; use self::unify_key::ToType; pub mod anon_types; pub mod at; pub mod canonical; mod combine; mod equate; pub mod error_reporting; mod fudge; mod glb; mod higher_ranked; pub mod lattice; mod lub; pub mod region_constraints; mod lexical_region_resolve; pub mod outlives; pub mod resolve; mod freshen; mod sub; pub mod type_variable; pub mod unify_key; #[must_use] #[derive(Debug)] pub struct InferOk<'tcx, T> { pub value: T, pub obligations: PredicateObligations<'tcx>, } pub type InferResult<'tcx, T> = Result, TypeError<'tcx>>; pub type Bound = Option; pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result" pub type FixupResult = Result; // "fixup result" pub struct InferCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { pub tcx: TyCtxt<'a, 'gcx, 'tcx>, /// During type-checking/inference of a body, `in_progress_tables` /// contains a reference to the tables 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_tables: Option<&'a RefCell>>, // Cache for projections. This cache is snapshotted along with the // infcx. // // Public so that `traits::project` can use it. pub projection_cache: RefCell>, // We instantiate UnificationTable with bounds because the // types that might instantiate a general type variable have an // order, represented by its upper and lower bounds. pub type_variables: RefCell>, // Map from integral variable to the kind of integer it represents int_unification_table: RefCell>>, // Map from floating variable to the kind of float it represents float_unification_table: RefCell>>, // 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_constraints: RefCell>>, // Once region inference is done, the values for each variable. lexical_region_resolutions: RefCell>>, /// Caches the results of trait selection. This cache is used /// for things that have to do with the parameters in scope. pub selection_cache: traits::SelectionCache<'tcx>, /// Caches the results of trait evaluation. pub evaluation_cache: traits::EvaluationCache<'tcx>, // the set of predicates on which errors have been reported, to // avoid reporting the same error twice. pub reported_trait_errors: RefCell>>>, // 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, // Track how many errors were reported when this infcx is created. // If the number of errors increases, that's also a sign (line // `tained_by_errors`) to avoid reporting certain kinds of errors. err_count_on_creation: usize, // This flag is true while there is an active snapshot. in_snapshot: Cell, // 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 // // struct Foo { ... } // // 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 // `process_region_obligations` (defined in `self::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. pub region_obligations: RefCell)>>, /// What is the innermost universe we have created? Starts out as /// `UniverseIndex::root()` but grows from there as we enter /// universal quantifiers. /// /// NB: 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, } /// A map returned by `skolemize_late_bound_regions()` indicating the skolemized /// region that each late-bound region was replaced with. pub type SkolemizationMap<'tcx> = LazyBTreeMap>; /// See `error_reporting` module for more details #[derive(Clone, Debug)] pub enum ValuePairs<'tcx> { Types(ExpectedFound>), Regions(ExpectedFound>), TraitRefs(ExpectedFound>), PolyTraitRefs(ExpectedFound>), } /// The trace designates the path through inference that we took to /// encounter an error or subtyping constraint. /// /// See `error_reporting` module for more details. #[derive(Clone)] pub struct TypeTrace<'tcx> { cause: ObligationCause<'tcx>, 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(TypeTrace<'tcx>), // Stack-allocated closures cannot outlive innermost loop // or function so as to ensure we only require finite stack InfStackClosure(Span), // Invocation of closure must be within its lifetime InvokeClosure(Span), // Dereference of reference must be within its lifetime DerefPointer(Span), // Closure bound must not outlive captured free variables FreeVariable(Span, ast::NodeId), // Index into slice must be within its lifetime IndexSlice(Span), // 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>), // The given region parameter was instantiated with a region // that must outlive some other region. RelateRegionParamBound(Span), // A bound placed on type parameters that states that must outlive // the moment of their instantiation. RelateDefaultParamBound(Span, Ty<'tcx>), // 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), // Type or region parameters must be in scope. ParameterInScope(ParameterOrigin, Span), // The type T of an expression E must outlive the lifetime for E. ExprTypeIsNotInScope(Ty<'tcx>, Span), // A `ref b` whose region does not enclose the decl site BindingTypeIsNotValidAtDecl(Span), // Regions appearing in a method receiver must outlive method call CallRcvr(Span), // Regions appearing in a function argument must outlive func call CallArg(Span), // Region in return type of invoked fn must enclose call CallReturn(Span), // Operands must be in scope Operand(Span), // Region resulting from a `&` expr must enclose the `&` expr AddrOf(Span), // An auto-borrow that does not enclose the expr where it occurs AutoBorrow(Span), // Region constraint arriving from destructor safety SafeDestructor(Span), // Comparing the signature and requirements of an impl method against // the containing trait. CompareImplMethodObligation { span: Span, item_name: ast::Name, impl_item_def_id: DefId, trait_item_def_id: DefId, }, } /// Places that type/region parameters can appear. #[derive(Clone, Copy, Debug)] pub enum ParameterOrigin { Path, // foo::bar MethodCall, // foo.bar() <-- parameters on impl providing bar() OverloadedOperator, // a + b when overloaded OverloadedDeref, // *a when overloaded } /// 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, InternedString), // Region variables created for bound regions // in a function or method that is called LateBoundRegion(Span, ty::BoundRegion, LateBoundRegionConversionTime), UpvarRegion(ty::UpvarId, Span), BoundRegionInCoherence(ast::Name), // This origin is used for the inference variables that we create // during NLL region processing. NLL(NLLRegionVariableOrigin), } #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] 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, Inferred(::mir::visit::TyContext), } #[derive(Copy, Clone, Debug)] pub enum FixupError { UnresolvedIntTy(IntVid), UnresolvedFloatTy(FloatVid), UnresolvedTy(TyVid) } /// 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 cause: ObligationCause<'tcx>, } impl fmt::Display for FixupError { 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") } } } /// Helper type of a temporary returned by tcx.infer_ctxt(). /// Necessary because we can't write the following bound: /// F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(InferCtxt<'b, 'gcx, 'tcx>). pub struct InferCtxtBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { global_tcx: TyCtxt<'a, 'gcx, 'gcx>, arena: SyncDroplessArena, fresh_tables: Option>>, } impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> { pub fn infer_ctxt(self) -> InferCtxtBuilder<'a, 'gcx, 'tcx> { InferCtxtBuilder { global_tcx: self, arena: SyncDroplessArena::new(), fresh_tables: None, } } } impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> { /// Used only by `rustc_typeck` during body type-checking/inference, /// will initialize `in_progress_tables` with fresh `TypeckTables`. pub fn with_fresh_in_progress_tables(mut self, table_owner: DefId) -> Self { self.fresh_tables = Some(RefCell::new(ty::TypeckTables::empty(Some(table_owner)))); self } pub fn enter(&'tcx mut self, f: F) -> R where F: for<'b> FnOnce(InferCtxt<'b, 'gcx, 'tcx>) -> R { let InferCtxtBuilder { global_tcx, ref arena, ref fresh_tables, } = *self; let in_progress_tables = fresh_tables.as_ref(); global_tcx.enter_local(arena, |tcx| f(InferCtxt { tcx, in_progress_tables, projection_cache: RefCell::new(traits::ProjectionCache::new()), type_variables: RefCell::new(type_variable::TypeVariableTable::new()), int_unification_table: RefCell::new(ut::UnificationTable::new()), float_unification_table: RefCell::new(ut::UnificationTable::new()), region_constraints: RefCell::new(Some(RegionConstraintCollector::new())), lexical_region_resolutions: RefCell::new(None), selection_cache: traits::SelectionCache::new(), evaluation_cache: traits::EvaluationCache::new(), reported_trait_errors: RefCell::new(FxHashMap()), tainted_by_errors_flag: Cell::new(false), err_count_on_creation: tcx.sess.err_count(), in_snapshot: Cell::new(false), region_obligations: RefCell::new(vec![]), universe: Cell::new(ty::UniverseIndex::ROOT), })) } } impl ExpectedFound { pub fn new(a_is_expected: bool, a: T, b: T) -> Self { if a_is_expected { ExpectedFound {expected: a, found: b} } else { ExpectedFound {expected: b, found: a} } } } impl<'tcx, T> InferOk<'tcx, T> { pub fn unit(self) -> InferOk<'tcx, ()> { InferOk { value: (), obligations: self.obligations } } } 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:'a> { projection_cache_snapshot: traits::ProjectionCacheSnapshot, type_snapshot: type_variable::Snapshot<'tcx>, int_snapshot: ut::Snapshot>, float_snapshot: ut::Snapshot>, region_constraints_snapshot: RegionSnapshot, region_obligations_snapshot: usize, universe: ty::UniverseIndex, was_in_snapshot: bool, _in_progress_tables: Option>>, } impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { pub fn is_in_snapshot(&self) -> bool { self.in_snapshot.get() } pub fn freshen>(&self, t: T) -> T { t.fold_with(&mut self.freshener()) } pub fn type_var_diverges(&'a self, ty: Ty) -> bool { match ty.sty { ty::TyInfer(ty::TyVar(vid)) => self.type_variables.borrow().var_diverges(vid), _ => false } } pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'gcx, 'tcx> { freshen::TypeFreshener::new(self) } pub fn type_is_unconstrained_numeric(&'a self, ty: Ty) -> UnconstrainedNumeric { use ty::error::UnconstrainedNumeric::Neither; use ty::error::UnconstrainedNumeric::{UnconstrainedInt, UnconstrainedFloat}; match ty.sty { ty::TyInfer(ty::IntVar(vid)) => { if self.int_unification_table.borrow_mut().probe_value(vid).is_some() { Neither } else { UnconstrainedInt } }, ty::TyInfer(ty::FloatVar(vid)) => { if self.float_unification_table.borrow_mut().probe_value(vid).is_some() { Neither } else { UnconstrainedFloat } }, _ => Neither, } } pub fn unsolved_variables(&self) -> Vec> { let mut variables = Vec::new(); { let mut type_variables = self.type_variables.borrow_mut(); variables.extend( type_variables .unsolved_variables() .into_iter() .map(|t| self.tcx.mk_var(t))); } { let mut int_unification_table = self.int_unification_table.borrow_mut(); variables.extend( (0..int_unification_table.len()) .map(|i| ty::IntVid { index: i as u32 }) .filter(|&vid| int_unification_table.probe_value(vid).is_none()) .map(|v| self.tcx.mk_int_var(v))); } { let mut float_unification_table = self.float_unification_table.borrow_mut(); variables.extend( (0..float_unification_table.len()) .map(|i| ty::FloatVid { index: i as u32 }) .filter(|&vid| float_unification_table.probe_value(vid).is_none()) .map(|v| self.tcx.mk_float_var(v))); } return variables; } fn combine_fields(&'a self, trace: TypeTrace<'tcx>, param_env: ty::ParamEnv<'tcx>) -> CombineFields<'a, 'gcx, 'tcx> { CombineFields { infcx: self, trace, cause: None, param_env, obligations: PredicateObligations::new(), } } // 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 RUST_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(&self, func: F) -> R where F: FnOnce(&Self) -> R { let flag = self.in_snapshot.get(); self.in_snapshot.set(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.get(); self.in_snapshot.set(true); CombinedSnapshot { projection_cache_snapshot: self.projection_cache.borrow_mut().snapshot(), type_snapshot: self.type_variables.borrow_mut().snapshot(), int_snapshot: self.int_unification_table.borrow_mut().snapshot(), float_snapshot: self.float_unification_table.borrow_mut().snapshot(), region_constraints_snapshot: self.borrow_region_constraints().start_snapshot(), region_obligations_snapshot: self.region_obligations.borrow().len(), universe: self.universe(), was_in_snapshot: in_snapshot, // Borrow tables "in progress" (i.e. during typeck) // to ban writes from within a snapshot to them. _in_progress_tables: self.in_progress_tables.map(|tables| { tables.borrow() }) } } fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) { debug!("rollback_to(cause={})", cause); let CombinedSnapshot { projection_cache_snapshot, type_snapshot, int_snapshot, float_snapshot, region_constraints_snapshot, region_obligations_snapshot, universe, was_in_snapshot, _in_progress_tables } = snapshot; self.in_snapshot.set(was_in_snapshot); self.universe.set(universe); self.projection_cache .borrow_mut() .rollback_to(projection_cache_snapshot); self.type_variables .borrow_mut() .rollback_to(type_snapshot); self.int_unification_table .borrow_mut() .rollback_to(int_snapshot); self.float_unification_table .borrow_mut() .rollback_to(float_snapshot); self.region_obligations .borrow_mut() .truncate(region_obligations_snapshot); self.borrow_region_constraints() .rollback_to(region_constraints_snapshot); } fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) { debug!("commit_from()"); let CombinedSnapshot { projection_cache_snapshot, type_snapshot, int_snapshot, float_snapshot, region_constraints_snapshot, region_obligations_snapshot: _, universe: _, was_in_snapshot, _in_progress_tables } = snapshot; self.in_snapshot.set(was_in_snapshot); self.projection_cache .borrow_mut() .commit(projection_cache_snapshot); self.type_variables .borrow_mut() .commit(type_snapshot); self.int_unification_table .borrow_mut() .commit(int_snapshot); self.float_unification_table .borrow_mut() .commit(float_snapshot); self.borrow_region_constraints() .commit(region_constraints_snapshot); } /// Execute `f` and commit the bindings pub fn commit_unconditionally(&self, f: F) -> R where F: FnOnce() -> R, { debug!("commit()"); let snapshot = self.start_snapshot(); let r = f(); self.commit_from(snapshot); r } /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)` pub fn commit_if_ok(&self, f: F) -> Result where F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result { debug!("commit_if_ok()"); 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` in a snapshot, and commit the bindings it creates pub fn in_snapshot(&self, f: F) -> T where F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> T { debug!("in_snapshot()"); let snapshot = self.start_snapshot(); let r = f(&snapshot); self.commit_from(snapshot); r } /// Execute `f` then unroll any bindings it creates pub fn probe(&self, f: F) -> R where F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R, { debug!("probe()"); let snapshot = self.start_snapshot(); let r = f(&snapshot); self.rollback_to("probe", snapshot); r } pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) { self.borrow_region_constraints().add_given(sub, sup); } pub fn can_sub(&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(&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. }) }) } pub fn sub_regions(&self, origin: SubregionOrigin<'tcx>, a: ty::Region<'tcx>, b: ty::Region<'tcx>) { debug!("sub_regions({:?} <: {:?})", a, b); self.borrow_region_constraints().make_subregion(origin, a, b); } pub fn subtype_predicate(&self, cause: &ObligationCause<'tcx>, param_env: ty::ParamEnv<'tcx>, predicate: &ty::PolySubtypePredicate<'tcx>) -> Option> { // Subtle: it's ok to skip the binder here and resolve because // `shallow_resolve` just ignores anything that is not a type // variable, and because type variable's can't (at present, at // least) capture any of the things bound by this binder. // // Really, there is no *particular* reason to do this // `shallow_resolve` here except as a // micro-optimization. Naturally I could not // resist. -nmatsakis let two_unbound_type_vars = { let a = self.shallow_resolve(predicate.skip_binder().a); let b = self.shallow_resolve(predicate.skip_binder().b); a.is_ty_var() && b.is_ty_var() }; if two_unbound_type_vars { // Two unbound type variables? Can't make progress. return None; } Some(self.commit_if_ok(|snapshot| { let (ty::SubtypePredicate { a_is_expected, a, b}, skol_map) = self.skolemize_late_bound_regions(predicate); let cause_span = cause.span; let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?; self.leak_check(false, cause_span, &skol_map, snapshot)?; self.pop_skolemized(skol_map, snapshot); Ok(ok.unit()) })) } pub fn region_outlives_predicate(&self, cause: &traits::ObligationCause<'tcx>, predicate: &ty::PolyRegionOutlivesPredicate<'tcx>) -> UnitResult<'tcx> { self.commit_if_ok(|snapshot| { let (ty::OutlivesPredicate(r_a, r_b), skol_map) = self.skolemize_late_bound_regions(predicate); let origin = SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span)); self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b` self.leak_check(false, cause.span, &skol_map, snapshot)?; Ok(self.pop_skolemized(skol_map, snapshot)) }) } pub fn next_ty_var_id(&self, diverging: bool, origin: TypeVariableOrigin) -> TyVid { self.type_variables .borrow_mut() .new_var(self.universe(), diverging, origin) } pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> { self.tcx.mk_var(self.next_ty_var_id(false, origin)) } pub fn next_diverging_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> { self.tcx.mk_var(self.next_ty_var_id(true, origin)) } pub fn next_int_var_id(&self) -> IntVid { self.int_unification_table .borrow_mut() .new_key(None) } pub fn next_float_var_id(&self) -> FloatVid { self.float_unification_table .borrow_mut() .new_key(None) } /// Create a fresh region variable with the next available index. /// /// # Parameters /// /// - `origin`: information about why we created this variable, for use /// during diagnostics / error-reporting. pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> { let region_var = self.borrow_region_constraints() .new_region_var(self.universe(), origin); self.tcx.mk_region(ty::ReVar(region_var)) } /// Number of region variables created so far. pub fn num_region_vars(&self) -> usize { self.borrow_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)) } /// Create a region inference variable for the given /// region parameter definition. pub fn region_var_for_def(&self, span: Span, def: &ty::RegionParameterDef) -> ty::Region<'tcx> { self.next_region_var(EarlyBoundRegion(span, def.name)) } /// 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(...);` when /// used in a path such as `Foo::::new()` will /// use an inference variable for `C` with `[T, U]` /// as the substitutions for the default, `(T, U)`. pub fn type_var_for_def(&self, span: Span, def: &ty::TypeParameterDef) -> Ty<'tcx> { let ty_var_id = self.type_variables .borrow_mut() .new_var(self.universe(), false, TypeVariableOrigin::TypeParameterDefinition(span, def.name)); self.tcx.mk_var(ty_var_id) } /// 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) -> &'tcx Substs<'tcx> { Substs::for_item(self.tcx, def_id, |def, _| { self.region_var_for_def(span, def) }, |def, _| { self.type_var_for_def(span, def) }) } /// 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) } /// 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_type_vars_if_possible` as well as `fully_resolve`. pub fn resolve_regions_and_report_errors( &self, region_context: DefId, region_map: ®ion::ScopeTree, outlives_env: &OutlivesEnvironment<'tcx>, ) { self.resolve_regions_and_report_errors_inner( region_context, region_map, outlives_env, false, ) } /// Like `resolve_regions_and_report_errors`, but skips error /// reporting if NLL is enabled. This is used for fn bodies where /// the same error may later be reported by the NLL-based /// inference. pub fn resolve_regions_and_report_errors_unless_nll( &self, region_context: DefId, region_map: ®ion::ScopeTree, outlives_env: &OutlivesEnvironment<'tcx>, ) { self.resolve_regions_and_report_errors_inner( region_context, region_map, outlives_env, true, ) } fn resolve_regions_and_report_errors_inner( &self, region_context: DefId, region_map: ®ion::ScopeTree, outlives_env: &OutlivesEnvironment<'tcx>, will_later_be_reported_by_nll: bool, ) { assert!(self.is_tainted_by_errors() || self.region_obligations.borrow().is_empty(), "region_obligations not empty: {:#?}", self.region_obligations.borrow()); let region_rels = &RegionRelations::new(self.tcx, region_context, region_map, outlives_env.free_region_map()); let (var_infos, data) = self.region_constraints.borrow_mut() .take() .expect("regions already resolved") .into_infos_and_data(); let (lexical_region_resolutions, errors) = lexical_region_resolve::resolve(region_rels, var_infos, data); let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions)); assert!(old_value.is_none()); 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(region_map, &errors, will_later_be_reported_by_nll); } } /// 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.region_obligations.borrow().is_empty(), "region_obligations not empty: {:#?}", self.region_obligations.borrow()); self.borrow_region_constraints().take_and_reset_data() } /// Gives temporary access to the region constraint data. #[allow(non_camel_case_types)] // bug with impl trait pub fn with_region_constraints( &self, op: impl FnOnce(&RegionConstraintData<'tcx>) -> R, ) -> R { let region_constraints = self.borrow_region_constraints(); op(region_constraints.data()) } /// Takes ownership of the list of variable regions. This implies /// that all the region constriants 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 vairables into the NLL region context. pub fn take_region_var_origins(&self) -> VarInfos { let (var_infos, data) = self.region_constraints.borrow_mut() .take() .expect("regions already resolved") .into_infos_and_data(); assert!(data.is_empty()); var_infos } pub fn ty_to_string(&self, t: Ty<'tcx>) -> String { self.resolve_type_vars_if_possible(&t).to_string() } pub fn tys_to_string(&self, ts: &[Ty<'tcx>]) -> String { let tstrs: Vec = ts.iter().map(|t| self.ty_to_string(*t)).collect(); format!("({})", tstrs.join(", ")) } pub fn trait_ref_to_string(&self, t: &ty::TraitRef<'tcx>) -> String { self.resolve_type_vars_if_possible(t).to_string() } pub fn shallow_resolve(&self, typ: Ty<'tcx>) -> Ty<'tcx> { match typ.sty { ty::TyInfer(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 unifyxing 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. self.type_variables.borrow_mut() .probe(v) .known() .map(|t| self.shallow_resolve(t)) .unwrap_or(typ) } ty::TyInfer(ty::IntVar(v)) => { self.int_unification_table .borrow_mut() .probe_value(v) .map(|v| v.to_type(self.tcx)) .unwrap_or(typ) } ty::TyInfer(ty::FloatVar(v)) => { self.float_unification_table .borrow_mut() .probe_value(v) .map(|v| v.to_type(self.tcx)) .unwrap_or(typ) } _ => { typ } } } pub fn resolve_type_vars_if_possible(&self, value: &T) -> T where T: TypeFoldable<'tcx> { /*! * Where possible, replaces type/int/float variables in * `value` with their final value. Note that region variables * are unaffected. If a type 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. */ if !value.needs_infer() { return value.clone(); // avoid duplicated subst-folding } let mut r = resolve::OpportunisticTypeResolver::new(self); value.fold_with(&mut r) } /// Returns true if `T` contains unresolved type variables. 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_type_vars_if_possible()`. pub fn any_unresolved_type_vars(&self, value: &T) -> bool where T: TypeFoldable<'tcx> { let mut r = resolve::UnresolvedTypeFinder::new(self); value.visit_with(&mut r) } pub fn resolve_type_and_region_vars_if_possible(&self, value: &T) -> T where T: TypeFoldable<'tcx> { let mut r = resolve::OpportunisticTypeAndRegionResolver::new(self); value.fold_with(&mut r) } pub fn fully_resolve>(&self, value: &T) -> FixupResult { /*! * Attempts to resolve all type/region 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 TyError (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 TyError, 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(&self, sp: Span, mk_diag: M, actual_ty: Ty<'tcx>) -> DiagnosticBuilder<'tcx> where M: FnOnce(String) -> DiagnosticBuilder<'tcx>, { let actual_ty = self.resolve_type_vars_if_possible(&actual_ty); debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty); // Don't report an error if actual type is TyError. if actual_ty.references_error() { return self.tcx.sess.diagnostic().struct_dummy(); } mk_diag(self.ty_to_string(actual_ty)) } pub fn report_mismatched_types(&self, cause: &ObligationCause<'tcx>, expected: Ty<'tcx>, actual: Ty<'tcx>, err: TypeError<'tcx>) -> DiagnosticBuilder<'tcx> { let trace = TypeTrace::types(cause, true, expected, actual); self.report_and_explain_type_error(trace, &err) } pub fn replace_late_bound_regions_with_fresh_var( &self, span: Span, lbrct: LateBoundRegionConversionTime, value: &ty::Binder) -> (T, LazyBTreeMap>) where T : TypeFoldable<'tcx> { self.tcx.replace_late_bound_regions( value, |br| self.next_region_var(LateBoundRegion(span, br, lbrct))) } /// Given a higher-ranked projection predicate like: /// /// for<'a> >::Output = &'a u32 /// /// and a target trait-ref like: /// /// > /// /// find a substitution `S` for the higher-ranked regions (here, /// `['a => 'x]`) such that the predicate matches the trait-ref, /// and then return the value (here, `&'a u32`) but with the /// substitution applied (hence, `&'x u32`). /// /// See `higher_ranked_match` in `higher_ranked/mod.rs` for more /// details. pub fn match_poly_projection_predicate(&self, cause: ObligationCause<'tcx>, param_env: ty::ParamEnv<'tcx>, match_a: ty::PolyProjectionPredicate<'tcx>, match_b: ty::TraitRef<'tcx>) -> InferResult<'tcx, HrMatchResult>> { let match_pair = match_a.map_bound(|p| (p.projection_ty.trait_ref(self.tcx), p.ty)); let trace = TypeTrace { cause, values: TraitRefs(ExpectedFound::new(true, match_pair.skip_binder().0, match_b)) }; let mut combine = self.combine_fields(trace, param_env); let result = combine.higher_ranked_match(&match_pair, &match_b, true)?; Ok(InferOk { value: result, obligations: combine.obligations }) } /// See `verify_generic_bound` method in `region_constraints` 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.borrow_region_constraints().verify_generic_bound(origin, kind, a, bound); } pub fn type_moves_by_default(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>, span: Span) -> bool { let ty = self.resolve_type_vars_if_possible(&ty); // Even if the type may have no inference variables, during // type-checking closure types are in local tables only. if !self.in_progress_tables.is_some() || !ty.has_closure_types() { if let Some((param_env, ty)) = self.tcx.lift_to_global(&(param_env, ty)) { return ty.moves_by_default(self.tcx.global_tcx(), param_env, span); } } let copy_def_id = self.tcx.require_lang_item(lang_items::CopyTraitLangItem); // this can get called from typeck (by euv), and moves_by_default // rightly refuses to work with inference variables, but // moves_by_default has a cache, which we want to use in other // cases. !traits::type_known_to_meet_bound(self, param_env, ty, copy_def_id, span) } /// 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_def_id: DefId, closure_substs: ty::ClosureSubsts<'tcx>) -> Option { let closure_kind_ty = closure_substs.closure_kind_ty(closure_def_id, self.tcx); let closure_kind_ty = self.shallow_resolve(&closure_kind_ty); closure_kind_ty.to_opt_closure_kind() } /// Obtain the signature of a closure. For closures, unlike /// `tcx.fn_sig(def_id)`, this method will work during the /// type-checking of the enclosing function and return the closure /// signature in its partially inferred state. pub fn closure_sig( &self, def_id: DefId, substs: ty::ClosureSubsts<'tcx> ) -> ty::PolyFnSig<'tcx> { let closure_sig_ty = substs.closure_sig_ty(def_id, self.tcx); let closure_sig_ty = self.shallow_resolve(&closure_sig_ty); closure_sig_ty.fn_sig(self.tcx) } /// Normalizes associated types in `value`, potentially returning /// new obligations that must further be processed. pub fn partially_normalize_associated_types_in(&self, span: Span, body_id: ast::NodeId, param_env: ty::ParamEnv<'tcx>, value: &T) -> InferOk<'tcx, T> where T : TypeFoldable<'tcx> { debug!("partially_normalize_associated_types_in(value={:?})", value); let mut selcx = traits::SelectionContext::new(self); let cause = ObligationCause::misc(span, body_id); let traits::Normalized { value, obligations } = traits::normalize(&mut selcx, param_env, cause, value); debug!("partially_normalize_associated_types_in: result={:?} predicates={:?}", value, obligations); InferOk { value, obligations } } pub fn borrow_region_constraints(&self) -> RefMut<'_, RegionConstraintCollector<'tcx>> { RefMut::map( self.region_constraints.borrow_mut(), |c| c.as_mut().expect("region constraints already solved")) } /// Clears the selection, evaluation, and projection cachesThis is useful when /// repeatedly attemping to select an Obligation while changing only /// its ParamEnv, since FulfillmentContext doesn't use 'probe' pub fn clear_caches(&self) { self.selection_cache.clear(); self.evaluation_cache.clear(); self.projection_cache.borrow_mut().clear(); } fn universe(&self) -> ty::UniverseIndex { self.universe.get() } } impl<'a, 'gcx, '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: Types(ExpectedFound::new(a_is_expected, a, b)) } } pub fn dummy(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> TypeTrace<'tcx> { TypeTrace { cause: ObligationCause::dummy(), values: Types(ExpectedFound { expected: tcx.types.err, found: tcx.types.err, }) } } } impl<'tcx> fmt::Debug for TypeTrace<'tcx> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "TypeTrace({:?})", self.cause) } } impl<'tcx> SubregionOrigin<'tcx> { pub fn span(&self) -> Span { match *self { Subtype(ref a) => a.span(), InfStackClosure(a) => a, InvokeClosure(a) => a, DerefPointer(a) => a, FreeVariable(a, _) => a, IndexSlice(a) => a, RelateObjectBound(a) => a, RelateParamBound(a, _) => a, RelateRegionParamBound(a) => a, RelateDefaultParamBound(a, _) => a, Reborrow(a) => a, ReborrowUpvar(a, _) => a, DataBorrowed(_, a) => a, ReferenceOutlivesReferent(_, a) => a, ParameterInScope(_, a) => a, ExprTypeIsNotInScope(_, a) => a, BindingTypeIsNotValidAtDecl(a) => a, CallRcvr(a) => a, CallArg(a) => a, CallReturn(a) => a, Operand(a) => a, AddrOf(a) => a, AutoBorrow(a) => a, SafeDestructor(a) => a, CompareImplMethodObligation { span, .. } => span, } } pub fn from_obligation_cause(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::CompareImplMethodObligation { item_name, impl_item_def_id, trait_item_def_id, } => SubregionOrigin::CompareImplMethodObligation { span: cause.span, item_name, impl_item_def_id, trait_item_def_id, }, _ => default(), } } } impl RegionVariableOrigin { pub fn span(&self) -> Span { match *self { MiscVariable(a) => a, PatternRegion(a) => a, AddrOfRegion(a) => a, Autoref(a) => a, Coercion(a) => a, EarlyBoundRegion(a, ..) => a, LateBoundRegion(a, ..) => a, BoundRegionInCoherence(_) => syntax_pos::DUMMY_SP, UpvarRegion(_, a) => a, NLL(..) => bug!("NLL variable used with `span`"), } } } EnumTypeFoldableImpl! { impl<'tcx> TypeFoldable<'tcx> for ValuePairs<'tcx> { (ValuePairs::Types)(a), (ValuePairs::Regions)(a), (ValuePairs::TraitRefs)(a), (ValuePairs::PolyTraitRefs)(a), } } 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) } }