9cc3bfcceb
This commit introduces the idea of an "impl header", which consists of everything outside the impl body: the Self type, the trait reference (when applicable), and predicates from `where` clauses. This type is usable with the type folding machinery, making it possible to work with impl headers at a higher and more generic level.
643 lines
22 KiB
Rust
643 lines
22 KiB
Rust
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Generalized type folding mechanism. The setup is a bit convoluted
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//! but allows for convenient usage. Let T be an instance of some
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//! "foldable type" (one which implements `TypeFoldable`) and F be an
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//! instance of a "folder" (a type which implements `TypeFolder`). Then
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//! the setup is intended to be:
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//!
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//! T.fold_with(F) --calls--> F.fold_T(T) --calls--> T.super_fold_with(F)
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//!
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//! This way, when you define a new folder F, you can override
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//! `fold_T()` to customize the behavior, and invoke `T.super_fold_with()`
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//! to get the original behavior. Meanwhile, to actually fold
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//! something, you can just write `T.fold_with(F)`, which is
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//! convenient. (Note that `fold_with` will also transparently handle
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//! things like a `Vec<T>` where T is foldable and so on.)
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//!
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//! In this ideal setup, the only function that actually *does*
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//! anything is `T.super_fold_with()`, which traverses the type `T`.
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//! Moreover, `T.super_fold_with()` should only ever call `T.fold_with()`.
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//!
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//! In some cases, we follow a degenerate pattern where we do not have
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//! a `fold_T` method. Instead, `T.fold_with` traverses the structure directly.
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//! This is suboptimal because the behavior cannot be overridden, but it's
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//! much less work to implement. If you ever *do* need an override that
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//! doesn't exist, it's not hard to convert the degenerate pattern into the
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//! proper thing.
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//!
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//! A `TypeFoldable` T can also be visited by a `TypeVisitor` V using similar setup:
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//! T.visit_with(V) --calls--> V.visit_T(T) --calls--> T.super_visit_with(V).
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//! These methods return true to indicate that the visitor has found what it is looking for
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//! and does not need to visit anything else.
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use middle::region;
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use middle::subst;
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use middle::ty::adjustment;
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use middle::ty::{self, Binder, Ty, TyCtxt, TypeFlags};
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use std::fmt;
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use util::nodemap::{FnvHashMap, FnvHashSet};
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/// The TypeFoldable trait is implemented for every type that can be folded.
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/// Basically, every type that has a corresponding method in TypeFolder.
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pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
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fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self;
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fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
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self.super_fold_with(folder)
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}
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fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool;
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fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
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self.super_visit_with(visitor)
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}
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fn has_regions_escaping_depth(&self, depth: u32) -> bool {
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self.visit_with(&mut HasEscapingRegionsVisitor { depth: depth })
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}
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fn has_escaping_regions(&self) -> bool {
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self.has_regions_escaping_depth(0)
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}
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fn has_type_flags(&self, flags: TypeFlags) -> bool {
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self.visit_with(&mut HasTypeFlagsVisitor { flags: flags })
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}
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fn has_projection_types(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_PROJECTION)
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}
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fn references_error(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_TY_ERR)
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}
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fn has_param_types(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_PARAMS)
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}
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fn has_self_ty(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_SELF)
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}
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fn has_infer_types(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_TY_INFER)
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}
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fn needs_infer(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER)
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}
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fn needs_subst(&self) -> bool {
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self.has_type_flags(TypeFlags::NEEDS_SUBST)
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}
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fn has_closure_types(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
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}
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fn has_erasable_regions(&self) -> bool {
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self.has_type_flags(TypeFlags::HAS_RE_EARLY_BOUND |
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TypeFlags::HAS_RE_INFER |
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TypeFlags::HAS_FREE_REGIONS)
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}
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/// Indicates whether this value references only 'global'
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/// types/lifetimes that are the same regardless of what fn we are
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/// in. This is used for caching. Errs on the side of returning
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/// false.
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fn is_global(&self) -> bool {
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!self.has_type_flags(TypeFlags::HAS_LOCAL_NAMES)
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}
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}
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/// The TypeFolder trait defines the actual *folding*. There is a
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/// method defined for every foldable type. Each of these has a
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/// default implementation that does an "identity" fold. Within each
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/// identity fold, it should invoke `foo.fold_with(self)` to fold each
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/// sub-item.
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pub trait TypeFolder<'tcx> : Sized {
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fn tcx<'a>(&'a self) -> &'a TyCtxt<'tcx>;
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/// Invoked by the `super_*` routines when we enter a region
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/// binding level (for example, when entering a function
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/// signature). This is used by clients that want to track the
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/// Debruijn index nesting level.
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fn enter_region_binder(&mut self) { }
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/// Invoked by the `super_*` routines when we exit a region
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/// binding level. This is used by clients that want to
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/// track the Debruijn index nesting level.
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fn exit_region_binder(&mut self) { }
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fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
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where T : TypeFoldable<'tcx>
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{
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// FIXME(#20526) this should replace `enter_region_binder`/`exit_region_binder`.
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t.super_fold_with(self)
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}
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fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
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t.super_fold_with(self)
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}
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fn fold_mt(&mut self, t: &ty::TypeAndMut<'tcx>) -> ty::TypeAndMut<'tcx> {
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t.super_fold_with(self)
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}
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fn fold_trait_ref(&mut self, t: &ty::TraitRef<'tcx>) -> ty::TraitRef<'tcx> {
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t.super_fold_with(self)
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}
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fn fold_impl_header(&mut self, imp: &ty::ImplHeader<'tcx>) -> ty::ImplHeader<'tcx> {
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imp.super_fold_with(self)
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}
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fn fold_substs(&mut self,
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substs: &subst::Substs<'tcx>)
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-> subst::Substs<'tcx> {
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substs.super_fold_with(self)
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}
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fn fold_fn_sig(&mut self,
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sig: &ty::FnSig<'tcx>)
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-> ty::FnSig<'tcx> {
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sig.super_fold_with(self)
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}
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fn fold_output(&mut self,
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output: &ty::FnOutput<'tcx>)
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-> ty::FnOutput<'tcx> {
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output.super_fold_with(self)
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}
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fn fold_bare_fn_ty(&mut self,
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fty: &ty::BareFnTy<'tcx>)
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-> ty::BareFnTy<'tcx>
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{
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fty.super_fold_with(self)
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}
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fn fold_closure_ty(&mut self,
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fty: &ty::ClosureTy<'tcx>)
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-> ty::ClosureTy<'tcx> {
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fty.super_fold_with(self)
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}
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fn fold_region(&mut self, r: ty::Region) -> ty::Region {
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r.super_fold_with(self)
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}
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fn fold_existential_bounds(&mut self, s: &ty::ExistentialBounds<'tcx>)
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-> ty::ExistentialBounds<'tcx> {
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s.super_fold_with(self)
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}
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fn fold_autoref(&mut self, ar: &adjustment::AutoRef<'tcx>)
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-> adjustment::AutoRef<'tcx> {
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ar.super_fold_with(self)
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}
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}
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pub trait TypeVisitor<'tcx> : Sized {
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fn enter_region_binder(&mut self) { }
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fn exit_region_binder(&mut self) { }
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fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
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t.super_visit_with(self)
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}
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fn visit_region(&mut self, r: ty::Region) -> bool {
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r.super_visit_with(self)
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Some sample folders
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pub struct BottomUpFolder<'a, 'tcx: 'a, F> where F: FnMut(Ty<'tcx>) -> Ty<'tcx> {
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pub tcx: &'a TyCtxt<'tcx>,
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pub fldop: F,
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}
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impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
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F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
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{
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fn tcx(&self) -> &TyCtxt<'tcx> { self.tcx }
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fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
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let t1 = ty.super_fold_with(self);
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(self.fldop)(t1)
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Region folder
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impl<'tcx> TyCtxt<'tcx> {
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/// Collects the free and escaping regions in `value` into `region_set`. Returns
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/// whether any late-bound regions were skipped
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pub fn collect_regions<T>(&self,
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value: &T,
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region_set: &mut FnvHashSet<ty::Region>)
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-> bool
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where T : TypeFoldable<'tcx>
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{
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let mut have_bound_regions = false;
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self.fold_regions(value, &mut have_bound_regions,
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|r, d| { region_set.insert(r.from_depth(d)); r });
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have_bound_regions
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}
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/// Folds the escaping and free regions in `value` using `f`, and
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/// sets `skipped_regions` to true if any late-bound region was found
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/// and skipped.
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pub fn fold_regions<T,F>(&self,
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value: &T,
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skipped_regions: &mut bool,
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mut f: F)
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-> T
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where F : FnMut(ty::Region, u32) -> ty::Region,
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T : TypeFoldable<'tcx>,
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{
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value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
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}
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}
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/// Folds over the substructure of a type, visiting its component
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/// types and all regions that occur *free* within it.
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///
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/// That is, `Ty` can contain function or method types that bind
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/// regions at the call site (`ReLateBound`), and occurrences of
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/// regions (aka "lifetimes") that are bound within a type are not
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/// visited by this folder; only regions that occur free will be
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/// visited by `fld_r`.
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pub struct RegionFolder<'a, 'tcx: 'a> {
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tcx: &'a TyCtxt<'tcx>,
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skipped_regions: &'a mut bool,
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current_depth: u32,
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fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
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}
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impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
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pub fn new<F>(tcx: &'a TyCtxt<'tcx>,
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skipped_regions: &'a mut bool,
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fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
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where F : FnMut(ty::Region, u32) -> ty::Region
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{
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RegionFolder {
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tcx: tcx,
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skipped_regions: skipped_regions,
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current_depth: 1,
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fld_r: fld_r,
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}
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}
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}
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impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
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{
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fn tcx(&self) -> &TyCtxt<'tcx> { self.tcx }
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fn enter_region_binder(&mut self) {
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self.current_depth += 1;
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}
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fn exit_region_binder(&mut self) {
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self.current_depth -= 1;
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}
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fn fold_region(&mut self, r: ty::Region) -> ty::Region {
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match r {
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ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
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debug!("RegionFolder.fold_region({:?}) skipped bound region (current depth={})",
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r, self.current_depth);
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*self.skipped_regions = true;
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r
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}
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_ => {
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debug!("RegionFolder.fold_region({:?}) folding free region (current_depth={})",
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r, self.current_depth);
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(self.fld_r)(r, self.current_depth)
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}
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}
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Late-bound region replacer
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// Replaces the escaping regions in a type.
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struct RegionReplacer<'a, 'tcx: 'a> {
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tcx: &'a TyCtxt<'tcx>,
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current_depth: u32,
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fld_r: &'a mut (FnMut(ty::BoundRegion) -> ty::Region + 'a),
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map: FnvHashMap<ty::BoundRegion, ty::Region>
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}
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impl<'tcx> TyCtxt<'tcx> {
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pub fn replace_late_bound_regions<T,F>(&self,
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value: &Binder<T>,
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mut f: F)
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-> (T, FnvHashMap<ty::BoundRegion, ty::Region>)
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where F : FnMut(ty::BoundRegion) -> ty::Region,
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T : TypeFoldable<'tcx>,
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{
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debug!("replace_late_bound_regions({:?})", value);
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let mut replacer = RegionReplacer::new(self, &mut f);
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let result = value.skip_binder().fold_with(&mut replacer);
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(result, replacer.map)
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}
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/// Replace any late-bound regions bound in `value` with free variants attached to scope-id
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/// `scope_id`.
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pub fn liberate_late_bound_regions<T>(&self,
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all_outlive_scope: region::CodeExtent,
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value: &Binder<T>)
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-> T
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where T : TypeFoldable<'tcx>
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{
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self.replace_late_bound_regions(value, |br| {
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ty::ReFree(ty::FreeRegion{scope: all_outlive_scope, bound_region: br})
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}).0
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}
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/// Flattens two binding levels into one. So `for<'a> for<'b> Foo`
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/// becomes `for<'a,'b> Foo`.
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pub fn flatten_late_bound_regions<T>(&self, bound2_value: &Binder<Binder<T>>)
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-> Binder<T>
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where T: TypeFoldable<'tcx>
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{
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let bound0_value = bound2_value.skip_binder().skip_binder();
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let value = self.fold_regions(bound0_value, &mut false,
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|region, current_depth| {
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match region {
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ty::ReLateBound(debruijn, br) if debruijn.depth >= current_depth => {
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// should be true if no escaping regions from bound2_value
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assert!(debruijn.depth - current_depth <= 1);
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ty::ReLateBound(ty::DebruijnIndex::new(current_depth), br)
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}
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_ => {
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region
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}
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}
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});
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Binder(value)
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}
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pub fn no_late_bound_regions<T>(&self, value: &Binder<T>) -> Option<T>
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where T : TypeFoldable<'tcx>
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{
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if value.0.has_escaping_regions() {
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None
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} else {
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Some(value.0.clone())
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}
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}
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/// Replace any late-bound regions bound in `value` with `'static`. Useful in trans but also
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/// method lookup and a few other places where precise region relationships are not required.
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pub fn erase_late_bound_regions<T>(&self, value: &Binder<T>) -> T
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where T : TypeFoldable<'tcx>
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{
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self.replace_late_bound_regions(value, |_| ty::ReStatic).0
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}
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/// Rewrite any late-bound regions so that they are anonymous. Region numbers are
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/// assigned starting at 1 and increasing monotonically in the order traversed
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/// by the fold operation.
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///
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/// The chief purpose of this function is to canonicalize regions so that two
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/// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
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/// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
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/// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
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pub fn anonymize_late_bound_regions<T>(&self, sig: &Binder<T>) -> Binder<T>
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where T : TypeFoldable<'tcx>,
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{
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let mut counter = 0;
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Binder(self.replace_late_bound_regions(sig, |_| {
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counter += 1;
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ty::ReLateBound(ty::DebruijnIndex::new(1), ty::BrAnon(counter))
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}).0)
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}
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}
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impl<'a, 'tcx> RegionReplacer<'a, 'tcx> {
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fn new<F>(tcx: &'a TyCtxt<'tcx>, fld_r: &'a mut F) -> RegionReplacer<'a, 'tcx>
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where F : FnMut(ty::BoundRegion) -> ty::Region
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{
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RegionReplacer {
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tcx: tcx,
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current_depth: 1,
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fld_r: fld_r,
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map: FnvHashMap()
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}
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}
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}
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impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx>
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{
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fn tcx(&self) -> &TyCtxt<'tcx> { self.tcx }
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fn enter_region_binder(&mut self) {
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self.current_depth += 1;
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}
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fn exit_region_binder(&mut self) {
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self.current_depth -= 1;
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}
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fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
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if !t.has_regions_escaping_depth(self.current_depth-1) {
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return t;
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}
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t.super_fold_with(self)
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}
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fn fold_region(&mut self, r: ty::Region) -> ty::Region {
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match r {
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ty::ReLateBound(debruijn, br) if debruijn.depth == self.current_depth => {
|
|
debug!("RegionReplacer.fold_region({:?}) folding region (current_depth={})",
|
|
r, self.current_depth);
|
|
let fld_r = &mut self.fld_r;
|
|
let region = *self.map.entry(br).or_insert_with(|| fld_r(br));
|
|
if let ty::ReLateBound(debruijn1, br) = region {
|
|
// If the callback returns a late-bound region,
|
|
// that region should always use depth 1. Then we
|
|
// adjust it to the correct depth.
|
|
assert_eq!(debruijn1.depth, 1);
|
|
ty::ReLateBound(debruijn, br)
|
|
} else {
|
|
region
|
|
}
|
|
}
|
|
r => r
|
|
}
|
|
}
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Region eraser
|
|
|
|
impl<'tcx> TyCtxt<'tcx> {
|
|
/// Returns an equivalent value with all free regions removed (note
|
|
/// that late-bound regions remain, because they are important for
|
|
/// subtyping, but they are anonymized and normalized as well)..
|
|
pub fn erase_regions<T>(&self, value: &T) -> T
|
|
where T : TypeFoldable<'tcx>
|
|
{
|
|
let value1 = value.fold_with(&mut RegionEraser(self));
|
|
debug!("erase_regions({:?}) = {:?}",
|
|
value, value1);
|
|
return value1;
|
|
|
|
struct RegionEraser<'a, 'tcx: 'a>(&'a TyCtxt<'tcx>);
|
|
|
|
impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
|
|
fn tcx(&self) -> &TyCtxt<'tcx> { self.0 }
|
|
|
|
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
|
|
match self.tcx().normalized_cache.borrow().get(&ty).cloned() {
|
|
None => {}
|
|
Some(u) => return u
|
|
}
|
|
|
|
let t_norm = ty.super_fold_with(self);
|
|
self.tcx().normalized_cache.borrow_mut().insert(ty, t_norm);
|
|
return t_norm;
|
|
}
|
|
|
|
fn fold_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
|
|
where T : TypeFoldable<'tcx>
|
|
{
|
|
let u = self.tcx().anonymize_late_bound_regions(t);
|
|
u.super_fold_with(self)
|
|
}
|
|
|
|
fn fold_region(&mut self, r: ty::Region) -> ty::Region {
|
|
// because late-bound regions affect subtyping, we can't
|
|
// erase the bound/free distinction, but we can replace
|
|
// all free regions with 'static.
|
|
//
|
|
// Note that we *CAN* replace early-bound regions -- the
|
|
// type system never "sees" those, they get substituted
|
|
// away. In trans, they will always be erased to 'static
|
|
// whenever a substitution occurs.
|
|
match r {
|
|
ty::ReLateBound(..) => r,
|
|
_ => ty::ReStatic
|
|
}
|
|
}
|
|
|
|
fn fold_substs(&mut self,
|
|
substs: &subst::Substs<'tcx>)
|
|
-> subst::Substs<'tcx> {
|
|
subst::Substs { regions: subst::ErasedRegions,
|
|
types: substs.types.fold_with(self) }
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Region shifter
|
|
//
|
|
// Shifts the De Bruijn indices on all escaping bound regions by a
|
|
// fixed amount. Useful in substitution or when otherwise introducing
|
|
// a binding level that is not intended to capture the existing bound
|
|
// regions. See comment on `shift_regions_through_binders` method in
|
|
// `subst.rs` for more details.
|
|
|
|
pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
|
|
match region {
|
|
ty::ReLateBound(debruijn, br) => {
|
|
ty::ReLateBound(debruijn.shifted(amount), br)
|
|
}
|
|
_ => {
|
|
region
|
|
}
|
|
}
|
|
}
|
|
|
|
pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>>(tcx: &TyCtxt<'tcx>,
|
|
amount: u32, value: &T) -> T {
|
|
debug!("shift_regions(value={:?}, amount={})",
|
|
value, amount);
|
|
|
|
value.fold_with(&mut RegionFolder::new(tcx, &mut false, &mut |region, _current_depth| {
|
|
shift_region(region, amount)
|
|
}))
|
|
}
|
|
|
|
/// An "escaping region" is a bound region whose binder is not part of `t`.
|
|
///
|
|
/// So, for example, consider a type like the following, which has two binders:
|
|
///
|
|
/// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
|
|
/// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
|
|
/// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
|
|
///
|
|
/// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
|
|
/// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
|
|
/// fn type*, that type has an escaping region: `'a`.
|
|
///
|
|
/// Note that what I'm calling an "escaping region" is often just called a "free region". However,
|
|
/// we already use the term "free region". It refers to the regions that we use to represent bound
|
|
/// regions on a fn definition while we are typechecking its body.
|
|
///
|
|
/// To clarify, conceptually there is no particular difference between an "escaping" region and a
|
|
/// "free" region. However, there is a big difference in practice. Basically, when "entering" a
|
|
/// binding level, one is generally required to do some sort of processing to a bound region, such
|
|
/// as replacing it with a fresh/skolemized region, or making an entry in the environment to
|
|
/// represent the scope to which it is attached, etc. An escaping region represents a bound region
|
|
/// for which this processing has not yet been done.
|
|
struct HasEscapingRegionsVisitor {
|
|
depth: u32,
|
|
}
|
|
|
|
impl<'tcx> TypeVisitor<'tcx> for HasEscapingRegionsVisitor {
|
|
fn enter_region_binder(&mut self) {
|
|
self.depth += 1;
|
|
}
|
|
|
|
fn exit_region_binder(&mut self) {
|
|
self.depth -= 1;
|
|
}
|
|
|
|
fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
|
|
t.region_depth > self.depth
|
|
}
|
|
|
|
fn visit_region(&mut self, r: ty::Region) -> bool {
|
|
r.escapes_depth(self.depth)
|
|
}
|
|
}
|
|
|
|
struct HasTypeFlagsVisitor {
|
|
flags: ty::TypeFlags,
|
|
}
|
|
|
|
impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
|
|
fn visit_ty(&mut self, t: Ty) -> bool {
|
|
t.flags.get().intersects(self.flags)
|
|
}
|
|
|
|
fn visit_region(&mut self, r: ty::Region) -> bool {
|
|
if self.flags.intersects(ty::TypeFlags::HAS_LOCAL_NAMES) {
|
|
// does this represent a region that cannot be named
|
|
// in a global way? used in fulfillment caching.
|
|
match r {
|
|
ty::ReStatic | ty::ReEmpty => {}
|
|
_ => return true,
|
|
}
|
|
}
|
|
if self.flags.intersects(ty::TypeFlags::HAS_RE_INFER) {
|
|
match r {
|
|
ty::ReVar(_) | ty::ReSkolemized(..) => { return true }
|
|
_ => {}
|
|
}
|
|
}
|
|
false
|
|
}
|
|
}
|