Uplift TypeVisitableExt into rustc_type_ir

compiler/rustc_middle/src/ty/consts.rs

@@ -35,6 +35,16 @@ impl<'tcx> IntoKind for Const<'tcx> {
     }
 }
 
+impl<'tcx> rustc_type_ir::visit::Flags for Const<'tcx> {
+    fn flags(&self) -> TypeFlags {
+        self.0.flags
+    }
+
+    fn outer_exclusive_binder(&self) -> rustc_type_ir::DebruijnIndex {
+        self.0.outer_exclusive_binder
+    }
+}
+
 impl<'tcx> ConstTy<TyCtxt<'tcx>> for Const<'tcx> {
     fn ty(self) -> Ty<'tcx> {
         self.ty()
@@ -63,11 +73,13 @@ impl<'tcx> Const<'tcx> {
         self.0.kind
     }
 
+    // FIXME(compiler-errors): Think about removing this.
     #[inline]
     pub fn flags(self) -> TypeFlags {
         self.0.flags
     }
 
+    // FIXME(compiler-errors): Think about removing this.
     #[inline]
     pub fn outer_exclusive_binder(self) -> ty::DebruijnIndex {
         self.0.outer_exclusive_binder

compiler/rustc_middle/src/ty/context.rs

@@ -88,6 +88,8 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type Term = ty::Term<'tcx>;
 
     type Binder<T> = Binder<'tcx, T>;
+    type BoundVars = &'tcx List<ty::BoundVariableKind>;
+    type BoundVar = ty::BoundVariableKind;
     type CanonicalVars = CanonicalVarInfos<'tcx>;
 
     type Ty = Ty<'tcx>;
@@ -151,6 +153,11 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     ) -> Self::Const {
         Const::new_bound(self, debruijn, var, ty)
     }
+
+    fn expect_error_or_delayed_bug() {
+        let has_errors = ty::tls::with(|tcx| tcx.dcx().has_errors_or_lint_errors_or_delayed_bugs());
+        assert!(has_errors.is_some());
+    }
 }
 
 type InternedSet<'tcx, T> = ShardedHashMap<InternedInSet<'tcx, T>, ()>;

compiler/rustc_middle/src/ty/mod.rs

@@ -503,6 +503,16 @@ impl<'tcx> IntoKind for Ty<'tcx> {
     }
 }
 
+impl<'tcx> rustc_type_ir::visit::Flags for Ty<'tcx> {
+    fn flags(&self) -> TypeFlags {
+        self.0.flags
+    }
+
+    fn outer_exclusive_binder(&self) -> DebruijnIndex {
+        self.0.outer_exclusive_binder
+    }
+}
+
 impl EarlyParamRegion {
     /// Does this early bound region have a name? Early bound regions normally
     /// always have names except when using anonymous lifetimes (`'_`).

compiler/rustc_middle/src/ty/predicate.rs

@@ -29,6 +29,16 @@ pub struct Predicate<'tcx>(
     pub(super) Interned<'tcx, WithCachedTypeInfo<ty::Binder<'tcx, PredicateKind<'tcx>>>>,
 );
 
+impl<'tcx> rustc_type_ir::visit::Flags for Predicate<'tcx> {
+    fn flags(&self) -> TypeFlags {
+        self.0.flags
+    }
+
+    fn outer_exclusive_binder(&self) -> ty::DebruijnIndex {
+        self.0.outer_exclusive_binder
+    }
+}
+
 impl<'tcx> Predicate<'tcx> {
     /// Gets the inner `ty::Binder<'tcx, PredicateKind<'tcx>>`.
     #[inline]
@@ -36,11 +46,13 @@ impl<'tcx> Predicate<'tcx> {
         self.0.internee
     }
 
+    // FIXME(compiler-errors): Think about removing this.
     #[inline(always)]
     pub fn flags(self) -> TypeFlags {
         self.0.flags
     }
 
+    // FIXME(compiler-errors): Think about removing this.
     #[inline(always)]
     pub fn outer_exclusive_binder(self) -> DebruijnIndex {
         self.0.outer_exclusive_binder

compiler/rustc_middle/src/ty/region.rs

@@ -26,6 +26,19 @@ impl<'tcx> rustc_type_ir::IntoKind for Region<'tcx> {
     }
 }
 
+impl<'tcx> rustc_type_ir::visit::Flags for Region<'tcx> {
+    fn flags(&self) -> TypeFlags {
+        self.type_flags()
+    }
+
+    fn outer_exclusive_binder(&self) -> ty::DebruijnIndex {
+        match **self {
+            ty::ReBound(debruijn, _) => debruijn.shifted_in(1),
+            _ => ty::INNERMOST,
+        }
+    }
+}
+
 impl<'tcx> Region<'tcx> {
     #[inline]
     pub fn new_early_param(

compiler/rustc_middle/src/ty/sty.rs

@@ -942,6 +942,16 @@ where
     }
 }
 
+impl<'tcx, T> rustc_type_ir::BoundVars<TyCtxt<'tcx>> for ty::Binder<'tcx, T> {
+    fn bound_vars(&self) -> &'tcx List<ty::BoundVariableKind> {
+        self.bound_vars
+    }
+
+    fn has_no_bound_vars(&self) -> bool {
+        self.bound_vars.is_empty()
+    }
+}
+
 impl<'tcx, T> Binder<'tcx, T> {
     /// Skips the binder and returns the "bound" value. This is a
     /// risky thing to do because it's easy to get confused about
@@ -1808,6 +1818,7 @@ impl<'tcx> Ty<'tcx> {
         self.0.0
     }
 
+    // FIXME(compiler-errors): Think about removing this.
     #[inline(always)]
     pub fn flags(self) -> TypeFlags {
         self.0.0.flags

compiler/rustc_middle/src/ty/util.rs

@@ -1320,6 +1320,7 @@ impl<'tcx> Ty<'tcx> {
         ty
     }
 
+    // FIXME(compiler-errors): Think about removing this.
     #[inline]
     pub fn outer_exclusive_binder(self) -> ty::DebruijnIndex {
         self.0.outer_exclusive_binder

compiler/rustc_middle/src/ty/visit.rs

@@ -1,140 +1,10 @@
 use crate::ty::{self, Binder, Ty, TyCtxt, TypeFlags};
-use rustc_errors::ErrorGuaranteed;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sso::SsoHashSet;
 use std::ops::ControlFlow;
 
-pub use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
+pub use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
-
-pub trait TypeVisitableExt<'tcx>: TypeVisitable<TyCtxt<'tcx>> {
-    /// Returns `true` if `self` has any late-bound regions that are either
-    /// bound by `binder` or bound by some binder outside of `binder`.
-    /// If `binder` is `ty::INNERMOST`, this indicates whether
-    /// there are any late-bound regions that appear free.
-    fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
-        self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder }).is_break()
-    }
-
-    /// Returns `true` if this type has any regions that escape `binder` (and
-    /// hence are not bound by it).
-    fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
-        self.has_vars_bound_at_or_above(binder.shifted_in(1))
-    }
-
-    /// Return `true` if this type has regions that are not a part of the type.
-    /// For example, `for<'a> fn(&'a i32)` return `false`, while `fn(&'a i32)`
-    /// would return `true`. The latter can occur when traversing through the
-    /// former.
-    ///
-    /// See [`HasEscapingVarsVisitor`] for more information.
-    fn has_escaping_bound_vars(&self) -> bool {
-        self.has_vars_bound_at_or_above(ty::INNERMOST)
-    }
-
-    fn has_type_flags(&self, flags: TypeFlags) -> bool {
-        let res =
-            self.visit_with(&mut HasTypeFlagsVisitor { flags }).break_value() == Some(FoundFlags);
-        trace!(?self, ?flags, ?res, "has_type_flags");
-        res
-    }
-    fn has_projections(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_PROJECTION)
-    }
-    fn has_inherent_projections(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_TY_INHERENT)
-    }
-    fn has_opaque_types(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
-    }
-    fn has_coroutines(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_TY_COROUTINE)
-    }
-    fn references_error(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_ERROR)
-    }
-    fn error_reported(&self) -> Result<(), ErrorGuaranteed> {
-        if self.references_error() {
-            // We must include lint errors and delayed bugs here.
-            if let Some(reported) =
-                ty::tls::with(|tcx| tcx.dcx().has_errors_or_lint_errors_or_delayed_bugs())
-            {
-                Err(reported)
-            } else {
-                bug!("expected some kind of error in `error_reported`");
-            }
-        } else {
-            Ok(())
-        }
-    }
-    fn has_non_region_param(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_PARAM - TypeFlags::HAS_RE_PARAM)
-    }
-    fn has_infer_regions(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_RE_INFER)
-    }
-    fn has_infer_types(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_TY_INFER)
-    }
-    fn has_non_region_infer(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_INFER - TypeFlags::HAS_RE_INFER)
-    }
-    fn has_infer(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_INFER)
-    }
-    fn has_placeholders(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_PLACEHOLDER)
-    }
-    fn has_non_region_placeholders(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_PLACEHOLDER - TypeFlags::HAS_RE_PLACEHOLDER)
-    }
-    fn has_param(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_PARAM)
-    }
-    /// "Free" regions in this context means that it has any region
-    /// that is not (a) erased or (b) late-bound.
-    fn has_free_regions(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
-    }
-
-    fn has_erased_regions(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_RE_ERASED)
-    }
-
-    /// True if there are any un-erased free regions.
-    fn has_erasable_regions(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
-    }
-
-    /// Indicates whether this value references only 'global'
-    /// generic parameters that are the same regardless of what fn we are
-    /// in. This is used for caching.
-    fn is_global(&self) -> bool {
-        !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
-    }
-
-    /// True if there are any late-bound regions
-    fn has_bound_regions(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_RE_BOUND)
-    }
-    /// True if there are any late-bound non-region variables
-    fn has_non_region_bound_vars(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_BOUND_VARS - TypeFlags::HAS_RE_BOUND)
-    }
-    /// True if there are any bound variables
-    fn has_bound_vars(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_BOUND_VARS)
-    }
-
-    /// Indicates whether this value still has parameters/placeholders/inference variables
-    /// which could be replaced later, in a way that would change the results of `impl`
-    /// specialization.
-    fn still_further_specializable(&self) -> bool {
-        self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
-    }
-}
-
-impl<'tcx, T: TypeVisitable<TyCtxt<'tcx>>> TypeVisitableExt<'tcx> for T {}
 
 ///////////////////////////////////////////////////////////////////////////
 // Region folder
@@ -370,185 +240,6 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ValidateBoundVars<'tcx> {
     }
 }
 
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-struct FoundEscapingVars;
-
-/// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
-/// bound region or a bound type.
-///
-/// 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 var" is often just called a "free var". However,
-/// we already use the term "free var". It refers to the regions or types that we use to represent
-/// bound regions or type params on a fn definition while we are type checking its body.
-///
-/// To clarify, conceptually there is no particular difference between
-/// an "escaping" var and a "free" var. 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 var, such as replacing it with a fresh/placeholder
-/// var, or making an entry in the environment to represent the
-/// scope to which it is attached, etc. An escaping var represents
-/// a bound var for which this processing has not yet been done.
-struct HasEscapingVarsVisitor {
-    /// Anything bound by `outer_index` or "above" is escaping.
-    outer_index: ty::DebruijnIndex,
-}
-
-impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasEscapingVarsVisitor {
-    type BreakTy = FoundEscapingVars;
-
-    fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
-        &mut self,
-        t: &Binder<'tcx, T>,
-    ) -> ControlFlow<Self::BreakTy> {
-        self.outer_index.shift_in(1);
-        let result = t.super_visit_with(self);
-        self.outer_index.shift_out(1);
-        result
-    }
-
-    #[inline]
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // If the outer-exclusive-binder is *strictly greater* than
-        // `outer_index`, that means that `t` contains some content
-        // bound at `outer_index` or above (because
-        // `outer_exclusive_binder` is always 1 higher than the
-        // content in `t`). Therefore, `t` has some escaping vars.
-        if t.outer_exclusive_binder() > self.outer_index {
-            ControlFlow::Break(FoundEscapingVars)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-
-    #[inline]
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // If the region is bound by `outer_index` or anything outside
-        // of outer index, then it escapes the binders we have
-        // visited.
-        if r.bound_at_or_above_binder(self.outer_index) {
-            ControlFlow::Break(FoundEscapingVars)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-
-    fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // If the outer-exclusive-binder is *strictly greater* than
-        // `outer_index`, that means that `ct` contains some content
-        // bound at `outer_index` or above (because
-        // `outer_exclusive_binder` is always 1 higher than the
-        // content in `t`). Therefore, `t` has some escaping vars.
-        if ct.outer_exclusive_binder() > self.outer_index {
-            ControlFlow::Break(FoundEscapingVars)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-
-    #[inline]
-    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
-        if predicate.outer_exclusive_binder() > self.outer_index {
-            ControlFlow::Break(FoundEscapingVars)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-}
-
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-struct FoundFlags;
-
-// FIXME: Optimize for checking for infer flags
-struct HasTypeFlagsVisitor {
-    flags: ty::TypeFlags,
-}
-
-impl std::fmt::Debug for HasTypeFlagsVisitor {
-    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.flags.fmt(fmt)
-    }
-}
-
-// Note: this visitor traverses values down to the level of
-// `Ty`/`Const`/`Predicate`, but not within those types. This is because the
-// type flags at the outer layer are enough. So it's faster than it first
-// looks, particular for `Ty`/`Predicate` where it's just a field access.
-//
-// N.B. The only case where this isn't totally true is binders, which also
-// add `HAS_{RE,TY,CT}_LATE_BOUND` flag depending on the *bound variables* that
-// are present, regardless of whether those bound variables are used. This
-// is important for anonymization of binders in `TyCtxt::erase_regions`. We
-// specifically detect this case in `visit_binder`.
-impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasTypeFlagsVisitor {
-    type BreakTy = FoundFlags;
-
-    fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
-        &mut self,
-        t: &Binder<'tcx, T>,
-    ) -> ControlFlow<Self::BreakTy> {
-        // If we're looking for the HAS_BINDER_VARS flag, check if the
-        // binder has vars. This won't be present in the binder's bound
-        // value, so we need to check here too.
-        if self.flags.intersects(TypeFlags::HAS_BINDER_VARS) && !t.bound_vars().is_empty() {
-            return ControlFlow::Break(FoundFlags);
-        }
-
-        t.super_visit_with(self)
-    }
-
-    #[inline]
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // Note: no `super_visit_with` call.
-        let flags = t.flags();
-        if flags.intersects(self.flags) {
-            ControlFlow::Break(FoundFlags)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-
-    #[inline]
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // Note: no `super_visit_with` call, as usual for `Region`.
-        let flags = r.type_flags();
-        if flags.intersects(self.flags) {
-            ControlFlow::Break(FoundFlags)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-
-    #[inline]
-    fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // Note: no `super_visit_with` call.
-        if c.flags().intersects(self.flags) {
-            ControlFlow::Break(FoundFlags)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-
-    #[inline]
-    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
-        // Note: no `super_visit_with` call.
-        if predicate.flags().intersects(self.flags) {
-            ControlFlow::Break(FoundFlags)
-        } else {
-            ControlFlow::Continue(())
-        }
-    }
-}
-
 /// Collects all the late-bound regions at the innermost binding level
 /// into a hash set.
 struct LateBoundRegionsCollector {

compiler/rustc_type_ir/src/binder.rs

@@ -0,0 +1,7 @@
+use crate::Interner;
+
+pub trait BoundVars<I: Interner> {
+    fn bound_vars(&self) -> I::BoundVars;
+
+    fn has_no_bound_vars(&self) -> bool;
+}

compiler/rustc_type_ir/src/interner.rs

@@ -3,8 +3,8 @@ use std::fmt::Debug;
 use std::hash::Hash;
 
 use crate::{
-    BoundVar, CanonicalVarInfo, ConstKind, DebruijnIndex, DebugWithInfcx, RegionKind, TyKind,
+    BoundVar, BoundVars, CanonicalVarInfo, ConstKind, DebruijnIndex, DebugWithInfcx, RegionKind,
-    UniverseIndex,
+    TyKind, UniverseIndex,
 };
 
 pub trait Interner: Sized {
@@ -19,7 +19,10 @@ pub trait Interner: Sized {
     type GenericArg: Copy + DebugWithInfcx<Self> + Hash + Ord;
     type Term: Copy + Debug + Hash + Ord;
 
-    type Binder<T>;
+    type Binder<T>: BoundVars<Self>;
+    type BoundVars: IntoIterator<Item = Self::BoundVar>;
+    type BoundVar;
+
     type CanonicalVars: Copy + Debug + Hash + Eq + IntoIterator<Item = CanonicalVarInfo<Self>>;
 
     // Kinds of tys
@@ -86,6 +89,9 @@ pub trait Interner: Sized {
     fn mk_bound_ty(self, debruijn: DebruijnIndex, var: BoundVar) -> Self::Ty;
     fn mk_bound_region(self, debruijn: DebruijnIndex, var: BoundVar) -> Self::Region;
     fn mk_bound_const(self, debruijn: DebruijnIndex, var: BoundVar, ty: Self::Ty) -> Self::Const;
+
+    /// Assert that an error has been delayed or emitted.
+    fn expect_error_or_delayed_bug();
 }
 
 /// Common capabilities of placeholder kinds

compiler/rustc_type_ir/src/lib.rs

@@ -30,6 +30,7 @@ pub mod visit;
 
 #[macro_use]
 mod macros;
+mod binder;
 mod canonical;
 mod const_kind;
 mod debug;
@@ -39,6 +40,7 @@ mod interner;
 mod predicate_kind;
 mod region_kind;
 
+pub use binder::*;
 pub use canonical::*;
 #[cfg(feature = "nightly")]
 pub use codec::*;

compiler/rustc_type_ir/src/visit.rs

@@ -45,8 +45,7 @@ use rustc_index::{Idx, IndexVec};
 use std::fmt;
 use std::ops::ControlFlow;
 
-use crate::Interner;
+use crate::{self as ty, BoundVars, Interner, IntoKind, Lrc, TypeFlags};
-use crate::Lrc;
 
 /// This trait is implemented for every type that can be visited,
 /// providing the skeleton of the traversal.
@@ -200,3 +199,393 @@ impl<I: Interner, T: TypeVisitable<I>, Ix: Idx> TypeVisitable<I> for IndexVec<Ix
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
+
+pub trait Flags {
+    fn flags(&self) -> TypeFlags;
+    fn outer_exclusive_binder(&self) -> ty::DebruijnIndex;
+}
+
+pub trait TypeVisitableExt<I: Interner>: TypeVisitable<I> {
+    fn has_type_flags(&self, flags: TypeFlags) -> bool;
+
+    /// Returns `true` if `self` has any late-bound regions that are either
+    /// bound by `binder` or bound by some binder outside of `binder`.
+    /// If `binder` is `ty::INNERMOST`, this indicates whether
+    /// there are any late-bound regions that appear free.
+    fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool;
+
+    /// Returns `true` if this type has any regions that escape `binder` (and
+    /// hence are not bound by it).
+    fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
+        self.has_vars_bound_at_or_above(binder.shifted_in(1))
+    }
+
+    /// Return `true` if this type has regions that are not a part of the type.
+    /// For example, `for<'a> fn(&'a i32)` return `false`, while `fn(&'a i32)`
+    /// would return `true`. The latter can occur when traversing through the
+    /// former.
+    ///
+    /// See [`HasEscapingVarsVisitor`] for more information.
+    fn has_escaping_bound_vars(&self) -> bool {
+        self.has_vars_bound_at_or_above(ty::INNERMOST)
+    }
+
+    fn has_projections(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_PROJECTION)
+    }
+
+    fn has_inherent_projections(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_TY_INHERENT)
+    }
+
+    fn has_opaque_types(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
+    }
+
+    fn has_coroutines(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_TY_COROUTINE)
+    }
+
+    fn references_error(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_ERROR)
+    }
+
+    fn error_reported(&self) -> Result<(), I::ErrorGuaranteed>;
+
+    fn has_non_region_param(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_PARAM - TypeFlags::HAS_RE_PARAM)
+    }
+
+    fn has_infer_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_RE_INFER)
+    }
+
+    fn has_infer_types(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_TY_INFER)
+    }
+
+    fn has_non_region_infer(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_INFER - TypeFlags::HAS_RE_INFER)
+    }
+
+    fn has_infer(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_INFER)
+    }
+
+    fn has_placeholders(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_PLACEHOLDER)
+    }
+
+    fn has_non_region_placeholders(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_PLACEHOLDER - TypeFlags::HAS_RE_PLACEHOLDER)
+    }
+
+    fn has_param(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_PARAM)
+    }
+
+    /// "Free" regions in this context means that it has any region
+    /// that is not (a) erased or (b) late-bound.
+    fn has_free_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
+    }
+
+    fn has_erased_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_RE_ERASED)
+    }
+
+    /// True if there are any un-erased free regions.
+    fn has_erasable_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
+    }
+
+    /// Indicates whether this value references only 'global'
+    /// generic parameters that are the same regardless of what fn we are
+    /// in. This is used for caching.
+    fn is_global(&self) -> bool {
+        !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
+    }
+
+    /// True if there are any late-bound regions
+    fn has_bound_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_RE_BOUND)
+    }
+    /// True if there are any late-bound non-region variables
+    fn has_non_region_bound_vars(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_BOUND_VARS - TypeFlags::HAS_RE_BOUND)
+    }
+    /// True if there are any bound variables
+    fn has_bound_vars(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_BOUND_VARS)
+    }
+
+    /// Indicates whether this value still has parameters/placeholders/inference variables
+    /// which could be replaced later, in a way that would change the results of `impl`
+    /// specialization.
+    fn still_further_specializable(&self) -> bool {
+        self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
+    }
+}
+
+impl<I: Interner, T: TypeVisitable<I>> TypeVisitableExt<I> for T
+where
+    I::Ty: Flags,
+    I::Region: Flags,
+    I::Const: Flags,
+    I::Predicate: Flags,
+{
+    fn has_type_flags(&self, flags: TypeFlags) -> bool {
+        let res =
+            self.visit_with(&mut HasTypeFlagsVisitor { flags }) == ControlFlow::Break(FoundFlags);
+        res
+    }
+
+    fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
+        self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder }).is_break()
+    }
+
+    fn error_reported(&self) -> Result<(), I::ErrorGuaranteed> {
+        if self.references_error() {
+            if let ControlFlow::Break(guar) = self.visit_with(&mut HasErrorVisitor) {
+                Err(guar)
+            } else {
+                panic!("type flags said there was an error, but now there is not")
+            }
+        } else {
+            Ok(())
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+struct FoundFlags;
+
+// FIXME: Optimize for checking for infer flags
+struct HasTypeFlagsVisitor {
+    flags: ty::TypeFlags,
+}
+
+impl std::fmt::Debug for HasTypeFlagsVisitor {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.flags.fmt(fmt)
+    }
+}
+
+// Note: this visitor traverses values down to the level of
+// `Ty`/`Const`/`Predicate`, but not within those types. This is because the
+// type flags at the outer layer are enough. So it's faster than it first
+// looks, particular for `Ty`/`Predicate` where it's just a field access.
+//
+// N.B. The only case where this isn't totally true is binders, which also
+// add `HAS_{RE,TY,CT}_LATE_BOUND` flag depending on the *bound variables* that
+// are present, regardless of whether those bound variables are used. This
+// is important for anonymization of binders in `TyCtxt::erase_regions`. We
+// specifically detect this case in `visit_binder`.
+impl<I: Interner> TypeVisitor<I> for HasTypeFlagsVisitor
+where
+    I::Ty: Flags,
+    I::Region: Flags,
+    I::Const: Flags,
+    I::Predicate: Flags,
+{
+    type BreakTy = FoundFlags;
+
+    fn visit_binder<T: TypeVisitable<I>>(&mut self, t: &I::Binder<T>) -> ControlFlow<Self::BreakTy>
+    where
+        I::Binder<T>: TypeSuperVisitable<I>,
+    {
+        // If we're looking for the HAS_BINDER_VARS flag, check if the
+        // binder has vars. This won't be present in the binder's bound
+        // value, so we need to check here too.
+        if self.flags.intersects(TypeFlags::HAS_BINDER_VARS) && !t.has_no_bound_vars() {
+            return ControlFlow::Break(FoundFlags);
+        }
+
+        t.super_visit_with(self)
+    }
+
+    #[inline]
+    fn visit_ty(&mut self, t: I::Ty) -> ControlFlow<Self::BreakTy> {
+        // Note: no `super_visit_with` call.
+        let flags = t.flags();
+        if flags.intersects(self.flags) {
+            ControlFlow::Break(FoundFlags)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
+    #[inline]
+    fn visit_region(&mut self, r: I::Region) -> ControlFlow<Self::BreakTy> {
+        // Note: no `super_visit_with` call, as usual for `Region`.
+        let flags = r.flags();
+        if flags.intersects(self.flags) {
+            ControlFlow::Break(FoundFlags)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
+    #[inline]
+    fn visit_const(&mut self, c: I::Const) -> ControlFlow<Self::BreakTy> {
+        // Note: no `super_visit_with` call.
+        if c.flags().intersects(self.flags) {
+            ControlFlow::Break(FoundFlags)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
+    #[inline]
+    fn visit_predicate(&mut self, predicate: I::Predicate) -> ControlFlow<Self::BreakTy> {
+        // Note: no `super_visit_with` call.
+        if predicate.flags().intersects(self.flags) {
+            ControlFlow::Break(FoundFlags)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+struct FoundEscapingVars;
+
+/// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
+/// bound region or a bound type.
+///
+/// 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 var" is often just called a "free var". However,
+/// we already use the term "free var". It refers to the regions or types that we use to represent
+/// bound regions or type params on a fn definition while we are type checking its body.
+///
+/// To clarify, conceptually there is no particular difference between
+/// an "escaping" var and a "free" var. 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 var, such as replacing it with a fresh/placeholder
+/// var, or making an entry in the environment to represent the
+/// scope to which it is attached, etc. An escaping var represents
+/// a bound var for which this processing has not yet been done.
+struct HasEscapingVarsVisitor {
+    /// Anything bound by `outer_index` or "above" is escaping.
+    outer_index: ty::DebruijnIndex,
+}
+
+impl<I: Interner> TypeVisitor<I> for HasEscapingVarsVisitor
+where
+    I::Ty: Flags,
+    I::Region: Flags,
+    I::Const: Flags,
+    I::Predicate: Flags,
+{
+    type BreakTy = FoundEscapingVars;
+
+    fn visit_binder<T: TypeVisitable<I>>(&mut self, t: &I::Binder<T>) -> ControlFlow<Self::BreakTy>
+    where
+        I::Binder<T>: TypeSuperVisitable<I>,
+    {
+        self.outer_index.shift_in(1);
+        let result = t.super_visit_with(self);
+        self.outer_index.shift_out(1);
+        result
+    }
+
+    #[inline]
+    fn visit_ty(&mut self, t: I::Ty) -> ControlFlow<Self::BreakTy> {
+        // If the outer-exclusive-binder is *strictly greater* than
+        // `outer_index`, that means that `t` contains some content
+        // bound at `outer_index` or above (because
+        // `outer_exclusive_binder` is always 1 higher than the
+        // content in `t`). Therefore, `t` has some escaping vars.
+        if t.outer_exclusive_binder() > self.outer_index {
+            ControlFlow::Break(FoundEscapingVars)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
+    #[inline]
+    fn visit_region(&mut self, r: I::Region) -> ControlFlow<Self::BreakTy> {
+        // If the region is bound by `outer_index` or anything outside
+        // of outer index, then it escapes the binders we have
+        // visited.
+        if r.outer_exclusive_binder() > self.outer_index {
+            ControlFlow::Break(FoundEscapingVars)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
+    fn visit_const(&mut self, ct: I::Const) -> ControlFlow<Self::BreakTy> {
+        // If the outer-exclusive-binder is *strictly greater* than
+        // `outer_index`, that means that `ct` contains some content
+        // bound at `outer_index` or above (because
+        // `outer_exclusive_binder` is always 1 higher than the
+        // content in `t`). Therefore, `t` has some escaping vars.
+        if ct.outer_exclusive_binder() > self.outer_index {
+            ControlFlow::Break(FoundEscapingVars)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
+    #[inline]
+    fn visit_predicate(&mut self, predicate: I::Predicate) -> ControlFlow<Self::BreakTy> {
+        if predicate.outer_exclusive_binder() > self.outer_index {
+            ControlFlow::Break(FoundEscapingVars)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+}
+
+struct HasErrorVisitor;
+
+impl<I: Interner> TypeVisitor<I> for HasErrorVisitor
+where
+    I::Ty: Flags,
+    I::Region: Flags,
+    I::Const: Flags,
+    I::Predicate: Flags,
+{
+    type BreakTy = I::ErrorGuaranteed;
+
+    fn visit_ty(&mut self, t: <I as Interner>::Ty) -> ControlFlow<Self::BreakTy>
+    where
+        <I as Interner>::Ty: TypeSuperVisitable<I>,
+    {
+        if let ty::Error(guar) = t.kind() {
+            ControlFlow::Break(guar)
+        } else {
+            t.super_visit_with(self)
+        }
+    }
+
+    fn visit_const(&mut self, c: <I as Interner>::Const) -> ControlFlow<Self::BreakTy>
+    where
+        <I as Interner>::Const: TypeSuperVisitable<I>,
+    {
+        if let ty::ConstKind::Error(guar) = c.kind() {
+            ControlFlow::Break(guar)
+        } else {
+            c.super_visit_with(self)
+        }
+    }
+
+    fn visit_region(&mut self, r: <I as Interner>::Region) -> ControlFlow<Self::BreakTy> {
+        if let ty::ReError(guar) = r.kind() {
+            ControlFlow::Break(guar)
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+}