1 files changed, 33 insertions, 34 deletions

diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 1884df0c67b..e352d0bc756 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -6,6 +6,7 @@ use self::TyKind::*;
 
 use crate::infer::canonical::Canonical;
 use crate::ty::fold::BoundVarsCollector;
+use crate::ty::fold::ValidateBoundVars;
 use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
 use crate::ty::InferTy::{self, *};
 use crate::ty::{
@@ -63,22 +64,10 @@ pub enum BoundRegionKind {
 #[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, TyDecodable, Debug, PartialOrd, Ord)]
 #[derive(HashStable)]
 pub struct BoundRegion {
+    pub var: BoundVar,
     pub kind: BoundRegionKind,
 }
 
-impl BoundRegion {
-    /// When canonicalizing, we replace unbound inference variables and free
-    /// regions with anonymous late bound regions. This method asserts that
-    /// we have an anonymous late bound region, which hence may refer to
-    /// a canonical variable.
-    pub fn assert_bound_var(&self) -> BoundVar {
-        match self.kind {
-            BoundRegionKind::BrAnon(var) => BoundVar::from_u32(var),
-            _ => bug!("bound region is not anonymous"),
-        }
-    }
-}
-
 impl BoundRegionKind {
     pub fn is_named(&self) -> bool {
         match *self {
@@ -987,13 +976,17 @@ where
         value.visit_with(&mut collector);
         Binder(value, collector.into_vars(tcx))
     }
-}
 
-impl<'tcx, T> Binder<'tcx, T> {
     pub fn bind_with_vars(value: T, vars: &'tcx List<BoundVariableKind>) -> Binder<'tcx, T> {
+        if cfg!(debug_assertions) {
+            let mut validator = ValidateBoundVars::new(vars);
+            value.visit_with(&mut validator);
+        }
         Binder(value, vars)
     }
+}
 
+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
     /// De Bruijn indices and the like. It is usually better to
@@ -1022,18 +1015,31 @@ impl<'tcx, T> Binder<'tcx, T> {
         Binder(&self.0, self.1)
     }
 
-    pub fn map_bound_ref<F, U>(&self, f: F) -> Binder<'tcx, U>
+    pub fn map_bound_ref_unchecked<F, U>(&self, f: F) -> Binder<'tcx, U>
+    where
+        F: FnOnce(&T) -> U,
+    {
+        let value = f(&self.0);
+        Binder(value, self.1)
+    }
+
+    pub fn map_bound_ref<F, U: TypeFoldable<'tcx>>(&self, f: F) -> Binder<'tcx, U>
     where
         F: FnOnce(&T) -> U,
     {
         self.as_ref().map_bound(f)
     }
 
-    pub fn map_bound<F, U>(self, f: F) -> Binder<'tcx, U>
+    pub fn map_bound<F, U: TypeFoldable<'tcx>>(self, f: F) -> Binder<'tcx, U>
     where
         F: FnOnce(T) -> U,
     {
-        Binder(f(self.0), self.1)
+        let value = f(self.0);
+        if cfg!(debug_assertions) {
+            let mut validator = ValidateBoundVars::new(self.1);
+            value.visit_with(&mut validator);
+        }
+        Binder(value, self.1)
     }
 
     /// Wraps a `value` in a binder, using the same bound variables as the
@@ -1045,7 +1051,14 @@ impl<'tcx, T> Binder<'tcx, T> {
     /// don't actually track bound vars. However, semantically, it is different
     /// because bound vars aren't allowed to change here, whereas they are
     /// in `bind`. This may be (debug) asserted in the future.
-    pub fn rebind<U>(&self, value: U) -> Binder<'tcx, U> {
+    pub fn rebind<U>(&self, value: U) -> Binder<'tcx, U>
+    where
+        U: TypeFoldable<'tcx>,
+    {
+        if cfg!(debug_assertions) {
+            let mut validator = ValidateBoundVars::new(self.bound_vars());
+            value.visit_with(&mut validator);
+        }
         Binder(value, self.1)
     }
 
@@ -1066,20 +1079,6 @@ impl<'tcx, T> Binder<'tcx, T> {
         if self.0.has_escaping_bound_vars() { None } else { Some(self.skip_binder()) }
     }
 
-    /// Given two things that have the same binder level,
-    /// and an operation that wraps on their contents, executes the operation
-    /// and then wraps its result.
-    ///
-    /// `f` should consider bound regions at depth 1 to be free, and
-    /// anything it produces with bound regions at depth 1 will be
-    /// bound in the resulting return value.
-    pub fn fuse<U, F, R>(self, u: Binder<'tcx, U>, f: F) -> Binder<'tcx, R>
-    where
-        F: FnOnce(T, U) -> R,
-    {
-        Binder(f(self.0, u.0), self.1)
-    }
-
     /// Splits the contents into two things that share the same binder
     /// level as the original, returning two distinct binders.
     ///
@@ -1204,7 +1203,7 @@ pub type PolyFnSig<'tcx> = Binder<'tcx, FnSig<'tcx>>;
 impl<'tcx> PolyFnSig<'tcx> {
     #[inline]
     pub fn inputs(&self) -> Binder<'tcx, &'tcx [Ty<'tcx>]> {
-        self.map_bound_ref(|fn_sig| fn_sig.inputs())
+        self.map_bound_ref_unchecked(|fn_sig| fn_sig.inputs())
     }
     #[inline]
     pub fn input(&self, index: usize) -> ty::Binder<'tcx, Ty<'tcx>> {