3 files changed, 77 insertions, 6 deletions

diff --git a/crates/hir_ty/src/autoderef.rs b/crates/hir_ty/src/autoderef.rs
index f8e9db9ae..71bc436e6 100644
--- a/crates/hir_ty/src/autoderef.rs
+++ b/crates/hir_ty/src/autoderef.rs
@@ -6,14 +6,15 @@
 use std::iter::successors;
 
 use base_db::CrateId;
-use chalk_ir::cast::Cast;
+use chalk_ir::{cast::Cast, fold::Fold, interner::HasInterner, VariableKind};
 use hir_def::lang_item::LangItemTarget;
 use hir_expand::name::name;
 use log::{info, warn};
 
 use crate::{
-    db::HirDatabase, AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds, DebruijnIndex,
-    InEnvironment, Interner, ProjectionTyExt, Solution, Ty, TyBuilder, TyKind,
+    db::HirDatabase, static_lifetime, AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds,
+    DebruijnIndex, InEnvironment, Interner, ProjectionTyExt, Solution, Substitution, Ty, TyBuilder,
+    TyKind,
 };
 
 const AUTODEREF_RECURSION_LIMIT: usize = 10;
@@ -103,7 +104,7 @@ fn deref_by_trait(
         binders: CanonicalVarKinds::from_iter(
             &Interner,
             ty.goal.binders.iter(&Interner).cloned().chain(Some(chalk_ir::WithKind::new(
-                chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General),
+                VariableKind::Ty(chalk_ir::TyVariableKind::General),
                 chalk_ir::UniverseIndex::ROOT,
             ))),
         ),
@@ -136,7 +137,9 @@ fn deref_by_trait(
                     return None;
                 }
             }
-            Some(Canonical {
+            // FIXME: we remove lifetime variables here since they can confuse
+            // the method resolution code later
+            Some(fixup_lifetime_variables(Canonical {
                 value: vars
                     .value
                     .subst
@@ -144,7 +147,7 @@ fn deref_by_trait(
                     .assert_ty_ref(&Interner)
                     .clone(),
                 binders: vars.binders.clone(),
-            })
+            }))
         }
         Solution::Ambig(_) => {
             info!("Ambiguous solution for derefing {:?}: {:?}", ty.goal, solution);
@@ -152,3 +155,32 @@ fn deref_by_trait(
         }
     }
 }
+
+fn fixup_lifetime_variables<T: Fold<Interner, Result = T> + HasInterner<Interner = Interner>>(
+    c: Canonical<T>,
+) -> Canonical<T> {
+    // Removes lifetime variables from the Canonical, replacing them by static lifetimes.
+    let mut i = 0;
+    let subst = Substitution::from_iter(
+        &Interner,
+        c.binders.iter(&Interner).map(|vk| match vk.kind {
+            VariableKind::Ty(_) => {
+                let index = i;
+                i += 1;
+                BoundVar::new(DebruijnIndex::INNERMOST, index).to_ty(&Interner).cast(&Interner)
+            }
+            VariableKind::Lifetime => static_lifetime().cast(&Interner),
+            VariableKind::Const(_) => unimplemented!(),
+        }),
+    );
+    let binders = CanonicalVarKinds::from_iter(
+        &Interner,
+        c.binders.iter(&Interner).filter(|vk| match vk.kind {
+            VariableKind::Ty(_) => true,
+            VariableKind::Lifetime => false,
+            VariableKind::Const(_) => true,
+        }),
+    );
+    let value = subst.apply(c.value, &Interner);
+    Canonical { binders, value }
+}
diff --git a/crates/hir_ty/src/method_resolution.rs b/crates/hir_ty/src/method_resolution.rs
index 55c7b1a09..ece884241 100644
--- a/crates/hir_ty/src/method_resolution.rs
+++ b/crates/hir_ty/src/method_resolution.rs
@@ -654,6 +654,7 @@ fn iterate_trait_method_candidates(
                 }
             }
             known_implemented = true;
+            // FIXME: we shouldn't be ignoring the binders here
             if callback(&self_ty.value, *item) {
                 return true;
             }
diff --git a/crates/hir_ty/src/tests/regression.rs b/crates/hir_ty/src/tests/regression.rs
index b69f86050..9cd9f473d 100644
--- a/crates/hir_ty/src/tests/regression.rs
+++ b/crates/hir_ty/src/tests/regression.rs
@@ -974,3 +974,41 @@ fn param_overrides_fn() {
         "#,
     )
 }
+
+#[test]
+fn lifetime_from_chalk_during_deref() {
+    check_types(
+        r#"
+        #[lang = "deref"]
+        pub trait Deref {
+            type Target;
+        }
+
+        struct Box<T: ?Sized> {}
+        impl<T> Deref for Box<T> {
+            type Target = T;
+
+            fn deref(&self) -> &Self::Target {
+                loop {}
+            }
+        }
+
+        trait Iterator {
+            type Item;
+        }
+
+        pub struct Iter<'a, T: 'a> {
+            inner: Box<dyn IterTrait<'a, T, Item = &'a T> + 'a>,
+        }
+
+        trait IterTrait<'a, T: 'a>: Iterator<Item = &'a T> {
+            fn clone_box(&self);
+        }
+
+        fn clone_iter<T>(s: Iter<T>) {
+            s.inner.clone_box();
+          //^^^^^^^^^^^^^^^^^^^ ()
+        }
+        "#,
+    )
+}