Don't check for alias bounds in liveness when aliases have escaping bound vars

Author: compiler-errors

compiler/rustc_infer/src/infer/outlives/for_liveness.rs

@@ -1,4 +1,6 @@
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
+use rustc_middle::ty::{
+    self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
+};
 
 use std::ops::ControlFlow;
 
@@ -49,6 +51,12 @@ where
             return ControlFlow::Continue(());
         }
 
+        // FIXME: Don't consider alias bounds on types that have escaping bound
+        // vars. See #117455.
+        if ty.has_escaping_bound_vars() {
+            return ty.super_visit_with(self);
+        }
+
         match ty.kind() {
             // We can prove that an alias is live two ways:
             // 1. All the components are live.

tests/ui/type-alias-impl-trait/alias-bounds-when-bounds-escape.rs

@@ -0,0 +1,16 @@
+// check-pass
+
+trait Foo {
+    type Assoc<'a, 'b>: 'static;
+}
+
+struct MentionsLifetimeAndType<'a, T>(&'a (), T);
+
+fn foo<'a, 'b, T: Foo>(_: <T as Foo>::Assoc<'a, 'b>) {}
+
+fn test<'b, T: Foo>() {
+    let y: MentionsLifetimeAndType<'_, for<'a> fn(<T as Foo>::Assoc<'a, 'b>)> =
+        MentionsLifetimeAndType(&(), foo);
+}
+
+fn main() {}