From f1679f7dd6330535cd2dbd0dd18ded0dc8a7e6d9 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 29 Aug 2023 23:47:01 +0000
Subject: [PATCH] Capture lifetimes for associated type bounds destined to be
 lowered to opaques

---
 compiler/rustc_ast_lowering/src/lib.rs        | 11 +++++++++++
 compiler/rustc_resolve/src/late.rs            |  1 +
 .../lifetime-in-associated-trait-bound.rs     | 19 +++++++++++++++++++
 3 files changed, 31 insertions(+)
 create mode 100644 tests/ui/impl-trait/in-trait/lifetime-in-associated-trait-bound.rs

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index a4ba1a5c9bf..a6d1ef33f40 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -153,6 +153,7 @@ trait ResolverAstLoweringExt {
     fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
     fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
     fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
+    fn remap_extra_lifetime_params(&mut self, from: NodeId, to: NodeId);
     fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
 }
 
@@ -213,6 +214,11 @@ fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, Life
         self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
     }
 
+    fn remap_extra_lifetime_params(&mut self, from: NodeId, to: NodeId) {
+        let lifetimes = self.extra_lifetime_params_map.remove(&from).unwrap_or_default();
+        self.extra_lifetime_params_map.insert(to, lifetimes);
+    }
+
     fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
         self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
     }
@@ -1089,6 +1095,11 @@ enum DesugarKind<'a> {
                         // constructing the HIR for `impl bounds...` and then lowering that.
 
                         let impl_trait_node_id = self.next_node_id();
+                        // Shift `impl Trait` lifetime captures from the associated type bound's
+                        // node id to the opaque node id, so that the opaque can actually use
+                        // these lifetime bounds.
+                        self.resolver
+                            .remap_extra_lifetime_params(constraint.id, impl_trait_node_id);
 
                         self.with_dyn_type_scope(false, |this| {
                             let node_id = this.next_node_id();
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 500004269c9..fa04a594555 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1109,6 +1109,7 @@ fn visit_assoc_constraint(&mut self, constraint: &'ast AssocConstraint) {
                 }
             },
             AssocConstraintKind::Bound { ref bounds } => {
+                self.record_lifetime_params_for_impl_trait(constraint.id);
                 walk_list!(self, visit_param_bound, bounds, BoundKind::Bound);
             }
         }
diff --git a/tests/ui/impl-trait/in-trait/lifetime-in-associated-trait-bound.rs b/tests/ui/impl-trait/in-trait/lifetime-in-associated-trait-bound.rs
new file mode 100644
index 00000000000..49d36d6c99c
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/lifetime-in-associated-trait-bound.rs
@@ -0,0 +1,19 @@
+// check-pass
+
+#![feature(associated_type_bounds, return_position_impl_trait_in_trait)]
+
+trait Trait {
+    type Type;
+
+    fn method(&self) -> impl Trait<Type: '_>;
+}
+
+impl Trait for () {
+    type Type = ();
+
+    fn method(&self) -> impl Trait<Type: '_> {
+        ()
+    }
+}
+
+fn main() {}