Rollup merge of #101468 - spastorino:fix-ice-rpit-hrtb-without-dyn, r=cjgillot

fix RPIT ICE for implicit HRTB when missing dyn

Closes #101297

r? `@cjgillot`

cc `@nikomatsakis`

4 files changed, 44 insertions, 2 deletions

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 3a94c7a91b2..29baa3a80c1 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -1561,8 +1561,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                 LifetimeRes::Fresh { param, binder: _ } => {
                     debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
-                    let old_def_id = self.local_def_id(param);
-                    if remapping.get(&old_def_id).is_none() {
+                    if let Some(old_def_id) = self.opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
                         let node_id = self.next_node_id();
 
                         let new_def_id = self.create_def(
diff --git a/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2015.stderr b/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2015.stderr
new file mode 100644
index 00000000000..fd2e454e7e4
--- /dev/null
+++ b/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2015.stderr
@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `(): AsRef<(dyn for<'r> Fn(&'r ()) + 'static)>` is not satisfied
+  --> $DIR/generic-with-implicit-hrtb-without-dyn.rs:6:13
+   |
+LL | fn ice() -> impl AsRef<Fn(&())> {
+   |             ^^^^^^^^^^^^^^^^^^^ the trait `AsRef<(dyn for<'r> Fn(&'r ()) + 'static)>` is not implemented for `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2021.stderr b/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2021.stderr
new file mode 100644
index 00000000000..c01c33a8931
--- /dev/null
+++ b/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.edition2021.stderr
@@ -0,0 +1,22 @@
+error[E0782]: trait objects must include the `dyn` keyword
+  --> $DIR/generic-with-implicit-hrtb-without-dyn.rs:6:24
+   |
+LL | fn ice() -> impl AsRef<Fn(&())> {
+   |                        ^^^^^^^
+   |
+help: add `dyn` keyword before this trait
+   |
+LL - fn ice() -> impl AsRef<Fn(&())> {
+LL + fn ice() -> impl AsRef<dyn Fn(&())> {
+   |
+
+error[E0277]: the trait bound `(): AsRef<(dyn for<'r> Fn(&'r ()) + 'static)>` is not satisfied
+  --> $DIR/generic-with-implicit-hrtb-without-dyn.rs:6:13
+   |
+LL | fn ice() -> impl AsRef<Fn(&())> {
+   |             ^^^^^^^^^^^^^^^^^^^ the trait `AsRef<(dyn for<'r> Fn(&'r ()) + 'static)>` is not implemented for `()`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0782.
+For more information about an error, try `rustc --explain E0277`.
diff --git a/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.rs b/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.rs
new file mode 100644
index 00000000000..856dc7a3f5a
--- /dev/null
+++ b/src/test/ui/impl-trait/generic-with-implicit-hrtb-without-dyn.rs
@@ -0,0 +1,12 @@
+// revisions: edition2015 edition2021
+//[edition2021]edition:2021
+
+#![allow(warnings)]
+
+fn ice() -> impl AsRef<Fn(&())> {
+    //~^ ERROR: the trait bound `(): AsRef<(dyn for<'r> Fn(&'r ()) + 'static)>` is not satisfied [E0277]
+    //[edition2021]~| ERROR: trait objects must include the `dyn` keyword [E0782]
+    todo!()
+}
+
+fn main() {}