Delay span bug when we can't map lifetimes back in collect_trait_impl_trait_tys

compiler/rustc_hir_analysis/src/check/compare_method.rs

@@ -598,8 +598,16 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
                 let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
                 let ty = tcx.fold_regions(ty, |region, _| {
                     let ty::ReFree(_) = region.kind() else { return region; };
-                    let ty::ReEarlyBound(e) = map[&region.into()].expect_region().kind()
-                        else { bug!("expected ReFree to map to ReEarlyBound"); };
+                    let Some(ty::ReEarlyBound(e)) = map.get(&region.into()).map(|r| r.expect_region().kind())
+                    else {
+                        tcx
+                            .sess
+                            .delay_span_bug(
+                                return_span,
+                                "expected ReFree to map to ReEarlyBound"
+                            );
+                        return tcx.lifetimes.re_static;
+                    };
                     tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
                         def_id: e.def_id,
                         name: e.name,

src/test/ui/impl-trait/in-trait/signature-mismatch.rs

@@ -0,0 +1,21 @@
+// edition:2021
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::future::Future;
+
+pub trait AsyncTrait {
+    fn async_fn(&self, buff: &[u8]) -> impl Future<Output = Vec<u8>>;
+}
+
+pub struct Struct;
+
+impl AsyncTrait for Struct {
+    fn async_fn<'a>(&self, buff: &'a [u8]) -> impl Future<Output = Vec<u8>> + 'a {
+        //~^ ERROR `impl` item signature doesn't match `trait` item signature
+        async move { buff.to_vec() }
+    }
+}
+
+fn main() {}

src/test/ui/impl-trait/in-trait/signature-mismatch.stderr

@@ -0,0 +1,16 @@
+error: `impl` item signature doesn't match `trait` item signature
+  --> $DIR/signature-mismatch.rs:15:5
+   |
+LL |     fn async_fn(&self, buff: &[u8]) -> impl Future<Output = Vec<u8>>;
+   |     ----------------------------------------------------------------- expected `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + 'static`
+...
+LL |     fn async_fn<'a>(&self, buff: &'a [u8]) -> impl Future<Output = Vec<u8>> + 'a {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '2`
+   |
+   = note: expected `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + 'static`
+              found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '2`
+   = help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
+   = help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
+
+error: aborting due to previous error
+