Make "no def-id for fresh lifetime" a span_delayed_bug.

Fixes #121431.

Author: nnethercote

compiler/rustc_ast_lowering/src/lib.rs

@@ -1636,7 +1636,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     if let Some(old_def_id) = self.orig_opt_local_def_id(param) {
                         old_def_id
                     } else {
-                        self.dcx().span_bug(lifetime.ident.span, "no def-id for fresh lifetime");
+                        self.dcx()
+                            .span_delayed_bug(lifetime.ident.span, "no def-id for fresh lifetime");
+                        continue;
                     }
                 }
 

tests/ui/lowering/issue-121431.rs

@@ -0,0 +1,4 @@
+fn bug<T>() -> impl CallbackMarker< Item = [(); { |_: &mut ()| 3; 4 }] > {}
+//~^ ERROR cannot find trait `CallbackMarker` in this scope
+
+fn main() {}

tests/ui/lowering/issue-121431.stderr

@@ -0,0 +1,9 @@
+error[E0405]: cannot find trait `CallbackMarker` in this scope
+  --> $DIR/issue-121431.rs:1:21
+   |
+LL | fn bug<T>() -> impl CallbackMarker< Item = [(); { |_: &mut ()| 3; 4 }] > {}
+   |                     ^^^^^^^^^^^^^^ not found in this scope
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0405`.