Delegation: fix ICE on recursive delegation

compiler/rustc_ast_lowering/src/delegation.rs

@@ -67,7 +67,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
             return false;
         };
         if let Some(local_sig_id) = sig_id.as_local() {
-            self.resolver.delegation_fn_sigs[&local_sig_id].has_self
+            // The value may be missing due to recursive delegation.
+            // Error will be emmited later during HIR ty lowering.
+            self.resolver.delegation_fn_sigs.get(&local_sig_id).map_or(false, |sig| sig.has_self)
         } else {
             match self.tcx.def_kind(sig_id) {
                 DefKind::Fn => false,

tests/ui/delegation/ice-issue-124347.rs

@@ -0,0 +1,12 @@
+#![feature(fn_delegation)]
+#![allow(incomplete_features)]
+
+trait Trait {
+    reuse Trait::foo { &self.0 }
+    //~^ ERROR recursive delegation is not supported yet
+}
+
+reuse foo;
+//~^ ERROR recursive delegation is not supported yet
+
+fn main() {}

tests/ui/delegation/ice-issue-124347.stderr

@@ -0,0 +1,14 @@
+error: recursive delegation is not supported yet
+  --> $DIR/ice-issue-124347.rs:5:18
+   |
+LL |     reuse Trait::foo { &self.0 }
+   |                  ^^^ callee defined here
+
+error: recursive delegation is not supported yet
+  --> $DIR/ice-issue-124347.rs:9:7
+   |
+LL | reuse foo;
+   |       ^^^ callee defined here
+
+error: aborting due to 2 previous errors
+