privacy: reachability: Don't ICE on traits' Self generic parameter

The `Self` type of a Trait is part of its generic parameter list. This
fails lookup since it's not a properly defined type. We need to be able
to identify `Self` parameters and skip them in the reachability pass.

Author: CohenArthur

gcc/rust/privacy/rust-reachability.cc

@@ -53,7 +53,13 @@ ReachabilityVisitor::visit_generic_predicates (
 	  TyTy::BaseType *generic_ty = nullptr;
 	  auto ok = ty_ctx.lookup_type (generic->get_mappings ().get_hirid (),
 					&generic_ty);
-	  rust_assert (ok);
+
+	  // FIXME: This fails lookup on the `Self` generic parameter of the
+	  // trait definition. We can skip it for now, but that's not a real fix
+	  if (!ok)
+	    break;
+
+	  // rust_assert (ok);
 	  rust_assert (generic_ty->get_kind () == TyTy::PARAM);
 
 	  auto generic_param = static_cast<TyTy::ParamType *> (generic_ty);

gcc/testsuite/rust/compile/1128-ice-reachability.rs

@@ -0,0 +1,13 @@
+trait Hasher {
+    fn write(&mut self, bytes: &[u8]);
+    fn write_u8(&mut self, i: u8) {
+        self.write(&[i])
+    }
+}
+
+pub trait PubHasher {
+    fn p_write(&mut self, bytes: &[u8]);
+    fn p_write_u8(&mut self, i: u8) {
+        self.write(&[i])
+    }
+}