Language protocol: use default settings of the rust language server. didChangeConfiguration has to be sent though, for some reason, or else the rust language server will not respond to all supported request types.

src/source_language_protocol.cc

@@ -153,7 +153,7 @@ LanguageProtocol::Capabilities LanguageProtocol::Client::initialize(Source::Lang
 
       write_notification("initialized", "");
       if(language_id == "rust")
-        write_notification("workspace/didChangeConfiguration", R"("settings":{"rust":{"sysroot":null,"target":null,"rustflags":null,"clear_env_rust_log":true,"build_lib":null,"build_bin":null,"cfg_test":false,"unstable_features":false,"wait_to_build":500,"show_warnings":true,"goto_def_racer_fallback":false,"use_crate_blacklist":true,"build_on_save":false,"workspace_mode":true,"analyze_package":null,"features":[],"all_features":false,"no_default_features":false}})");
+        write_notification("workspace/didChangeConfiguration", R"("settings":{"rust":{}})");
     }
     result_processed.set_value();
   });