Keep previous compiler_refs

[ismaelga]

Was seeing this errors from NextLS. They where caused by starting new compilation before last one completed. Keeping compiler refs seems to do the trick.
I was wondering if a better approach would be to kill the old one as it's probably not relevant anymore

14:24:17.546 [error] GenServer #PID<0.271.0> terminating
** (FunctionClauseError) no function clause matching in NextLS.Runtime.handle_info/2
    (next_ls 0.12.6) lib/next_ls/runtime.ex:241: NextLS.Runtime.handle_info({#Reference<0.0.34691.4055572929.3734306818.94126>, [%Mix.Task.Compiler.Diagnostic{file: "...", severity: :error, message: "...", position: 6, compiler_name: "Elixir", details: nil, stacktrace: [{UsedSailboat.Repo, :__MODULE__, 0, [file: "...", line: 6]}]}, %Mix.Task.Compiler.Diagnostic{file: "...", severity: :error, message: "...", position: 0, compiler_name: "Elixir", details: nil, stacktrace: [{:elixir_expand, :expand, 3, [file: ~c"src/elixir_expand.erl", line: 92]}, {:elixir_expand, :expand_block, 5, [file: ~c"src/elixir_expand.erl", line: 538]}, {:elixir_expand, :expand, 3, [file: ~c"src/elixir_expand.erl", line: 46]}, {Kernel, :use, 2, [file: ~c"expanding macro"]}, {UsedSailboat.Repo, :__MODULE__, 0, [file: ~c"lib/used_sailboat/repo.ex", line: 6]}]}]}, %{logger: #PID<0.259.0>, name: "...", node: :"...", parent: ~c"", port: #Port<0.10>, registry: NextLS.Registry, errors: nil, task_supervisor: :runtime_task_supervisor, on_initialized: #Function<33.24109284/1 in NextLS.handle_notification/2>, working_dir: "...", compiler_ref: %{#Reference<0.0.34691.4055572929.3734306817.102674> => {#PID<0.286.0>, #Reference<0.4055572929.3734241281.102671>}, #Reference<0.0.34691.4055572929.3734306817.110339> => {#PID<0.288.0>, #Reference<0.4055572929.3734241281.110336>}}})
    (stdlib 5.0.2) gen_server.erl:1077: :gen_server.try_handle_info/3
    (stdlib 5.0.2) gen_server.erl:1165: :gen_server.handle_msg/6
    (stdlib 5.0.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3

[mhanberg]

I was wondering if a better approach would be to kill the old one as it's probably not relevant anymore

Yes, cancelling them should be done. You can see an example of that in next_ls.ex

Thanks for this patch!