Handle not_found result from docsh (erlang-ls#1198)

Also make sure that functions dealing with temporary group leader
here have no chance to get stuck altogether.

Fixes erlang-ls#1177.

apps/els_lsp/src/els_docs.erl

@@ -342,16 +342,22 @@ edoc(M, F, A) ->
  , [doc, spec]]),
  flush_group_leader_proxy(GL),
 
- {ok, [{{function, F, A}, _Anno,
- _Signature, Desc, _Metadata}|_]} = Res,
- format_edoc(Desc)
+ case Res of
+ {ok, [{{function, F, A}, _Anno,
+ _Signature, Desc, _Metadata}|_]} ->
+ format_edoc(Desc);
+ {not_found, _} ->
+ []
+ end
  catch C:E:ST ->
  IO = flush_group_leader_proxy(GL),
  ?LOG_DEBUG("[hover] Error fetching edoc [error=~p]",
  [{M, F, A, C, E, ST, IO}]),
  case IO of
  timeout ->
  [];
+ noproc ->
+ [];
  IO ->
  [{text, IO}]
  end
@@ -389,15 +395,24 @@ setup_group_leader_proxy() ->
 -spec flush_group_leader_proxy(pid()) -> [term()] | term().
 flush_group_leader_proxy(OrigGL) ->
  GL = group_leader(),
- Ref = monitor(process, GL),
- group_leader(OrigGL, self()),
- GL ! {get, Ref, self()},
- receive
- {Ref, Msg} ->
+ case GL of
+ OrigGL ->
+ % This is the effect of setting a monitor on nonexisting process.
+ noproc;
+ _ ->
+ Ref = monitor(process, GL),
+ group_leader(OrigGL, self()),
+ GL ! {get, Ref, self()},
+ receive
+ {Ref, Msg} ->
  demonitor(Ref, [flush]),
  Msg;
- {'DOWN', process, Ref, Reason} ->
+  {'DOWN', process, Ref, Reason} ->
  Reason
+ after 5000 ->
+ demonitor(Ref, [flush]),
+ timeout
+ end
  end.
 
 -spec spawn_group_proxy([any()]) -> ok.