LSP crash: cannot convert the given list to a string

[kape1395]

I'm getting this crash quite often (VSCode)

2026-03-03 10:18:53.212 [info]   Message: ** (ErlangError) Erlang error: {:exception, %ArgumentError{message: "cannot convert the given list to a string.\n\nTo be converted to a string, a list must either be empty or only\ncontain the following elements:\n\n  * strings\n  * integers representing Unicode code points\n  * a list containing one of these three elements\n\nPlease check the given list or call inspect/1 to get the list representation, got:\n\n[{:describe_opt, [closing: [line: 90, column: 32], line: 90, column: 19], []}]\n"}, [{List, :to_string, 1, [file: ~c"lib/list.ex", line: 1128]}, {XPEngine.Search.Indexer.Extractors.ExUnit, :extract, 2, [file: ~c"lib/engine/search/indexer/extractors/ex_unit.ex", line: 45]}, {XPEngine.Search.Indexer.Source.Reducer, :"-apply_extractors/2-fun-0-", 2, [file: ~c"lib/engine/search/indexer/source/reducer.ex", line: 97]}, {Enum, :"-reduce/3-lists^foldl/2-0-", 3, [file: ~c"lib/enum.ex", line: 2520]}, {XPEngine.Search.Indexer.Quoted, :"-extract_entries/2-fun-0-", 2, [file: ~c"lib/engine/search/indexer/quoted.ex", line: 27]}, {Macro, :"-do_traverse_args/4-fun-0-", 4, [file: ~c"lib/macro.ex", line: 663]}, {:lists, :mapfoldl_1, 3, [file: ~c"lists.erl", line: 2673]}, {Macro, :do_traverse, 4, [file: ~c"lib/macro.ex", line: 628]}]}
    (kernel 10.2.7.1) erpc.erl:1368: :erpc.call/5
    (xp_expert 0.1.0-rc.5-44a43e2) lib/expert/provider/handlers/document_symbols.ex:21: XPExpert.Provider.Handlers.DocumentSymbols.handle/1
    (xp_expert 0.1.0-rc.5-44a43e2) lib/expert.ex:119: XPExpert.handle_request/2
    (xp_gen_lsp 0.11.3) lib/gen_lsp.ex:390: anonymous fn/2 in XPGenLSP.loop/3
    (xp_telemetry 1.3.0) /home/runner/work/expert/expert/apps/expert/deps/telemetry/src/telemetry.erl:324: :xp_telemetry.span/3
    (xp_gen_lsp 0.11.3) lib/gen_lsp.ex:389: anonymous fn/5 in XPGenLSP.loop/3
    (xp_gen_lsp 0.11.3) lib/gen_lsp.ex:559: anonymous fn/4 in XPGenLSP.attempt/4
    (elixir 1.17.3) lib/task/supervised.ex:101: Task.Supervised.invoke_mfa/2

  Code: -32603 

Expert version:

2026-03-03 10:17:07.806 [info] Latest release is tagged "nightly", published at 2026-02-28T00:28:16Z
2026-03-03 10:17:08.292 [info] Checksums match for nightly nightly; using installed version, no download needed

[katafrakt]

This is comming from test files. I'm able to reproduce the crash with code like this:

describe [:a, :b, :c] do
    test "w00t" do
      assert true
    end
  end

But this is also incorrect code that does not compile, so I doubt you are doing anything like that. However, do you do anything special with the describes in this codebase?

[kape1395]

I don't have ex_unit describe in the codebase directly.
This error happened when I was editing a non-test file, and no test files were opened.
The code is compiling. It is enough to open a file, not even edit it.

But, with your hint, I made a reproducible case:

defmodule ExExpert do
  @spec describe([term()]) :: :ok
  def describe(opts)

  def describe(_opts) do
    :ok
  end
end

It doesn't crash if the function is called differently, but if it's named describe, then the crashes happen.