From 37c70198c4acf54625a13faeb87390bb97ba9d24 Mon Sep 17 00:00:00 2001
From: Lukasz Samson <lukaszsamson@gmail.com>
Date: Tue, 4 Jun 2024 10:18:13 +0200
Subject: [PATCH] return OTP 27 process labels in debug adapter threads
 response

---
 .../debug_adapter/lib/debug_adapter/server.ex | 26 +++++--
 apps/debug_adapter/test/debugger_test.exs     | 72 +++++++++++++++++++
 2 files changed, 92 insertions(+), 6 deletions(-)

diff --git a/apps/debug_adapter/lib/debug_adapter/server.ex b/apps/debug_adapter/lib/debug_adapter/server.ex
index 41077f5b2..a0d80d83a 100644
--- a/apps/debug_adapter/lib/debug_adapter/server.ex
+++ b/apps/debug_adapter/lib/debug_adapter/server.ex
@@ -2278,13 +2278,27 @@ defmodule ElixirLS.DebugAdapter.Server do
   end
 
   defp process_name(process_info) do
-    registered_name = Keyword.get(process_info, :registered_name)
+    # if present registered_name is na atom
+    registered_name = Keyword.fetch(process_info, :registered_name)
+    # OTP 27+ process label may be any term
+    # it's not documented but :proc_lib.get_label reads `:$process_label` key from process dictionary
+    # https://github.com/erlang/otp/blob/601a012837ea0a5c8095bf24223132824177124d/lib/stdlib/src/proc_lib.erl#L876
+    # we have already read it so can get it directly
+    label = process_info |> Keyword.fetch!(:dictionary) |> Keyword.fetch(:"$process_label")
 
-    if registered_name do
-      inspect(registered_name)
-    else
-      {mod, func, arity} = Keyword.fetch!(process_info, :initial_call)
-      "#{inspect(mod)}.#{to_string(func)}/#{arity}"
+    case {registered_name, label} do
+      {{:ok, registered_name}, {:ok, label}} ->
+        "#{registered_name}: #{inspect(label)}"
+
+      {{:ok, registered_name}, _} ->
+        to_string(registered_name)
+
+      {_, {:ok, label}} ->
+        inspect(label)
+
+      _ ->
+        {mod, func, arity} = Keyword.fetch!(process_info, :initial_call)
+        "#{inspect(mod)}.#{to_string(func)}/#{arity}"
     end
   end
 
diff --git a/apps/debug_adapter/test/debugger_test.exs b/apps/debug_adapter/test/debugger_test.exs
index 66e05c172..24692cc74 100644
--- a/apps/debug_adapter/test/debugger_test.exs
+++ b/apps/debug_adapter/test/debugger_test.exs
@@ -3303,6 +3303,78 @@ defmodule ElixirLS.DebugAdapter.ServerTest do
     end)
   end
 
+  if System.otp_release() |> String.to_integer() >= 27 do
+    @tag :fixture
+    test "returns process label", %{server: server} do
+      in_fixture(__DIR__, "mix_project", fn ->
+        Server.receive_packet(server, initialize_req(1, %{}))
+
+        assert_receive(
+          response(_, 1, "initialize", %{"supportsConfigurationDoneRequest" => true})
+        )
+
+        Server.receive_packet(
+          server,
+          launch_req(2, %{
+            "request" => "launch",
+            "type" => "mix_task",
+            "task" => "run",
+            "taskArgs" => ["-e", "MixProject.Some.sleep()"],
+            "projectDir" => File.cwd!()
+          })
+        )
+
+        assert_receive(response(_, 2, "launch", %{}), 5000)
+        assert_receive(event(_, "initialized", %{}))
+
+        Server.receive_packet(server, request(5, "configurationDone", %{}))
+        assert_receive(response(_, 5, "configurationDone", %{}))
+        Process.sleep(1000)
+
+        {:ok, pid} =
+          Task.start(fn ->
+            :proc_lib.set_label("foo")
+
+            receive do
+              :done -> :ok
+            end
+          end)
+
+        Process.monitor(pid)
+
+        send(server, :update_threads)
+        state = :sys.get_state(server)
+
+        thread_id = state.pids_to_thread_ids[pid]
+        assert thread_id
+        assert state.thread_ids_to_pids[thread_id] == pid
+
+        Server.receive_packet(server, request(6, "threads", %{}))
+        assert_receive(response(_, 6, "threads", %{"threads" => threads}), 1_000)
+
+        assert Enum.find(threads, &(&1["id"] == thread_id))["name"] ==
+                 "\"foo\" #{:erlang.pid_to_list(pid)}"
+
+        send(pid, :done)
+
+        receive do
+          {:DOWN, _, _, ^pid, _} -> :ok
+        end
+
+        send(server, :update_threads)
+        state = :sys.get_state(server)
+
+        refute Map.has_key?(state.pids_to_thread_ids, pid)
+        refute Map.has_key?(state.thread_ids_to_pids, thread_id)
+
+        Server.receive_packet(server, request(6, "threads", %{}))
+        assert_receive(response(_, 6, "threads", %{"threads" => threads}), 1_000)
+
+        refute Enum.find(threads, &(&1["id"] == thread_id))
+      end)
+    end
+  end
+
   describe "evaluate" do
     defp gen_watch_expression_packet(seq, expr) do
       %{