fix(dap): keep evaluator registry when continuing all processes

apps/debug_adapter/lib/debug_adapter/server.ex

@@ -1644,8 +1644,9 @@ defmodule ElixirLS.DebugAdapter.Server do
 
       # Get the existing evaluator registry
       existing_registry =
-        case Map.fetch!(state.paused_processes, :evaluator) do
-          %PausedProcess{registry: registry} -> registry
+        case Map.fetch(state.paused_processes, :evaluator) do
+          {:ok, %PausedProcess{registry: registry}} -> registry
+          :error -> %PausedProcess{}.registry
         end
 
       {updated_registry, var_id} =
@@ -1847,13 +1848,15 @@ defmodule ElixirLS.DebugAdapter.Server do
       end
 
     # continue erlang debugger paused processes
-    for {paused_pid, %PausedProcess{ref: ref}} <- state.paused_processes do
+    for {paused_pid, %PausedProcess{ref: ref}} <- state.paused_processes, is_pid(paused_pid) do
       safe_int_action(paused_pid, :continue)
       if ref, do: Process.demonitor(ref, [:flush])
       paused_pid
     end
 
-    %{state | paused_processes: %{}}
+    # the :evaluator entry is not a real process - it holds variables from
+    # evaluate requests and needs to outlive paused processes
+    %{state | paused_processes: Map.take(state.paused_processes, [:evaluator])}
   end
 
   # Defensive wrapper around :int actions. :int is finicky and can raise from

apps/debug_adapter/test/debugger_test.exs

@@ -4203,6 +4203,41 @@ defmodule ElixirLS.DebugAdapter.ServerTest do
         assert Process.alive?(server)
       end)
     end
+
+    test "evaluate expression after continuing all processes", %{server: server} do
+      in_fixture(__DIR__, "mix_project", fn ->
+        Server.receive_packet(server, initialize_req_(1))
+        assert_receive(response(_, 1, "initialize", _))
+
+        Server.receive_packet(
+          server,
+          launch_req(2, %{
+            "request" => "launch",
+            "type" => "mix_task",
+            "task" => "run",
+            "taskArgs" => ["-e", "MixProject.Dbg.simple()"],
+            "projectDir" => File.cwd!()
+          })
+        )
+
+        assert_receive(response(_, 2, "launch"), 3000)
+        assert_receive(event(_, "initialized", _), 5000)
+
+        Server.receive_packet(server, request(5, "configurationDone", %{}))
+        assert_receive(response(_, 5, "configurationDone"))
+
+        assert_receive event(_, "stopped", %{"threadId" => thread_id}), 5_000
+
+        # continuing all processes must not drop the evaluator entry
+        Server.receive_packet(server, continue_req(6, thread_id))
+        assert_receive response(_, 6, "continue", %{"allThreadsContinued" => true})
+
+        Server.receive_packet(server, gen_watch_expression_packet(7, "1 + 2 + 3 + 4"))
+        assert_receive(%{"body" => %{"result" => "10"}}, 5000)
+
+        assert Process.alive?(server)
+      end)
+    end
   end
 
   test "completions", %{server: server} do