Bug: LiveDebugger stops working after code reload (#384)

* load modules after code reload

* fix tests

* add comment

* listen to Mix.Tasks.Compile.Elixir for modules load

* fix tests

* fix pattern match

Author: GuzekAlan

lib/live_debugger/gen_servers/callback_tracing_server.ex

@@ -47,26 +47,15 @@ defmodule LiveDebugger.GenServers.CallbackTracingServer do
     Dbg.tracer(:process, {&handle_trace/2, 0})
     Dbg.p(:all, [:c, :timestamp])
 
-    all_modules = ModuleDiscoveryService.all_modules()
-
-    callbacks =
-      all_modules
-      |> ModuleDiscoveryService.live_view_modules()
-      |> CallbackUtils.live_view_callbacks()
-
-    all_modules
-    |> ModuleDiscoveryService.live_component_modules()
-    |> CallbackUtils.live_component_callbacks()
-    |> Enum.concat(callbacks)
-    |> Enum.each(fn mfa ->
-      Dbg.tp(mfa, [{:_, [], [{:return_trace}]}])
-      Dbg.tp(mfa, [{:_, [], [{:exception_trace}]}])
-    end)
+    add_live_modules_to_tracer()
 
     # This is not a callback created by user
     # We trace it to refresh the components tree
     Dbg.tp({Phoenix.LiveView.Diff, :delete_component, 2}, [])
 
+    # We need to get information when code reloads to properly trace modules
+    Dbg.tp({Mix.Tasks.Compile.Elixir, :run, 1}, [{:_, [], [{:return_trace}]}])
+
     {:noreply, state}
   end
 
@@ -79,6 +68,16 @@ defmodule LiveDebugger.GenServers.CallbackTracingServer do
   # Because of that we do it asynchronously to speed up tracer a bit
   # We do not persist this trace because it is not displayed to user
   @spec handle_trace(term(), n :: integer()) :: integer()
+  defp handle_trace({_, _, :return_from, {Mix.Tasks.Compile.Elixir, _, _}, _, _}, n) do
+    Process.sleep(100)
+    add_live_modules_to_tracer()
+    n
+  end
+
+  defp handle_trace({_, _, _, {Mix.Tasks.Compile.Elixir, _, _}, _}, n) do
+    n
+  end
+
   defp handle_trace(
          {_, pid, _, {Phoenix.LiveView.Diff, :delete_component, [cid | _] = args}, timestamp},
          n
@@ -144,6 +143,24 @@ defmodule LiveDebugger.GenServers.CallbackTracingServer do
     n
   end
 
+  defp add_live_modules_to_tracer() do
+    all_modules = ModuleDiscoveryService.all_modules()
+
+    callbacks =
+      all_modules
+      |> ModuleDiscoveryService.live_view_modules()
+      |> CallbackUtils.live_view_callbacks()
+
+    all_modules
+    |> ModuleDiscoveryService.live_component_modules()
+    |> CallbackUtils.live_component_callbacks()
+    |> Enum.concat(callbacks)
+    |> Enum.each(fn mfa ->
+      Dbg.tp(mfa, [{:_, [], [{:return_trace}]}])
+      Dbg.tp(mfa, [{:_, [], [{:exception_trace}]}])
+    end)
+  end
+
   @spec persist_trace(Trace.t()) :: :ok | {:error, term()}
   defp persist_trace(%Trace{} = trace) do
     TraceService.insert(trace)

test/gen_servers/callback_tracing_server_test.exs

@@ -50,6 +50,9 @@ defmodule LiveDebugger.GenServers.CallbackTracingServerTest do
 
     MockDbg
     |> expect(:tp, fn {Phoenix.LiveView.Diff, :delete_component, 2}, [] -> :ok end)
+    |> expect(:tp, fn {Mix.Tasks.Compile.Elixir, :run, 1}, [{:_, [], [{:return_trace}]}] ->
+      :ok
+    end)
 
     assert {:noreply, %{}} = CallbackTracingServer.handle_info(:setup_tracing, %{})
   end
@@ -62,6 +65,9 @@ defmodule LiveDebugger.GenServers.CallbackTracingServerTest do
       MockDbg
       |> expect(:p, fn :all, [:c, :timestamp] -> :ok end)
       |> expect(:tp, fn {Phoenix.LiveView.Diff, :delete_component, 2}, [] -> :ok end)
+      |> expect(:tp, fn {Mix.Tasks.Compile.Elixir, :run, 1}, [{:_, [], [{:return_trace}]}] ->
+        :ok
+      end)
 
       # In order to keep CallbackTracingServer.handle_trace function private we extract it here
       # and send to test process so that we can test it