Handle Task/GenServer exits correctly in Google formatter

We were running into a situation where errors caused by GenServers
terminating were not being formatted because they were a slightly
different shape to what was expected in the formatter. This updates the
formatter to handle them.

lib/logger_json/formatters/google_cloud.ex

@@ -188,11 +188,15 @@ defmodule LoggerJSON.Formatters.GoogleCloud do
     format_reported_error_event(message, ruby_stacktrace, service_context, meta)
   end
 
-  def format_crash_reason(binary, {error, reason}, service_context, meta) do
+  def format_crash_reason(binary, {error, reason}, service_context, meta) when is_atom(error) or is_binary(error) do
     stacktrace = "** (#{error}) #{inspect(reason)}"
     format_reported_error_event(binary, stacktrace, service_context, meta)
   end
 
+  def format_crash_reason(binary, {error, reason}, service_context, meta) do
+    format_crash_reason(binary, {inspect(error), reason}, service_context, meta)
+  end
+
   defp format_reported_error_event(message, stacktrace, service_context, meta) do
     %{
       "@type": "type.googleapis.com/google.devtools.clouderrorreporting.v1beta1.ReportedErrorEvent",

test/logger_json/formatters/google_cloud_test.exs

@@ -414,6 +414,51 @@ defmodule LoggerJSON.Formatters.GoogleCloudTest do
            } = log_entry
   end
 
+  test "logs Task/GenServer termination" do
+    test_pid = self()
+
+    logs =
+      capture_log(fn ->
+        {:ok, _} = Supervisor.start_link([{CrashingGenServer, :ok}], strategy: :one_for_one)
+
+        {:ok, _} =
+          Task.start(fn ->
+            try do
+              GenServer.call(CrashingGenServer, :boom)
+            catch
+              _ -> nil
+            after
+              send(test_pid, :done)
+            end
+          end)
+
+        # Wait for task to finish
+        receive do
+          :done -> nil
+        end
+
+        # Let logs flush
+        Process.sleep(100)
+      end)
+
+    refute logs =~ "FORMATTER CRASH"
+
+    [_, log_entry] =
+      logs
+      |> String.trim()
+      |> String.split("\n")
+      |> Enum.map(&decode_or_print_error/1)
+
+    assert %{
+             "@type" => "type.googleapis.com/google.devtools.clouderrorreporting.v1beta1.ReportedErrorEvent",
+             "message" => message,
+             "stack_trace" => "** ({{%RuntimeError{message: \"boom\"}" <> _,
+             "serviceContext" => %{"service" => "nonode@nohost"}
+           } = log_entry
+
+    assert message =~ ~r/Task #PID<\d+.\d+.\d+> started from #{inspect(test_pid)} terminating/
+  end
+
   test "logs process exits" do
     Logger.metadata(crash_reason: {{:EXIT, self()}, :sad_failure})
 

test/support/crashing_gen_server.ex

@@ -0,0 +1,15 @@
+defmodule CrashingGenServer do
+  use GenServer
+
+  def start_link(_) do
+    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
+  end
+
+  def init(state) do
+    {:ok, state}
+  end
+
+  def handle_call(:boom, _, _) do
+    raise "boom"
+  end
+end