Handle a few cases of unchecked Task.Supervisor.start_child returns

lib/livebook/hubs.ex

@@ -127,15 +127,16 @@ defmodule Livebook.Hubs do
   defp disconnect_hub(hub) do
     # We use a task supervisor because the hub connection itself
     # calls delete_hub (which calls this function), otherwise we deadlock.
-    Task.Supervisor.start_child(Livebook.TaskSupervisor, fn ->
-      # Since other processes may have been communicating
-      # with the hub, we don't want to terminate abruptly and
-      # make them crash, so we give it some time to shut down.
-      #
-      # The default backoff is 5.5s, so we round it down to 5s.
-      Process.sleep(30_000)
-      :ok = Provider.disconnect(hub)
-    end)
+    {:ok, _pid} =
+      Task.Supervisor.start_child(Livebook.TaskSupervisor, fn ->
+        # Since other processes may have been communicating
+        # with the hub, we don't want to terminate abruptly and
+        # make them crash, so we give it some time to shut down.
+        #
+        # The default backoff is 5.5s, so we round it down to 5s.
+        Process.sleep(30_000)
+        :ok = Provider.disconnect(hub)
+      end)
 
     :ok
   end

lib/livebook/runtime/dependencies.ex

@@ -235,10 +235,11 @@ defmodule Livebook.Runtime.Dependencies do
   def search_packages_on_hex(send_to, search) do
     ref = make_ref()
 
-    Task.Supervisor.start_child(Livebook.TaskSupervisor, fn ->
-      response = search_hex(search)
-      send(send_to, {:runtime_search_packages_response, ref, response})
-    end)
+    {:ok, _pid} =
+      Task.Supervisor.start_child(Livebook.TaskSupervisor, fn ->
+        response = search_hex(search)
+        send(send_to, {:runtime_search_packages_response, ref, response})
+      end)
 
     ref
   end

lib/livebook/runtime/erl_dist/runtime_server.ex

@@ -172,30 +172,31 @@ defmodule Livebook.Runtime.ErlDist.RuntimeServer do
     if same_host?(pid) do
       callback.(path)
     else
-      Task.Supervisor.start_child(Livebook.TaskSupervisor, fn ->
-        md5 = file_md5(path)
-
-        target_path =
-          case GenServer.call(pid, {:transfer_file_open, file_id, md5}, :infinity) do
-            {:noop, target_path} ->
-              target_path
-
-            {:transfer, target_path, target_pid} ->
-              try do
-                path
-                |> File.stream!(64_000, [])
-                |> Enum.each(fn chunk -> IO.binwrite(target_pid, chunk) end)
+      {:ok, _pid} =
+        Task.Supervisor.start_child(Livebook.TaskSupervisor, fn ->
+          md5 = file_md5(path)
 
+          target_path =
+            case GenServer.call(pid, {:transfer_file_open, file_id, md5}, :infinity) do
+              {:noop, target_path} ->
                 target_path
-              rescue
-                _error -> nil
-              after
-                File.close(target_pid)
-              end
-          end
 
-        callback.(target_path)
-      end)
+              {:transfer, target_path, target_pid} ->
+                try do
+                  path
+                  |> File.stream!(64_000, [])
+                  |> Enum.each(fn chunk -> IO.binwrite(target_pid, chunk) end)
+
+                  target_path
+                rescue
+                  _error -> nil
+                after
+                  File.close(target_pid)
+                end
+            end
+
+          callback.(target_path)
+        end)
     end
 
     :ok

test/livebook/runtime/dependencies_test.exs

@@ -325,6 +325,14 @@ defmodule Livebook.Runtime.DependenciesTest do
     end
   end
 
+  describe "search_packages_on_hex/2" do
+    test "sends a response message to the caller with the search results" do
+      ref = Dependencies.search_packages_on_hex(self(), "")
+      assert is_reference(ref)
+      assert_receive {:runtime_search_packages_response, ^ref, {:ok, []}}
+    end
+  end
+
   describe "search_hex/2" do
     setup do
       bypass = Bypass.open()