Put a label (like Repo name) in these errors

The label must be passed in - see elixir-ecto/ecto_sql#698

Assuming it's the repo name, this is helpful if the application has more
than one repo (eg read replicas). For example:

Before: "** (DBConnection.ConnectionError) connection is closed because
of an error, disconnect or timeout"

After: "** (DBConnection.ConnectionError) MyApp.Repo connection is
closed because of an error, disconnect or timeout"

Author: nathanl

lib/db_connection/holder.ex

@@ -137,25 +137,43 @@ defmodule DBConnection.Holder do
       :ets.lookup(holder, :conn)
     rescue
       ArgumentError ->
-        msg = "connection is closed because of an error, disconnect or timeout"
+        msg =
+          maybe_prefix_label(
+            "connection is closed because of an error, disconnect or timeout",
+            opts
+          )
+
         {:disconnect, DBConnection.ConnectionError.exception(msg), _state = :unused}
     else
       [conn(lock: conn_lock)] when conn_lock != lock ->
-        raise "an outdated connection has been given to DBConnection on #{fun}/#{length(args) + 2}"
+        raise maybe_prefix_label(
+                "an outdated connection has been given to DBConnection on #{fun}/#{length(args) + 2}",
+                opts,
+                ":"
+              )
 
       [conn(status: :error)] ->
-        msg = "connection is closed because of an error, disconnect or timeout"
+        msg =
+          maybe_prefix_label(
+            "connection is closed because of an error, disconnect or timeout",
+            opts
+          )
+
         {:disconnect, DBConnection.ConnectionError.exception(msg), _state = :unused}
 
       [conn(status: :aborted)] when type != :cleanup ->
-        msg = "transaction rolling back"
+        msg = maybe_prefix_label("transaction rolling back", opts)
         {:disconnect, DBConnection.ConnectionError.exception(msg), _state = :unused}
 
       [conn(module: module, state: state)] ->
         holder_apply(holder, module, fun, args ++ [opts, state])
     end
   end
 
+  defp maybe_prefix_label(msg, opts, separator \\ "") do
+    if opts[:label], do: "#{inspect(opts[:label])} " <> separator <> msg, else: msg
+  end
+
   ## Pool state helpers API (invoked by callers)
 
   @spec put_state(pool_ref :: any, term) :: :ok

lib/db_connection/ownership/manager.ex

@@ -107,7 +107,8 @@ defmodule DBConnection.Ownership.Manager do
        mode: mode,
        mode_ref: nil,
        ets: ets,
-       log: log
+       log: log,
+       label: pool_opts[:label]
      }}
   end
 
@@ -223,7 +224,7 @@ defmodule DBConnection.Ownership.Manager do
         {:noreply, state}
 
       :not_found when mode == :manual ->
-        not_found(from, mode)
+        not_found(from, mode, state.label)
         {:noreply, state}
 
       :not_found ->
@@ -405,10 +406,12 @@ defmodule DBConnection.Ownership.Manager do
     caller
   end
 
-  defp not_found({pid, _} = from, mode) do
+  defp not_found({pid, _} = from, mode, label) do
     msg = """
     cannot find ownership process for #{Util.inspect_pid(pid)}
-    using mode #{inspect(mode)}.
+    #{if label, do: "(#{inspect(label)})"} using mode #{inspect(mode)}.
+    (Note that a connection's mode reverts to :manual if its owner
+    terminates.)
 
     When using ownership, you must manage connections in one
     of the four ways: