Put a label (like Repo name) in these errors

[nathanl]

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

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

Before: ** (DBConnection.OwnershipError) cannot find ownership process for #PID<0.1128.0> ({Phoenix.LiveView, MyAppWeb.FooLive, "lv:phx-GHKljxU3bpZfbx9j"}) using mode :manual

After: ** (DBConnection.OwnershipError) cannot find ownership process for #PID<0.1128.0> ({Phoenix.LiveView, MyAppWeb.FooLive, "lv:phx-GHKljxU3bpZfbx9j"}) using mode :manual on repo MyApp.Repo

[nathanl]

on line 381

[josevalim]

Hi @nathanl. I would prefer to not depend on repo, because it is really not a db_connection configuration or concern. Can you find anything on Process.info(self()) or Process.info(self(), :registered_name) you could use?

[nathanl]

@josevalim good point, but won't 99% of users pass a repo? In maybe_prefix_repo it's optional - would you be satisfied if it were optional everywhere in these messages?

[realglebivanov]

@nathanl would you consider adding some libary-agnostic metadata(contained e.g. in a kw-list) to the exception a viable option?

[nathanl]

@realglebivanov Can you elaborate a bit on what that might look like?

[realglebivanov]

@realglebivanov Can you elaborate a bit on what that might look like?

So, right now DBConnection.ConnectionError contains only message, reason and severity.
Instead of modifying the existing message text, we could add an additional field to the DBConnection.ConnectionError that could contain useful metadata.
Also, in this case we wouldn't have to rely on specific option types, it could be just a keyword list.
Of course, that could cost us an overhead of storing and copying around the list.
Hopefully, I made my point clear.

[nathanl]

Updated so that callers can optionally pass a label. If it's the repo name, like in elixir-ecto/ecto_sql#698, it shows up like this:

11:21:51.330 [error] Process #PID<0.1502.0> raised an exception
** (DBConnection.OwnershipError) cannot find ownership process for #PID<0.1502.0> (:erlang)
(GridPoint.Repo) using mode :manual.
(Note that a connection's mode reverts to :manual if its owner
terminates.)

[nathanl]

@josevalim what do you think of this approach?