log errors on make_encoder()

[patrick-prima]

We have an odd problem where a small schema update is causing avrogen to fail on startup. We think a little more logging might help us understand what is going on.

For reference, these PRs fail:

• https://github.com/primait/uk-quote-request-transformers/pull/29
• https://github.com/primait/uk-quote-request-transformers/pull/34

** (Mix) Could not start application uk_avro_schema: UkAvroSchema.Application.start(:normal, []) returned an error: shutdown: failed to start child: Avrogen.Schema.SchemaRegistry
    ** (EXIT) an exception was raised:
        ** (ErlangError) Erlang error: "union should have at least one member type"
            (erlavro 2.9.10) /Users/xxx/projects/uk-quote-request-transformers/deps/erlavro/src/avro_union.erl:73: :avro_union.type/1
            (erlavro 2.9.10) /Users/xxx/projects/uk-quote-request-transformers/deps/erlavro/src/avro_json_decoder.erl:72: :avro_json_decoder.decode_schema/2
            (erlavro 2.9.10) /Users/xxx/projects/uk-quote-request-transformers/deps/erlavro/src/avro_util.erl:77: :avro_util.ensure_lkup_fun/1
            (erlavro 2.9.10) /Users/xxx/projects/uk-quote-request-transformers/deps/erlavro/src/avro.erl:208: :avro.make_encoder/2
            (avrogen 0.6.6) lib/avrogen/schema/schema_registry.ex:43: anonymous fn/1 in Avrogen.Schema.SchemaRegistry.init/1
            (noether 0.2.5) lib/noether/either.ex:23: Noether.Either.map/2
            (avrogen 0.6.6) lib/avrogen/schema/schema_registry.ex:41: Avrogen.Schema.SchemaRegistry.init/1
            (stdlib 4.3.1.3) gen_server.erl:851: :gen_server.init_it/2

[oxg558]

LGTM! Would be a lot easier to debug if we could recreate the problem locally...

[oxg558]

Though since the error itself happens quite deep in an erlavro call I'm not sure if this log will tell us much more... it will at least show us what order the schemas are being sorted in, which might be what has changed.

[patrick-prima]

We found the culprit.