Query collectionFormat not working despite existing support

[agologan]

While there is support added via annotations and CollectionFormatConverterFactory.kt this does not work and will instead pass the parameters as multiple values.
E.g. snippet definition snippet:

      # expected: color=red,black,white
      # actual: color=red&color=black&color=white
      parameters:
        - in: query
          name: color
          type: array
          collectionFormat: csv
          items:
            type: string

This happens because Retrofit applies the converter on a per value basis so the type check in CollectionFormatConverter will always go through the string branch returning an unmodified value which than gets appended to the query as an extra parameter.

Looking at the retrofit code (RequestFactory.java#L442) if we get an Iterable, than each value in that list will get converted and added to the query. So while our CSV stringConverter is selected, it will never get applied as we want it to be.

While I have a few ideas on how to approach this, they all involve making ParameterHandler.java in Retrofit, aware of apply'ing the conversion as a single value if a converter exists while keeping the current multi-value behavior for the BuiltInConverter string converter.

This does imply a significant change in Retrofit but maybe I'm missing something and there's already a better way to do this.
Any ideas? @JakeWharton maybe you could share your perspective.

[cortinico]

This does imply a significant change in Retrofit but maybe I'm missing something and there's already a better way to do this.

You're right. That's a limitation of Retrofit at the moment.

I invite you to subscribe to this issue for further updates: square/retrofit#626 (comment)

Closing here as it's unrelated to this project.