suggestion to replace `"value"` with `"contents"` in `Either` decoder, encoder

[peterbecich]

Is your change request related to a problem? Please describe.

In Haskell's Aeson library, the default contentsFieldName is "contents":
https://hackage.haskell.org/package/aeson-2.2.1.0/docs/Data-Aeson.html#v:defaultTaggedObject

In argonaut-codecs, it appears the default is "value":

purescript-argonaut-codecs/src/Data/Argonaut/Decode/Decoders.purs

Line 69 in 50e79f6

val <- note (AtKey "value" MissingValue) $ FO.lookup "value" obj

Examples:
https://github.com/coot/purescript-argonaut-aeson-generic depends on argonaut-codecs and attempts to provide compatibility between PureScript's Argonaut and Haskell's Aeson. It uses "contents". For most data types, it works great. However, it cannot decode/encode Either to be compatible with Haskell's Aeson.
I have provided an example in this issue: coot/purescript-argonaut-aeson-generic#22

I have attempted to fix this on the Haskell side by overriding the instances to use "value", but haven't managed to make this work: https://github.com/peterbecich/purescript-bridge/blob/55e265b0d44c001357cd3aef3ac4a894128df12f/example/src/Types.hs#L96

Describe the solution you'd like
My request is to change "value" to "contents" here:

purescript-argonaut-codecs/src/Data/Argonaut/Decode/Decoders.purs

Line 69 in 50e79f6

val <- note (AtKey "value" MissingValue) $ FO.lookup "value" obj

and in the encoder

I have tested this: eskimor/purescript-bridge@55e265b This change fixes argonaut-aeson-generic. Either is encoded and decoded successfully.

Additional context
I am attempting to update Purescript Bridge and encountered this issue: eskimor/purescript-bridge#89

Thank you

[kindaro]

Hi @peterbecich and thanks for your continuing effort to merge IOHK's changes to purescript-bridge.

Please take a look at this comment nearby: #113 (comment) — and the conversation preceding it. Note the following:

I recommend being careful here. Argonaut does not promise to match Aeson, though it borrows heavily from that library. I don't expect that all instances in this library are the same as the Aeson forms, and they may diverge in the future. If you need to have a JSON library that exactly matches Aeson for use with purescript-bridge, then I think you should fork this library or create a new one with that explicit goal (that would also let you write any additional instances you want).

— Thomas Honeyman

This is bad news for us. We can fork this package under a different name, say argonaut-aeson-codecs, say that our new package promises to be compatible with Haskell's aeson, and make argonaut-aeson-generic depend on the fork. Then we shall have a solid foundation for purescript-bridge. This seems to be the most constructive way forward.

[peterbecich]

Thanks @kindaro , I have read all of #113 (comment) now; I incorrectly assumed Argonaut promised to match Aeson.

I agree we should fork https://github.com/purescript-contrib/purescript-argonaut-codecs.

However, now that we have identified this issue, I believe it will be an issue for both the purescript-bridge master branch, and for my PR eskimor/purescript-bridge#89 If I'm correct about this, we should merge eskimor/purescript-bridge#89 regardless because master is currently broken anyways.

The IOHK fork implemented better test coverage. Specifically, the RoundTrip test detects the issue: https://github.com/eskimor/purescript-bridge/tree/920c23672baec3b26a92fd0ff08f52d3a7929139/test/RoundTripArgonautAesonGeneric