error messages for JSON parsing

[marcosh]

Currently yesod-core is using Aeson.fromJSON to parse JSON values from Http requests.

Currently fromJSON do not provide any information on the path of a parsing error, when that happens.

IMHO, it would be interesting to use ifromJSON or any similar function which actually keeps track of the path of parsing errors.

[parsonsmatt]

There's a PR for this here #1807

[marcosh]

thanks, closing as duplicate