Error or warn on unknown fields

[soenkehahn]

Is it possible to use autodocodec to parse json or yaml while either failing or warning on unknown fields? aeson provides rejectUnknownFields, but I couldn't find a way to plug in Options into autodocodec.

[NorfairKing]

@soenkehahn You'd have to write your own decoder, but I think it's possible because we know all the fields statically.

[soenkehahn]

Thanks for the reply! Are you saying it's possible for me to implement this without modifying autodocodec? If yes, I'm not sure what you mean by "write your own decoder". Codecs seem to encompass both encoders and decoders, and I'm not sure how I would go about writing my own decoder while using a provided decoder, if that makes sense. Any pointers appreciated!

[NorfairKing]

@soenkehahn Sorry I've not been very clear. It's easy for me to forget context that I only have because I wrote this code.

A codec is just a value that represents an idea.
This function does the decoding:

autodocodec/autodocodec/src/Autodocodec/Aeson/Decode.hs

Lines 31 to 37 in fa4d53e

	-- | Parse via a general codec.
	--
	-- You probably won't need this. See 'eitherDecodeViaCodec', 'parseJSONViaCodec' and 'parseJSONVia' instead.
	parseJSONContextVia :: Codec context void a -> context -> JSON.Parser a
	parseJSONContextVia codec_ context_ =
	modifyFailure (\s -> if '\n' `elem` s then "\n" ++ s else s) $
	go context_ codec_

You could write your own version to warn or reject on unknown fields.

[Icelandjack]

Is it possible to add support for this (decoder?) to the library so that users can configure this behaviour. I know you have already closed this but would you accept a pull request?

[NorfairKing]

@Icelandjack I think my "closed" communication was not clear. I just meant that I haven't planned to add it myself. A PR would be welcome!