Make string key access fallback to atom key access

[drathier]

Description of the change
With this change Simple.Json.write and Simple.Json.read works round-trip. Without this change, it always encodes record keys as atoms, and it always reads record keys by string, so all record accesses fail. It feels like a safe default to first check exactly what was asked for, and then fall back to atom access. Also, it's unlikely that we'll do record accesses on user input field names, so atom leaks should not be an issue.

Details

class Codec a where
  toSerializable :: a -> Versioned
  fromSerializable :: Versioned -> Either String a

type Versioned
  = { _version :: Int, value :: Foreign }

encodeJSON :: forall a. Codec a => a -> String
encodeJSON a = SimpleJson.writeJSON (toSerializable a)

decodeJSON :: forall a. Codec a => String -> Either String a
decodeJSON a = case SimpleJson.readJSON a of
  Left err -> Left ("codec-decode:" <> show (map renderForeignError err))
  Right versioned -> fromSerializable versioned

{- blocked on https://github.com/purerl/purescript-foreign/pull/1

encodeForeign :: forall a. Codec a => a -> Foreign
encodeForeign a = SimpleJson.write (toSerializable a)

decodeForeign :: forall a. Codec a => Foreign -> Either String a
decodeForeign a = case SimpleJson.read a of
  Left err -> Left ("codec-decode:" <> show (map renderForeignError err))
  Right versioned -> fromSerializable versioned
-}

Json works fine

{:swedishPersonnummer, "19991231-0123"}
iex(62)> jsn = cm.encodeJSON(um.codecUserId(), pnr)          
"{\"_version\":1,\"value\":{\"__type\":\"UserIdV1SwedishPersonnummer\",\"value\":\"19991231-0123\"}}"
iex(63)> res = cm.decodeJSON(um.codecUserId(), jsn)          
{:right, {:swedishPersonnummer, "19991231-0123"}}

but foreign doesn't work:

iex(69)> pnr = um.'SwedishPersonnummer'.("19991231-0123")
{:swedishPersonnummer, "19991231-0123"}
iex(70)> raw = cm.encodeForeign(um.codecUserId(), pnr)          
%{
  _version: 1,
  value: %{__type: "UserIdV1SwedishPersonnummer", value: "19991231-0123"}
}
iex(71)> res = cm.decodeForeign(um.codecUserId(), raw)          
{:left,
 "codec-decode:(NonEmptyList (NonEmpty (ErrorAtProperty \"_version\" (TypeMismatch \"integer\" \"atom\")) Nil))"}
iex(72)> jsn = cm.encodeJSON(um.codecUserId(), pnr)      
"{\"_version\":1,\"value\":{\"__type\":\"UserIdV1SwedishPersonnummer\",\"value\":\"19991231-0123\"}}"
iex(73)> resjsn = cm.decodeJSON(um.codecUserId(), jsn)
{:right, {:swedishPersonnummer, "19991231-0123"}}

until I made the change in the pr, and then it works fine

iex(111)> raw = cm.encodeForeign(um.codecUserId(), pnr)   
%{
  _version: 1,
  value: %{__type: "UserIdV1SwedishPersonnummer", value: "19991231-0123"}
}
iex(112)> rawres = cm.decodeForeign(um.codecUserId(), raw)
{:right, {:swedishPersonnummer, "19991231-0123"}}

---

Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)

[drathier]

Do you want me to fill out the form above? Seems like it's mostly for the parent repo

[nwolverson]

No that's just inherited from the upstream; I'm going to reflect on this a bit, as the right fix may be in simple-json (or in fact both).

Actually it looks like this Index module has accumulated JS cruft since some merge, I probably want to fix that properly also