empty object in json schema should accept arbitrary json

[1inguini]

Empty object {} in json schema should accepts arbitrary json.

I first noticed this behavior in Haskell codegen.
Output from { "additionalProperties": true } and { "additionalProperties": {} } is proper, but {} which should be interpreted identically was interpreted as a string.

The existence of "additionalPropertis" seems to change output in many other languages.
Elm's and Dart's output from the 2 json schemas seem same, but I'm not sure if that means their outputs are right.

[schani]

Triage note (systematic backlog sweep, assisted by Claude): confirmed reproducible on current master (v23.3.0, 68ecb284).

Root cause: this is specific to the Haskell target. Core correctly treats {} as the "any" type — TypeScript emits any, Dart emits dynamic, Elm emits Jdec.value. But HaskellRenderer.ts:112 renders anyType as Maybe Text, which only decodes JSON strings or null. Any other JSON value (number, bool, array, object) fails to decode. The same defect surfaces wherever an "any" appears nested, e.g. additionalProperties: true producing Vector (Maybe Text) / HashMap Text (Maybe Text). (The other cross-language differences you noticed between {} and {"additionalProperties": true} are not bugs — the latter unifies into a 7-way union of all JSON types, which is semantically equivalent output, just spelled differently.)

Fix sketch: render anyType as Aeson's Value with identity encode/decode, following the pattern already used for Elm's any-type (ElmRenderer.ts:238,295).

Assessment:

• Severity: medium — produces outright wrong code (fails to decode valid JSON) with default options, but only affects the Haskell target combined with any-typed schemas.
• Difficulty: easy — localized to the Haskell renderer's primitive-type mapping.

Reproduction:

echo '{}' > empty.schema
node quicktype --lang haskell --src-lang schema empty.schema

Output includes:

type Empty = Maybe Text

which cannot represent e.g. a JSON object or number, even though the schema accepts arbitrary JSON.