atdml: add <json repr="object"> for sum types (externally-tagged encoding)
Tagged variants are now encoded as single-key JSON objects
{"Constructor": payload} when the sum type is annotated with
<json repr="object">. Unit variants remain "Constructor" strings.
This matches Serde's externally-tagged representation.
Both of_yojson and of_jsonlike readers are generated. The yojson
writer (yojson_of_*) also produces the object encoding.
Implementation:
- atd/src/json.ml,mli: new json_sum_repr = Array | Object type and
field on json_sum; get_json_sum reads <json repr="object">
- atdml Codegen.ml: new sum_object_tagged_pat mode field for the
pattern strings; gen_reader and gen_yojson_of switch on json_sum_repr
- atdgen/src/oj_emit.ml: fill new json_sum_repr field (Array) in one
hand-constructed json_sum literal
- Support matrix: new "Sum as JSON object" feature row (atdml=Yes,
all others=Planned)
Closes #479
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2e48d9
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Mar 30 18:38 +00:00