Lower bare type: object to an open map

[4t145]

Summary

A type: object schema with no declared properties was classified as Shape::Object and lowered through build_struct, emitting a fieldless pub struct Foo {}. That type drops every key on serialize and carries nothing on deserialize, so a client holding one has no way to send the real payload.

The array case is what surfaced this. Given:

references:
  type: array
  items:
    type: object

the generator hoisted pub struct XxxReferences {} and produced Vec<XxxReferences> — an array the caller can only fill with empty objects, silently discarding whatever they meant to send.

JSON Schema defaults additionalProperties to true, so a bare type: object in fact accepts any object. It is now classified as Shape::Map, which already lowers to BTreeMap<String, serde_json::Value>.

additionalProperties: false stays on the struct path: with no declared properties it genuinely describes the empty object and nothing else, so the fieldless struct is the faithful lowering.

Version bumped to 0.1.3, following the two prior codegen fixes.

Before / after

spec	before	after
type: object	pub struct Opaque {}	pub type Opaque = BTreeMap<String, Value>
type: object, additionalProperties: false	pub struct Sentinel {}	unchanged
type: object with properties	pub struct User { .. }	unchanged
array of items: {type: object}	Vec<XxxItems> (empty struct)	Vec<BTreeMap<String, Value>>
array of items: {}	Vec<Value>	unchanged

Test plan

• cargo test -p toac-build -p toac — all 22 test targets pass, including the petstore 3.1 and e2b real-spec snapshot tests, so no existing lowering shifted
• cargo clippy -p toac-build -p toac --all-targets — no warnings
• cargo fmt — clean
• New toac-build/tests/test_bare_object_schemas.rs, 4 cases: bare object → open map, array-of-bare-objects keeps the payload reachable, additionalProperties: false keeps its struct, object-with-properties as a control
• Mutation-checked: reverting classify() fails the 3 behavioural cases and leaves the control passing

Not covered: no test asserts the generated code round-trips a real payload through serde. The assertions are on the emitted type, not on wire behaviour.

🤖 Generated with Claude Code