OpenAPI / JSON Schema Generation

The same typeinfo field walk that drives serialization also produces API contracts. Mapping int → "integer", bool → "boolean", and str → "string" at compile time yields a ready-made OpenAPI properties block — the same pattern applies to GraphQL SDL, protobuf messages, or typed HTTP clients.

Walk typeinfo(Product).fields and map each type.kind to a JSON Schema type string, producing a ready-made OpenAPI "properties" block at compile time.

08-api-openapi.zolo

Playground

// Use case 5 — BINDINGS / API (OpenAPI · JSON Schema · GraphQL · protobuf)
//
// Generate an OpenAPI / JSON-Schema `properties` fragment from a type. Each
// field's `type.kind` maps to a JSON-Schema type; the same walk produces
// GraphQL SDL, protobuf messages, or a typed client. Computed at compile time.

struct Product {
  id: int,
  title: str,
  in_stock: bool,
}

let schema_json = comptime {
  var s = "\"properties\": \{\n"
  var first = true
  for f in typeinfo(Product).fields {
    if first == false { s = s + ",\n" }
    var jstype = "string"
    if f.type.kind == "int" { jstype = "integer" }
    if f.type.kind == "bool" { jstype = "boolean" }
    s = s + "  \"" + f.name + "\": \{ \"type\": \"" + jstype + "\" \}"
    first = false
  }
  s = s + "\n\}"
  s
}

print(schema_json)
// expected:
// "properties": {
//   "id": { "type": "integer" },
//   "title": { "type": "string" },
//   "in_stock": { "type": "boolean" }
// }