#Smithy JSON AST

#Read and write a document

///|
test {
  let document = @json_ast.parse(
    (
      #|{"smithy":"2.0","shapes":{"example.weather#CityName":{"type":"string"}}}
    ),
  )
  inspect(document.smithy, content="2.0")
  let shape = document.shapes.unwrap().get("example.weather#CityName").unwrap()
  inspect(shape.kind.keyword(), content="string")
  assert_eq(@json_ast.parse(@json_ast.stringify(document)), document)
}

#Construct a document

///|
test {
  let names = @json_ast.JsonShape::new(
    List(Some(@json_ast.JsonMember::new("smithy.api#String"))),
  )
  let document = @json_ast.JsonAst::new(shapes={
    "example.weather#Names": names,
  })
  assert_eq(@json_ast.decode(@json_ast.encode(document)), document)
}

#Preservation and validation

• Absent fields stay absent. Explicit empty maps and arrays stay present. Explicit null is rejected for structural fields; metadata and trait values can contain any JSON value, including null.
• Object maps retain insertion order, including the order of members. Encoding can rearrange a shape's fixed properties and changes whitespace and string escaping. This is a document codec, without source spans or CST.
• parse preserves every numeric token's spelling, including long decimals, large integers, signed zero and exponents beyond Double's range. It first validates with core JSON, then rebuilds values with an explicit stack to retain number representations. Duplicate object keys follow core JSON's last-key-wins behavior.
• decode retains the numeric representations present in its Json input. It cannot recover precision already lost by another parser. Use parse when reading Smithy JSON text. Core Json equality compares numbers as Doubles; use numeric representations or encoded text when checking exact precision.
• The decoder checks property types, required smithy, type and target fields, absolute ID syntax, member names and service rename names. Unknown properties are errors, including properties belonging to another shape kind. References permit target only; members permit target and traits.
• Model validation belongs to the semantic loader. This includes version support, reference resolution, target kinds, case-insensitive member collisions, mixin expansion, trait semantics and model merging. Collection members, map keys/values, named members and service versions may be absent because mixins can supply them. The codec preserves the version string and accepts legacy set without deciding whether a model's version allows it.