Stable ordering of traits?

[kubukoz]

Hi! I ran into what appears to be a discrepancy between how traits get ordered between multiple machines. For example, for this shape:

structure TraitOrderingTest {
    @required
    @length(min: 3)
    ident: String
}

My CI machine (Linux, x86) shows required first, then length (when traits are queried via model.expectShape(ShapeId.from("example.public#TraitOrderingTest$ident")).getAllTraits()).

My local machine (Mac, arm64) shows length first.

This doesn't seem to be just a difference in the file location (which has been a culprit before), as I tried the CI path and it yields the same result as my local path.

Here's a scala-cli snippet to quickly see the order (and the reported line numbers of the traits, which are correct):

//> using dep software.amazon.smithy:smithy-model:1.53.0
//> using dep com.lihaoyi::os-lib:0.11.3
import software.amazon.smithy.model.Model
import software.amazon.smithy.model.shapes.ShapeId
import scala.jdk.CollectionConverters.*

def showcase(name: String) = {
  val model = Model
    .assembler()
    .addUnparsedModel(
      name,
      """$version: "2"
        |
        |namespace example.public
        |
        |structure AnotherModel {
        |    @required
        |    @length(min: 3)
        |    ident: String
        |}
        |
        |structure TraitOrderingTest {
        |    @required
        |    @length(min: 3)
        |    ident: String
        |}
        |""".stripMargin,
    )
    .assemble()
    .unwrap()

  println(model.expectShape(ShapeId.from("example.public#TraitOrderingTest$ident")).getAllTraits())
  println(
    model
      .expectShape(ShapeId.from("example.public#TraitOrderingTest$ident"))
      .getAllTraits()
      .asScala
      .values
      .toList
      .map(t => t.getSourceLocation().getLine())
  )
}

@main def demo = showcase("example-service.smithy")

On my machine, it outputs:

{smithy.api#length=Trait `smithy.api#length`, defined at example-service.smithy [13, 5], smithy.api#required=software.amazon.smithy.model.traits.RequiredTrait@f4b52789}
List(13, 12)

I suppose the question is: is this OK, or should traits be returned in the order they're written? Or at least, in deterministic order.