Optional Field Incorrectly Generated for Required Parameter in Python Codegen

[rangerthegood]

Steps to reproduce:

cd smithy-python/codegen
./gradlew smithy-python-codegen-test:build

This produces the file: smithy-python/codegen/smithy-python-codegen-test/build/smithyprojections/smithy-python-codegen-test/source/python-client-codegen/weather/models.py.

Looking at the GetCityInput structure you will see showing that city_id is not required because it allows None.

class GetCityInput:

    city_id: str | None = None

The smithy model for GetCityInput shows:

@http(method: "GET", uri: "/cities/{cityId}")
operation GetCity {
    input := {
        // "cityId" provides the identifier for the resource and
        // has to be marked as required.
        @required
        @httpLabel
        cityId: CityId
    }

The determination to see if a field is required is done in StructureGenerator.java.

        var required = new ArrayList<MemberShape>();
        var optional = new ArrayList<MemberShape>();
        var index = NullableIndex.of(context.model());
        for (MemberShape member: shape.members()) {
            if (index.isMemberNullable(member) || member.hasTrait(DefaultTrait.class)) {
                optional.add(member);
            } else {
                required.add(member);
            }
        }

isMemberNullable is returning True for the cityId, and therefore is marked as optional.

I'll PR adding an additional check to see if the RequiredTrait.class is set on the member.

When that is in place the structure then becomes:

class GetCityInput:

    city_id: str

Or maybe this is by design? #182

[JordonPhillips]

This is by design. When you use the inline syntax for creating an input structure (:=), the structure created has the @input trait, which changes nullability for the sake of backwards compatibility.

[rangerthegood]

Here is another case where my data is considered optional.

@idempotent
@http(method: "PUT", uri: "/car/{id}")
operation UpdateCar {
    input: UpdateCarInput
    output: UpdateCarOutput
}

structure UpdateCarlInput {
    @required
    @httpLabel
    id: String
...
}

The id would be optional in the generated Python code. Maybe the httpLabel makes it nullable?