Dart generator: Add default value for optional params

[djibouleau]

When the spec mentions a default value for a parameter, it is recorded as an optional param. I updated the template to include the default value. Tested with FastAPI :

async def get_api_version(
    x_api_version: Annotated[str, Header(alias="X-API-Version")] = "1.2.3"
) -> str:
    return x_api_version

app = FastAPI(
    dependencies=[Depends(get_api_version)]
)

Generated code :

  /// Search
  ///
  /// Parameters:
  ///
  /// * [String] q (required):
  ///
  /// * [String] xAPIVersion:
  Future<List<Product>?> search(String q, { String? xAPIVersion = '1.2.3', }) async {
  ...

[Mattias-Sehlstedt]

This looks to be generated client code? If that is the case, then I believe it is technically incorrect to submit the default value as a client with a call. See section Default Parameter Values here.

The default value is the value that the server will use if the client does not send a value for that field. So if the client is fine with the default, then it is best to omit sending a value. If the generated code mirrors the default, then one might misalign with the server if they were to change their default.