[Dart] Generated methods aren't annotated with @deprecated

[mway-dmueller]

Description

For other languages, the generated method is annotated with @Deprecated to inform the developer that this method (or in this case: REST endpoint) is deprecated and will be removed soon.
For this purpose, Dart supports two annotations:

1. @deprecated which is taking a mandatory parameter to describe since when this method is deprecated.
2. @deprecated which doesn't require any parameters or imports.
   Because of the fact that the Swagger data model doesn't provide us any information since when a REST endpoint is marked as deprecated, we could at least choose the second option so the client developer can react on the deprecation.

Swagger-codegen version

2.4.14

Swagger declaration file content or url

Command line used for generation

Both executed in https://github.com/swagger-api/swagger-codegen/tree/master/modules/swagger-codegen:

• mvn clean package
• ./bin/dart-petstore.sh

Steps to reproduce

1. Use the Dart Petstore sample.
2. Check file https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/test/resources/2_0/petstore.yaml : it contains the deprecated REST endpoint GET /pet/findByTags.
3. Execute ./bin/dart-petstore.sh to generate the Dart Swagger client.
4. Check the locally generated file swagger-codegen/samples/client/petstore/dart/swagger/lib/api/pet_api.dart in which the method findPetsByTags(List<String> tags) isn't marked as deprecated.

Related issues/PRs

Pull Request: #10324

Suggest a fix/enhancement

I'll extend the api.mustache file for Dart in a separate Pull Request.

[frantuma]

fixed in #10324