[BUG][typescript-angular] Unused imports are generated that cause TS errors with "noUnusedLocals" enabled

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

If you use typescript-angular the generated code might contain imports that are unused.

If the tsconfig configuration noUnusedLocals is enabled and you directly consume generated OpenAPI code within an Angular application, the TypeScript compiler errors:

✘ [ERROR] TS6133: 'FooDto' is declared but its value is never read. [plugin angular-compiler]

In my repo this occurs on model files with discriminators.

openapi-generator version

7.10.0

OpenAPI declaration file content or url

see https://github.com/jase88/openapi-ts-ng-unused-locals/blob/main/api-definition.openapi.yaml

Generation Details

MacOS 15.1
openjdk 23.0.1 2024-10-15
Node v22.8.0

Steps to reproduce

• checkout https://github.com/jase88/openapi-ts-ng-unused-locals/tree/main
• run npm i and npm run openapi:generate
• run npm run build to start a Angular build that errors

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/pull/16297
• https://github.com/OpenAPITools/openapi-generator/pull/12591
• https://github.com/OpenAPITools/openapi-generator/issues/1880

Suggest a fix

Ideally, it can be determined during generation that the import is not required in the file and can be discarded.

Alternatively, you could add @ts-check to every import, but in my opinion this should be a last resort.

Start with the linked reproduction repository, run npm i, npm run openapi:generate, and npm run build to reproduce the TS6133 errors. Compare the generated discriminator model files and trace them back to the typescript-angular generator templates; done means generation no longer emits unused imports and the Angular build succeeds with noUnusedLocals enabled.