refactor: split 'with_quota_project' into separate base class

[busunkim96]

#546 (comment)

Isn't this a breaking change? Should it have been released as 1.19.0?

We are already seeing test failures in downstream libs like firebase-admin where we extend this interface.

firebase_admin/db.py:983:0: W0223: Method 'with_quota_project' is abstract in class 'Credentials' but is not overridden (abstract-method)

#546 (comment)

Actually this seems to be because pylint considers any method in an abstract class that throws NotImplementedError to be abstract: http://pylint-messages.wikidot.com/messages:w0223

Not quite sure if that should be considered a breaking change, or write it off as pylint being too pedantic.

CC @hiranya911

[tseaver]

FWIW, the NotImplementedError in the abstract base class could be considered "correct", as it adds a contract that all concrete subclasses must implement. For better backward-compatibility, it might be better to add another abstract class with that method, rather than changing it to raise ValueError. E.g.:

class CredentialsWithQuotaProject(Credentials):
    @abc.abstractmethod
    def with_quota_project(self, quota_project_id):
        """Returns a copy of these credentials with a modified quota project
        Args:
            quota_project_id (str): The project to use for quota and
                billing purposes
        Returns:
            google.oauth2.credentials.Credentials: A new credentials instance.
        """
        raise NotImplementedError("This class does not support quota project.")

[hiranya911]

Any plans to implement the change suggested by @tseaver? This is currently causing a failure in our CI system. I'm thinking of adding a lint ignore directive for now.

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[tseaver]

@google-cla I consent.

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[tseaver]

@google-cla I consent

@busunkim96 I've pushed dc3ae79 with my suggested refactoring. I don't know why the CLA bot is unhappy with that commit. If you don't like how that looks, feel free to rebase my commit away.

[tseaver]

@googlebot I consent.

[busunkim96]

@tseaver Thank you! 🙏