azure-cli-core has hard dependency on previous version of azure-mgmt-resource

[fhoy]

Describe the bug
We use the azure-cli-core package to utilize CLI auth-mechanisms in some infrastructure deployment scripts, and some of that infrastructure is deployed using the azure-mgmt-resource package. After having upgraded the latter to its newest version, 15.0.0, we discovered that azure-cli-core has a hard dependency on azure-mgmt-resource 10.2.0. Since it does not seem like azure-cli-core actually uses much of azure-mgmt-resource, this version mismatch has not actually caused any problems for us yet, but with the new dependency resolver coming in pip, this conflict can not be ignored as easily. Does azure-cli-core really need to depend on azure-mgmt-resource? A cursory examination turned up use of an enum from the latter, which I would assume could easily be copied, but I may certainly have missed something.

To Reproduce
Include latest versions of azure-cli-core (2.12.1) and azure-mgmt-resource (15.0.0) in a setup.py and run pip install . --use-feature=2020-resolver.

Expected behavior
No dependency conflict.

Environment summary
Tested with pip on Ubuntu 18.04.1.

Additional context
n/a

[jiasli]

azure-cli-core Azure CLI does rely on azure-mgmt-resource to do tenant and subscription discovery:

azure-cli/src/azure-cli-core/azure/cli/core/_profile.py

Lines 808 to 811 in 6f0deec

	client_type = get_client_class(ResourceType.MGMT_RESOURCE_SUBSCRIPTIONS)
	api_version = get_api_version(cli_ctx, ResourceType.MGMT_RESOURCE_SUBSCRIPTIONS)
	client = client_type(credentials, api_version=api_version,
	base_url=self.cli_ctx.cloud.endpoints.resource_manager)

I am also able to repro

> pip install azure-cli-core==2.12.1 azure-mgmt-resource==15.0.0 --use-feature=2020-resolver
...
ERROR: Cannot install azure-mgmt-resource==15.0.0 and azure-cli-core 2.12.1 because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested azure-mgmt-resource==15.0.0
    azure-cli-core 2.12.1 depends on azure-mgmt-resource==10.2.0

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies

Let's keep an eye on how pip will do in the future for 2020-resolver. We will consider bumping the version of azure-mgmt-resource to the latest version if that is necessary. + @zhoxing-ms

[jsntcy]

We'll plan to bump the version azure-mgmt-resource to the latest version next sprint (11/17).

[glaubitz]

This bug also causes issues for Linux distribution packagers which are now stuck with an old version of azure-mgmt-resource as Linux distributions usually don't allow shipping multiple versions of the same package in one repository.

This should definitely get fixed for the next release.