{Packaging} Use proper PEP 508 environment marker for dependencies

[jiasli]

Description

Similar to microsoft/knack#257, use proper PEP 508 environment marker for dependencies.

Dependencies added by DEPENDENCIES.append() are only added to the list of requirements if the setup.py is executed. However, azure-cli and azure-cli-core are being distributed as a wheel packages and setup.py is not executed when installing a wheel package. Instead, dependencies are translated into azure_cli-2.34.1-py3-none-any.whl/azure_cli-2.34.1.dist-info/METADATA when building wheels:

Requires-Dist: argcomplete
Requires-Dist: jmespath
Requires-Dist: pygments
Requires-Dist: pyyaml
Requires-Dist: tabulate

What's in the wheel is determined by the packaging system, which is like taking a snapshot when packaging the wheel and the condition evaluation result is frozen into the wheel. Therefore, these conditional install won't work as expected.

conditional install in setup.py -----------> Requires-Dist in whl METADATA -----------> pip
                        frozen by packaging system

[jiasli]

These lines were added by #15076.

This brought back #9399, making it impossible to install azure-cli on cygwin:

Collecting psutil~=5.9
  Using cached psutil-5.9.0.tar.gz (478 kB)
  Preparing metadata (setup.py) ... error
  error: subprocess-exited-with-error

  × python setup.py egg_info did not run successfully.
  │ exit code: 1
  ╰─> [1 lines of output]
      platform cygwin is not supported
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.

[jiasli]

This is what it becomes in generated wheel METADATA:

Requires-Dist: psutil (~=5.9) ; sys_platform != "cygwin"

[jiasli]

Well, anyway, latest cryptography doesn't have cygwin support either: pyca/cryptography#6834

[jiasli]

This is what it becomes in generated wheel METADATA:

Requires-Dist: distro ; sys_platform == "linux"

[niander]

You should use platform_system == "Linux" .

Here: https://peps.python.org/pep-0508/#environment-markers
It says that sys_platform will be linux in python3 and linux2 in python2

[jiasli]

It's ok. We have dropped support for Python 2 anyway.

We also use sys.platform elsewhere:

azure-cli/src/azure-cli-core/azure/cli/core/auth/persistence.py

Lines 41 to 50 in fb805f4

	if sys.platform.startswith('win'):
	return FilePersistenceWithDataProtection(location)
	if sys.platform.startswith('darwin'):
	return KeychainPersistence(location, "my_service_name", "my_account_name")
	if sys.platform.startswith('linux'):
	return LibsecretPersistence(
	location,
	schema_name="my_schema_name",
	attributes={"my_attr1": "foo", "my_attr2": "bar"}
	)

[jiasli]

platform.system() looks weird on cygwin, and sys.platform seems to be easier:

$ python3 -c "import os; print(os.name)"
posix

$ python3 -c "import sys; print(sys.platform)"
cygwin

$ python3 -c "import platform; print(platform.system())"
CYGWIN_NT-10.0-19044

[niander]

Ok sounds good to me

[yonzhan]

Packaging