Question regarding on how Apple rules propagate configuration/targets to cc_library or objc_library

[Winnaries]

With the release of @platforms, I can change targets of cc_library easily to arm64 by defining a set of constraints and using select() on those values. However, since Apple rules doesn't support @platforms and instead pass the config to C build configuration through --cpu and --crosstool_top. Being new to bazel, I am confused on how things operate over the boundary. Would be very helpful if someone can answer the following questions for me:

1. How does the Apple rules pass configuration to the underlying dependencies such as cc_library and objc_library? For example, if I want to build an XCFramework targeting x86_64 and arm64 that depends on cc_library target, how does the C target know which target to build and which toolchain to use under the absense of @platforms.
2. If I have a cc_library rule that uses select() on @platforms (eg. emiting TARGET_IOS local defines if the target is @platforms//os:ios) and have a apple_static_xcframework rules depends on it, what would be the result of the select? From my understanding, it would resolve to default condition, right? If that is the case, should I instead make select() on cpu for compatibility with Apple rules?
3. What would be the current best way to build Apple multi-arch library? Should I stick to using --cpu, or --platforms?
4. Lastly, will Apple rules adopt @platforms any time soon? I would be happy to help under some guidance.

[thii]

1. Transitions. For example, the XCFramework rules use this to pass down the target environment, etc. to the dependencies

   rules_apple/apple/internal/transition_support.bzl

   Lines 566 to 591 in 77155d9

   	def _xcframework_transition_impl(settings, attr):
   	"""Starlark 1:2+ transition for generation of multiple frameworks for the current target."""
   	output_dictionary = {}
   	for platform_type in ["ios", "tvos", "watchos", "macos"]:
   	if not hasattr(attr, platform_type):
   	continue
   	target_environments = ["device"]
   	if platform_type != "macos":
   	target_environments.append("simulator")
   	command_line_options = _command_line_options_for_xcframework_platform(
   	minimum_os_version = attr.minimum_os_versions.get(platform_type),
   	platform_attr = getattr(attr, platform_type),
   	platform_type = platform_type,
   	settings = settings,
   	target_environments = target_environments,
   	)
   	output_dictionary = dicts.add(command_line_options, output_dictionary)
   	return output_dictionary
   	_xcframework_transition = transition(
   	implementation = _xcframework_transition_impl,
   	inputs = _apple_rule_common_transition_inputs,
   	outputs = _apple_rule_base_transition_outputs,
   	)

2. I don't entirely understand the question, but if you build an apple_static_xcframework for multiple platforms, and use select() on @platforms//os:ios for part of the deps, those should be built only when Bazel is building them for the iOS platform. Please file any issues you find.
3. Building with --platforms is not ready yet, I believe the current best way is still using --cpu.
4. Platform support for Apple rules is in-progress.