Add new cargo creds feature

[ericmcbride]

• Add Cargo Credentials to the Module.bazel from_cargo and vendor calls.
• Currently private crates repositories cannot pull from repos by default. You have to set CARGO_BAZEL_ISOLATED=false for it to work
• Addresses rules_rust 0.57.1 cargo login is ineffective #3261 and rules_rust 0.57.1 Private Crates repo not pulling #3243

[ericmcbride]

@UebelAndre @illicitonion Is there some other way to check that im not aware of to see if the environment is isolated? Can i check CARGO_BAZEL_ISOLATED is set, and if its false, we ignore this and just assume if its not set, or a true we can symlink credentials.toml to cargo home? I could pass isolated thru to the splicing config but im not sure if thats desireable.

I think the way to go here would be to pass the isolated flag into the splicer and then check since isolated can be set by env or field on the vendor / from_cargo

[UebelAndre]

I don't think we've had to care if the environment is isolated from within the cargo-bazel binary. Isn't the starlark responsible for setting up the isolated CARGO_HOME? If you want credentials to be installed there (which would come from the user's CARGO_HOME anyway), why not install it there?

I would pass an explicit flag indicating isolation is enabled though, that sounds fine 😄

[ericmcbride]

@UebelAndre The symlink appears to happen whenever get_rust_tools is called in starlark, and the extensions.bzl does not use that call to get the rustc / cargo and i do not see a way to re use that func call using the module_ctx as it and the repository_ctx do not share the same attributes. This has confused me and caused alot of pain on my side because i didn't realize they diverged in code paths lol.

This part of the code i want to change to use the isolated flag, this was just a short circuit for me to make sure it worked and i could symlink to cargo home. We still will need to symlink to it for the extensions.bzl side as module_ctx does not have a symlink method like repository_ctx that i can find documented.

rules_rust/crate_universe/private/common_utils.bzl

Line 108 in 8f118ee

def get_rust_tools(repository_ctx, host_triple):

[UebelAndre]

I think this is shared with both bzlmod and workspace modes

rules_rust/crate_universe/private/common_utils.bzl

Lines 64 to 82 in f525346

	def new_cargo_bazel_fn(
	repository_ctx,
	cargo_bazel_path,
	cargo_path,
	rustc_path,
	isolated = True,
	quiet = False):
	"""A helper function to allow executing cargo_bazel in repository rules module extensions.
	Args:
	repository_ctx (repository_ctx): The repository rule or module extension's context.
	cargo_bazel_path (path): Path The path to a `cargo-bazel` binary
	cargo_path (path): Path to a Cargo binary.
	rustc_path (path): Path to a rustc binary.
	isolated (bool): Enable isolation upon request.
	quiet (bool): Whether or not to print output from the executable.
	Returns:
	A function that can be called to execute cargo_bazel.
	"""

Where if you follow through to

rules_rust/crate_universe/private/common_utils.bzl

Lines 144 to 153 in f525346

	def _cargo_home_path(repository_ctx):
	"""Define a path within the repository to use in place of `CARGO_HOME`
	Args:
	repository_ctx (repository_ctx): The rules context object
	Returns:
	path: The path to a directory to use as `CARGO_HOME`
	"""
	return repository_ctx.path(".cargo_home")

You'll see here is where the isolated CARGO_HOME is defined. Perhaps this would be a good spot to link credentials? Admittedly, this code became super complicated in an effort to avoid making large changes but resulted in higher complexity and diverging code paths. But given that workspace support is on it's way out, I wouldn't be opposed to a bzlmod-only introduction of this feature. Do you think there's a path forward here to do symlinking in starlark?

[ericmcbride]

I can look into it! I just got it working by passing isolated to the splicing cli.