Cannot add extra actions using variables

[keith]

Currently @rules_cc//cc/toolchains/actions:compile_actions doesn't contain @rules_cc//cc/toolchains/actions:objc_compile. If I want to define a toolchain that supports objc_compile, I would expect to be able to create cc_args like this:

cc_args(
    name = "my_user_compile_args",
    actions = [
        "@rules_cc//cc/toolchains/actions:compile_actions",
        "@rules_cc//cc/toolchains/actions:objc_compile",
    ],
    args = ["{flags}"],
    format = {
        "flags": "@rules_cc//cc/toolchains/variables:user_compile_flags",
    },
    iterate_over = "@rules_cc//cc/toolchains/variables:user_compile_flags",
)

But when I do this it fails with:

ERROR: /Users/ksmiley/dev/keith/bazel-cc-toolchain-example/toolchain/llvm/BUILD.bazel:276:8: in _cc_args rule //toolchain/llvm:user_compile_args2:
Traceback (most recent call last):
        File "/private/var/tmp/_bazel_ksmiley/9ab617f34b5a1a9018f0a6157e69be65/external/rules_cc~/cc/toolchains/args.bzl", line 46, column 29, in _cc_args_impl
                validate_nested_args(
        File "/private/var/tmp/_bazel_ksmiley/9ab617f34b5a1a9018f0a6157e69be65/external/rules_cc~/cc/toolchains/impl/args_utils.bzl", line 63, column 28, in validate_nested_args
                type = get_type(
        File "/private/var/tmp/_bazel_ksmiley/9ab617f34b5a1a9018f0a6157e69be65/external/rules_cc~/cc/toolchains/impl/variables.bzl", line 132, column 21, in get_type
                fail("The variable {var} is inaccessible from the action {action}. This is required because it is referenced in {nested_label}, which is included by {args_label}, which references that action".format(
Error in fail: The variable @@rules_cc~//cc/toolchains/variables:user_compile_flags is inaccessible from the action @@rules_cc~//cc/toolchains/actions:objc_compile. This is required because it is referenced in @@//toolchain/llvm:user_compile_args2, which is included by @@//toolchain/llvm:user_compile_args2, which references that action

If I remove the fail

rules_cc/cc/toolchains/impl/variables.bzl

Lines 127 to 136 in 848d56a

	if variables[outer].actions != None:
	valid_actions = variables[outer].actions.to_list()
	for action in actions:
	if action not in valid_actions:
	fail("The variable {var} is inaccessible from the action {action}. This is required because it is referenced in {nested_label}, which is included by {args_label}, which references that action".format(
	var = variables[outer].label,
	nested_label = nested_label,
	args_label = args_label,
	action = action.label,
	))

it does seem to work as I expect, but I assume that would have some unintended side effects eventually?

My first attempt at this was to override the default feature, which suffered from the same issue.

[keith]

This specific example would be fixed by #245, but I suppose there might be more cases like this

[keith]

Actually this example isn't fixed automatically with that change, since the upstream feature also doesn't have objc-compile in that set. But with my fix I can define my custom feature overriding the default to fix it.