custom cc_toolchain used in bazel rule - build

Question

I've been trying to write a bazel rule to wrap compiling for risc-v source files, does some other stuff, etc, but I've been having some trouble with getting a CcToolchainInfo provider.
I have a rule that works that looks like
rv_cc_toolchain_config = rule(
implementation = _impl,
attrs = {},
provides = [CcToolchainConfigInfo],
)
in order to provide config info. I have the following in toolchains/BUILD:
load(":cc_toolchain_config.bzl", "rv_cc_toolchain_config")
package(default_visibility = ['//visibility:public'])
rv_cc_toolchain_config(name="rv_toolchain_cfg")
cc_toolchain(
name='rv_toolchain',
toolchain_identifier='rv-toolchain',
toolchain_config=':rv_toolchain_cfg',
all_files=':nofile',
strip_files=':nofile',
objcopy_files=':nofile',
dwp_files=':nofile',
compiler_files=':nofile',
linker_files=':nofile',
)
This seems to all work fine; I then have my custom rule to compile with riscv:
def _compile_impl(ctx):
deps = []
cc_toolchain = find_cpp_toolchain(ctx)
print(ctx.attr._cc_toolchain)
compilation_contexts = [dep[CcInfo].compilation_context for dep in deps]
print(type(cc_toolchain))
feature_configuration = cc_common.configure_features( #fails here
ctx = ctx,
cc_toolchain = cc_toolchain,
requested_features = ctx.features, #currently does nothing
unsupported_features = ctx.disabled_features,
)
rv_compile = rule(
_compile_impl,
output_to_genfiles = True,
attrs = {
"srcs": attr.label_list(
doc = "List of source files",
mandatory = False,
allow_files = [".cc", ".cpp", ".h", ".c"],
),
"hdrs": attr.label_list(
doc = "List of header files",
allow_files = [".h"],
),
"_cc_toolchain": attr.label(
#default = Label("#bazel_tools//tools/cpp:current_cc_toolchain"),
default = Label("//toolchains:rv_toolchain")
),
},
provides = [
DefaultInfo,
CcInfo,
],
toolchains = [
"#bazel_tools//tools/cpp:toolchain_type",
],
fragments = ["cpp"]
)
Where I fail when trying to configure the toolchain because cc_toolchain is of type ToolchainInfo and not the required CcToolchainInfo. Does anyone have any insight on how to provide CcToolchainInfo within a rule? Or is there a better way of doing this? Documentation seems to go dark on this.

Answer 1

Oops -- figured this out after trolling through github. Turns out the problem is directly referencing cc_toolchain is incorrect, and that CcToolchainInfo is provided via cc_toolchain_suite
updating toolchains/BUILD to look something like
load(":cc_toolchain_config.bzl", "rv_cc_toolchain_config")
package(default_visibility = ['//visibility:public'])
rv_cc_toolchain_config(name="rv_toolchain_cfg")
filegroup(name = 'empty')
cc_toolchain(
name='rv_toolchain',
toolchain_identifier='sanity-toolchain',
toolchain_config=':rv_toolchain_cfg',
all_files=':empty',
strip_files=':empty',
objcopy_files=':empty',
dwp_files=':empty',
compiler_files=':empty',
linker_files=':empty',
)
cc_toolchain_suite(
name='rv',
toolchains={
'darwin': ':rv_toolchain', #use whatever OS you need here...
}
)
and the rv compile rule to something like
rv_compile = rule(
_compile_impl,
output_to_genfiles = True,
attrs = {
"srcs": attr.label_list(
doc = "List of source files",
mandatory = False,
allow_files = [".cc", ".cpp", ".h", ".c"],
),
"hdrs": attr.label_list(
doc = "List of header files",
allow_files = [".h"],
),
"_cc_toolchain": attr.label(
#default = Label("#bazel_tools//tools/cpp:current_cc_toolchain"),
default = Label("//toolchains:rv")
),
},
provides = [
DefaultInfo,
CcInfo,
],
toolchains = [
"#bazel_tools//tools/cpp:toolchain_type",
],
fragments = ["cpp"]
)
works like a charm :) anyone reading this should also enable expirimental skylark cpp apis as well. if anyone knows how to make cc_toolchain_suite cpu agnostic, i'd love to hear it. cheers.