How do I properly set include paths for external dependencies in cc_toolchain

[stefanlada]

Hi there,

we are currently integrating a multi-ecu (multiple embedded controller targets) project in bazel. We have an abstraction layer for the different ecu platforms and the different AL implementations are handled elsewhere so we would like to include these as external dependencies.

The problem is, that the different implementations will have slight different files and folder structures that we do not want to touch. We have created BUILD files for each of the different implementations and these provide filegroups that we can use in our cc_binary srcs list.

But we cannot figure out how to properly handle include paths. As filegroup do not support folders we cannot simply bind them together.

Short example:

WORKSPACE
---------------------------------------------------------------------------
http_archive(name = "some_lib_ecu_a")
http_archive(name = "some_lib_ecu_b")

BUILD.bazel
---------------------------------------------------------------------------
cc_binary(
  name = "my_binary"
  srcs = select({
	"//platforms:ecu_a": [ @some_lib_ecu_a//:all_sources ],
	"//platforms:ecu_b": [ @some_lib_ecu_b//:all_sources ],
  }),
  copts = select({
	"//platforms:ecu_a": [ 
		"-Iexternal/some_lib_ecu_a/comp_1_headers",
		"-Iexternal/some_lib_ecu_a/comp_2_headers",
		"-Iexternal/some_lib_ecu_a/comp_3/headers",
	],
	"//platforms:ecu_b": [ 
		"-Iexternal/some_lib_ecu_a/hdrs",
		"-Iexternal/some_lib_ecu_a/comp_a/dev/hdrs",
	],
  })
)

The problem here is, that I am not able to define the header paths adequately in the BUILD file of the external library. This yields two problems: The integrator has to search the whole library for the build information. And bazel has no chances to recognize errors with the used -I copt flags.

Do you have any suggestions?

Is there a reason why there is no way to define folders like you can define files? If there was something like 'dirgroup' that you could use to configure a set of folder-labels this would absolutely solve the problem. And would probably help on other things as well.

BR Stefan

[illicitonion]

See also #23139

[tpudlik]

For the example you show, I'd suggest a slightly different structure: define per-platform binaries in @some_lib_ecu_a and @some_lib_ecu_b, and have an alias in the root repo:

alias(
  name = "my_binary",
  actual = select({
    "//platforms:ecu_a": "@some_lib_ecu_a//:my_binary",
    "//platforms:ecu_b": "@some_lib_ecu_b//:my_binary",
  }),
)

Is there a reason why there is no way to define folders like you can define files?

There is in fact a new build rule for accessing directories, https://github.com/bazelbuild/bazel-skylib/tree/main/rules/directory. But defining actual cc_binary or cc_library targets in the individual per-platform repositories, and then aliasing to them from the main repository, is tidier.