platform dependent linker flags in bazel (for glut) - cross-platform

Question

I am trying to build the c++ app with glut using bazel. It should work on both macos and linux. Now the problem is that on macos it requires passing "-framework OpenGL", "-framework GLUT" to linker flags, while on linux I should probably do soemthing like
cc_library(
name = "glut",
srcs = glob(["local/lib/libglut*.dylib", "lib/libglut*.so"]),
...
in glut.BUILD.
So the question is
1. How to provide platform-dependent linker options to cc_library rules in general?
2. And in particular how to link to glut in platform-independent way using bazel?

Answer 1

You can do this using the Bazel select() function. Something like this might work:
config_setting(
name = "linux_x86_64",
values = {"cpu": "k8"},
visibility = ["//visibility:public"],
)
config_setting(
name = "darwin_x86_64",
values = {"cpu": "darwin_x86_64"},
visibility = ["//visibility:public"],
)
cc_library(
name = "glut",
srcs = select({
":darwin_x86_64": [],
":linux_x86_64": glob(["local/lib/libglut*.dylib", "lib/libglut*.so"]),
}),
linkopts = select({
":darwin_x86_64": [
"-framework OpenGL",
"-framework GLUT"
],
":linux_x86_64": [],
})
...
)
Dig around in the Bazel github repository, it's got some good real world examples of using select().

Answer 2

I had a similar problem but with picking the right compiler depending on the platform and #zlalanne's solution didn't work for me. After 2 days of frustration, I finally found the following solution:
config_setting (
name = "darwin",
constraint_values = [ "#bazel_tools//platforms:osx" ]
)
config_setting (
name = "windows",
constraint_values = [ "#bazel_tools//platforms:windows" ]
)
I didn't have any need for linux, but adding this to your BUILD file should work:
config_setting (
name = "linux",
constraint_values = [ "#bazel_tools//platforms:linux" ]
)
Use ":darwin", ":windows" and ":linux" in your selects and you should have a solution that works.