platform-specific_dependencies.md

Platform-specific dependencies

When cross-compiling, you may have some platform-specific sources and dependencies. Source files from all platforms can be mixed freely in a single srcs list. Source files are filtered using build constraints (filename suffixes and +build tags) before being passed to the compiler.

Platform-specific dependencies are another story. For example, if you are building a binary for Linux, and it has dependency that should only be built when targeting Windows, you will need to filter it out using Bazel select expressions:

go_binary(
    name = "cmd",
    srcs = [
        "foo_linux.go",
        "foo_windows.go",
    ],
    deps = [
        # platform agnostic dependencies
        "//bar",
    ] + select({
        # OS-specific dependencies
        "@io_bazel_rules_go//go/platform:linux": [
            "//baz_linux",
        ],
        "@io_bazel_rules_go//go/platform:windows": [
            "//quux_windows",
        ],
        "//conditions:default": [],
    }),
)

select accepts a dictionary argument. The keys are labels that reference config_setting rules. The values are lists of labels. Exactly one of these lists will be selected, depending on the target configuration. rules_go has pre-declared config_setting rules for each OS, architecture, and OS-architecture pair. For a full list, run this command:

$ bazel query 'kind(config_setting, @io_bazel_rules_go//go/platform:all)'

Gazelle will generate dependencies in this format automatically.