pub fn platform_direct_deps(&self, build_platform: BuildPlatform) -> &PackageSet<'g> {
        match build_platform {
            BuildPlatform::Target => self.target_direct_deps(),
            BuildPlatform::Host => self.host_direct_deps(),
        }
    }
Returns the set of workspace and direct dependency packages on the specified build platform.
guppy/src/graph/cargo/cargo_api.rs