SwiftPM: how to migrate system package library to system library target?

Using Swift
1

When building, SwiftPM emits the following message:

'Cdns_sd' (...): warning: system packages are deprecated; use system library targets instead

I'm not aware of what constitutes a system library target and the Documentation regarding system packages (not libraries) still shows how to create a package-per-library.

OTOH there's manifest v4.2, that shows how to create a system library target:

// swift-tools-version:4.2
import PackageDescription

let package = Package(
    name: "ZLib",
    products: [
        .library(name: "ZLib", targets: ["ZLib"]),
    ],
    targets: [
        .systemLibrary(
            name: "CZLib")
        .target(
            name: "ZLib",
            dependencies: ["CZLib"]),
    ]
)

However, that documentation doesn't include any information (if at all possible) on how to specify pkgConfig and providers; e.g.

// swift-tools-version:4.2
import PackageDescription

let package = Package(
    name: "Cdns_sd",
    pkgConfig: "avahi-compat-libdns_sd",
    providers: [
        .apt(["libavahi-compat-libdnssd-dev"])
    ]
)

Finally; there might be shim.h files involved to import the desired headers.

#include <dns_sd.h>

And even module maps:

module Cdns_sd [system] {
    header "shim.h"
    link "dns_sd"
    export *
}

So I'm left wondering, what is this warning about; how does one actually migrate to this new target?

2

There’s a link to some documentation in my question here:

(If you have any ideas how to resolve my issue, I’d be grateful!)

3

Diving further into the source code for SwiftPM, it seems that all properties can be provided as one might've expected:

        .systemLibrary(name: "CLibSodium",
                       pkgConfig: "libsodium",
                       providers: [
                           .brew(["libsodium"]),
                           .apt(["libsodium-dev"])
                       ]),

A quick smoke test shows that it works, but there appears to be a regression in that using the same library within a dependency tree, it cannot reuse the same name:

error: multiple targets named 'CLibSodium' in: A, B