[swift-users] System Modules and pkgConfig

[Etan Kissling]

Hi,

before Swift 3, for System Modules to work, these steps were necessary:
1. Creating module map
2. Creating System Module package
3. Creating git repo for System Module package, tagging with version
4. Referencing the System Module package from main package
5. Adding -Xcc -I and -Xlinker -L flags to the swift build command.

The problem here is, that absolute system-depending paths are required at:
- module map "header" entry.
- Xcc -I flag when building.
- Xlinker -L flag when building.

To solve this, Swift 3 introduced support for System Module search paths:
https://github.com/apple/swift-evolution/blob/master/proposals/0063-swiftpm-system-module-search-paths.md

In my case, I end up with the following for the System Module package:

module CFoo [system] {
  header "/system/depending/path/to/my/header.h"
  link "foo"
  export *
}


import PackageDescription

let package = Package(
    name: "CFoo",
    pkgConfig: "foo",
    providers: [
        .Brew("foo")
    ]
)


With this setup, I can run
PKG_CONFIG_PATH=/system/depending/path/to/my/pc/file swift build
and build the project without specifying custom Xcc -I / Xlinker -L flags.

However, the absolute system-depending path is still required in the modulemap.

When I change the module map to

module CFoo [system] {
  header "header.h"
  link "foo"
  export *
}

, I get build errors like

/module.modulemap:2:##: error: header 'header.h' not found

This is kind of different than what is suggested by the proposal (that it should recommend installing via Brew / Apt in that case).


==> How do I need to set up the project so that system-depending paths are required at no point?
==> Is there an example project available on github that demonstrates the pkgConfig feature of SwiftPM?


Thanks

Etan