Passing compilation flags to local Swift packages

[dmhts (Dima Hutsuliak)]

I have a project that uses a dozen of local Swift packages and I am trying to find a way of passing some compilation flags when building those packages from Xcode. Unfortunately, setting SWIFT_ACTIVE_COMPILATION_CONDITIONS has no effect when compiling packages.

It is possible, of course, to do that in the swiftSettings target argument in a manifest file or directly using swift build -Xswiftc, but I need to set the flags based on different build configurations.

Is there a way of configuring the xcodebuild tool the way that the flags are passed to package compiler invocations?

[dmhts (Dima Hutsuliak)]

It seems like it was done like this by design, and xcodebuild intentionally ignores setting active compilation conditions for custom build configurations when it comes to compiling packages (expectedly it works only for the predefined debug build configuration). I will probably have to resort to using environment variables to set the flags conditionally in the package manifest file for now.

[piotrch]

Hey @dmhts , how did you solve it? passing Xcode build configuration through pre-build phase and process environment or else?

[dmhts (Dima Hutsuliak)]

Fortunately, with your own local packages, you have more freedom, so we decided to pull the build configuration-specific logic from the packages up to the application level, leaving the packages configuration-agnostic.

[piotrch]

Thanks for getting back to me.
Yeah, I think that we will have to make the code in the package build settings agnostic and then inject the configuration at the runtime in code in the hosting code side.

[H2wk (Andrew)]

@piotrch & @dmhts how did you achieve this for a local swift package?

Interested as i am facing the same issue.

Do you have any links?

[piotrch]

Hey,
TLDR; we have dropped this path.
The bottom line is that any non swiftPM way of workaround that you find is not sustainable enough. Even, when you set the Jenkins CI env to have all the flags set per build type, then the problem starts with building the project locally. The swiftPM is disconnected from the main Xcode project.

[dmhts (Dima Hutsuliak)]

To bring a bit of historical context here:

1. There was already an idea of introducing package flavors
2. and a note from one of the (past?) SwiftPM maintainters:

@ddunbar

"Package Features": It would be very useful have something akin to Cargo's features mechanism in SwiftPM, so that packages could expose "knobs & switches" by which their clients could enable or control how the package was built. SwiftPM currently allows environment variables to be used for this purpose in the manifest, but it is a hack we really only allow because we don't have a proper feature for it. This is also somewhat related to more flexible build configurations or Bazel's configurable build attributes , although I see this as potentially orthogonal features.