Adds SWIFT_PACKAGE preprocessor definition

[lukewakeford]

Adds SWIFT_PACKAGE flag for resolving correct path to yoga imports.

Fixes issue #219 where including FlexLayout as a dependency of another swift package would fail to build - because it isn't possible to set the preprocessor definition FLEXLAYOUT_SWIFT_PACKAGE=1 without an Xcode project.

From the SPM Documentation:

You may be working with code that builds both as a package and not. For example, you may be packaging a project that also builds with Xcode.

In these cases, you can use the preprocessor definition SWIFT_PACKAGE to conditionally compile code for Swift packages.

In your source file:

#if SWIFT_PACKAGE
import Foundation
#endif

edit: I have update this PR to avoid breaking changes. It now avoids removing the FLEXLAYOUT_SWIFT_PACKAGE flag that people are already using.

#if FLEXLAYOUT_SWIFT_PACKAGE || SWIFT_PACKAGE

[lucdion]

@lukewakeford, I agree that it is a good idea to support the previous FLEXLAYOUT_SWIFT_PACKAGE, but why did you revert all other changes, including Readme and sample's xcodeproj changes? Your idea of using the SWIFT_PACKAGE preprocessor definition is a very good idea.

[lukewakeford]

@lucdion glad you like it 👍🏻

why did you revert all other changes, including Readme and sample's xcodeproj changes?

Because adding a flag is still required when installing the package in to an Xcode project - and I actually think using the custom FLEXLAYOUT_SWIFT_PACKAGE flag in this context is better for clarity of what it's being used for. Also the SWIFT_PACKAGE flag is very generic and may have undesired affects on other frameworks if used in this scenario.

The only bit I wasn't sure about were the target settings in Package.swift - I'm not 100% sure what these are for so I reverted my change, that said, the project did build fine without them for me. What do you think?

cSettings: [
  .define("FLEXLAYOUT_SWIFT_PACKAGE")
],
cxxSettings: [
  .define("FLEXLAYOUT_SWIFT_PACKAGE"),
  .headerSearchPath("include/yoga/"),
  .headerSearchPath("./")
],
swiftSettings: [
  .define("FLEXLAYOUT_SWIFT_PACKAGE")
]

[lucdion]

The release https://github.com/layoutBox/FlexLayout/releases/tag/1.3.30 includes your change. Thanks

[lukewakeford]

Excellent thanks 🚀

[lucdion]

Hi @lukewakeford , someone has open a story that revert your changes: #226

To be honest, I am not sure what to think

You can comment directly on this new PR. Thanks

[lukewakeford]

Thanks @lucdion i'll take another look. hopefully there is a way that both routes can still work.

[lucdion]

Yes, thanks for checking that.