Build Library For Distribution
It turns on all the features that are necessary to build your library in such a way that it can be distributed
What does this error actually mean? Well, when the Swift compiler goes to import a module, it looks for a file called the Compiled Module for that library. If it finds one of these files, it reads off the manifest of public APIs that you can call into, and lets you use them. Now, this Compiled Module Format is a binary format that basically contains internal compiler data structures.
And since they’re just internal data structures, they’re subject to change with every version of the Swift Compiler. So what this means is that if one person tries to import a module using one version of Swift, and that module was created by another version of Swift, their compiler can’t understand it, and they won’t be able to use it.
Well, in order to solve this version lock, Xcode 11 introduces a new format for Swift Modules, called Swift Module Interfaces. And just like the Compiled Module Format, they list out all the public APIs of a module, but in a textual form that behaves more like source code. And since they behave like source code, then future versions of the Swift Compiler will be able to import module interfaces created with older versions. And when you enable Build Libraries for Distribution, you’re telling the compiler to generate one of these stable interfaces whenever it builds your framework