.swiftinterface と .swiftmodule のどっちが「正」かっていうのは議論あるかも。 https://forums.swift.org/t/explicit-module-builds-the-new-swift-driver-and-swiftpm/36990 ここでは "there are four forms of module"

Explicit Module Builds, the new Swift Driver, and SwiftPM

Hi all, In the llbuild2 announcement, @ddunbar mentioned the goal of supporting "explicit modules" in the build system. I wanted to describe what explicit modules are, why they are important, and the developer work we're doing to bring the benefits of explicit module builds to SwiftPM. Modules in Swift Swift programs are composed of a number o...