[omochi@omochi-iMacPro sif]$ cat c1.swift @inlinable public func foo() -> Int { #if os(macOS) return 1 #else return 2 #endif } [omochi@omochi-iMacPro sif]$ swiftc -emit-module-interface -enable-library-evolution c1.swift && cat c1.swiftinterface // swift-interface-format-version: 1.0 // swift-compiler-version: Apple Swift version 5.1.3 (swiftlang-1100.0.282.1 clang-1100.0.33.15) // swift-module-flags: -target x86_64-apple-darwin19.2.0 -enable-objc-interop -enable-library-evolution -module-name c1 import Swift @inlinable public func foo() -> Swift.Int { return 1 }