Build error on Android: call to `signal` yields "error: function is unused"

[marcprux]

#3167 introduced a failure in my hourly Android builds of swift-nio (see https://github.com/swift-everywhere/swift-package-builds/actions/runs/14312839641/job/40111885760), which is a stopgap until swiftlang/github-workflows#106 gets approved.

/Users/runner/work/swift-package-builds/swift-package-builds/swift-nio/Sources/NIOCrashTester/main.swift:140:5: error: function is unused
138 |         try! group.syncShutdownGracefully()
139 |     }
140 |     signal(SIGPIPE, SIG_IGN)
    |     `- error: function is unused

@finagolfin, have you ever seen anything like this?

[marcprux]

I guess because signal is defined as:

sighandler_t _Nonnull signal(int __signal, sighandler_t _Nullable __handler);

and the return value is being treated as a function (which we can presumably ignore), then the solution might be simply:

    #if os(Android)
    _ = signal(SIGPIPE, SIG_IGN)
    #else
    signal(SIGPIPE, SIG_IGN)
    #endif

[finagolfin]

No, never, it is related to the new strict concurrency checking, which was just enabled for this executable in the pull you linked, that just broke my Android CI too and is reproducible natively in Termux. Your linked fix works for me when I just tried it natively on Android.

Why do you think this only hits on Android: is it that these are C macros in linux's signal.h so such type-checking is abandoned there, but is only being performed on Android's more simple C declarations?