TL;DR;

/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Time.swift:127:3: error: unknown attribute '_downgrade_exhaustivity_check'
        @_downgrade_exhaustivity_check
            ^
/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/IO.swift:71:21: error: invalid redeclaration of 'init(type:path:oflag:mode:queue:cleanupHandler:)'
        public convenience init?(
                                       ^          




I'm going to build Swift rpm package from source on Fedora 26.

This error occurs with 3.1 and 3.1.1 releases of swift and its dependencies including swift-llbuild, 
swift-cmark, swift-lldb, etc.

I used this script (https://github.com/corinnekrych/swift-rpm/blob/master/rpm-from-source.sh)  and changed it a bit in order to work in Fedora 26 (it apparently worked on previous versions of Fedora).

The latest error(s) I faced is(are):   

"""
/home/ali/rpmbuild/BUILD/build/buildbot_linux/swift-linux-x86_64/bin/swiftc -whole-module-optimization -emit-library -c /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Block.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Data.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Dispatch.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/IO.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Private.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Queue.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Source.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Time.swift /home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Wrapper.swift \
-Xcc -fmodule-map-file=/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/dispatch/module.modulemap -I/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch -Xcc -fblocks -O -module-name Dispatch -module-link-name dispatch \
-o /home/ali/rpmbuild/BUILD/build/buildbot_linux/libdispatch-linux-x86_64/src/swift/swift_overlay.o -emit-module-path /home/ali/rpmbuild/BUILD/build/buildbot_linux/libdispatch-linux-x86_64/src/swift/Dispatch.swiftmodule
/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/Time.swift:127:3: error: unknown attribute '_downgrade_exhaustivity_check'
        @_downgrade_exhaustivity_check
         ^
/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/IO.swift:71:21: error: invalid redeclaration of 'init(type:path:oflag:mode:queue:cleanupHandler:)'
        public convenience init?(
                           ^
/home/ali/rpmbuild/BUILD/swift-corelibs-libdispatch/src/swift/IO.swift:59:21: note: 'init(type:path:oflag:mode:queue:cleanupHandler:)' previously declared here
        public convenience init(
                           ^
make[2]: *** [Makefile:1004: /home/ali/rpmbuild/BUILD/build/buildbot_linux/libdispatch-linux-x86_64/src/swift/swift_overlay.o] Error 1
make[2]: Leaving directory '/home/ali/rpmbuild/BUILD/build/buildbot_linux/libdispatch-linux-x86_64/src'
make[1]: *** [Makefile:545: all] Error 2
make[1]: Leaving directory '/home/ali/rpmbuild/BUILD/build/buildbot_linux/libdispatch-linux-x86_64/src'
make: *** [Makefile:453: all-recursive] Error 1
./utils/build-script: fatal error: command terminated with a non-zero exit status 2, aborting
./utils/build-script: fatal error: command terminated with a non-zero exit status 1, aborting
error: Bad exit status from /var/tmp/rpm-tmp.VPka9M (%build)


RPM build errors:
    Bad exit status from /var/tmp/rpm-tmp.VPka9M (%build)

"""

Please let me know if you need something else.

Ali