Support Nix 2.17

[lheckemann]

cc @Ericson2314 who authored the API changes, to make sure I'm not doing something really silly here.

I don't think it's nice to use the WriteConn/ReadConn and the FdSinks wrapped by them simultaneously, but I'm guessing the flushes are important -- and they can't be performed through the WriteConn because not all Sinks are flushable.

[Ericson2314]

@lheckemann You did it correctly. The flushing nuscience is indeed a symptom of this code being spaghetti-ish, making conceptual operations with low-level serialization details too much

#1180 and then eventually https://github.com/NixOS/nix/pull/6134/files would solve this problem, separating concerns so the "serialization on the inside, misc IO like flushing on the outside" structure was more clear.

[Ma27]

Successfully deployed my Hydra with Nix 2.17 and this change and so far, everything works fine.

One problem though: in my deployment I'm not using nix from Hydra's flake input, but nixVersions.nix_2_17 from nixpkgs. Turns out that Hydra fails to link against this if --enable-lto is specified for nixVersions.nix_2_17:

hydra-0.1.20230804.DIRTY> /nix/store/7q1b1bsmxi91zci6g8714rcljl620y7f-bash-5.2-p15/bin/bash ../../libtool  --tag=CXX   --mode=link g++ -std=c++2a -I/nix/store/2wc8v442wwy4zqcnwr1l62v1vp9da2sq-nix-2.17.0-dev/include/nix -I/nix/store/ksqbb3np13si616y71y1bbxyyhqcm0pr-boehm-gc-8.2.2-dev/include -Wall -I ../libhydra -Wno-deprecated-declarations -g -O2 -include nix/config.h   -o hydra-queue-runner hydra_queue_runner-hydra-queue-runner.o hydra_queue_runner-queue-monitor.o hydra_queue_runner-dispatcher.o hydra_queue_runner-builder.o hydra_queue_runner-build-result.o hydra_queue_runner-build-remote.o hydra_queue_runner-nar-extractor.o -L/nix/store/11vbrp5bsvh31ddb8vxl82ryyb1rqq2z-nix-2.17.0/lib -L/nix/store/3a9r1dwgnszi7x9vybsx8y8mhhl8s0n0-boehm-gc-8.2.2/lib -lnixmain -lnixexpr -lgc -lpthread -ldl -lnixstore -lnixutil -lpqxx -lprometheus-cpp-pull -lprometheus-cpp-core 
hydra-0.1.20230804.DIRTY> libtool: link: g++ -std=c++2a -I/nix/store/2wc8v442wwy4zqcnwr1l62v1vp9da2sq-nix-2.17.0-dev/include/nix -I/nix/store/ksqbb3np13si616y71y1bbxyyhqcm0pr-boehm-gc-8.2.2-dev/include -Wall -I ../libhydra -Wno-deprecated-declarations -g -O2 -include nix/config.h -o hydra-queue-runner hydra_queue_runner-hydra-queue-runner.o hydra_queue_runner-queue-monitor.o hydra_queue_runner-dispatcher.o hydra_queue_runner-builder.o hydra_queue_runner-build-result.o hydra_queue_runner-build-remote.o hydra_queue_runner-nar-extractor.o  -L/nix/store/11vbrp5bsvh31ddb8vxl82ryyb1rqq2z-nix-2.17.0/lib -L/nix/store/3a9r1dwgnszi7x9vybsx8y8mhhl8s0n0-boehm-gc-8.2.2/lib -lnixmain -lnixexpr /nix/store/3a9r1dwgnszi7x9vybsx8y8mhhl8s0n0-boehm-gc-8.2.2/lib/libgc.so -lpthread -ldl -lnixstore -lnixutil /nix/store/cwjk8rvgpvi8dd3ga76a4z0wca2s5vlg-libpqxx-7.7.0/lib/libpqxx.so -lprometheus-cpp-pull -lprometheus-cpp-core -Wl,-rpath -Wl,/nix/store/3a9r1dwgnszi7x9vybsx8y8mhhl8s0n0-boehm-gc-8.2.2/lib -Wl,-rpath -Wl,/nix/store/cwjk8rvgpvi8dd3ga76a4z0wca2s5vlg-libpqxx-7.7.0/lib -Wl,-rpath -Wl,/nix/store/3a9r1dwgnszi7x9vybsx8y8mhhl8s0n0-boehm-gc-8.2.2/lib -Wl,-rpath -Wl,/nix/store/cwjk8rvgpvi8dd3ga76a4z0wca2s5vlg-libpqxx-7.7.0/lib
hydra-0.1.20230804.DIRTY> /nix/store/dx8hynidprz3kf4ngcjipnwaxp6h229f-binutils-2.40/bin/ld: hydra_queue_runner-build-remote.o: in function `void nix::WorkerProto::write<std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > >(nix::Store const&, nix::WorkerProto::WriteConn, std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > const&)':
hydra-0.1.20230804.DIRTY> /nix/store/2wc8v442wwy4zqcnwr1l62v1vp9da2sq-nix-2.17.0-dev/include/nix/worker-protocol.hh:112: undefined reference to `nix::WorkerProto::Serialise<std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > >::write(nix::Store const&, nix::WorkerProto::WriteConn, std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > const&)'
hydra-0.1.20230804.DIRTY> /nix/store/dx8hynidprz3kf4ngcjipnwaxp6h229f-binutils-2.40/bin/ld: hydra_queue_runner-build-remote.o: in function `State::buildRemote(nix::ref<nix::Store>, std::shared_ptr<Machine>, std::shared_ptr<Step>, unsigned int, unsigned int, unsigned int, RemoteResult&, std::shared_ptr<State::ActiveStep>, std::function<void (StepState)>, std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, NarMemberData, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, NarMemberData> > >&)':
hydra-0.1.20230804.DIRTY> /build/source/src/hydra-queue-runner/build-remote.cc:127: undefined reference to `nix::WorkerProto::Serialise<std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > >::read(nix::Store const&, nix::WorkerProto::ReadConn)'
hydra-0.1.20230804.DIRTY> /nix/store/dx8hynidprz3kf4ngcjipnwaxp6h229f-binutils-2.40/bin/ld: /build/source/src/hydra-queue-runner/build-remote.cc:375: undefined reference to `nix::WorkerProto::Serialise<std::map<nix::DrvOutput, nix::Realisation, std::less<nix::DrvOutput>, std::allocator<std::pair<nix::DrvOutput const, nix::Realisation> > > >::read(nix::Store const&, nix::WorkerProto::ReadConn)'
hydra-0.1.20230804.DIRTY> /nix/store/dx8hynidprz3kf4ngcjipnwaxp6h229f-binutils-2.40/bin/ld: hydra_queue_runner-build-remote.o: in function `void nix::WorkerProto::write<std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > >(nix::Store const&, nix::WorkerProto::WriteConn, std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > const&)':
hydra-0.1.20230804.DIRTY> /nix/store/2wc8v442wwy4zqcnwr1l62v1vp9da2sq-nix-2.17.0-dev/include/nix/worker-protocol.hh:112: undefined reference to `nix::WorkerProto::Serialise<std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > >::write(nix::Store const&, nix::WorkerProto::WriteConn, std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > const&)'
hydra-0.1.20230804.DIRTY> /nix/store/dx8hynidprz3kf4ngcjipnwaxp6h229f-binutils-2.40/bin/ld: hydra_queue_runner-build-remote.o: in function `State::buildRemote(nix::ref<nix::Store>, std::shared_ptr<Machine>, std::shared_ptr<Step>, unsigned int, unsigned int, unsigned int, RemoteResult&, std::shared_ptr<State::ActiveStep>, std::function<void (StepState)>, std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, NarMemberData, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, NarMemberData> > >&)':
hydra-0.1.20230804.DIRTY> /build/source/src/hydra-queue-runner/build-remote.cc:458: undefined reference to `nix::WorkerProto::Serialise<std::set<nix::StorePath, std::less<nix::StorePath>, std::allocator<nix::StorePath> > >::read(nix::Store const&, nix::WorkerProto::ReadConn)'
hydra-0.1.20230804.DIRTY> collect2: error: ld returned 1 exit status
hydra-0.1.20230804.DIRTY> make[3]: *** [Makefile:435: hydra-queue-runner] Error 1
hydra-0.1.20230804.DIRTY> make[3]: Leaving directory '/build/source/src/hydra-queue-runner'
hydra-0.1.20230804.DIRTY> make[2]: *** [Makefile:363: all-recursive] Error 1
hydra-0.1.20230804.DIRTY> make[2]: Leaving directory '/build/source/src'
hydra-0.1.20230804.DIRTY> make[1]: *** [Makefile:422: all-recursive] Error 1
hydra-0.1.20230804.DIRTY> make[1]: Leaving directory '/build/source'
hydra-0.1.20230804.DIRTY> make: *** [Makefile:350: all] Error 2

This can also be reproduced with the nixos/nix flake when on the PR's (at rev b23431a) branch with the following diff:

diff --git a/flake.nix b/flake.nix
index 7e7d50e2..d83a18e0 100644
--- a/flake.nix
+++ b/flake.nix
@@ -14,7 +14,7 @@
 
       pkgsBySystem = forEachSystem (system: import nixpkgs {
         inherit system;
-        overlays = [ self.overlays.default nix.overlays.default ];
+        overlays = [ nix.overlays.default self.overlays.default ];
       });
 
       # NixOS configuration used for VM tests.
@@ -40,6 +40,9 @@
 
       # A Nixpkgs overlay that provides a 'hydra' package.
       overlays.default = final: prev: {
+        nix = prev.nix.overrideAttrs ({ configureFlags ? [], ... }: {
+          configureFlags = configureFlags ++ [ "--enable-lto" ];
+        });
 
         # Add LDAP dependencies that aren't currently found within nixpkgs.
         perlPackages = prev.perlPackages // {

Will also file a bug against Nix @Ericson2314 .