can reproduce now:

$ nix build github:huantianad/nixos-config#tjaplayer3-f
error: builder for '/nix/store/rscfr5ivym33v9w1n7p20zbarn5cif77-tjaplayer3-f-1.8.2.1-dependencies-source.drv' failed with exit code 139;
       last 1 log lines:
       > /nix/store/a4v3az5zmqfc2x3gyjgds5azgdhf9b54-stdenv-linux/setup: line 1560:     7 Segmentation fault      (core dumped) nuget init "/nix/store/gv7vh34zghgnmla0qjgfgzxmvjxb6k2d-tjaplayer3-f-1.8.2.1-nuget-deps" "$out/lib"
       For full logs, run 'nix log /nix/store/rscfr5ivym33v9w1n7p20zbarn5cif77-tjaplayer3-f-1.8.2.1-dependencies-source.drv'.

nixos-unstable d6b863fd9b7bb962e6f9fdf292419a775e772891 worked, 1a411f23ba299db155a5b45d5e145b85a7aafc42 is broken. will try to bisect this

       > openat(AT_FDCWD, "/build/tmp.sWUePkJTQX/.mono/config", O_RDONLY) = -1 ENOENT (No such file or directory)
       > access("/proc/self/maps", F_OK)         = 0
       > access("/proc/xen", F_OK)               = -1 ENOENT (No such file or directory)
       > mmap(NULL, 65536, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANONYMOUS|MAP_32BIT, -1, 0) = -1 ENOMEM (Cannot allocate memory)
       > openat(AT_FDCWD, "/dev/zero", O_RDONLY) = 3
       > mmap(NULL, 65536, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANONYMOUS|MAP_32BIT, 3, 0) = -1 ENOMEM (Cannot allocate memory)
       > close(3)                                = 0
       > --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=NULL} ---
       > +++ killed by SIGSEGV (core dumped) +++
       > /nix/store/2s0i8w7717g97wmj0r3rhdlhlwac0hj8-stdenv-linux/setup: line 1560:     7 Segmentation fault      (core dumped) strace nuget init "/nix/store/l0d2d7h78n87fsr7s8aw8k6n6k15b028-tjaplayer3-f-1.8.2.1-nuget-deps" "$out/lib"

In reply to @raphi:tapesoftware.net
ugh mkNugetSource is using mono to run nuget