this derivation will be built:
  /nix/store/c1j2k46h7b468h1pqbavfj0043rjvnd0-spec-nixfmt.drv
building '/nix/store/c1j2k46h7b468h1pqbavfj0043rjvnd0-spec-nixfmt.drv'
spec-nixfmt> invalid/a.nix:1:7:
spec-nixfmt>   |
spec-nixfmt> 1 | { a = ;
spec-nixfmt>   |       ^^
spec-nixfmt> unexpected ";<newline>"
spec-nixfmt> expecting expression
spec-nixfmt> 

upload niks3: ok