hydra-queue-runner: Write GC roots for outputs paths

Dependencies

• [2] FHVJYJFE Upload build logs to the binary cache
• [*] MHVIT4JY Split hydra-queue-runner.cc more
• [*] 24BMQDZA Start of single-process hydra-queue-runner
• [*] NSBNNM77 Add hydra.conf option "nar_buffer_size" to configure memoryTokens limit
• [*] BRAESISH Warn if PostgreSQL appears stalled
• [*] HJOEIMLR Refactor
• [*] 7LWB2J2Z Periodically clear orphaned build steps

Change contents

• edit in src/hydra-queue-runner/builder.cc at line 266
  [4.5815]

  [4.5815]
  + for (auto & path : step->drv.outputPaths())

  + writeFile(rootsDir + "/" + baseNameOf(path), "");

  +
• edit in src/hydra-queue-runner/hydra-queue-runner.cc at line 90
  [2.775]

  [6.1572]
  + , rootsDir(config->getStrOption("gc_roots_dir", fmt("%s/gcroots/per-user/%s/hydra-roots", settings.nixStateDir, getEnv("USER"))))
• edit in src/hydra-queue-runner/queue-monitor.cc at line 224
  [4.24983]

  [7.707]
  + for (auto & path : drv.outputPaths())

  + writeFile(rootsDir + "/" + baseNameOf(path), "");

  +
• edit in src/hydra-queue-runner/state.hh at line 439
  [9.1951]

  [8.6778]
  + /* Where to store GC roots. Defaults to

  + /nix/var/nix/gcroots/per-user/$USER/hydra-roots, overridable

  + via gc_roots_dir. */

  + nix::Path rootsDir;

  +