PathSubstitutionGoal: Clean up pipe

If there were many top-level goals (which are not destroyed until the
very end), commands like

  $ nix copy --to 'ssh://localhost?remote-store=/tmp/nix' \
    /run/current-system --no-check-sigs --substitute-on-destination

could fail with "Too many open files". So now we do some explicit
cleanup from amDone(). It would be cleaner to separate goals from
their temporary internal state, but that would be a bigger refactor.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/libstore/build/goal.cc b/src/libstore/build/goal.cc
index 2dd7a4d37..9de40bdf2 100644
--- a/src/libstore/build/goal.cc
+++ b/src/libstore/build/goal.cc
@@ -78,6 +78,8 @@ void Goal::amDone(ExitCode result, std::optional<Error> ex)
     }
     waiters.clear();
     worker.removeGoal(shared_from_this());
+
+    cleanup();
 }