Keep created temp dirs inside store, but protect from GC

Implements the approach suggested by feedback on PR #6994, where
tempdir paths are created in the store (now with an exclusive lock).

As part of this work, the currently-broken and unused
`createTempDirInStore` function is updated to create an exclusive lock
on the temp directory in the store.

The GC now makes a non-blocking attempt to lock any store directories
that "look like" the temp directories created by this function, and if
it can't acquire one, ignores the directory.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 70d225be3..bd0ce1fe6 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -256,7 +256,7 @@ private:
 
     void findRuntimeRoots(Roots & roots, bool censor);
 
-    Path createTempDirInStore();
+    std::pair<Path, AutoCloseFD> createTempDirInStore();
 
     void checkDerivationOutputs(const StorePath & drvPath, const Derivation & drv);