[PATCH proxmox-backup] config: lock guard: label BackupLockGuard by must_use attribute

[Christian Ebner <c.ebner@proxmox.com>]

The BackupLockGuard is used to store the open file descriptor of a
flocked file. Once dropped, the file lock is release.

Since not binding the BackupLockGuard to a variable will result in
dropping of the struct and therefore immediate unlocking of the file,
set the must_use attribute with a meaningful description to get
clippy warnings for this.

Suggested-by: Daniel Kral <d.kral@proxmox.com>
Suggested-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-config/src/lib.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pbs-config/src/lib.rs b/pbs-config/src/lib.rs
index 18b27d23a..88a31904f 100644
--- a/pbs-config/src/lib.rs
+++ b/pbs-config/src/lib.rs
@@ -59,6 +59,7 @@ pub fn priv_user() -> Result<nix::unistd::User, Error> {
     }
 }
 
+#[must_use = "lock guard must be used to keep file locked"]
 pub struct BackupLockGuard {
     file: Option<std::fs::File>,
     // TODO: Remove `_legacy_dir` with PBS 5
-- 
2.47.3