tmpfiles: Minor PR followup nit

It's clearer if `increment` mutates self.

Signed-off-by: Colin Walters <[email protected]>

Author: cgwalters

tmpfiles/src/lib.rs

@@ -28,8 +28,9 @@ const BOOTC_GENERATED_PREFIX: &str = "bootc-autogenerated-var";
 struct BootcTmpfilesGeneration(u32);
 
 impl BootcTmpfilesGeneration {
-    fn increment(&self) -> Self {
-        Self(self.0 + 1)
+    fn increment(&mut self) {
+        // SAFETY: We shouldn't ever wrap here
+        self.0 = self.0.checked_add(1).unwrap();
     }
 
     fn path(&self) -> Utf8PathBuf {
@@ -478,7 +479,7 @@ fn read_tmpfiles(rootfs: &Dir) -> Result<(BTreeMap<PathBuf, String>, BootcTmpfil
         }
         if let Ok(s) = stem.as_str() {
             if s.starts_with(BOOTC_GENERATED_PREFIX) {
-                generation = generation.increment();
+                generation.increment();
             }
         }
         let r = BufReader::new(entry.open()?);
@@ -588,7 +589,7 @@ mod tests {
         var_to_tmpfiles(rootfs, userdb, userdb).unwrap();
 
         // This is the first run
-        let gen = BootcTmpfilesGeneration(0);
+        let mut gen = BootcTmpfilesGeneration(0);
         let autovar_path = &gen.path();
         assert!(rootfs.try_exists(autovar_path).unwrap());
         let entries: Vec<String> = rootfs
@@ -615,7 +616,7 @@ mod tests {
         let wg = w.generated.as_ref().unwrap();
         assert_eq!(wg.0, NonZeroUsize::new(1).unwrap());
         assert_eq!(w.unsupported, 0);
-        let gen = gen.increment();
+        gen.increment();
         let autovar_path = &gen.path();
         assert_eq!(autovar_path, &wg.1);
         assert!(rootfs.try_exists(autovar_path).unwrap());