Repository: Handle non-existing directories in garbage collection

For example, if there has been no streams created, we don't want to
fail with some random ENOENT.

Signed-off-by: Alexander Larsson <alexl@redhat.com>

Author: alexlarsson

crates/composefs/src/repository.rs

@@ -513,15 +513,30 @@ impl<ObjectID: FsVerityHashValue> Repository<ObjectID> {
     fn gc_category(&self, category: &str) -> Result<HashSet<ObjectID>> {
         let mut objects = HashSet::new();
 
-        let category_fd = self.openat(category, OFlags::RDONLY | OFlags::DIRECTORY)?;
+        let category_fd = match self.openat(category, OFlags::RDONLY | OFlags::DIRECTORY) {
+            Ok(fd) => fd,
+            Err(Errno::NOENT) => {
+                return Ok(objects);
+            }
+            Err(other) => {
+                return Err(other).context("Opening {category} dir in repository")?;
+            }
+        };
 
-        let refs = openat(
+        match openat(
             &category_fd,
             "refs",
             OFlags::RDONLY | OFlags::DIRECTORY,
             Mode::empty(),
-        )?;
-        Self::walk_symlinkdir(refs, &mut objects)?;
+        ) {
+            Ok(refs) => {
+                Self::walk_symlinkdir(refs, &mut objects)?;
+            }
+            Err(Errno::NOENT) => {}
+            Err(other) => {
+                return Err(other).context("Opening {category}/refs dir in repository")?;
+            }
+        };
 
         for item in Dir::read_from(&category_fd)? {
             let entry = item?;