check: do not consider orphan chunks a problem

if we use AdHocCache or NewCache, we do not have precise refcounting.
thus, we do not delete repo objects as their refcount does not go to zero.

check --repair will just remove the orphans.

src/borg/archive.py

@@ -2331,10 +2331,10 @@ class ArchiveChecker:
             unused = {id_ for id_, entry in self.chunks.iteritems() if entry.refcount == 0}
             orphaned = unused - self.possibly_superseded
             if orphaned:
-                logger.error(f"{len(orphaned)} orphaned objects found!")
+                logger.info(f"{len(orphaned)} orphaned (unused) objects found.")
                 for chunk_id in orphaned:
                     logger.debug(f"chunk {bin_to_hex(chunk_id)} is orphaned.")
-                self.error_found = True
+                # To support working with AdHocCache or NewCache, we do not set self.error_found = True.
             if self.repair and unused:
                 logger.info(
                     "Deleting %d orphaned and %d superseded objects..." % (len(orphaned), len(self.possibly_superseded))

src/borg/testsuite/archiver/check_cmd.py

@@ -338,10 +338,11 @@ def test_extra_chunks(archivers, request):
     with Repository(archiver.repository_location, exclusive=True) as repository:
         repository.put(b"01234567890123456789012345678901", b"xxxx")
         repository.commit(compact=False)
-    cmd(archiver, "check", exit_code=1)
-    cmd(archiver, "check", exit_code=1)
+    output = cmd(archiver, "check", "-v", exit_code=0)  # orphans are not considered warnings anymore
+    assert "1 orphaned (unused) objects found." in output
     cmd(archiver, "check", "--repair", exit_code=0)
-    cmd(archiver, "check", exit_code=0)
+    output = cmd(archiver, "check", "-v", exit_code=0)
+    assert "orphaned (unused) objects found." not in output
     cmd(archiver, "extract", "archive1", "--dry-run", exit_code=0)