borg delete: fix --cache-only for broken caches

This also makes --cache-only idempotent: it won't fail if the cache
is already deleted.

Fixes #874

borg/archiver.py

@@ -396,22 +396,23 @@ class Archiver:
         cache.commit()
         return self.exit_code
 
-    @with_repository(exclusive=True, cache=True)
-    def do_delete(self, args, repository, manifest, key, cache):
+    @with_repository(exclusive=True)
+    def do_delete(self, args, repository, manifest, key):
         """Delete an existing repository or archive"""
         if args.location.archive:
-            archive = Archive(repository, key, manifest, args.location.archive, cache=cache)
-            stats = Statistics()
-            archive.delete(stats, progress=args.progress)
-            manifest.write()
-            repository.commit(save_space=args.save_space)
-            cache.commit()
-            logger.info("Archive deleted.")
-            if args.stats:
-                log_multi(DASHES,
-                          stats.summary.format(label='Deleted data:', stats=stats),
-                          str(cache),
-                          DASHES)
+            with Cache(repository, key, manifest, lock_wait=self.lock_wait) as cache:
+                archive = Archive(repository, key, manifest, args.location.archive, cache=cache)
+                stats = Statistics()
+                archive.delete(stats, progress=args.progress)
+                manifest.write()
+                repository.commit(save_space=args.save_space)
+                cache.commit()
+                logger.info("Archive deleted.")
+                if args.stats:
+                    log_multi(DASHES,
+                              stats.summary.format(label='Deleted data:', stats=stats),
+                              str(cache),
+                              DASHES)
         else:
             if not args.cache_only:
                 msg = []
@@ -426,7 +427,7 @@ class Archiver:
                     return self.exit_code
                 repository.destroy()
                 logger.info("Repository deleted.")
-            cache.destroy()
+            Cache.destroy(repository)
             logger.info("Cache deleted.")
         return self.exit_code
 

borg/cache.py

@@ -37,6 +37,15 @@ class Cache:
         path = path or os.path.join(get_cache_dir(), hexlify(repository.id).decode('ascii'))
         UpgradableLock(os.path.join(path, 'lock'), exclusive=True).break_lock()
 
+    @staticmethod
+    def destroy(repository, path=None):
+        """destroy the cache for ``repository`` or at ``path``"""
+        path = path or os.path.join(get_cache_dir(), hexlify(repository.id).decode('ascii'))
+        config = os.path.join(path, 'config')
+        if os.path.exists(config):
+            os.remove(config)  # kill config first
+            shutil.rmtree(path)
+
     def __init__(self, repository, key, manifest, path=None, sync=True, do_files=False, warn_if_unencrypted=True,
                  lock_wait=None):
         self.lock = None
@@ -120,13 +129,6 @@ Chunk index:    {0.total_unique_chunks:20d} {0.total_chunks:20d}"""
         with open(os.path.join(self.path, 'files'), 'wb') as fd:
             pass  # empty file
 
-    def destroy(self):
-        """destroy the cache at `self.path`
-        """
-        self.close()
-        os.remove(os.path.join(self.path, 'config'))  # kill config first
-        shutil.rmtree(self.path)
-
     def _do_open(self):
         self.config = configparser.ConfigParser(interpolation=None)
         config_path = os.path.join(self.path, 'config')