validation: remove snapshot datadirs upon validation failure

If a UTXO snapshot fails to validate, don't leave the resulting datadir
on disk as this will confuse initialization on next startup and we'll
get an assertion error.

Author: jamesob

src/validation.cpp

@@ -4876,7 +4876,22 @@ bool ChainstateManager::ActivateSnapshot(
         }
     }
     if (!snapshot_ok) {
-        WITH_LOCK(::cs_main, this->MaybeRebalanceCaches());
+        LOCK(::cs_main);
+        this->MaybeRebalanceCaches();
+
+        // PopulateAndValidateSnapshot can return (in error) before the leveldb datadir
+        // has been created, so only attempt removal if we got that far.
+        if (auto snapshot_datadir = node::FindSnapshotChainstateDir()) {
+            // We have to destruct leveldb::DB in order to release the db lock, otherwise
+            // DestroyDB() (in DeleteCoinsDBFromDisk()) will fail. See `leveldb::~DBImpl()`.
+            // Destructing the chainstate (and so resetting the coinsviews object) does this.
+            snapshot_chainstate.reset();
+            bool removed = DeleteCoinsDBFromDisk(*snapshot_datadir, /*is_snapshot=*/true);
+            if (!removed) {
+                AbortNode(strprintf("Failed to remove snapshot chainstate dir (%s). "
+                    "Manually remove it before restarting.\n", fs::PathToString(*snapshot_datadir)));
+            }
+        }
         return false;
     }