assumeutxo: Check snapshot base block is not marked invalid

Co-authored-by: Alfonso Roman Zubeldia <alfonsoromanz24@gmail.com>

Author: fjahr

src/validation.cpp

@@ -5677,6 +5677,11 @@ util::Result<void> ChainstateManager::ActivateSnapshot(
                           base_blockhash.ToString())};
         }
 
+        bool start_block_invalid = snapshot_start_block->nStatus & BLOCK_FAILED_MASK;
+        if (start_block_invalid) {
+            return util::Error{strprintf(_("The base block header (%s) is part of an invalid chain."), base_blockhash.ToString())};
+        }
+
         if (Assert(m_active_chainstate->GetMempool())->size() > 0) {
             return util::Error{_("Can't activate a snapshot when mempool not empty.")};
         }

test/functional/feature_assumeutxo.py

@@ -205,6 +205,19 @@ def test_snapshot_with_less_work(self, dump_output_path):
             assert_raises_rpc_error(-32603, "Unable to load UTXO snapshot", node.loadtxoutset, dump_output_path)
         self.restart_node(0, extra_args=self.extra_args[0])
 
+    def test_snapshot_block_invalidated(self, dump_output_path):
+        self.log.info("Test snapshot is not loaded when base block is invalid.")
+        node = self.nodes[0]
+        # We are testing the case where the base block is invalidated itself
+        # and also the case where one of its parents is invalidated.
+        for height in [SNAPSHOT_BASE_HEIGHT, SNAPSHOT_BASE_HEIGHT - 1]:
+            block_hash = node.getblockhash(height)
+            node.invalidateblock(block_hash)
+            assert_equal(node.getblockcount(), height - 1)
+            msg = "Unable to load UTXO snapshot: The base block header (3bb7ce5eba0be48939b7a521ac1ba9316afee2c7bada3a0cca24188e6d7d96c0) is part of an invalid chain."
+            assert_raises_rpc_error(-32603, msg, node.loadtxoutset, dump_output_path)
+            node.reconsiderblock(block_hash)
+
     def run_test(self):
         """
         Bring up two (disconnected) nodes, mine some new blocks on the first,
@@ -291,6 +304,7 @@ def run_test(self):
         self.test_invalid_snapshot_scenarios(dump_output['path'])
         self.test_invalid_chainstate_scenarios()
         self.test_invalid_file_path()
+        self.test_snapshot_block_invalidated(dump_output['path'])
 
         self.log.info(f"Loading snapshot into second node from {dump_output['path']}")
         loaded = n1.loadtxoutset(dump_output['path'])