test: coverage for wallet birth time interaction with -reindex

Verifying the wallet updates the birth time accordingly when it
detects a transaction with a time older than the oldest descriptor
timestamp.
This could happen when the user blindly imports a descriptor with
'timestamp=now'.

test/functional/test_runner.py

@@ -206,6 +206,8 @@
     'wallet_createwallet.py --descriptors',
     'wallet_watchonly.py --legacy-wallet',
     'wallet_watchonly.py --usecli --legacy-wallet',
+    'wallet_reindex.py --legacy-wallet',
+    'wallet_reindex.py --descriptors',
     'wallet_reorgsrestore.py',
     'wallet_conflicts.py --legacy-wallet',
     'wallet_conflicts.py --descriptors',

test/functional/wallet_reindex.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+# Copyright (c) 2023-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://www.opensource.org/licenses/mit-license.php.
+
+"""Test wallet-reindex interaction"""
+
+import time
+
+from test_framework.blocktools import COINBASE_MATURITY
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+)
+BLOCK_TIME = 60 * 10
+
+class WalletReindexTest(BitcoinTestFramework):
+    def add_options(self, parser):
+        self.add_wallet_options(parser)
+
+    def set_test_params(self):
+        self.num_nodes = 1
+        self.setup_clean_chain = True
+
+    def skip_test_if_missing_module(self):
+        self.skip_if_no_wallet()
+
+    def advance_time(self, node, secs):
+        self.node_time += secs
+        node.setmocktime(self.node_time)
+
+    # Verify the wallet updates the birth time accordingly when it detects a transaction
+    # with a time older than the oldest descriptor timestamp.
+    # This could happen when the user blindly imports a descriptor with 'timestamp=now'.
+    def birthtime_test(self, node, miner_wallet):
+        self.log.info("Test birth time update during tx scanning")
+        # Fund address to test
+        wallet_addr = miner_wallet.getnewaddress()
+        tx_id = miner_wallet.sendtoaddress(wallet_addr, 2)
+
+        # Generate 50 blocks, one every 10 min to surpass the 2 hours rescan window the wallet has
+        for _ in range(50):
+            self.generate(node, 1)
+            self.advance_time(node, BLOCK_TIME)
+
+        # Now create a new wallet, and import the descriptor
+        node.createwallet(wallet_name='watch_only', disable_private_keys=True, blank=True, load_on_startup=True)
+        wallet_watch_only = node.get_wallet_rpc('watch_only')
+
+        # For a descriptors wallet: Import address with timestamp=now.
+        # For legacy wallet: There is no way of importing a script/address with a custom time. The wallet always imports it with birthtime=1.
+        # In both cases, disable rescan to not detect the transaction.
+        wallet_watch_only.importaddress(wallet_addr, rescan=False)
+        assert_equal(len(wallet_watch_only.listtransactions()), 0)
+
+        # Rescan the wallet to detect the missing transaction
+        wallet_watch_only.rescanblockchain()
+        assert_equal(wallet_watch_only.gettransaction(tx_id)['confirmations'], 50)
+        assert_equal(wallet_watch_only.getbalances()['mine' if self.options.descriptors else 'watchonly']['trusted'], 2)
+
+        # Reindex and wait for it to finish
+        with node.assert_debug_log(expected_msgs=["initload thread exit"]):
+            self.restart_node(0, extra_args=['-reindex=1', f'-mocktime={self.node_time}'])
+        node.syncwithvalidationinterfacequeue()
+
+        # Verify the transaction is still 'confirmed' after reindex
+        wallet_watch_only = node.get_wallet_rpc('watch_only')
+        assert_equal(wallet_watch_only.gettransaction(tx_id)['confirmations'], 50)
+
+        wallet_watch_only.unloadwallet()
+
+    def run_test(self):
+        node = self.nodes[0]
+        self.node_time = int(time.time())
+        node.setmocktime(self.node_time)
+
+        # Fund miner
+        node.createwallet(wallet_name='miner', load_on_startup=True)
+        miner_wallet = node.get_wallet_rpc('miner')
+        self.generatetoaddress(node, COINBASE_MATURITY + 10, miner_wallet.getnewaddress())
+
+        # Tests
+        self.birthtime_test(node, miner_wallet)
+
+
+if __name__ == '__main__':
+    WalletReindexTest().main()