wallet: migration, fix watch-only and solvables wallets names

Because the default wallet has no name, the watch-only and solvables
wallets created during migration end up having no name either.

This fixes it by applying the same prefix name we use for the backup
file for an unnamed default wallet.

Before: watch-only wallet named "_watchonly"
After:  watch-only wallet named "default_wallet_watchonly"

Github-Pull: bitcoin/bitcoin#34156
Rebased-From: 82caa8193a

test/functional/wallet_migration.py

@@ -5,6 +5,7 @@
 """Test Migrating a wallet from legacy to descriptor."""
 
 import os
+from pathlib import Path
 import random
 import shutil
 import struct
@@ -25,6 +26,7 @@ from test_framework.script import hash160
 from test_framework.script_util import key_to_p2pkh_script, key_to_p2pk_script, script_to_p2sh_script, script_to_p2wsh_script
 from test_framework.util import (
     assert_equal,
+    assert_greater_than,
     assert_raises_rpc_error,
     find_vout_for_address,
     sha256sum_file,
@@ -523,6 +525,14 @@ class WalletMigrationTest(BitcoinTestFramework):
 
         assert_equal(bals, wallet.getbalances())
 
+    def clear_default_wallet(self, backup_file):
+        # Test cleanup: Clear unnamed default wallet for subsequent tests
+        (self.old_node.wallets_path / "wallet.dat").unlink()
+        (self.master_node.wallets_path / "wallet.dat").unlink(missing_ok=True)
+        shutil.rmtree(self.master_node.wallets_path / "default_wallet_watchonly", ignore_errors=True)
+        shutil.rmtree(self.master_node.wallets_path / "default_wallet_solvables", ignore_errors=True)
+        backup_file.unlink()
+
     def test_default_wallet(self):
         self.log.info("Test migration of the wallet named as the empty string")
         wallet = self.create_legacy_wallet("")
@@ -549,6 +559,36 @@ class WalletMigrationTest(BitcoinTestFramework):
 
         self.master_node.setmocktime(0)
 
+        wallet.unloadwallet()
+        self.clear_default_wallet(backup_file=Path(res["backup_path"]))
+
+    def test_default_wallet_watch_only(self):
+        self.log.info("Test unnamed (default) watch-only wallet migration")
+        master_wallet = self.master_node.get_wallet_rpc(self.default_wallet_name)
+        wallet = self.create_legacy_wallet("", blank=True)
+        wallet.importaddress(master_wallet.getnewaddress(address_type="legacy"))
+
+        res, def_wallet = self.migrate_and_get_rpc("")
+        wallet = self.master_node.get_wallet_rpc("default_wallet_watchonly")
+
+        info = wallet.getwalletinfo()
+        assert_equal(info["descriptors"], True)
+        assert_equal(info["format"], "sqlite")
+        assert_equal(info["private_keys_enabled"], False)
+        assert_equal(info["walletname"], "default_wallet_watchonly")
+
+        # The default wallet will still exist and have newly generated descriptors
+        assert (self.master_node.wallets_path / "wallet.dat").exists()
+        def_wallet_info = def_wallet.getwalletinfo()
+        assert_equal(def_wallet_info["descriptors"], True)
+        assert_equal(def_wallet_info["format"], "sqlite")
+        assert_equal(def_wallet_info["private_keys_enabled"], True)
+        assert_equal(def_wallet_info["walletname"], "")
+        assert_greater_than(def_wallet_info["keypoolsize"], 0)
+
+        wallet.unloadwallet()
+        self.clear_default_wallet(backup_file=Path(res["backup_path"]))
+
     def test_default_wallet_failure(self):
         self.log.info("Test failure during unnamed (default) wallet migration")
         master_wallet = self.master_node.get_wallet_rpc(self.default_wallet_name)
@@ -557,7 +597,7 @@ class WalletMigrationTest(BitcoinTestFramework):
 
         # Create wallet directory with the watch-only name and a wallet file.
         # Because the wallet dir exists, this will cause migration to fail.
-        watch_only_dir = self.master_node.wallets_path / "_watchonly"
+        watch_only_dir = self.master_node.wallets_path / "default_wallet_watchonly"
         os.mkdir(watch_only_dir)
         shutil.copyfile(self.old_node.wallets_path / "wallet.dat", watch_only_dir / "wallet.dat")
 
@@ -580,7 +620,7 @@ class WalletMigrationTest(BitcoinTestFramework):
             assert_equal(magic, BTREE_MAGIC)
 
         # Test cleanup: clear default wallet for next test
-        os.remove(self.old_node.wallets_path / "wallet.dat")
+        self.clear_default_wallet(backup_path)
 
     def test_direct_file(self):
         self.log.info("Test migration of a wallet that is not in a wallet directory")
@@ -1408,6 +1448,7 @@ class WalletMigrationTest(BitcoinTestFramework):
         self.test_unloaded_by_path()
         self.test_default_wallet_failure()
         self.test_default_wallet()
+        self.test_default_wallet_watch_only()
         self.test_direct_file()
         self.test_addressbook()
         self.test_migrate_raw_p2sh()