test: Fix 0.16 wallet paths and downgrade test

The test for 0.16 wallet downgrading was using the wrong wallet path and
thus incorrectly finding that 0.16 could open wallets created in master.

Author: achow101

test/functional/wallet_backwards_compatibility.py

@@ -72,11 +72,6 @@ def setup_nodes(self):
         self.start_nodes()
         self.import_deterministic_coinbase_privkeys()
 
-    def nodes_wallet_dir(self, node):
-        if node.version < 170000:
-            return node.chain_path
-        return node.wallets_path
-
     def split_version(self, node):
         major = node.version // 10000
         minor = (node.version % 10000) // 100
@@ -178,18 +173,21 @@ def run_test(self):
         node_master_wallets_dir = node_master.wallets_path
         node_v19_wallets_dir = node_v19.wallets_path
         node_v17_wallets_dir = node_v17.wallets_path
-        node_v16_wallets_dir = node_v16.chain_path
+        node_v16_wallets_dir = node_v16.wallets_path
         node_master.unloadwallet("w1")
         node_master.unloadwallet("w2")
         node_master.unloadwallet("w3")
 
         for node in legacy_nodes:
             # Copy wallets to previous version
             for wallet in os.listdir(node_master_wallets_dir):
-                shutil.copytree(
-                    os.path.join(node_master_wallets_dir, wallet),
-                    os.path.join(self.nodes_wallet_dir(node), wallet)
-                )
+                dest = node.wallets_path / wallet
+                source = node_master_wallets_dir / wallet
+                if self.major_version_equals(node, 16):
+                    # 0.16 node expect the wallet to be in the wallet dir but as a plain file rather than in directories
+                    shutil.copyfile(source / "wallet.dat", dest)
+                else:
+                    shutil.copytree(source, dest)
 
         if not self.options.descriptors:
             # Descriptor wallets break compatibility, only run this test for legacy wallet
@@ -249,13 +247,14 @@ def run_test(self):
             node_v17.assert_start_raises_init_error(["-wallet=w3"], "Error: Error loading w3: Wallet requires newer version of Bitcoin Core")
         self.start_node(node_v17.index)
 
-        if not self.options.descriptors:
-            # Descriptor wallets break compatibility, only run this test for legacy wallets
-            # Open most recent wallet in v0.16 (no loadwallet RPC)
-            self.restart_node(node_v16.index, extra_args=["-wallet=w2"])
-            wallet = node_v16.get_wallet_rpc("w2")
-            info = wallet.getwalletinfo()
-            assert info['keypoolsize'] == 1
+        # No wallet created in master can be opened in 0.16
+        self.log.info("Test that wallets created in master are too new for 0.16")
+        self.stop_node(node_v16.index)
+        for wallet_name in ["w1", "w2", "w3"]:
+            if self.options.descriptors:
+                node_v16.assert_start_raises_init_error([f"-wallet={wallet_name}"], f"Error: {wallet_name} corrupt, salvage failed")
+            else:
+                node_v16.assert_start_raises_init_error([f"-wallet={wallet_name}"], f"Error: Error loading {wallet_name}: Wallet requires newer version of Bitcoin Core")
 
         # Create upgrade wallet in v0.16
         self.restart_node(node_v16.index, extra_args=["-wallet=u1_v16"])
@@ -278,7 +277,7 @@ def run_test(self):
             # Old wallets are BDB and will only work if BDB is compiled
             # Copy the 0.16 wallet to the last Bitcoin Core version and open it:
             shutil.copyfile(
-                os.path.join(node_v16_wallets_dir, "wallets/u1_v16"),
+                os.path.join(node_v16_wallets_dir, "u1_v16"),
                 os.path.join(node_master_wallets_dir, "u1_v16")
             )
             load_res = node_master.loadwallet("u1_v16")
@@ -297,10 +296,10 @@ def run_test(self):
 
             # Now copy that same wallet back to 0.16 to make sure no automatic upgrade breaks it
             node_master.unloadwallet("u1_v16")
-            os.remove(os.path.join(node_v16_wallets_dir, "wallets/u1_v16"))
+            os.remove(os.path.join(node_v16_wallets_dir, "u1_v16"))
             shutil.copyfile(
                 os.path.join(node_master_wallets_dir, "u1_v16"),
-                os.path.join(node_v16_wallets_dir, "wallets/u1_v16")
+                os.path.join(node_v16_wallets_dir, "u1_v16")
             )
             self.start_node(node_v16.index, extra_args=["-wallet=u1_v16"])
             wallet = node_v16.get_wallet_rpc("u1_v16")