rpc: deprecate addresses and reqSigs from rpc outputs

1) add a new sane "address" field (for outputs that have an
   identifiable address, which doesn't include bare multisig)
2) with -deprecatedrpc: leave "reqSigs" and "addresses" intact
   (with all weird/wrong behavior they have now)
3) without -deprecatedrpc: drop "reqSigs" and "addresses" entirely,
   always.

test/functional/rpc_addresses_deprecation.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+# Copyright (c) 2020 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test deprecation of reqSigs and addresses RPC fields."""
+
+from io import BytesIO
+
+from test_framework.messages import CTransaction
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    hex_str_to_bytes
+)
+
+
+class AddressesDeprecationTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 2
+        self.extra_args = [[], ["-deprecatedrpc=addresses"]]
+
+    def skip_test_if_missing_module(self):
+        self.skip_if_no_wallet()
+
+    def run_test(self):
+        self.test_addresses_deprecation()
+
+    def test_addresses_deprecation(self):
+        node = self.nodes[0]
+        coin = node.listunspent().pop()
+
+        inputs = [{'txid': coin['txid'], 'vout': coin['vout']}]
+        outputs = {node.getnewaddress(): 0.99}
+        raw = node.createrawtransaction(inputs, outputs)
+        signed = node.signrawtransactionwithwallet(raw)['hex']
+
+        # This transaction is derived from test/util/data/txcreatemultisig1.json
+        tx = CTransaction()
+        tx.deserialize(BytesIO(hex_str_to_bytes(signed)))
+        tx.vout[0].scriptPubKey = hex_str_to_bytes("522102a5613bd857b7048924264d1e70e08fb2a7e6527d32b7ab1bb993ac59964ff39721021ac43c7ff740014c3b33737ede99c967e4764553d1b2b83db77c83b8715fa72d2102df2089105c77f266fa11a9d33f05c735234075f2e8780824c6b709415f9fb48553ae")
+        tx_signed = node.signrawtransactionwithwallet(tx.serialize().hex())['hex']
+        txid = node.sendrawtransaction(hexstring=tx_signed, maxfeerate=0)
+
+        self.log.info("Test RPCResult scriptPubKey no longer returns the fields addresses or reqSigs by default")
+        hash = node.generateblock(output=node.getnewaddress(), transactions=[txid])['hash']
+        # Ensure both nodes have the newly generated block on disk.
+        self.sync_blocks()
+        script_pub_key = node.getblock(blockhash=hash, verbose=2)['tx'][-1]['vout'][0]['scriptPubKey']
+        assert 'addresses' not in script_pub_key and 'reqSigs' not in script_pub_key
+
+        self.log.info("Test RPCResult scriptPubKey returns the addresses field with -deprecatedrpc=addresses")
+        script_pub_key = self.nodes[1].getblock(blockhash=hash, verbose=2)['tx'][-1]['vout'][0]['scriptPubKey']
+        assert_equal(script_pub_key['addresses'], ['mvKDK6D54HU8wQumJBLHY95eq5iHFqXSBz', 'mv3rHCQSwKp2BLSuMHD8uCS32LW5xiNAA5', 'mirrsyhAQYzo5CwVhcaYJKwUJu1WJRCRJe'])
+        assert_equal(script_pub_key['reqSigs'], 2)
+
+
+if __name__ == "__main__":
+    AddressesDeprecationTest().main()