Merge bitcoin#15899: rpc: Document iswitness flag and fix bug in conv…

…erttopsbt

fa499b5 rpc: bugfix: Properly use iswitness in converttopsbt (MarcoFalke)
fa5c5cd rpc: Switch touched RPCs to IsValidNumArgs (MarcoFalke)

Pull request description:

  When a serialized transaction has inputs, there is no risk in only trying to deserialize it with witness allowed. (This is how all transactions from p2p are deserialized.) In fact, it would avoid a common issue where a transaction with inputs can be deserialized in two ways:
  * Fixes bitcoin#12989
  * Fixes bitcoin#15872
  * Fixes bitcoin#15701
  * Fixes bitcoin#13738
  * ...

  When a serialized transaction has no inputs, there is no risk in only trying to deserialze it with witness disallowed. (A transaction without inputs can't have corresponding witness data)

ACKs for commit fa499b:
  meshcollider:
    utACK bitcoin@fa499b5
  ryanofsky:
    utACK fa499b5. Changes since last review: consolidating commits and making iswitness documentation the same across methods.
  PastaPastaPasta:
    utACK fa499b5

Tree-SHA512: a64423a3131f3f0222a40da557c8b590c9ff01b45bcd40796f77a1a64ae74c6680a6be9d01ece95c492dfbcc7e2810409d2c2b336c2894af00bb213972fc85c6

src/rpc/rawtransaction.cpp

@@ -1359,7 +1359,7 @@ UniValue converttopsbt(const JSONRPCRequest& request)
                 "createpsbt and walletcreatefundedpsbt should be used for new applications.\n",
                 {
                     {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of a raw transaction"},
-                    {"permitsigdata", RPCArg::Type::BOOL, /* default */ "false", "If true, any signatures in the input will be discarded and conversion.\n"
+                    {"permitsigdata", RPCArg::Type::BOOL, /* default */ "false", "If true, any signatures in the input will be discarded and conversion\n"
                             "                              will continue. If false, RPC will fail if any signatures are present."},
                 },
                 RPCResult{

test/functional/rpc_psbt.py

@@ -110,8 +110,8 @@ def run_test(self):
 
         # Make sure that a psbt with signatures cannot be converted
         signedtx = self.nodes[0].signrawtransactionwithwallet(rawtx['hex'])
-        assert_raises_rpc_error(-22, "Inputs must not have scriptSigs", self.nodes[0].converttopsbt, signedtx['hex'])
-        assert_raises_rpc_error(-22, "Inputs must not have scriptSigs", self.nodes[0].converttopsbt, signedtx['hex'], False)
+        assert_raises_rpc_error(-22, "Inputs must not have scriptSigs", self.nodes[0].converttopsbt, hexstring=signedtx['hex'])
+        assert_raises_rpc_error(-22, "Inputs must not have scriptSigs", self.nodes[0].converttopsbt, hexstring=signedtx['hex'], permitsigdata=False)
         # Unless we allow it to convert and strip signatures
         self.nodes[0].converttopsbt(signedtx['hex'], True)