Merge #19215: psbt: Include and allow both non_witness_utxo and witness_utxo for segwit inputs

84d295e51341a126a6c3cbeea7a8caa04c7b5bc3 tests: Check that segwit inputs in psbt have both UTXO types (Andrew Chow)
46004790588c24174a0bec49b540d158ce163ffd psbt: always put a non_witness_utxo and don't remove it (Andrew Chow)
5279d8bc07d601fe6a67ad665fbc7591fe73c7de psbt: Allow both non_witness_utxo and witness_utxo (Andrew Chow)
72f6bec1da198764d4648a10a61c485e7ab65e9e rpc: show both UTXOs in decodepsbt (Andrew Chow)

Pull request description:

  Due to recent changes to hardware wallets, the full previous transaction will need to be provided for segwit inputs. Since some software may be checking for the existence of a `witness_utxo` to determine whether to produce a segwit signature, we keep that field to ease the transition.

  Because all of the sanity checks implemented by the `IsSane` functions were related to having mixed segwit and non-segwit data in a PSBT, those functions are removed as those checks are no longer proper.

  Some tests are updated/removed to accommodate this and a simple test added to check that both UTXOs are being added to segwit inputs.

  As discussed in the wallet IRC meeting, our own signer will not require `non_witness_utxo` for segwit inputs.

ACKs for top commit:
  Sjors:
    utACK 84d295e51341a126a6c3cbeea7a8caa04c7b5bc3 (didn't retest compared to 836d6fc, but fortunately HWI's CI tracks our master branch, with a bunch of hardware wallet simulators)
  ryanofsky:
    Code review re-ACK 84d295e51341a126a6c3cbeea7a8caa04c7b5bc3. No changes since last review, but now I understand the context better. I think it would good to improve the comments as suggested https://github.com/bitcoin/bitcoin/pull/19215#discussion_r447889473 and maybe refer to
  meshcollider:
    utACK 84d295e51341a126a6c3cbeea7a8caa04c7b5bc3

Tree-SHA512: ccc1fd3c16ac3859f5aca4fa489bd40f68be0b81bbdc4dd51188bbf28827a8642dc8b605a37318e5f16cf40f1c4910052dace2f27eca21bb58435f02a443e940

1 files changed, 7 insertions, 2 deletions

diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index faec359d1c..5f8c02df65 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1104,6 +1104,7 @@ UniValue decodepsbt(const JSONRPCRequest& request)
         const PSBTInput& input = psbtx.inputs[i];
         UniValue in(UniValue::VOBJ);
         // UTXOs
+        bool have_a_utxo = false;
         if (!input.witness_utxo.IsNull()) {
             const CTxOut& txout = input.witness_utxo;
 
@@ -1121,7 +1122,9 @@ UniValue decodepsbt(const JSONRPCRequest& request)
             ScriptToUniv(txout.scriptPubKey, o, true);
             out.pushKV("scriptPubKey", o);
             in.pushKV("witness_utxo", out);
-        } else if (input.non_witness_utxo) {
+            have_a_utxo = true;
+        }
+        if (input.non_witness_utxo) {
             UniValue non_wit(UniValue::VOBJ);
             TxToUniv(*input.non_witness_utxo, uint256(), non_wit, false);
             in.pushKV("non_witness_utxo", non_wit);
@@ -1132,7 +1135,9 @@ UniValue decodepsbt(const JSONRPCRequest& request)
                 // Hack to just not show fee later
                 have_all_utxos = false;
             }
-        } else {
+            have_a_utxo = true;
+        }
+        if (!have_a_utxo) {
             have_all_utxos = false;
         }