Have a PSBTAnalysis state that indicates invalid PSBT

Invalid PSBTs need to be re-created, so the next role is the
Creator (new PSBTRole). Additionally, we need to know what went
wrong so an error field was added to PSBTAnalysis.

A PSBTAnalysis indicating invalid will have empty everything,
next will be set to PSBTRole::CREATOR, and an error message.

src/node/psbt.h

@@ -30,6 +30,17 @@ struct PSBTAnalysis {
     Optional<CAmount> fee;                 //!< Amount of fee being paid by the transaction
     std::vector<PSBTInputAnalysis> inputs; //!< More information about the individual inputs of the transaction
     PSBTRole next;                         //!< Which of the BIP 174 roles needs to handle the transaction next
+    std::string error;                     //!< Error message
+
+    void SetInvalid(std::string err_msg)
+    {
+        estimated_vsize = nullopt;
+        estimated_feerate = nullopt;
+        fee = nullopt;
+        inputs.clear();
+        next = PSBTRole::CREATOR;
+        error = err_msg;
+    }
 };
 
 /**

src/psbt.cpp

@@ -348,6 +348,7 @@ TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector
 
 std::string PSBTRoleName(PSBTRole role) {
     switch (role) {
+    case PSBTRole::CREATOR: return "creator";
     case PSBTRole::UPDATER: return "updater";
     case PSBTRole::SIGNER: return "signer";
     case PSBTRole::FINALIZER: return "finalizer";

src/psbt.h

@@ -560,6 +560,7 @@ struct PartiallySignedTransaction
 };
 
 enum class PSBTRole {
+    CREATOR,
     UPDATER,
     SIGNER,
     FINALIZER,

src/rpc/rawtransaction.cpp

@@ -1672,6 +1672,7 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
                 "  \"estimated_feerate\" : feerate   (numeric, optional) Estimated feerate of the final signed transaction in " + CURRENCY_UNIT + "/kB. Shown only if all UTXO slots in the PSBT have been filled.\n"
                 "  \"fee\" : fee                     (numeric, optional) The transaction fee paid. Shown only if all UTXO slots in the PSBT have been filled.\n"
                 "  \"next\" : \"role\"                 (string) Role of the next person that this psbt needs to go to\n"
+                "  \"error\" : \"error\"               (string) Error message if there is one"
                 "}\n"
             },
             RPCExamples {
@@ -1724,7 +1725,7 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
         }
         inputs_result.push_back(input_univ);
     }
-    result.pushKV("inputs", inputs_result);
+    if (!inputs_result.empty()) result.pushKV("inputs", inputs_result);
 
     if (psbta.estimated_vsize != nullopt) {
         result.pushKV("estimated_vsize", (int)*psbta.estimated_vsize);
@@ -1736,6 +1737,9 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
         result.pushKV("fee", ValueFromAmount(*psbta.fee));
     }
     result.pushKV("next", PSBTRoleName(psbta.next));
+    if (!psbta.error.empty()) {
+        result.pushKV("error", psbta.error);
+    }
 
     return result;
 }