Merge #19644: rpc: document returned error fields as optional if applicable

f110b7c rpc: document returned error fields as optional if applicable (Sebastian Falbesoner)

Pull request description:

  The following RPCs return error fields (named `"error"` or `"errors"`) that are optional, but don't show up as optional in the help text yet:
  * `analyzepsbt`
  * `estimatesmartfee`
  * `signrawtransactionwithkey`
  * `signrawtransactionwithwallet`

  The following RPC has the errors field already marked as optional, but doesn't match the usual format in the description (like `"if there are any"` in parantheses):
  * `estimaterawfee`

  This PR adds the missing optional flags and adapts the description strings. Inspired by a recent PR #19634 by justinmoon.

  The instances were found via `git grep "RPCResult.*\"error"`. Note that there is one RPC so far where the return error is not optional (i.e. in case of no error, the field is included in the result, but is just empty), namely `bumpfee`.

ACKs for top commit:
  adaminsky:
    ACK `f110b7c`
  laanwj:
    ACK f110b7c, new documentation looks consistent with actual behavior
  achow101:
    ACK f110b7c
  meshcollider:
    utACK f110b7c

Tree-SHA512: 30c00f78a575b60e32b4536496af986d53a25f33e6ebbf553adcdcf825ad21a44f90267f3d1ea53326dac83bcfa9983fdb3dad6d3126e20f97f3c08ce286e188

Author: meshcollider

src/rpc/mining.cpp

@@ -1019,7 +1019,7 @@ static UniValue estimatesmartfee(const JSONRPCRequest& request)
                     RPCResult::Type::OBJ, "", "",
                     {
                         {RPCResult::Type::NUM, "feerate", /* optional */ true, "estimate fee rate in " + CURRENCY_UNIT + "/kB (only present if no errors were encountered)"},
-                        {RPCResult::Type::ARR, "errors", "Errors encountered during processing",
+                        {RPCResult::Type::ARR, "errors", /* optional */ true, "Errors encountered during processing (if there are any)",
                             {
                                 {RPCResult::Type::STR, "", "error"},
                             }},
@@ -1098,7 +1098,7 @@ static UniValue estimaterawfee(const JSONRPCRequest& request)
                                 {
                                     {RPCResult::Type::ELISION, "", ""},
                                 }},
-                                {RPCResult::Type::ARR, "errors", /* optional */ true, "Errors encountered during processing",
+                                {RPCResult::Type::ARR, "errors", /* optional */ true, "Errors encountered during processing (if there are any)",
                                 {
                                     {RPCResult::Type::STR, "error", ""},
                                 }},

src/rpc/rawtransaction.cpp

@@ -744,7 +744,7 @@ static UniValue signrawtransactionwithkey(const JSONRPCRequest& request)
                     {
                         {RPCResult::Type::STR_HEX, "hex", "The hex-encoded raw transaction with signature(s)"},
                         {RPCResult::Type::BOOL, "complete", "If the transaction has a complete set of signatures"},
-                        {RPCResult::Type::ARR, "errors", "Script verification errors (if there are any)",
+                        {RPCResult::Type::ARR, "errors", /* optional */ true, "Script verification errors (if there are any)",
                         {
                             {RPCResult::Type::OBJ, "", "",
                             {
@@ -1722,7 +1722,7 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
                     {RPCResult::Type::STR_AMOUNT, "estimated_feerate", /* optional */ true, "Estimated feerate of the final signed transaction in " + CURRENCY_UNIT + "/kB. Shown only if all UTXO slots in the PSBT have been filled"},
                     {RPCResult::Type::STR_AMOUNT, "fee", /* optional */ true, "The transaction fee paid. Shown only if all UTXO slots in the PSBT have been filled"},
                     {RPCResult::Type::STR, "next", "Role of the next person that this psbt needs to go to"},
-                    {RPCResult::Type::STR, "error", "Error message if there is one"},
+                    {RPCResult::Type::STR, "error", /* optional */ true, "Error message (if there is one)"},
                 }
             },
             RPCExamples {

src/wallet/rpcwallet.cpp

@@ -3166,7 +3166,7 @@ UniValue signrawtransactionwithwallet(const JSONRPCRequest& request)
                     {
                         {RPCResult::Type::STR_HEX, "hex", "The hex-encoded raw transaction with signature(s)"},
                         {RPCResult::Type::BOOL, "complete", "If the transaction has a complete set of signatures"},
-                        {RPCResult::Type::ARR, "errors", "Script verification errors (if there are any)",
+                        {RPCResult::Type::ARR, "errors", /* optional */ true, "Script verification errors (if there are any)",
                         {
                             {RPCResult::Type::OBJ, "", "",
                             {