Merge #21679: rpc: Keep default argument value in correct type

bee56c78e94417f89b1f48682404e2821b57bdec rpc: Check default value type againts argument type (João Barbosa)
f81ef4303e057e85aa24772c865287c17ffa4350 rpc: Keep default argument value in correct type (João Barbosa)

Pull request description:

  Store default values of RPC arguments in the corresponding type instead of a string. The value is then serialized when the help output is needed. This change simplifies #20017.

  The following examples illustrates how to use the new `RPCArg::Default` and `RPCArg::DefaultHint`:

  ```diff
  - {"verbose", RPCArg::Type::BOOL, /* default */ "false", "True for a json object, false for array of transaction ids"}
  + {"verbose", RPCArg::Type::BOOL, RPCArg::Default(false), "True for a json object, false for array of transaction ids"}
  ```

  ```diff
  - {"nblocks", RPCArg::Type::NUM, /* default */ "one month", "Size of the window in number of blocks"}
  + {"nblocks", RPCArg::Type::NUM, RPCArg::DefaultHint("one month"), "Size of the window in number of blocks"}
  ```

  No behavior change is expected.

ACKs for top commit:
  LarryRuane:
    ACK bee56c78e94417f89b1f48682404e2821b57bdec
  MarcoFalke:
    ACK bee56c78e94417f89b1f48682404e2821b57bdec 🦅

Tree-SHA512: c47d78c918e996d36631d4ad3c933b270a34c5b446b8d736be94cf4a0a7b8c0e33d954149ec786cf9550639865b79deb6a130ad044de6030f95aac33f524293a

8 files changed, 84 insertions, 53 deletions

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 833882ae3f..e7fd97ee1f 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -254,7 +254,7 @@ static RPCHelpMan waitfornewblock()
                 "\nWaits for a specific new block and returns useful info about it.\n"
                 "\nReturns the current block on timeout or exit.\n",
                 {
-                    {"timeout", RPCArg::Type::NUM, /* default */ "0", "Time in milliseconds to wait for a response. 0 indicates no timeout."},
+                    {"timeout", RPCArg::Type::NUM, RPCArg::Default{0}, "Time in milliseconds to wait for a response. 0 indicates no timeout."},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -297,7 +297,7 @@ static RPCHelpMan waitforblock()
                 "\nReturns the current block on timeout or exit.\n",
                 {
                     {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "Block hash to wait for."},
-                    {"timeout", RPCArg::Type::NUM, /* default */ "0", "Time in milliseconds to wait for a response. 0 indicates no timeout."},
+                    {"timeout", RPCArg::Type::NUM, RPCArg::Default{0}, "Time in milliseconds to wait for a response. 0 indicates no timeout."},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -344,7 +344,7 @@ static RPCHelpMan waitforblockheight()
                 "\nReturns the current block on timeout or exit.\n",
                 {
                     {"height", RPCArg::Type::NUM, RPCArg::Optional::NO, "Block height to wait for."},
-                    {"timeout", RPCArg::Type::NUM, /* default */ "0", "Time in milliseconds to wait for a response. 0 indicates no timeout."},
+                    {"timeout", RPCArg::Type::NUM, RPCArg::Default{0}, "Time in milliseconds to wait for a response. 0 indicates no timeout."},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -558,8 +558,8 @@ static RPCHelpMan getrawmempool()
                 "\nReturns all transaction ids in memory pool as a json array of string transaction ids.\n"
                 "\nHint: use getmempoolentry to fetch a specific transaction from the mempool.\n",
                 {
-                    {"verbose", RPCArg::Type::BOOL, /* default */ "false", "True for a json object, false for array of transaction ids"},
-                    {"mempool_sequence", RPCArg::Type::BOOL, /* default */ "false", "If verbose=false, returns a json object with transaction list and mempool sequence number attached."},
+                    {"verbose", RPCArg::Type::BOOL, RPCArg::Default{false}, "True for a json object, false for array of transaction ids"},
+                    {"mempool_sequence", RPCArg::Type::BOOL, RPCArg::Default{false}, "If verbose=false, returns a json object with transaction list and mempool sequence number attached."},
                 },
                 {
                     RPCResult{"for verbose = false",
@@ -608,7 +608,7 @@ static RPCHelpMan getmempoolancestors()
                 "\nIf txid is in the mempool, returns all in-mempool ancestors.\n",
                 {
                     {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id (must be in mempool)"},
-                    {"verbose", RPCArg::Type::BOOL, /* default */ "false", "True for a json object, false for array of transaction ids"},
+                    {"verbose", RPCArg::Type::BOOL, RPCArg::Default{false}, "True for a json object, false for array of transaction ids"},
                 },
                 {
                     RPCResult{"for verbose = false",
@@ -672,7 +672,7 @@ static RPCHelpMan getmempooldescendants()
                 "\nIf txid is in the mempool, returns all in-mempool descendants.\n",
                 {
                     {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id (must be in mempool)"},
-                    {"verbose", RPCArg::Type::BOOL, /* default */ "false", "True for a json object, false for array of transaction ids"},
+                    {"verbose", RPCArg::Type::BOOL, RPCArg::Default{false}, "True for a json object, false for array of transaction ids"},
                 },
                 {
                     RPCResult{"for verbose = false",
@@ -800,7 +800,7 @@ static RPCHelpMan getblockheader()
                 "If verbose is true, returns an Object with information about blockheader <hash>.\n",
                 {
                     {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The block hash"},
-                    {"verbose", RPCArg::Type::BOOL, /* default */ "true", "true for a json object, false for the hex-encoded data"},
+                    {"verbose", RPCArg::Type::BOOL, RPCArg::Default{true}, "true for a json object, false for the hex-encoded data"},
                 },
                 {
                     RPCResult{"for verbose = true",
@@ -902,7 +902,7 @@ static RPCHelpMan getblock()
                 "If verbosity is 2, returns an Object with information about block <hash> and information about each transaction. \n",
                 {
                     {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The block hash"},
-                    {"verbosity|verbose", RPCArg::Type::NUM, /* default */ "1", "0 for hex-encoded data, 1 for a json object, and 2 for json object with transaction data"},
+                    {"verbosity|verbose", RPCArg::Type::NUM, RPCArg::Default{1}, "0 for hex-encoded data, 1 for a json object, and 2 for json object with transaction data"},
                 },
                 {
                     RPCResult{"for verbosity = 0",
@@ -1070,7 +1070,7 @@ static RPCHelpMan gettxoutsetinfo()
                 "\nReturns statistics about the unspent transaction output set.\n"
                 "Note this call may take some time.\n",
                 {
-                    {"hash_type", RPCArg::Type::STR, /* default */ "hash_serialized_2", "Which UTXO set hash should be calculated. Options: 'hash_serialized_2' (the legacy algorithm), 'muhash', 'none'."},
+                    {"hash_type", RPCArg::Type::STR, RPCArg::Default{"hash_serialized_2"}, "Which UTXO set hash should be calculated. Options: 'hash_serialized_2' (the legacy algorithm), 'muhash', 'none'."},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -1137,7 +1137,7 @@ static RPCHelpMan gettxout()
         {
             {"txid", RPCArg::Type::STR, RPCArg::Optional::NO, "The transaction id"},
             {"n", RPCArg::Type::NUM, RPCArg::Optional::NO, "vout number"},
-            {"include_mempool", RPCArg::Type::BOOL, /* default */ "true", "Whether to include the mempool. Note that an unspent output that is spent in the mempool won't appear."},
+            {"include_mempool", RPCArg::Type::BOOL, RPCArg::Default{true}, "Whether to include the mempool. Note that an unspent output that is spent in the mempool won't appear."},
         },
         {
             RPCResult{"If the UTXO was not found", RPCResult::Type::NONE, "", ""},
@@ -1220,9 +1220,9 @@ static RPCHelpMan verifychain()
     return RPCHelpMan{"verifychain",
                 "\nVerifies blockchain database.\n",
                 {
-                    {"checklevel", RPCArg::Type::NUM, /* default */ strprintf("%d, range=0-4", DEFAULT_CHECKLEVEL),
+                    {"checklevel", RPCArg::Type::NUM, RPCArg::DefaultHint{strprintf("%d, range=0-4", DEFAULT_CHECKLEVEL)},
                         strprintf("How thorough the block verification is:\n - %s", Join(CHECKLEVEL_DOC, "\n- "))},
-                    {"nblocks", RPCArg::Type::NUM, /* default */ strprintf("%d, 0=all", DEFAULT_CHECKBLOCKS), "The number of blocks to check."},
+                    {"nblocks", RPCArg::Type::NUM, RPCArg::DefaultHint{strprintf("%d, 0=all", DEFAULT_CHECKBLOCKS)}, "The number of blocks to check."},
                 },
                 RPCResult{
                     RPCResult::Type::BOOL, "", "Verified or not"},
@@ -1704,8 +1704,8 @@ static RPCHelpMan getchaintxstats()
     return RPCHelpMan{"getchaintxstats",
                 "\nCompute statistics about the total number and rate of transactions in the chain.\n",
                 {
-                    {"nblocks", RPCArg::Type::NUM, /* default */ "one month", "Size of the window in number of blocks"},
-                    {"blockhash", RPCArg::Type::STR_HEX, /* default */ "chain tip", "The hash of the block that ends the window."},
+                    {"nblocks", RPCArg::Type::NUM, RPCArg::DefaultHint{"one month"}, "Size of the window in number of blocks"},
+                    {"blockhash", RPCArg::Type::STR_HEX, RPCArg::DefaultHint{"chain tip"}, "The hash of the block that ends the window."},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -1852,7 +1852,7 @@ static RPCHelpMan getblockstats()
                 "It won't work for some heights with pruning.\n",
                 {
                     {"hash_or_height", RPCArg::Type::NUM, RPCArg::Optional::NO, "The block hash or height of the target block", "", {"", "string or numeric"}},
-                    {"stats", RPCArg::Type::ARR, /* default */ "all values", "Values to plot (see result below)",
+                    {"stats", RPCArg::Type::ARR, RPCArg::DefaultHint{"all values"}, "Values to plot (see result below)",
                         {
                             {"height", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "Selected statistic"},
                             {"time", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "Selected statistic"},
@@ -2221,7 +2221,7 @@ static RPCHelpMan scantxoutset()
                 {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "An object with output descriptor and metadata",
                 {
                     {"desc", RPCArg::Type::STR, RPCArg::Optional::NO, "An output descriptor"},
-                    {"range", RPCArg::Type::RANGE, /* default */ "1000", "The range of HD chain indexes to explore (either end or [begin,end])"},
+                    {"range", RPCArg::Type::RANGE, RPCArg::Default{1000}, "The range of HD chain indexes to explore (either end or [begin,end])"},
                 }},
             },
                         "[scanobjects,...]"},
@@ -2360,7 +2360,7 @@ static RPCHelpMan getblockfilter()
                 "\nRetrieve a BIP 157 content filter for a particular block.\n",
                 {
                     {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hash of the block"},
-                    {"filtertype", RPCArg::Type::STR, /*default*/ "basic", "The type name of the filter"},
+                    {"filtertype", RPCArg::Type::STR, RPCArg::Default{"basic"}, "The type name of the filter"},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 0cef310c50..32318dd484 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -89,8 +89,8 @@ static RPCHelpMan getnetworkhashps()
                 "Pass in [blocks] to override # of blocks, -1 specifies since last difficulty change.\n"
                 "Pass in [height] to estimate the network speed at the time when a certain block was found.\n",
                 {
-                    {"nblocks", RPCArg::Type::NUM, /* default */ "120", "The number of blocks, or -1 for blocks since last difficulty change."},
-                    {"height", RPCArg::Type::NUM, /* default */ "-1", "To estimate at the time of the given height."},
+                    {"nblocks", RPCArg::Type::NUM, RPCArg::Default{120}, "The number of blocks, or -1 for blocks since last difficulty change."},
+                    {"height", RPCArg::Type::NUM, RPCArg::Default{-1}, "To estimate at the time of the given height."},
                 },
                 RPCResult{
                     RPCResult::Type::NUM, "", "Hashes per second estimated"},
@@ -214,7 +214,7 @@ static RPCHelpMan generatetodescriptor()
         {
             {"num_blocks", RPCArg::Type::NUM, RPCArg::Optional::NO, "How many blocks are generated immediately."},
             {"descriptor", RPCArg::Type::STR, RPCArg::Optional::NO, "The descriptor to send the newly generated bitcoin to."},
-            {"maxtries", RPCArg::Type::NUM, /* default */ ToString(DEFAULT_MAX_TRIES), "How many iterations to try."},
+            {"maxtries", RPCArg::Type::NUM, RPCArg::Default{DEFAULT_MAX_TRIES}, "How many iterations to try."},
         },
         RPCResult{
             RPCResult::Type::ARR, "", "hashes of blocks generated",
@@ -258,7 +258,7 @@ static RPCHelpMan generatetoaddress()
                 {
                     {"nblocks", RPCArg::Type::NUM, RPCArg::Optional::NO, "How many blocks are generated immediately."},
                     {"address", RPCArg::Type::STR, RPCArg::Optional::NO, "The address to send the newly generated bitcoin to."},
-                    {"maxtries", RPCArg::Type::NUM, /* default */ ToString(DEFAULT_MAX_TRIES), "How many iterations to try."},
+                    {"maxtries", RPCArg::Type::NUM, RPCArg::Default{DEFAULT_MAX_TRIES}, "How many iterations to try."},
                 },
                 RPCResult{
                     RPCResult::Type::ARR, "", "hashes of blocks generated",
@@ -525,7 +525,7 @@ static RPCHelpMan getblocktemplate()
         "    https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki#getblocktemplate_changes\n"
         "    https://github.com/bitcoin/bips/blob/master/bip-0145.mediawiki\n",
         {
-            {"template_request", RPCArg::Type::OBJ, "{}", "Format of the template",
+            {"template_request", RPCArg::Type::OBJ, RPCArg::Default{UniValue::VOBJ}, "Format of the template",
             {
                 {"mode", RPCArg::Type::STR, /* treat as named arg */ RPCArg::Optional::OMITTED_NAMED_ARG, "This must be set to \"template\", \"proposal\" (see BIP 23), or omitted"},
                 {"capabilities", RPCArg::Type::ARR, /* treat as named arg */ RPCArg::Optional::OMITTED_NAMED_ARG, "A list of strings",
@@ -960,7 +960,7 @@ static RPCHelpMan submitblock()
         "See https://en.bitcoin.it/wiki/BIP_0022 for full specification.\n",
         {
             {"hexdata", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "the hex-encoded block data to submit"},
-            {"dummy", RPCArg::Type::STR, /* default */ "ignored", "dummy value, for compatibility with BIP22. This value is ignored."},
+            {"dummy", RPCArg::Type::STR, RPCArg::DefaultHint{"ignored"}, "dummy value, for compatibility with BIP22. This value is ignored."},
         },
         {
             RPCResult{"If the block was accepted", RPCResult::Type::NONE, "", ""},
@@ -1069,7 +1069,7 @@ static RPCHelpMan estimatesmartfee()
         "in BIP 141 (witness data is discounted).\n",
         {
             {"conf_target", RPCArg::Type::NUM, RPCArg::Optional::NO, "Confirmation target in blocks (1 - 1008)"},
-            {"estimate_mode", RPCArg::Type::STR, /* default */ "conservative", "The fee estimate mode.\n"
+            {"estimate_mode", RPCArg::Type::STR, RPCArg::Default{"conservative"}, "The fee estimate mode.\n"
             "                   Whether to return a more conservative estimate which also satisfies\n"
             "                   a longer history. A conservative estimate potentially returns a\n"
             "                   higher feerate and is more likely to be sufficient for the desired\n"
@@ -1140,7 +1140,7 @@ static RPCHelpMan estimaterawfee()
                 "defined in BIP 141 (witness data is discounted).\n",
                 {
                     {"conf_target", RPCArg::Type::NUM, RPCArg::Optional::NO, "Confirmation target in blocks (1 - 1008)"},
-                    {"threshold", RPCArg::Type::NUM, /* default */ "0.95", "The proportion of transactions in a given feerate range that must have been\n"
+                    {"threshold", RPCArg::Type::NUM, RPCArg::Default{0.95}, "The proportion of transactions in a given feerate range that must have been\n"
             "               confirmed within conf_target in order to consider those feerates as high enough and proceed to check\n"
             "               lower buckets."},
                 },
diff --git a/src/rpc/misc.cpp b/src/rpc/misc.cpp
index 8e98919391..00a06260ea 100644
--- a/src/rpc/misc.cpp
+++ b/src/rpc/misc.cpp
@@ -90,7 +90,7 @@ static RPCHelpMan createmultisig()
                         {
                             {"key", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "The hex-encoded public key"},
                         }},
-                    {"address_type", RPCArg::Type::STR, /* default */ "legacy", "The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},
+                    {"address_type", RPCArg::Type::STR, RPCArg::Default{"legacy"}, "The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -475,7 +475,7 @@ static RPCHelpMan getmemoryinfo()
     return RPCHelpMan{"getmemoryinfo",
                 "Returns an object containing information about memory usage.\n",
                 {
-                    {"mode", RPCArg::Type::STR, /* default */ "\"stats\"", "determines what kind of information is returned.\n"
+                    {"mode", RPCArg::Type::STR, RPCArg::Default{"stats"}, "determines what kind of information is returned.\n"
             "  - \"stats\" returns general statistics about memory usage in the daemon.\n"
             "  - \"mallocinfo\" returns an XML string describing low-level heap state (only available if compiled with glibc 2.10+)."},
                 },
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index a5159fb792..be068edf68 100644
--- a/src/rpc/net.cpp
+++ b/src/rpc/net.cpp
@@ -376,8 +376,8 @@ static RPCHelpMan disconnectnode()
                 "\nStrictly one out of 'address' and 'nodeid' can be provided to identify the node.\n"
                 "\nTo disconnect by nodeid, either set 'address' to the empty string, or call using the named 'nodeid' argument only.\n",
                 {
-                    {"address", RPCArg::Type::STR, /* default */ "fallback to nodeid", "The IP address/port of the node"},
-                    {"nodeid", RPCArg::Type::NUM, /* default */ "fallback to address", "The node ID (see getpeerinfo for node IDs)"},
+                    {"address", RPCArg::Type::STR, RPCArg::DefaultHint{"fallback to nodeid"}, "The IP address/port of the node"},
+                    {"nodeid", RPCArg::Type::NUM, RPCArg::DefaultHint{"fallback to address"}, "The node ID (see getpeerinfo for node IDs)"},
                 },
                 RPCResult{RPCResult::Type::NONE, "", ""},
                 RPCExamples{
@@ -422,7 +422,7 @@ static RPCHelpMan getaddednodeinfo()
                 "\nReturns information about the given added node, or all added nodes\n"
                 "(note that onetry addnodes are not listed here)\n",
                 {
-                    {"node", RPCArg::Type::STR, /* default */ "all nodes", "If provided, return information about this specific node, otherwise all nodes are returned."},
+                    {"node", RPCArg::Type::STR, RPCArg::DefaultHint{"all nodes"}, "If provided, return information about this specific node, otherwise all nodes are returned."},
                 },
                 RPCResult{
                     RPCResult::Type::ARR, "", "",
@@ -663,8 +663,8 @@ static RPCHelpMan setban()
                 {
                     {"subnet", RPCArg::Type::STR, RPCArg::Optional::NO, "The IP/Subnet (see getpeerinfo for nodes IP) with an optional netmask (default is /32 = single IP)"},
                     {"command", RPCArg::Type::STR, RPCArg::Optional::NO, "'add' to add an IP/Subnet to the list, 'remove' to remove an IP/Subnet from the list"},
-                    {"bantime", RPCArg::Type::NUM, /* default */ "0", "time in seconds how long (or until when if [absolute] is set) the IP is banned (0 or empty means using the default time of 24h which can also be overwritten by the -bantime startup argument)"},
-                    {"absolute", RPCArg::Type::BOOL, /* default */ "false", "If set, the bantime must be an absolute timestamp expressed in " + UNIX_EPOCH_TIME},
+                    {"bantime", RPCArg::Type::NUM, RPCArg::Default{0}, "time in seconds how long (or until when if [absolute] is set) the IP is banned (0 or empty means using the default time of 24h which can also be overwritten by the -bantime startup argument)"},
+                    {"absolute", RPCArg::Type::BOOL, RPCArg::Default{false}, "If set, the bantime must be an absolute timestamp expressed in " + UNIX_EPOCH_TIME},
                 },
                 RPCResult{RPCResult::Type::NONE, "", ""},
                 RPCExamples{
@@ -842,7 +842,7 @@ static RPCHelpMan getnodeaddresses()
     return RPCHelpMan{"getnodeaddresses",
                 "\nReturn known addresses, which can potentially be used to find new nodes in the network.\n",
                 {
-                    {"count", RPCArg::Type::NUM, /* default */ "1", "The maximum number of addresses to return. Specify 0 to return all known addresses."},
+                    {"count", RPCArg::Type::NUM, RPCArg::Default{1}, "The maximum number of addresses to return. Specify 0 to return all known addresses."},
                 },
                 RPCResult{
                     RPCResult::Type::ARR, "", "",
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index ecdd00dcca..16ca3bb47d 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -85,7 +85,7 @@ static RPCHelpMan getrawtransaction()
                 "If verbose is 'false' or omitted, returns a string that is serialized, hex-encoded data for 'txid'.\n",
                 {
                     {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
-                    {"verbose", RPCArg::Type::BOOL, /* default */ "false", "If false, return a string, otherwise return a json object"},
+                    {"verbose", RPCArg::Type::BOOL, RPCArg::Default{false}, "If false, return a string, otherwise return a json object"},
                     {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED_NAMED_ARG, "The block in which to look for the transaction"},
                 },
                 {
@@ -387,7 +387,7 @@ static RPCHelpMan createrawtransaction()
                                 {
                                     {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                                     {"vout", RPCArg::Type::NUM, RPCArg::Optional::NO, "The output number"},
-                                    {"sequence", RPCArg::Type::NUM, /* default */ "depends on the value of the 'replaceable' and 'locktime' arguments", "The sequence number"},
+                                    {"sequence", RPCArg::Type::NUM, RPCArg::DefaultHint{"depends on the value of the 'replaceable' and 'locktime' arguments"}, "The sequence number"},
                                 },
                                 },
                         },
@@ -409,8 +409,8 @@ static RPCHelpMan createrawtransaction()
                                 },
                         },
                         },
-                    {"locktime", RPCArg::Type::NUM, /* default */ "0", "Raw locktime. Non-0 value also locktime-activates inputs"},
-                    {"replaceable", RPCArg::Type::BOOL, /* default */ "false", "Marks this transaction as BIP125-replaceable.\n"
+                    {"locktime", RPCArg::Type::NUM, RPCArg::Default{0}, "Raw locktime. Non-0 value also locktime-activates inputs"},
+                    {"replaceable", RPCArg::Type::BOOL, RPCArg::Default{false}, "Marks this transaction as BIP125-replaceable.\n"
             "                             Allows this transaction to be replaced by a transaction with higher fees. If provided, it is an error if explicit sequence numbers are incompatible."},
                 },
                 RPCResult{
@@ -449,7 +449,7 @@ static RPCHelpMan decoderawtransaction()
                 "\nReturn a JSON object representing the serialized, hex-encoded transaction.\n",
                 {
                     {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction hex string"},
-                    {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction.\n"
+                    {"iswitness", RPCArg::Type::BOOL, RPCArg::DefaultHint{"depends on heuristic tests"}, "Whether the transaction hex is a serialized witness transaction.\n"
                         "If iswitness is not present, heuristic tests will be used in decoding.\n"
                         "If true, only witness deserialization will be tried.\n"
                         "If false, only non-witness deserialization will be tried.\n"
@@ -752,7 +752,7 @@ static RPCHelpMan signrawtransactionwithkey()
                                 },
                         },
                         },
-                    {"sighashtype", RPCArg::Type::STR, /* default */ "ALL", "The signature hash type. Must be one of:\n"
+                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"ALL"}, "The signature hash type. Must be one of:\n"
             "       \"ALL\"\n"
             "       \"NONE\"\n"
             "       \"SINGLE\"\n"
@@ -832,7 +832,7 @@ static RPCHelpMan sendrawtransaction()
                 "\nRelated RPCs: createrawtransaction, signrawtransactionwithkey\n",
                 {
                     {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of the raw transaction"},
-                    {"maxfeerate", RPCArg::Type::AMOUNT, /* default */ FormatMoney(DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK()),
+                    {"maxfeerate", RPCArg::Type::AMOUNT, RPCArg::Default{FormatMoney(DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK())},
                         "Reject transactions whose fee rate is higher than the specified value, expressed in " + CURRENCY_UNIT +
                             "/kB.\nSet to 0 to accept any fee rate.\n"},
                 },
@@ -895,7 +895,7 @@ static RPCHelpMan testmempoolaccept()
                             {"rawtx", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, ""},
                         },
                         },
-                    {"maxfeerate", RPCArg::Type::AMOUNT, /* default */ FormatMoney(DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK()), "Reject transactions whose fee rate is higher than the specified value, expressed in " + CURRENCY_UNIT + "/kB\n"},
+                    {"maxfeerate", RPCArg::Type::AMOUNT, RPCArg::Default{FormatMoney(DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK())}, "Reject transactions whose fee rate is higher than the specified value, expressed in " + CURRENCY_UNIT + "/kB\n"},
                 },
                 RPCResult{
                     RPCResult::Type::ARR, "", "The result of the mempool acceptance test for each raw transaction in the input array.\n"
@@ -1362,7 +1362,7 @@ static RPCHelpMan finalizepsbt()
                 "Implements the Finalizer and Extractor roles.\n",
                 {
                     {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"},
-                    {"extract", RPCArg::Type::BOOL, /* default */ "true", "If true and the transaction is complete,\n"
+                    {"extract", RPCArg::Type::BOOL, RPCArg::Default{true}, "If true and the transaction is complete,\n"
             "                             extract and return the complete transaction in normal network serialization instead of the PSBT."},
                 },
                 RPCResult{
@@ -1424,7 +1424,7 @@ static RPCHelpMan createpsbt()
                                 {
                                     {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                                     {"vout", RPCArg::Type::NUM, RPCArg::Optional::NO, "The output number"},
-                                    {"sequence", RPCArg::Type::NUM, /* default */ "depends on the value of the 'replaceable' and 'locktime' arguments", "The sequence number"},
+                                    {"sequence", RPCArg::Type::NUM, RPCArg::DefaultHint{"depends on the value of the 'replaceable' and 'locktime' arguments"}, "The sequence number"},
                                 },
                                 },
                         },
@@ -1446,8 +1446,8 @@ static RPCHelpMan createpsbt()
                                 },
                         },
                         },
-                    {"locktime", RPCArg::Type::NUM, /* default */ "0", "Raw locktime. Non-0 value also locktime-activates inputs"},
-                    {"replaceable", RPCArg::Type::BOOL, /* default */ "false", "Marks this transaction as BIP125 replaceable.\n"
+                    {"locktime", RPCArg::Type::NUM, RPCArg::Default{0}, "Raw locktime. Non-0 value also locktime-activates inputs"},
+                    {"replaceable", RPCArg::Type::BOOL, RPCArg::Default{false}, "Marks this transaction as BIP125 replaceable.\n"
                             "                             Allows this transaction to be replaced by a transaction with higher fees. If provided, it is an error if explicit sequence numbers are incompatible."},
                 },
                 RPCResult{
@@ -1499,9 +1499,9 @@ static RPCHelpMan converttopsbt()
                 "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, RPCArg::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."},
-                    {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction.\n"
+                    {"iswitness", RPCArg::Type::BOOL, RPCArg::DefaultHint{"depends on heuristic tests"}, "Whether the transaction hex is a serialized witness transaction.\n"
                         "If iswitness is not present, heuristic tests will be used in decoding.\n"
                         "If true, only witness deserialization will be tried.\n"
                         "If false, only non-witness deserialization will be tried.\n"
@@ -1571,7 +1571,7 @@ static RPCHelpMan utxoupdatepsbt()
                     {"", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "An output descriptor"},
                     {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "An object with an output descriptor and extra information", {
                          {"desc", RPCArg::Type::STR, RPCArg::Optional::NO, "An output descriptor"},
-                         {"range", RPCArg::Type::RANGE, "1000", "Up to what index HD chains should be explored (either end or [begin,end])"},
+                         {"range", RPCArg::Type::RANGE, RPCArg::Default{1000}, "Up to what index HD chains should be explored (either end or [begin,end])"},
                     }},
                 }},
             },
diff --git a/src/rpc/server.cpp b/src/rpc/server.cpp
index 5d816ba5bb..cf80b08b96 100644
--- a/src/rpc/server.cpp
+++ b/src/rpc/server.cpp
@@ -135,7 +135,7 @@ static RPCHelpMan help()
     return RPCHelpMan{"help",
                 "\nList all commands, or get help for a specified command.\n",
                 {
-                    {"command", RPCArg::Type::STR, /* default */ "all commands", "The command to get help on"},
+                    {"command", RPCArg::Type::STR, RPCArg::DefaultHint{"all commands"}, "The command to get help on"},
                 },
                 {
                     RPCResult{RPCResult::Type::STR, "", "The help text"},
diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
index ba3105ca01..df3ee9f007 100644
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -498,6 +498,33 @@ RPCHelpMan::RPCHelpMan(std::string name, std::string description, std::vector<RP
         for (const std::string& name : names) {
             CHECK_NONFATAL(named_args.insert(name).second);
         }
+        // Default value type should match argument type only when defined
+        if (arg.m_fallback.index() == 2) {
+            const RPCArg::Type type = arg.m_type;
+            switch (std::get<RPCArg::Default>(arg.m_fallback).getType()) {
+            case UniValue::VOBJ:
+                CHECK_NONFATAL(type == RPCArg::Type::OBJ);
+                break;
+            case UniValue::VARR:
+                CHECK_NONFATAL(type == RPCArg::Type::ARR);
+                break;
+            case UniValue::VSTR:
+                CHECK_NONFATAL(type == RPCArg::Type::STR || type == RPCArg::Type::STR_HEX || type == RPCArg::Type::AMOUNT);
+                break;
+            case UniValue::VNUM:
+                CHECK_NONFATAL(type == RPCArg::Type::NUM || type == RPCArg::Type::AMOUNT || type == RPCArg::Type::RANGE);
+                break;
+            case UniValue::VBOOL:
+                CHECK_NONFATAL(type == RPCArg::Type::BOOL);
+                break;
+            case UniValue::VNULL:
+                // Null values are accepted in all arguments
+                break;
+            default:
+                CHECK_NONFATAL(false);
+                break;
+            }
+        }
     }
 }
 
@@ -646,7 +673,7 @@ std::string RPCArg::GetName() const
 
 bool RPCArg::IsOptional() const
 {
-    if (m_fallback.index() == 1) {
+    if (m_fallback.index() != 0) {
         return true;
     } else {
         return RPCArg::Optional::NO != std::get<RPCArg::Optional>(m_fallback);
@@ -694,7 +721,9 @@ std::string RPCArg::ToDescriptionString() const
         } // no default case, so the compiler can warn about missing cases
     }
     if (m_fallback.index() == 1) {
-        ret += ", optional, default=" + std::get<std::string>(m_fallback);
+        ret += ", optional, default=" + std::get<RPCArg::DefaultHint>(m_fallback);
+    } else if (m_fallback.index() == 2) {
+        ret += ", optional, default=" + std::get<RPCArg::Default>(m_fallback).write();
     } else {
         switch (std::get<RPCArg::Optional>(m_fallback)) {
         case RPCArg::Optional::OMITTED: {
diff --git a/src/rpc/util.h b/src/rpc/util.h
index 6e783e19fb..8ec18b2f35 100644
--- a/src/rpc/util.h
+++ b/src/rpc/util.h
@@ -145,7 +145,9 @@ struct RPCArg {
          */
         OMITTED,
     };
-    using Fallback = std::variant<Optional, /* default value for optional args */ std::string>;
+    using DefaultHint = std::string;
+    using Default = UniValue;
+    using Fallback = std::variant<Optional, /* hint for default value */ DefaultHint, /* default constant value */ Default>;
     const std::string m_names; //!< The name of the arg (can be empty for inner args, can contain multiple aliases separated by | for named request arguments)
     const Type m_type;
     const bool m_hidden;