Merge #19005: doc: Add documentation for 'checklevel' argument in 'verifychain' RPC…

501e6ab4e778d8f4e95fdc807eeb8644df16203b doc: Add documentation for 'checklevel' argument in 'verifychain' RPC call (Calvin Kim)

Pull request description:

  Rationale: When ```bitcoin-cli help verifychain``` is called, the user doesn't get any documentation about the ```checklevel``` argument, leading to issues like #18995.

  This PR addresses that issue and adds documentation for what each level does, and that each level includes the checks of the previous levels.

ACKs for top commit:
  jonatack:
    ACK 501e6ab4e778d8f4e95fdc807eeb8644df16203b `git diff 292ed3c 501e6ab` shows only change since last review is the verifychain RPCHelpMan edit; rebuild and retested manually anyway
  MarcoFalke:
    ACK 501e6ab4e778d8f4e95fdc807eeb8644df16203b 🚝

Tree-SHA512: 09239f79c25b5c3022b8eb1f76198ba681305d7e8775038e46becffe5f6a14c572e0c5d06b0723fe9d4a015ec42c9f7ca7b80a2a93df0b1b66f5a84a80eeeeb1

4 files changed, 14 insertions, 9 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 12cecd68d8..4c5c0051ca 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -500,14 +500,7 @@ void SetupServerArgs(NodeContext& node)
 #endif
 
     gArgs.AddArg("-checkblocks=<n>", strprintf("How many blocks to check at startup (default: %u, 0 = all)", DEFAULT_CHECKBLOCKS), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
-    gArgs.AddArg("-checklevel=<n>", strprintf("How thorough the block verification of -checkblocks is: "
-        "level 0 reads the blocks from disk, "
-        "level 1 verifies block validity, "
-        "level 2 verifies undo data, "
-        "level 3 checks disconnection of tip blocks, "
-        "and level 4 tries to reconnect the blocks, "
-        "each level includes the checks of the previous levels "
-        "(0-4, default: %u)", DEFAULT_CHECKLEVEL), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
+    gArgs.AddArg("-checklevel=<n>", strprintf("How thorough the block verification of -checkblocks is: %s (0-4, default: %u)", Join(CHECKLEVEL_DOC, ", "), DEFAULT_CHECKLEVEL), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-checkblockindex", strprintf("Do a consistency check for the block tree, chainstate, and other validation data structures occasionally. (default: %u, regtest: %u)", defaultChainParams->DefaultConsistencyChecks(), regtestChainParams->DefaultConsistencyChecks()), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-checkmempool=<n>", strprintf("Run checks every <n> transactions (default: %u, regtest: %u)", defaultChainParams->DefaultConsistencyChecks(), regtestChainParams->DefaultConsistencyChecks()), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-checkpoints", strprintf("Enable rejection of any forks from the known historical chain until block 295000 (default: %u)", DEFAULT_CHECKPOINTS_ENABLED), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::DEBUG_TEST);
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index b0936cef5a..eedb1c3d71 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1095,7 +1095,8 @@ static UniValue verifychain(const JSONRPCRequest& request)
             RPCHelpMan{"verifychain",
                 "\nVerifies blockchain database.\n",
                 {
-                    {"checklevel", RPCArg::Type::NUM, /* default */ strprintf("%d, range=0-4", DEFAULT_CHECKLEVEL), "How thorough the block verification is."},
+                    {"checklevel", RPCArg::Type::NUM, /* default */ 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."},
                 },
                 RPCResult{
diff --git a/src/validation.cpp b/src/validation.cpp
index 81b22a7e1f..c7a1423536 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -76,6 +76,14 @@ static constexpr std::chrono::hours DATABASE_WRITE_INTERVAL{1};
 static constexpr std::chrono::hours DATABASE_FLUSH_INTERVAL{24};
 /** Maximum age of our tip for us to be considered current for fee estimation */
 static constexpr std::chrono::hours MAX_FEE_ESTIMATION_TIP_AGE{3};
+const std::vector<std::string> CHECKLEVEL_DOC {
+    "level 0 reads the blocks from disk",
+    "level 1 verifies block validity",
+    "level 2 verifies undo data",
+    "level 3 checks disconnection of tip blocks",
+    "level 4 tries to reconnect the blocks",
+    "each level includes the checks of the previous levels",
+};
 
 bool CBlockIndexWorkComparator::operator()(const CBlockIndex *pa, const CBlockIndex *pb) const {
     // First sort by most total work, ...
diff --git a/src/validation.h b/src/validation.h
index 8112e38704..e403bcb51a 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -29,6 +29,7 @@
 #include <memory>
 #include <set>
 #include <stdint.h>
+#include <string>
 #include <utility>
 #include <vector>
 
@@ -149,6 +150,8 @@ extern bool fHavePruned;
 extern bool fPruneMode;
 /** Number of MiB of block files that we're trying to stay below. */
 extern uint64_t nPruneTarget;
+/** Documentation for argument 'checklevel'. */
+extern const std::vector<std::string> CHECKLEVEL_DOC;
 
 /** Open a block file (blk?????.dat) */
 FILE* OpenBlockFile(const FlatFilePos &pos, bool fReadOnly = false);