Merge bitcoin/bitcoin#24347: rpc: Fix implicit-integer-sign-change in verifychain

fa8dad0 rpc: Fix implicit-integer-sign-change in verifychain (MarcoFalke)

Pull request description:

  It doesn't really make sense to treat `DEFAULT_CHECKLEVEL` as unsigned as long as `VerifyDB` accepts a signed integer.

  Making it signed also avoids a cast round trip from signed->unsigned->signed in the RPC.

ACKs for top commit:
  luke-jr:
    utACK fa8dad0
  theStack:
    Code-review ACK fa8dad0

Tree-SHA512: 75499dbe4ace2962792e5fbec7defb10c25fdbbfde951d5e542a91daa880cc50395da0287173e2c84a28e18267c74af7b44b9f38ce364bcb0216c402f65b7641

Author: MarcoFalke

src/rpc/blockchain.cpp

@@ -1417,7 +1417,7 @@ static RPCHelpMan verifychain()
                 },
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
 {
-    const int check_level(request.params[0].isNull() ? DEFAULT_CHECKLEVEL : request.params[0].get_int());
+    const int check_level{request.params[0].isNull() ? DEFAULT_CHECKLEVEL : request.params[0].get_int()};
     const int check_depth{request.params[1].isNull() ? DEFAULT_CHECKBLOCKS : request.params[1].get_int()};
 
     ChainstateManager& chainman = EnsureAnyChainman(request.context);

src/validation.h

@@ -90,7 +90,7 @@ static const int DEFAULT_STOPATHEIGHT = 0;
 /** Block files containing a block-height within MIN_BLOCKS_TO_KEEP of ActiveChain().Tip() will not be pruned. */
 static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
 static const signed int DEFAULT_CHECKBLOCKS = 6;
-static const unsigned int DEFAULT_CHECKLEVEL = 3;
+static constexpr int DEFAULT_CHECKLEVEL{3};
 // Require that user allocate at least 550 MiB for block & undo files (blk???.dat and rev???.dat)
 // At 1MB per block, 288 blocks = 288MB.
 // Add 15% for Undo data = 331MB