Fix clang-tidy performance-unnecessary-copy-initialization warnings

Author: MarcoFalke

src/external_signer.cpp

@@ -42,7 +42,7 @@ bool ExternalSigner::Enumerate(const std::string& command, std::vector<ExternalS
         if (fingerprint.isNull()) {
             throw std::runtime_error(strprintf("'%s' received invalid response, missing signer fingerprint", command));
         }
-        const std::string fingerprintStr = fingerprint.get_str();
+        const std::string& fingerprintStr{fingerprint.get_str()};
         // Skip duplicate signer
         bool duplicate = false;
         for (const ExternalSigner& signer : signers) {

src/rpc/rawtransaction_util.cpp

@@ -223,8 +223,8 @@ void ParsePrevouts(const UniValue& prevTxsUnival, FillableSigningProvider* keyst
                         {"redeemScript", UniValueType(UniValue::VSTR)},
                         {"witnessScript", UniValueType(UniValue::VSTR)},
                     }, true);
-                UniValue rs = prevOut.find_value("redeemScript");
-                UniValue ws = prevOut.find_value("witnessScript");
+                const UniValue& rs{prevOut.find_value("redeemScript")};
+                const UniValue& ws{prevOut.find_value("witnessScript")};
                 if (rs.isNull() && ws.isNull()) {
                     throw JSONRPCError(RPC_INVALID_PARAMETER, "Missing redeemScript/witnessScript");
                 }

src/rpc/request.cpp

@@ -168,7 +168,7 @@ void JSONRPCRequest::parse(const UniValue& valRequest)
     id = request.find_value("id");
 
     // Parse method
-    UniValue valMethod = request.find_value("method");
+    const UniValue& valMethod{request.find_value("method")};
     if (valMethod.isNull())
         throw JSONRPCError(RPC_INVALID_REQUEST, "Missing method");
     if (!valMethod.isStr())
@@ -181,7 +181,7 @@ void JSONRPCRequest::parse(const UniValue& valRequest)
         LogPrint(BCLog::RPC, "ThreadRPCServer method=%s user=%s\n", SanitizeString(strMethod), this->authUser);
 
     // Parse params
-    UniValue valParams = request.find_value("params");
+    const UniValue& valParams{request.find_value("params")};
     if (valParams.isArray() || valParams.isObject())
         params = valParams;
     else if (valParams.isNull())

src/rpc/util.cpp

@@ -1133,10 +1133,10 @@ std::vector<CScript> EvalDescriptorStringOrObject(const UniValue& scanobject, Fl
     if (scanobject.isStr()) {
         desc_str = scanobject.get_str();
     } else if (scanobject.isObject()) {
-        UniValue desc_uni = scanobject.find_value("desc");
+        const UniValue& desc_uni{scanobject.find_value("desc")};
         if (desc_uni.isNull()) throw JSONRPCError(RPC_INVALID_PARAMETER, "Descriptor needs to be provided in scan object");
         desc_str = desc_uni.get_str();
-        UniValue range_uni = scanobject.find_value("range");
+        const UniValue& range_uni{scanobject.find_value("range")};
         if (!range_uni.isNull()) {
             range = ParseDescriptorRange(range_uni);
         }