Merge #20480: Replace boost::variant with std::variant

faa8f68943 Replace boost::variant with std::variant (MarcoFalke)

Pull request description:

  Now that we can use std::variant from the vanilla standard library, drop the third-party boost variant dependency

ACKs for top commit:
  fjahr:
    Code review ACK faa8f68943
  fanquake:
    ACK faa8f68943

Tree-SHA512: 6e3aecd33b00c2e31a763f999247944d5b2ce5e3018f1965c516c1000cd08ff6703a8d50fb0be64883153da2925ae72986b8a6b96586db74057bd05d6f4986e6

src/script/descriptor.cpp

@@ -565,7 +565,7 @@ public:
 
     Optional<OutputType> GetOutputType() const override
     {
-        switch (m_destination.which()) {
+        switch (m_destination.index()) {
             case 1 /* PKHash */:
             case 2 /* ScriptHash */: return OutputType::LEGACY;
             case 3 /* WitnessV0ScriptHash */:
@@ -593,7 +593,7 @@ public:
     {
         CTxDestination dest;
         ExtractDestination(m_script, dest);
-        switch (dest.which()) {
+        switch (dest.index()) {
             case 1 /* PKHash */:
             case 2 /* ScriptHash */: return OutputType::LEGACY;
             case 3 /* WitnessV0ScriptHash */:

src/script/signingprovider.cpp

@@ -179,18 +179,18 @@ CKeyID GetKeyForDestination(const SigningProvider& store, const CTxDestination&
 {
     // Only supports destinations which map to single public keys, i.e. P2PKH,
     // P2WPKH, and P2SH-P2WPKH.
-    if (auto id = boost::get<PKHash>(&dest)) {
+    if (auto id = std::get_if<PKHash>(&dest)) {
         return ToKeyID(*id);
     }
-    if (auto witness_id = boost::get<WitnessV0KeyHash>(&dest)) {
+    if (auto witness_id = std::get_if<WitnessV0KeyHash>(&dest)) {
         return ToKeyID(*witness_id);
     }
-    if (auto script_hash = boost::get<ScriptHash>(&dest)) {
+    if (auto script_hash = std::get_if<ScriptHash>(&dest)) {
         CScript script;
         CScriptID script_id(*script_hash);
         CTxDestination inner_dest;
         if (store.GetCScript(script_id, script) && ExtractDestination(script, inner_dest)) {
-            if (auto inner_witness_id = boost::get<WitnessV0KeyHash>(&inner_dest)) {
+            if (auto inner_witness_id = std::get_if<WitnessV0KeyHash>(&inner_dest)) {
                 return ToKeyID(*inner_witness_id);
             }
         }

src/script/standard.cpp

@@ -261,9 +261,8 @@ bool ExtractDestinations(const CScript& scriptPubKey, TxoutType& typeRet, std::v
     return true;
 }
 
-namespace
-{
-class CScriptVisitor : public boost::static_visitor<CScript>
+namespace {
+class CScriptVisitor
 {
 public:
     CScript operator()(const CNoDestination& dest) const
@@ -300,7 +299,7 @@ public:
 
 CScript GetScriptForDestination(const CTxDestination& dest)
 {
-    return boost::apply_visitor(CScriptVisitor(), dest);
+    return std::visit(CScriptVisitor(), dest);
 }
 
 CScript GetScriptForRawPubKey(const CPubKey& pubKey)
@@ -320,5 +319,5 @@ CScript GetScriptForMultisig(int nRequired, const std::vector<CPubKey>& keys)
 }
 
 bool IsValidDestination(const CTxDestination& dest) {
-    return dest.which() != 0;
+    return dest.index() != 0;
 }

src/script/standard.h

@@ -9,10 +9,8 @@
 #include <script/interpreter.h>
 #include <uint256.h>
 
-#include <boost/variant.hpp>
-
 #include <string>
-
+#include <variant>
 
 static const bool DEFAULT_ACCEPT_DATACARRIER = true;
 
@@ -211,7 +209,7 @@ struct WitnessUnknown
  *    (taproot outputs do not require their own type as long as no wallet support exists)
  *  A CTxDestination is the internal data type encoded in a bitcoin address
  */
-typedef boost::variant<CNoDestination, PKHash, ScriptHash, WitnessV0ScriptHash, WitnessV0KeyHash, WitnessUnknown> CTxDestination;
+using CTxDestination = std::variant<CNoDestination, PKHash, ScriptHash, WitnessV0ScriptHash, WitnessV0KeyHash, WitnessUnknown>;
 
 /** Check whether a CTxDestination is a CNoDestination. */
 bool IsValidDestination(const CTxDestination& dest);