Fix clang-tidy readability-const-return-type violations

25 files changed, 54 insertions, 52 deletions

diff --git a/src/.clang-tidy b/src/.clang-tidy
index 3ad463e99b..b2c1b49588 100644
--- a/src/.clang-tidy
+++ b/src/.clang-tidy
@@ -9,6 +9,7 @@ performance-for-range-copy,
 performance-move-const-arg,
 performance-no-automatic-move,
 performance-unnecessary-copy-initialization,
+readability-const-return-type,
 readability-redundant-declaration,
 readability-redundant-string-init,
 '
diff --git a/src/arith_uint256.h b/src/arith_uint256.h
index a6065dd9bd..c710fe9471 100644
--- a/src/arith_uint256.h
+++ b/src/arith_uint256.h
@@ -58,7 +58,7 @@ public:
 
     explicit base_uint(const std::string& str);
 
-    const base_uint operator~() const
+    base_uint operator~() const
     {
         base_uint ret;
         for (int i = 0; i < WIDTH; i++)
@@ -66,7 +66,7 @@ public:
         return ret;
     }
 
-    const base_uint operator-() const
+    base_uint operator-() const
     {
         base_uint ret;
         for (int i = 0; i < WIDTH; i++)
@@ -171,7 +171,7 @@ public:
         return *this;
     }
 
-    const base_uint operator++(int)
+    base_uint operator++(int)
     {
         // postfix operator
         const base_uint ret = *this;
@@ -188,7 +188,7 @@ public:
         return *this;
     }
 
-    const base_uint operator--(int)
+    base_uint operator--(int)
     {
         // postfix operator
         const base_uint ret = *this;
@@ -199,16 +199,16 @@ public:
     int CompareTo(const base_uint& b) const;
     bool EqualTo(uint64_t b) const;
 
-    friend inline const base_uint operator+(const base_uint& a, const base_uint& b) { return base_uint(a) += b; }
-    friend inline const base_uint operator-(const base_uint& a, const base_uint& b) { return base_uint(a) -= b; }
-    friend inline const base_uint operator*(const base_uint& a, const base_uint& b) { return base_uint(a) *= b; }
-    friend inline const base_uint operator/(const base_uint& a, const base_uint& b) { return base_uint(a) /= b; }
-    friend inline const base_uint operator|(const base_uint& a, const base_uint& b) { return base_uint(a) |= b; }
-    friend inline const base_uint operator&(const base_uint& a, const base_uint& b) { return base_uint(a) &= b; }
-    friend inline const base_uint operator^(const base_uint& a, const base_uint& b) { return base_uint(a) ^= b; }
-    friend inline const base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
-    friend inline const base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
-    friend inline const base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
+    friend inline base_uint operator+(const base_uint& a, const base_uint& b) { return base_uint(a) += b; }
+    friend inline base_uint operator-(const base_uint& a, const base_uint& b) { return base_uint(a) -= b; }
+    friend inline base_uint operator*(const base_uint& a, const base_uint& b) { return base_uint(a) *= b; }
+    friend inline base_uint operator/(const base_uint& a, const base_uint& b) { return base_uint(a) /= b; }
+    friend inline base_uint operator|(const base_uint& a, const base_uint& b) { return base_uint(a) |= b; }
+    friend inline base_uint operator&(const base_uint& a, const base_uint& b) { return base_uint(a) &= b; }
+    friend inline base_uint operator^(const base_uint& a, const base_uint& b) { return base_uint(a) ^= b; }
+    friend inline base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
+    friend inline base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
+    friend inline base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
     friend inline bool operator==(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) == 0; }
     friend inline bool operator!=(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) != 0; }
     friend inline bool operator>(const base_uint& a, const base_uint& b) { return a.CompareTo(b) > 0; }
diff --git a/src/bench/gcs_filter.cpp b/src/bench/gcs_filter.cpp
index 51fbe15760..0af4ee98fe 100644
--- a/src/bench/gcs_filter.cpp
+++ b/src/bench/gcs_filter.cpp
@@ -5,7 +5,7 @@
 #include <bench/bench.h>
 #include <blockfilter.h>
 
-static const GCSFilter::ElementSet GenerateGCSTestElements()
+static GCSFilter::ElementSet GenerateGCSTestElements()
 {
     GCSFilter::ElementSet elements;
 
diff --git a/src/bench/wallet_loading.cpp b/src/bench/wallet_loading.cpp
index 2f7dc53b0c..6b09adcc9d 100644
--- a/src/bench/wallet_loading.cpp
+++ b/src/bench/wallet_loading.cpp
@@ -24,7 +24,7 @@ using wallet::WALLET_FLAG_DESCRIPTORS;
 using wallet::WalletContext;
 using wallet::WalletDatabase;
 
-static const std::shared_ptr<CWallet> BenchLoadWallet(std::unique_ptr<WalletDatabase> database, WalletContext& context, DatabaseOptions& options)
+static std::shared_ptr<CWallet> BenchLoadWallet(std::unique_ptr<WalletDatabase> database, WalletContext& context, DatabaseOptions& options)
 {
     bilingual_str error;
     std::vector<bilingual_str> warnings;
diff --git a/src/external_signer.cpp b/src/external_signer.cpp
index 8a3e17a292..5524b943f4 100644
--- a/src/external_signer.cpp
+++ b/src/external_signer.cpp
@@ -16,7 +16,7 @@
 
 ExternalSigner::ExternalSigner(const std::string& command, const std::string chain, const std::string& fingerprint, const std::string name): m_command(command), m_chain(chain), m_fingerprint(fingerprint), m_name(name) {}
 
-const std::string ExternalSigner::NetworkArg() const
+std::string ExternalSigner::NetworkArg() const
 {
     return " --chain " + m_chain;
 }
diff --git a/src/external_signer.h b/src/external_signer.h
index e40fd7f010..90f07478e3 100644
--- a/src/external_signer.h
+++ b/src/external_signer.h
@@ -24,7 +24,7 @@ private:
     //! Bitcoin mainnet, testnet, etc
     std::string m_chain;
 
-    const std::string NetworkArg() const;
+    std::string NetworkArg() const;
 
 public:
     //! @param[in] command      the command which handles interaction with the external signer
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index cd0a1a19ee..00b7952ca4 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -31,7 +31,7 @@
 
 const char *DEFAULT_GUI_PROXY_HOST = "127.0.0.1";
 
-static const QString GetDefaultProxyAddress();
+static QString GetDefaultProxyAddress();
 
 /** Map GUI option ID to node setting name. */
 static const char* SettingName(OptionsModel::OptionID option)
@@ -308,7 +308,7 @@ static std::string ProxyString(bool is_set, QString ip, QString port)
     return is_set ? QString(ip + ":" + port).toStdString() : "";
 }
 
-static const QString GetDefaultProxyAddress()
+static QString GetDefaultProxyAddress()
 {
     return QString("%1:%2").arg(DEFAULT_GUI_PROXY_HOST).arg(DEFAULT_GUI_PROXY_PORT);
 }
diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index 72b9f2230e..8991bda340 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -1833,17 +1833,17 @@ DescriptorCache DescriptorCache::MergeAndDiff(const DescriptorCache& other)
     return diff;
 }
 
-const ExtPubKeyMap DescriptorCache::GetCachedParentExtPubKeys() const
+ExtPubKeyMap DescriptorCache::GetCachedParentExtPubKeys() const
 {
     return m_parent_xpubs;
 }
 
-const std::unordered_map<uint32_t, ExtPubKeyMap> DescriptorCache::GetCachedDerivedExtPubKeys() const
+std::unordered_map<uint32_t, ExtPubKeyMap> DescriptorCache::GetCachedDerivedExtPubKeys() const
 {
     return m_derived_xpubs;
 }
 
-const ExtPubKeyMap DescriptorCache::GetCachedLastHardenedExtPubKeys() const
+ExtPubKeyMap DescriptorCache::GetCachedLastHardenedExtPubKeys() const
 {
     return m_last_hardened_xpubs;
 }
diff --git a/src/script/descriptor.h b/src/script/descriptor.h
index 16ee2f6d97..cb3b366acf 100644
--- a/src/script/descriptor.h
+++ b/src/script/descriptor.h
@@ -66,11 +66,11 @@ public:
     bool GetCachedLastHardenedExtPubKey(uint32_t key_exp_pos, CExtPubKey& xpub) const;
 
     /** Retrieve all cached parent xpubs */
-    const ExtPubKeyMap GetCachedParentExtPubKeys() const;
+    ExtPubKeyMap GetCachedParentExtPubKeys() const;
     /** Retrieve all cached derived xpubs */
-    const std::unordered_map<uint32_t, ExtPubKeyMap> GetCachedDerivedExtPubKeys() const;
+    std::unordered_map<uint32_t, ExtPubKeyMap> GetCachedDerivedExtPubKeys() const;
     /** Retrieve all cached last hardened xpubs */
-    const ExtPubKeyMap GetCachedLastHardenedExtPubKeys() const;
+    ExtPubKeyMap GetCachedLastHardenedExtPubKeys() const;
 
     /** Combine another DescriptorCache into this one.
      * Returns a cache containing the items from the other cache unknown to current cache
diff --git a/src/test/fuzz/miniscript.cpp b/src/test/fuzz/miniscript.cpp
index 1d6a8d89e4..d5667e0cf3 100644
--- a/src/test/fuzz/miniscript.cpp
+++ b/src/test/fuzz/miniscript.cpp
@@ -104,7 +104,7 @@ struct ScriptParserContext {
         return key.data;
     }
 
-    const std::vector<unsigned char> ToPKHBytes(const Key& key) const
+    std::vector<unsigned char> ToPKHBytes(const Key& key) const
     {
         if (key.is_hash) return key.data;
         const auto h = Hash160(key.data);
diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
index af1d65cd38..c14f633029 100644
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -47,7 +47,7 @@ size_t CallOneOf(FuzzedDataProvider& fuzzed_data_provider, Callables... callable
 template <typename Collection>
 auto& PickValue(FuzzedDataProvider& fuzzed_data_provider, Collection& col)
 {
-    const auto sz = col.size();
+    auto sz{col.size()};
     assert(sz >= 1);
     auto it = col.begin();
     std::advance(it, fuzzed_data_provider.ConsumeIntegralInRange<decltype(sz)>(0, sz - 1));
diff --git a/src/test/versionbits_tests.cpp b/src/test/versionbits_tests.cpp
index 4a42cec4af..91383ee4a5 100644
--- a/src/test/versionbits_tests.cpp
+++ b/src/test/versionbits_tests.cpp
@@ -13,7 +13,7 @@
 /* Define a virtual block time, one block per 10 minutes after Nov 14 2014, 0:55:36am */
 static int32_t TestTime(int nHeight) { return 1415926536 + 600 * nHeight; }
 
-static const std::string StateName(ThresholdState state)
+static std::string StateName(ThresholdState state)
 {
     switch (state) {
     case ThresholdState::DEFINED:   return "DEFINED";
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index aa04f8a4d0..378123ce0f 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -1128,7 +1128,7 @@ void CTxMemPool::SetLoadTried(bool load_tried)
 }
 
 
-const std::string RemovalReasonToString(const MemPoolRemovalReason& r) noexcept
+std::string RemovalReasonToString(const MemPoolRemovalReason& r) noexcept
 {
     switch (r) {
         case MemPoolRemovalReason::EXPIRY: return "expiry";
diff --git a/src/txmempool.h b/src/txmempool.h
index 51b8af3286..2c3cb7e9db 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -237,7 +237,7 @@ enum class MemPoolRemovalReason {
     REPLACED,    //!< Removed for replacement
 };
 
-const std::string RemovalReasonToString(const MemPoolRemovalReason& r) noexcept;
+std::string RemovalReasonToString(const MemPoolRemovalReason& r) noexcept;
 
 /**
  * CTxMemPool stores valid-according-to-the-current-best-chain transactions
diff --git a/src/util/fees.cpp b/src/util/fees.cpp
index cbefe18dbb..8ada02ce54 100644
--- a/src/util/fees.cpp
+++ b/src/util/fees.cpp
@@ -49,7 +49,7 @@ std::string FeeModes(const std::string& delimiter)
     return Join(FeeModeMap(), delimiter, [&](const std::pair<std::string, FeeEstimateMode>& i) { return i.first; });
 }
 
-const std::string InvalidEstimateModeErrorMessage()
+std::string InvalidEstimateModeErrorMessage()
 {
     return "Invalid estimate_mode parameter, must be one of: \"" + FeeModes("\", \"") + "\"";
 }
diff --git a/src/util/fees.h b/src/util/fees.h
index 9ef2389d3e..10ba1e4f85 100644
--- a/src/util/fees.h
+++ b/src/util/fees.h
@@ -13,6 +13,6 @@ enum class FeeReason;
 bool FeeModeFromString(const std::string& mode_string, FeeEstimateMode& fee_estimate_mode);
 std::string StringForFeeReason(FeeReason reason);
 std::string FeeModes(const std::string& delimiter);
-const std::string InvalidEstimateModeErrorMessage();
+std::string InvalidEstimateModeErrorMessage();
 
 #endif // BITCOIN_UTIL_FEES_H
diff --git a/src/util/system.cpp b/src/util/system.cpp
index 309595ff5b..0cea283ece 100644
--- a/src/util/system.cpp
+++ b/src/util/system.cpp
@@ -242,7 +242,7 @@ static std::optional<util::SettingsValue> InterpretValue(const KeyInfo& key, con
 ArgsManager::ArgsManager() = default;
 ArgsManager::~ArgsManager() = default;
 
-const std::set<std::string> ArgsManager::GetUnsuitableSectionOnlyArgs() const
+std::set<std::string> ArgsManager::GetUnsuitableSectionOnlyArgs() const
 {
     std::set<std::string> unsuitables;
 
@@ -262,7 +262,7 @@ const std::set<std::string> ArgsManager::GetUnsuitableSectionOnlyArgs() const
     return unsuitables;
 }
 
-const std::list<SectionInfo> ArgsManager::GetUnrecognizedSections() const
+std::list<SectionInfo> ArgsManager::GetUnrecognizedSections() const
 {
     // Section names to be recognized in the config file.
     static const std::set<std::string> available_sections{
diff --git a/src/util/system.h b/src/util/system.h
index 671491f2ff..c053adf8c3 100644
--- a/src/util/system.h
+++ b/src/util/system.h
@@ -250,12 +250,12 @@ protected:
      * on the command line or in a network-specific section in the
      * config file.
      */
-    const std::set<std::string> GetUnsuitableSectionOnlyArgs() const;
+    std::set<std::string> GetUnsuitableSectionOnlyArgs() const;
 
     /**
      * Log warnings for unrecognized section names in the config file.
      */
-    const std::list<SectionInfo> GetUnrecognizedSections() const;
+    std::list<SectionInfo> GetUnrecognizedSections() const;
 
     struct Command {
         /** The command (if one has been registered with AddCommand), or empty */
diff --git a/src/validationinterface.cpp b/src/validationinterface.cpp
index 900cb0474a..d344c8bfbd 100644
--- a/src/validationinterface.cpp
+++ b/src/validationinterface.cpp
@@ -17,7 +17,7 @@
 #include <unordered_map>
 #include <utility>
 
-const std::string RemovalReasonToString(const MemPoolRemovalReason& r) noexcept;
+std::string RemovalReasonToString(const MemPoolRemovalReason& r) noexcept;
 
 /**
  * MainSignalsImpl manages a list of shared_ptr<CValidationInterface> callbacks.
diff --git a/src/wallet/rpc/transactions.cpp b/src/wallet/rpc/transactions.cpp
index 4a076a7040..e590aa1f08 100644
--- a/src/wallet/rpc/transactions.cpp
+++ b/src/wallet/rpc/transactions.cpp
@@ -397,7 +397,7 @@ static void ListTransactions(const CWallet& wallet, const CWalletTx& wtx, int nM
 }
 
 
-static const std::vector<RPCResult> TransactionDescriptionString()
+static std::vector<RPCResult> TransactionDescriptionString()
 {
     return{{RPCResult::Type::NUM, "confirmations", "The number of confirmations for the transaction. Negative confirmations means the\n"
                "transaction conflicted that many blocks ago."},
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index d8fb926c9a..59cf87355b 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -1664,7 +1664,7 @@ std::set<CKeyID> LegacyScriptPubKeyMan::GetKeys() const
     return set_address;
 }
 
-const std::unordered_set<CScript, SaltedSipHasher> LegacyScriptPubKeyMan::GetScriptPubKeys() const
+std::unordered_set<CScript, SaltedSipHasher> LegacyScriptPubKeyMan::GetScriptPubKeys() const
 {
     LOCK(cs_KeyStore);
     std::unordered_set<CScript, SaltedSipHasher> spks;
@@ -2650,17 +2650,17 @@ void DescriptorScriptPubKeyMan::WriteDescriptor()
     }
 }
 
-const WalletDescriptor DescriptorScriptPubKeyMan::GetWalletDescriptor() const
+WalletDescriptor DescriptorScriptPubKeyMan::GetWalletDescriptor() const
 {
     return m_wallet_descriptor;
 }
 
-const std::unordered_set<CScript, SaltedSipHasher> DescriptorScriptPubKeyMan::GetScriptPubKeys() const
+std::unordered_set<CScript, SaltedSipHasher> DescriptorScriptPubKeyMan::GetScriptPubKeys() const
 {
     return GetScriptPubKeys(0);
 }
 
-const std::unordered_set<CScript, SaltedSipHasher> DescriptorScriptPubKeyMan::GetScriptPubKeys(int32_t minimum_index) const
+std::unordered_set<CScript, SaltedSipHasher> DescriptorScriptPubKeyMan::GetScriptPubKeys(int32_t minimum_index) const
 {
     LOCK(cs_desc_man);
     std::unordered_set<CScript, SaltedSipHasher> script_pub_keys;
diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
index d74388b3e8..4399ac2087 100644
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -36,7 +36,7 @@ class WalletStorage
 {
 public:
     virtual ~WalletStorage() = default;
-    virtual const std::string GetDisplayName() const = 0;
+    virtual std::string GetDisplayName() const = 0;
     virtual WalletDatabase& GetDatabase() const = 0;
     virtual bool IsWalletFlagSet(uint64_t) const = 0;
     virtual void UnsetBlankWalletFlag(WalletBatch&) = 0;
@@ -243,7 +243,7 @@ public:
     virtual uint256 GetID() const { return uint256(); }
 
     /** Returns a set of all the scriptPubKeys that this ScriptPubKeyMan watches */
-    virtual const std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const { return {}; };
+    virtual std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const { return {}; };
 
     /** Prepends the wallet name in logging output to ease debugging in multi-wallet use cases */
     template<typename... Params>
@@ -512,7 +512,7 @@ public:
     const std::map<CKeyID, int64_t>& GetAllReserveKeys() const { return m_pool_key_to_index; }
 
     std::set<CKeyID> GetKeys() const override;
-    const std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const override;
+    std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const override;
 
     /** Get the DescriptorScriptPubKeyMans (with private keys) that have the same scriptPubKeys as this LegacyScriptPubKeyMan.
      * Does not modify this ScriptPubKeyMan. */
@@ -641,9 +641,9 @@ public:
     void AddDescriptorKey(const CKey& key, const CPubKey &pubkey);
     void WriteDescriptor();
 
-    const WalletDescriptor GetWalletDescriptor() const EXCLUSIVE_LOCKS_REQUIRED(cs_desc_man);
-    const std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const override;
-    const std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys(int32_t minimum_index) const;
+    WalletDescriptor GetWalletDescriptor() const EXCLUSIVE_LOCKS_REQUIRED(cs_desc_man);
+    std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys() const override;
+    std::unordered_set<CScript, SaltedSipHasher> GetScriptPubKeys(int32_t minimum_index) const;
     int32_t GetEndRange() const;
 
     bool GetDescriptorString(std::string& out, const bool priv) const;
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 53321e98ee..f056c54734 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -43,7 +43,7 @@ static_assert(WALLET_INCREMENTAL_RELAY_FEE >= DEFAULT_INCREMENTAL_RELAY_FEE, "wa
 
 BOOST_FIXTURE_TEST_SUITE(wallet_tests, WalletTestingSetup)
 
-static const std::shared_ptr<CWallet> TestLoadWallet(WalletContext& context)
+static std::shared_ptr<CWallet> TestLoadWallet(WalletContext& context)
 {
     DatabaseOptions options;
     options.create_flags = WALLET_FLAG_DESCRIPTORS;
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 108db11d32..f104a15f98 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -821,7 +821,8 @@ public:
     bool IsLegacy() const;
 
     /** Returns a bracketed wallet name for displaying in logs, will return [default wallet] if the wallet has no name */
-    const std::string GetDisplayName() const override {
+    std::string GetDisplayName() const override
+    {
         std::string wallet_name = GetName().length() == 0 ? "default wallet" : GetName();
         return strprintf("[%s]", wallet_name);
     };
diff --git a/src/wallet/wallettool.cpp b/src/wallet/wallettool.cpp
index f93b666bd5..96537b9873 100644
--- a/src/wallet/wallettool.cpp
+++ b/src/wallet/wallettool.cpp
@@ -47,7 +47,7 @@ static void WalletCreate(CWallet* wallet_instance, uint64_t wallet_creation_flag
     wallet_instance->TopUpKeyPool();
 }
 
-static const std::shared_ptr<CWallet> MakeWallet(const std::string& name, const fs::path& path, const ArgsManager& args, DatabaseOptions options)
+static std::shared_ptr<CWallet> MakeWallet(const std::string& name, const fs::path& path, const ArgsManager& args, DatabaseOptions options)
 {
     DatabaseStatus status;
     bilingual_str error;