From d8e04255e0a3d4b5f09c555e3e2acb1d60b990de Mon Sep 17 00:00:00 2001
From: Kittywhiskers Van Gogh <63189531+kwvg@users.noreply.github.com>
Date: Fri, 1 Nov 2024 11:41:28 +0000
Subject: [PATCH 1/4] refactor: remove `rfind` workaround with `starts_with`

---
 src/bitcoin-cli.cpp   | 2 +-
 src/test/fuzz/rpc.cpp | 4 +---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/bitcoin-cli.cpp b/src/bitcoin-cli.cpp
index cd691e151ca4a..bd121d01e396b 100644
--- a/src/bitcoin-cli.cpp
+++ b/src/bitcoin-cli.cpp
@@ -551,7 +551,7 @@ class NetinfoRequestHandler : public BaseRequestHandler
                     peer.is_outbound ? "out" : "in",
                     ConnectionTypeForNetinfo(peer.conn_type),
                     peer.network,
-                    peer.transport_protocol_type.rfind('v', 0) == 0 ? peer.transport_protocol_type[1] : ' ',
+                    peer.transport_protocol_type.starts_with('v') == 0 ? peer.transport_protocol_type[1] : ' ',
                     PingTimeToString(peer.min_ping),
                     PingTimeToString(peer.ping),
                     peer.last_send ? ToString(m_time_now - peer.last_send) : "",
diff --git a/src/test/fuzz/rpc.cpp b/src/test/fuzz/rpc.cpp
index 435ebc1b91b09..fe65a717365fe 100644
--- a/src/test/fuzz/rpc.cpp
+++ b/src/test/fuzz/rpc.cpp
@@ -357,9 +357,7 @@ FUZZ_TARGET_INIT(rpc, initialize_rpc)
         rpc_testing_setup->CallRPC(rpc_command, arguments);
     } catch (const UniValue& json_rpc_error) {
         const std::string error_msg{find_value(json_rpc_error, "message").get_str()};
-        // Once c++20 is allowed, starts_with can be used.
-        // if (error_msg.starts_with("Internal bug detected")) {
-        if (0 == error_msg.rfind("Internal bug detected", 0)) {
+        if (error_msg.starts_with("Internal bug detected")) {
             // Only allow the intentional internal bug
             assert(error_msg.find("trigger_internal_bug") != std::string::npos);
         }

From acda80ed4ffa61644593d575930e13da75843403 Mon Sep 17 00:00:00 2001
From: Kittywhiskers Van Gogh <63189531+kwvg@users.noreply.github.com>
Date: Fri, 1 Nov 2024 11:54:19 +0000
Subject: [PATCH 2/4] refactor: use `constexpr` `std::`{`copy`, `fill`} in
 `V2ShortIDs`

---
 src/net.cpp | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/src/net.cpp b/src/net.cpp
index 3b54c7422cd13..9fac69f7f916e 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -1120,16 +1120,9 @@ constexpr std::array<std::string_view, 256> V2ShortIDs() {
     static_assert(std::size(V2_DASH_IDS) <= 128);
 
     std::array<std::string_view, 256> ret{};
-    for (size_t idx{0}; idx < std::size(ret); idx++) {
-        if (idx < 128 && idx < std::size(V2_BITCOIN_IDS)) {
-            ret[idx] = V2_BITCOIN_IDS[idx];
-        } else if (idx >= 128 && idx - 128 < std::size(V2_DASH_IDS)) {
-            ret[idx] = V2_DASH_IDS[idx - 128];
-        } else {
-            ret[idx] = "";
-        }
-    }
-
+    std::fill(ret.begin(), ret.end(), "");
+    std::copy(V2_BITCOIN_IDS.begin(), V2_BITCOIN_IDS.end(), ret.begin());
+    std::copy(V2_DASH_IDS.begin(), V2_DASH_IDS.end(), ret.begin() + 128);
     return ret;
 }
 

From 4717fe8045c887db365ab48a3a17a4980d4fd373 Mon Sep 17 00:00:00 2001
From: Kittywhiskers Van Gogh <63189531+kwvg@users.noreply.github.com>
Date: Fri, 1 Nov 2024 14:06:59 +0000
Subject: [PATCH 3/4] refactor: avoid convoluted casting by not using
 `std::time_t`

std::clock_cast is a part of C++20, hence the original TODO comment but
it's still not implemented in Clang, as of this writing. We can sidestep
the cast by not using time_t to begin with.
---
 src/wallet/wallet.cpp | 38 ++++++++++++--------------------------
 1 file changed, 12 insertions(+), 26 deletions(-)

diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 576703ab60824..79ecd2318b9be 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -22,6 +22,7 @@
 #include <policy/settings.h>
 #include <primitives/block.h>
 #include <primitives/transaction.h>
+#include <reverse_iterator.h>
 #include <script/descriptor.h>
 #include <script/script.h>
 #include <script/sign.h>
@@ -5309,44 +5310,29 @@ bool CWallet::AutoBackupWallet(const fs::path& wallet_path, bilingual_str& error
     }
 
     // Keep only the last 10 backups, including the new one of course
-    typedef std::multimap<std::time_t, fs::path> folder_set_t;
-    folder_set_t folder_set;
-    fs::directory_iterator end_iter;
+    std::multimap<fs::file_time_type, fs::path> folder_set;
     // Build map of backup files for current(!) wallet sorted by last write time
     fs::path currentFile;
-    for (fs::directory_iterator dir_iter(backupsDir); dir_iter != end_iter; ++dir_iter)
-    {
+    for (const auto& entry : fs::directory_iterator(backupsDir)) {
         // Only check regular files
-        if ( fs::is_regular_file(dir_iter->status()))
-        {
-            currentFile = dir_iter->path().filename();
+        if (entry.is_regular_file()) {
+            currentFile = entry.path().filename();
             // Only add the backups for the current wallet, e.g. wallet.dat.*
-            if (fs::PathToString(dir_iter->path().stem()) == strWalletName) {
-                folder_set.insert(folder_set_t::value_type(
-                    // TODO: C++17 compliant time conversion code is abominable, switch to C++20
-                    //       compliant code when C++17 support is dropped
-                    std::chrono::system_clock::to_time_t(
-                        std::chrono::time_point_cast<std::chrono::system_clock::duration>(
-                            fs::last_write_time(dir_iter->path()) - fs::file_time_type::clock::now() + std::chrono::system_clock::now()
-                        )
-                    ),
-                    *dir_iter
-                ));
+            if (fs::PathToString(entry.path().stem()) == strWalletName) {
+                folder_set.insert(decltype(folder_set)::value_type(fs::last_write_time(entry.path()), entry));
             }
         }
     }
 
     // Loop backward through backup files and keep the N newest ones (1 <= N <= 10)
-    int counter = 0;
-    for(auto it = folder_set.rbegin(); it != folder_set.rend(); ++it) {
-        std::pair<const std::time_t, fs::path> file = *it;
+    int counter{0};
+    for (const auto& [entry_time, entry] : reverse_iterate(folder_set)) {
         counter++;
-        if (counter > nWalletBackups)
-        {
+        if (counter > nWalletBackups) {
             // More than nWalletBackups backups: delete oldest one(s)
             try {
-                fs::remove(file.second);
-                WalletLogPrintf("Old backup deleted: %s\n", fs::PathToString(file.second));
+                fs::remove(entry);
+                WalletLogPrintf("Old backup deleted: %s\n", fs::PathToString(entry));
             } catch(fs::filesystem_error &error) {
                 warnings.push_back(strprintf(_("Failed to delete backup, error: %s"), fsbridge::get_filesystem_error_message(error)));
                 WalletLogPrintf("%s\n", Join(warnings, Untranslated("\n")).original);

From 0577b4d9deccd6444da59abf5060e54a4a07344d Mon Sep 17 00:00:00 2001
From: Kittywhiskers Van Gogh <63189531+kwvg@users.noreply.github.com>
Date: Fri, 1 Nov 2024 16:02:27 +0000
Subject: [PATCH 4/4] refactor: make namespace `ranges` mostly an alias of
 `std::ranges`

---
 src/util/ranges.h | 38 +++++++++-----------------------------
 1 file changed, 9 insertions(+), 29 deletions(-)

diff --git a/src/util/ranges.h b/src/util/ranges.h
index dca6866eea31d..aec61de960a10 100644
--- a/src/util/ranges.h
+++ b/src/util/ranges.h
@@ -5,40 +5,20 @@
 #ifndef BITCOIN_UTIL_RANGES_H
 #define BITCOIN_UTIL_RANGES_H
 
-#include <algorithm>
+#include <ranges>
 #include <optional>
 
-//#if __cplusplus > 201703L // C++20 compiler
-//namespace ranges = std::ranges;
-//#else
-
-#define MK_RANGE(FUN) \
-template <typename X, typename Z>               \
-inline auto FUN(const X& ds, const Z& fn) {     \
-    return std::FUN(cbegin(ds), cend(ds), fn);  \
-}                                               \
-template <typename X, typename Z>               \
-inline auto FUN(X& ds, const Z& fn) {           \
-    return std::FUN(begin(ds), end(ds), fn);    \
-}
-
-
 namespace ranges {
-    MK_RANGE(all_of)
-    MK_RANGE(any_of)
-    MK_RANGE(count_if)
-    MK_RANGE(find_if)
+using namespace std::ranges;
 
-    template <typename X, typename Z>
-    constexpr inline auto find_if_opt(const X& ds, const Z& fn) {
-        const auto it = ranges::find_if(ds, fn);
-        if (it != end(ds)) {
-            return std::make_optional(*it);
-        }
-        return std::optional<std::decay_t<decltype(*it)>>{};
+template <typename X, typename Z>
+constexpr inline auto find_if_opt(const X& ds, const Z& fn) {
+    const auto it = std::ranges::find_if(ds, fn);
+    if (it != std::end(ds)) {
+        return std::make_optional(*it);
     }
-
+    return std::optional<std::decay_t<decltype(*it)>>{};
+}
 }
 
-//#endif // C++20 compiler
 #endif // BITCOIN_UTIL_RANGES_H