Merge bitcoin/bitcoin#31904: refactor: modernize outdated trait patterns using helper aliases (C++14/C++17)

4cd95a2921 refactor: modernize remaining outdated trait patterns (Lőrinc)
ab2b67fce2 scripted-diff: modernize outdated trait patterns - values (Lőrinc)
8327889f35 scripted-diff: modernize outdated trait patterns - types (Lőrinc)

Pull request description:

  The use of [`std::underlying_type_t<T>`](https://en.cppreference.com/w/cpp/types/underlying_type) or [`std::is_enum_v<T>`](https://en.cppreference.com/w/cpp/types/is_enum) (and similar ones, introduced in C++14) replace the `typename std::underlying_type<T>::type` and  `std::is_enum<T>::value` constructs (available in C++11).

  The `_t` and `_v` helper alias templates offer a more concise way to extract the type and value directly.

  I've modified the instances I found in the codebase one-by-one (noticed them while investigating https://github.com/bitcoin/bitcoin/pull/31868), and afterwards extracted scripted diff commits to do the trivial ones automatically.
  The last commit contains the values that were easier done manually.

  I've excluded changes from `src/bench/nanobench.h`, `src/leveldb`, `src/minisketch`, `src/span.h` and `src/sync.h` - let me know if you think they should be included instead.

  A few of the code changes can also be reproduced by clang-tidy (but not all of them):
  ```bash
  cmake -B build -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DBUILD_BENCH=ON -DBUILD_FUZZ_BINARY=ON -DBUILD_FOR_FUZZING=ON && cmake --build build -j$(nproc)
  run-clang-tidy -quiet -p build -j $(nproc) -checks='-*,modernize-type-traits' -fix $(git grep -lE '::(value|type)' ./src ':(exclude)src/bench/nanobench.h' ':(exclude)src/leveldb' ':(exclude)src/minisketch' ':(exclude)src/span.h' ':(exclude)src/sync.h')
  ```

ACKs for top commit:
  laanwj:
    Concept and code review ACK 4cd95a2921

Tree-SHA512: a4bcf0f267c0f4e02983b4d548ed6f58d464ec379ac5cd1f998b9ec0cf698b53a9f2557a05a342b661f1d94adefc9a0ce2dc8f764d49453aaea95451e2c4c581

src/bench/prevector.cpp

@@ -16,11 +16,11 @@ struct nontrivial_t {
     nontrivial_t() = default;
     SERIALIZE_METHODS(nontrivial_t, obj) { READWRITE(obj.x); }
 };
-static_assert(!std::is_trivially_default_constructible<nontrivial_t>::value,
+static_assert(!std::is_trivially_default_constructible_v<nontrivial_t>,
               "expected nontrivial_t to not be trivially constructible");
 
 typedef unsigned char trivial_t;
-static_assert(std::is_trivially_default_constructible<trivial_t>::value,
+static_assert(std::is_trivially_default_constructible_v<trivial_t>,
               "expected trivial_t to be trivially constructible");
 
 template <typename T>

src/deploymentstatus.cpp

@@ -24,7 +24,7 @@ static_assert(!ValidDeployment(static_cast<Consensus::BuriedDeployment>(Consensu
 template<typename T, T x>
 static constexpr bool is_minimum()
 {
-    using U = typename std::underlying_type<T>::type;
+    using U = std::underlying_type_t<T>;
     return x == std::numeric_limits<U>::min();
 }
 

src/interfaces/wallet.h

@@ -45,7 +45,7 @@ enum class AddressPurpose;
 enum isminetype : unsigned int;
 struct CRecipient;
 struct WalletContext;
-using isminefilter = std::underlying_type<isminetype>::type;
+using isminefilter = std::underlying_type_t<isminetype>;
 } // namespace wallet
 
 namespace interfaces {

src/logging/timer.h

@@ -67,11 +67,11 @@ public:
         }
         const auto duration{end_time - *m_start_t};
 
-        if constexpr (std::is_same<TimeType, std::chrono::microseconds>::value) {
+        if constexpr (std::is_same_v<TimeType, std::chrono::microseconds>) {
             return strprintf("%s: %s (%iμs)", m_prefix, msg, Ticks<std::chrono::microseconds>(duration));
-        } else if constexpr (std::is_same<TimeType, std::chrono::milliseconds>::value) {
+        } else if constexpr (std::is_same_v<TimeType, std::chrono::milliseconds>) {
             return strprintf("%s: %s (%.2fms)", m_prefix, msg, Ticks<MillisecondsDouble>(duration));
-        } else if constexpr (std::is_same<TimeType, std::chrono::seconds>::value) {
+        } else if constexpr (std::is_same_v<TimeType, std::chrono::seconds>) {
             return strprintf("%s: %s (%.2fs)", m_prefix, msg, Ticks<SecondsDouble>(duration));
         } else {
             static_assert(ALWAYS_FALSE<TimeType>, "Error: unexpected time type");

src/net_permissions.h

@@ -48,7 +48,7 @@ enum class NetPermissionFlags : uint32_t {
 };
 static inline constexpr NetPermissionFlags operator|(NetPermissionFlags a, NetPermissionFlags b)
 {
-    using t = typename std::underlying_type<NetPermissionFlags>::type;
+    using t = std::underlying_type_t<NetPermissionFlags>;
     return static_cast<NetPermissionFlags>(static_cast<t>(a) | static_cast<t>(b));
 }
 
@@ -59,7 +59,7 @@ public:
     static std::vector<std::string> ToStrings(NetPermissionFlags flags);
     static inline bool HasFlag(NetPermissionFlags flags, NetPermissionFlags f)
     {
-        using t = typename std::underlying_type<NetPermissionFlags>::type;
+        using t = std::underlying_type_t<NetPermissionFlags>;
         return (static_cast<t>(flags) & static_cast<t>(f)) == static_cast<t>(f);
     }
     static inline void AddFlag(NetPermissionFlags& flags, NetPermissionFlags f)
@@ -74,7 +74,7 @@ public:
     static inline void ClearFlag(NetPermissionFlags& flags, NetPermissionFlags f)
     {
         assert(f == NetPermissionFlags::Implicit);
-        using t = typename std::underlying_type<NetPermissionFlags>::type;
+        using t = std::underlying_type_t<NetPermissionFlags>;
         flags = static_cast<NetPermissionFlags>(static_cast<t>(flags) & ~static_cast<t>(f));
     }
 };

src/netbase.h

@@ -37,12 +37,12 @@ enum class ConnectionDirection {
     Both = (In | Out),
 };
 static inline ConnectionDirection& operator|=(ConnectionDirection& a, ConnectionDirection b) {
-    using underlying = typename std::underlying_type<ConnectionDirection>::type;
+    using underlying = std::underlying_type_t<ConnectionDirection>;
     a = ConnectionDirection(underlying(a) | underlying(b));
     return a;
 }
 static inline bool operator&(ConnectionDirection a, ConnectionDirection b) {
-    using underlying = typename std::underlying_type<ConnectionDirection>::type;
+    using underlying = std::underlying_type_t<ConnectionDirection>;
     return (underlying(a) & underlying(b));
 }
 

src/random.h

@@ -334,7 +334,7 @@ public:
 
     /** Generate a uniform random duration in the range [0..max). Precondition: max.count() > 0 */
     template <StdChronoDuration Dur>
-    Dur randrange(typename std::common_type_t<Dur> range) noexcept
+    Dur randrange(std::common_type_t<Dur> range) noexcept
     // Having the compiler infer the template argument from the function argument
     // is dangerous, because the desired return value generally has a different
     // type than the function argument. So std::common_type is used to force the

src/randomenv.cpp

@@ -70,10 +70,10 @@ namespace {
  */
 template<typename T>
 CSHA512& operator<<(CSHA512& hasher, const T& data) {
-    static_assert(!std::is_same<typename std::decay<T>::type, char*>::value, "Calling operator<<(CSHA512, char*) is probably not what you want");
+    static_assert(!std::is_same_v<std::decay_t<T>, char*>, "Calling operator<<(CSHA512, char*) is probably not what you want");
-    static_assert(!std::is_same<typename std::decay<T>::type, unsigned char*>::value, "Calling operator<<(CSHA512, unsigned char*) is probably not what you want");
+    static_assert(!std::is_same_v<std::decay_t<T>, unsigned char*>, "Calling operator<<(CSHA512, unsigned char*) is probably not what you want");
-    static_assert(!std::is_same<typename std::decay<T>::type, const char*>::value, "Calling operator<<(CSHA512, const char*) is probably not what you want");
+    static_assert(!std::is_same_v<std::decay_t<T>, const char*>, "Calling operator<<(CSHA512, const char*) is probably not what you want");
-    static_assert(!std::is_same<typename std::decay<T>::type, const unsigned char*>::value, "Calling operator<<(CSHA512, const unsigned char*) is probably not what you want");
+    static_assert(!std::is_same_v<std::decay_t<T>, const unsigned char*>, "Calling operator<<(CSHA512, const unsigned char*) is probably not what you want");
     hasher.Write((const unsigned char*)&data, sizeof(data));
     return hasher;
 }

src/rpc/util.cpp

@@ -49,7 +49,7 @@ const std::string EXAMPLE_ADDRESS[2] = {"bc1q09vm5lfy0j5reeulh4x5752q25uqqvz34hu
 std::string GetAllOutputTypes()
 {
     std::vector<std::string> ret;
-    using U = std::underlying_type<TxoutType>::type;
+    using U = std::underlying_type_t<TxoutType>;
     for (U i = (U)TxoutType::NONSTANDARD; i <= (U)TxoutType::WITNESS_UNKNOWN; ++i) {
         ret.emplace_back(GetTxnOutputType(static_cast<TxoutType>(i)));
     }

src/serialize.h

@@ -154,7 +154,7 @@ const Out& AsBase(const In& x)
 }
 
 #define READWRITE(...) (ser_action.SerReadWriteMany(s, __VA_ARGS__))
-#define SER_READ(obj, code) ser_action.SerRead(s, obj, [&](Stream& s, typename std::remove_const<Type>::type& obj) { code; })
+#define SER_READ(obj, code) ser_action.SerRead(s, obj, [&](Stream& s, std::remove_const_t<Type>& obj) { code; })
 #define SER_WRITE(obj, code) ser_action.SerWrite(s, obj, [&](Stream& s, const Type& obj) { code; })
 
 /**
@@ -220,13 +220,13 @@ const Out& AsBase(const In& x)
     template <typename Stream>                                                                      \
     void Serialize(Stream& s) const                                                                 \
     {                                                                                               \
-        static_assert(std::is_same<const cls&, decltype(*this)>::value, "Serialize type mismatch"); \
+        static_assert(std::is_same_v<const cls&, decltype(*this)>, "Serialize type mismatch");      \
         Ser(s, *this);                                                                              \
     }                                                                                               \
     template <typename Stream>                                                                      \
     void Unserialize(Stream& s)                                                                     \
     {                                                                                               \
-        static_assert(std::is_same<cls&, decltype(*this)>::value, "Unserialize type mismatch");     \
+        static_assert(std::is_same_v<cls&, decltype(*this)>, "Unserialize type mismatch");          \
         Unser(s, *this);                                                                            \
     }
 
@@ -408,8 +408,8 @@ template <VarIntMode Mode, typename I>
 struct CheckVarIntMode {
     constexpr CheckVarIntMode()
     {
-        static_assert(Mode != VarIntMode::DEFAULT || std::is_unsigned<I>::value, "Unsigned type required with mode DEFAULT.");
+        static_assert(Mode != VarIntMode::DEFAULT || std::is_unsigned_v<I>, "Unsigned type required with mode DEFAULT.");
-        static_assert(Mode != VarIntMode::NONNEGATIVE_SIGNED || std::is_signed<I>::value, "Signed type required with mode NONNEGATIVE_SIGNED.");
+        static_assert(Mode != VarIntMode::NONNEGATIVE_SIGNED || std::is_signed_v<I>, "Signed type required with mode NONNEGATIVE_SIGNED.");
     }
 };
 
@@ -474,7 +474,7 @@ I ReadVarInt(Stream& is)
 template<typename Formatter, typename T>
 class Wrapper
 {
-    static_assert(std::is_lvalue_reference<T>::value, "Wrapper needs an lvalue reference type T");
+    static_assert(std::is_lvalue_reference_v<T>, "Wrapper needs an lvalue reference type T");
 protected:
     T m_object;
 public:
@@ -507,12 +507,12 @@ struct VarIntFormatter
 {
     template<typename Stream, typename I> void Ser(Stream &s, I v)
     {
-        WriteVarInt<Stream,Mode,typename std::remove_cv<I>::type>(s, v);
+        WriteVarInt<Stream,Mode, std::remove_cv_t<I>>(s, v);
     }
 
     template<typename Stream, typename I> void Unser(Stream& s, I& v)
     {
-        v = ReadVarInt<Stream,Mode,typename std::remove_cv<I>::type>(s);
+        v = ReadVarInt<Stream,Mode, std::remove_cv_t<I>>(s);
     }
 };
 
@@ -545,7 +545,7 @@ struct CustomUintFormatter
 
     template <typename Stream, typename I> void Unser(Stream& s, I& v)
     {
-        using U = typename std::conditional<std::is_enum<I>::value, std::underlying_type<I>, std::common_type<I>>::type::type;
+        using U = typename std::conditional_t<std::is_enum_v<I>, std::underlying_type<I>, std::common_type<I>>::type;
         static_assert(std::numeric_limits<U>::max() >= MAX && std::numeric_limits<U>::min() <= 0, "Assigned type too small");
         uint64_t raw = 0;
         if (BigEndian) {
@@ -577,7 +577,7 @@ struct CompactSizeFormatter
     template<typename Stream, typename I>
     void Ser(Stream& s, I v)
     {
-        static_assert(std::is_unsigned<I>::value, "CompactSize only supported for unsigned integers");
+        static_assert(std::is_unsigned_v<I>, "CompactSize only supported for unsigned integers");
         static_assert(std::numeric_limits<I>::max() <= std::numeric_limits<uint64_t>::max(), "CompactSize only supports 64-bit integers and below");
 
         WriteCompactSize<Stream>(s, v);

src/sync.cpp

@@ -148,8 +148,8 @@ template <typename MutexType>
 static void push_lock(MutexType* c, const CLockLocation& locklocation)
 {
     constexpr bool is_recursive_mutex =
-        std::is_base_of<RecursiveMutex, MutexType>::value ||
+        std::is_base_of_v<RecursiveMutex, MutexType> ||
-        std::is_base_of<std::recursive_mutex, MutexType>::value;
+        std::is_base_of_v<std::recursive_mutex, MutexType>;
 
     LockData& lockdata = GetLockData();
     std::lock_guard<std::mutex> lock(lockdata.dd_mutex);

src/test/fuzz/FuzzedDataProvider.h

@@ -203,7 +203,7 @@ template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
 // be less than or equal to |max|.
 template <typename T>
 T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
-  static_assert(std::is_integral<T>::value, "An integral type is required.");
+  static_assert(std::is_integral_v<T>, "An integral type is required.");
   static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
 
   if (min > max)
@@ -271,14 +271,14 @@ T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
 // Returns a floating point number in the range [0.0, 1.0]. If there's no
 // input data left, always returns 0.
 template <typename T> T FuzzedDataProvider::ConsumeProbability() {
-  static_assert(std::is_floating_point<T>::value,
+  static_assert(std::is_floating_point_v<T>,
                 "A floating point type is required.");
 
   // Use different integral types for different floating point types in order
   // to provide better density of the resulting values.
   using IntegralType =
-      typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
+      typename std::conditional_t<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
-                                uint64_t>::type;
+                                  uint64_t>;
 
   T result = static_cast<T>(ConsumeIntegral<IntegralType>());
   result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
@@ -294,7 +294,7 @@ inline bool FuzzedDataProvider::ConsumeBool() {
 // also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
 // enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
 template <typename T> T FuzzedDataProvider::ConsumeEnum() {
-  static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
+  static_assert(std::is_enum_v<T>, "|T| must be an enum type.");
   return static_cast<T>(
       ConsumeIntegralInRange<uint32_t>(0, static_cast<uint32_t>(T::kMaxValue)));
 }

src/test/fuzz/integer.cpp

@@ -63,7 +63,7 @@ FUZZ_TARGET(integer, .init = initialize_integer)
     const int16_t i16 = fuzzed_data_provider.ConsumeIntegral<int16_t>();
     const uint8_t u8 = fuzzed_data_provider.ConsumeIntegral<uint8_t>();
     const int8_t i8 = fuzzed_data_provider.ConsumeIntegral<int8_t>();
-    // We cannot assume a specific value of std::is_signed<char>::value:
+    // We cannot assume a specific value of std::is_signed_v<char>:
     // ConsumeIntegral<char>() instead of casting from {u,}int8_t.
     const char ch = fuzzed_data_provider.ConsumeIntegral<char>();
     const bool b = fuzzed_data_provider.ConsumeBool();

src/test/fuzz/util.h

@@ -134,7 +134,7 @@ template <typename WeakEnumType, size_t size>
 {
     return fuzzed_data_provider.ConsumeBool() ?
                fuzzed_data_provider.PickValueInArray<WeakEnumType>(all_types) :
-               WeakEnumType(fuzzed_data_provider.ConsumeIntegral<typename std::underlying_type<WeakEnumType>::type>());
+               WeakEnumType(fuzzed_data_provider.ConsumeIntegral<std::underlying_type_t<WeakEnumType>>());
 }
 
 [[nodiscard]] inline opcodetype ConsumeOpcodeType(FuzzedDataProvider& fuzzed_data_provider) noexcept
@@ -207,7 +207,7 @@ template <typename WeakEnumType, size_t size>
 template <typename T>
 [[nodiscard]] bool MultiplicationOverflow(const T i, const T j) noexcept
 {
-    static_assert(std::is_integral<T>::value, "Integral required.");
+    static_assert(std::is_integral_v<T>, "Integral required.");
     if (std::numeric_limits<T>::is_signed) {
         if (i > 0) {
             if (j > 0) {

src/univalue/include/univalue.h

@@ -137,7 +137,7 @@ void UniValue::push_backV(It first, It last)
 template <typename Int>
 Int UniValue::getInt() const
 {
-    static_assert(std::is_integral<Int>::value);
+    static_assert(std::is_integral_v<Int>);
     checkType(VNUM);
     Int result;
     const auto [first_nonmatching, error_condition] = std::from_chars(val.data(), val.data() + val.size(), result);

src/util/fs.h

@@ -163,7 +163,7 @@ static inline std::string PathToString(const path& path)
 #ifdef WIN32
     return path.utf8string();
 #else
-    static_assert(std::is_same<path::string_type, std::string>::value, "PathToString not implemented on this platform");
+    static_assert(std::is_same_v<path::string_type, std::string>, "PathToString not implemented on this platform");
     return path.std::filesystem::path::string();
 #endif
 }

src/util/overflow.h

@@ -14,7 +14,7 @@
 template <class T>
 [[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
 {
-    static_assert(std::is_integral<T>::value, "Integral required.");
+    static_assert(std::is_integral_v<T>, "Integral required.");
     if constexpr (std::numeric_limits<T>::is_signed) {
         return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
                (i < 0 && j < std::numeric_limits<T>::min() - i);

src/util/strencodings.cpp

@@ -204,7 +204,7 @@ namespace {
 template <typename T>
 bool ParseIntegral(std::string_view str, T* out)
 {
-    static_assert(std::is_integral<T>::value);
+    static_assert(std::is_integral_v<T>);
     // Replicate the exact behavior of strtol/strtoll/strtoul/strtoull when
     // handling leading +/- for backwards compatibility.
     if (str.length() >= 2 && str[0] == '+' && str[1] == '-') {

src/util/strencodings.h

@@ -117,7 +117,7 @@ bool SplitHostPort(std::string_view in, uint16_t& portOut, std::string& hostOut)
 template <typename T>
 T LocaleIndependentAtoi(std::string_view str)
 {
-    static_assert(std::is_integral<T>::value);
+    static_assert(std::is_integral_v<T>);
     T result;
     // Emulate atoi(...) handling of white space and leading +/-.
     std::string_view s = util::TrimStringView(str);
@@ -178,7 +178,7 @@ constexpr inline bool IsSpace(char c) noexcept {
 template <typename T>
 std::optional<T> ToIntegral(std::string_view str)
 {
-    static_assert(std::is_integral<T>::value);
+    static_assert(std::is_integral_v<T>);
     T result;
     const auto [first_nonmatching, error_condition] = std::from_chars(str.data(), str.data() + str.size(), result);
     if (first_nonmatching != str.data() + str.size() || error_condition != std::errc{}) {

src/util/vector.h

@@ -20,9 +20,9 @@
  *   (list initialization always copies).
  */
 template<typename... Args>
-inline std::vector<typename std::common_type<Args...>::type> Vector(Args&&... args)
+inline std::vector<std::common_type_t<Args...>> Vector(Args&&... args)
 {
-    std::vector<typename std::common_type<Args...>::type> ret;
+    std::vector<std::common_type_t<Args...>> ret;
     ret.reserve(sizeof...(args));
     // The line below uses the trick from https://www.experts-exchange.com/articles/32502/None-recursive-variadic-templates-with-std-initializer-list.html
     (void)std::initializer_list<int>{(ret.emplace_back(std::forward<Args>(args)), 0)...};

src/wallet/types.h

@@ -48,7 +48,7 @@ enum isminetype : unsigned int {
     ISMINE_ENUM_ELEMENTS,
 };
 /** used for bitflags of isminetype */
-using isminefilter = std::underlying_type<isminetype>::type;
+using isminefilter = std::underlying_type_t<isminetype>;
 
 /**
  * Address purpose field that has been been stored with wallet sending and