Merge bitcoin/bitcoin#31904: refactor: modernize outdated trait patterns using helper aliases (C++14/C++17)

4cd95a2 refactor: modernize remaining outdated trait patterns (Lőrinc)
ab2b67f scripted-diff: modernize outdated trait patterns - values (Lőrinc)
8327889 scripted-diff: modernize outdated trait patterns - types (Lőrinc)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 bitcoin/bitcoin#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 4cd95a2

Tree-SHA512: a4bcf0f267c0f4e02983b4d548ed6f58d464ec379ac5cd1f998b9ec0cf698b53a9f2557a05a342b661f1d94adefc9a0ce2dc8f764d49453aaea95451e2c4c581

Author: fanquake

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 @@ class Timer
         }
         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 @@ class NetPermissions
     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 @@ class NetPermissions
     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 @@ class RandomMixin
 
     /** 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<typename std::decay<T>::type, unsigned char*>::value, "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<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>, char*>, "Calling operator<<(CSHA512, 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_v<std::decay_t<T>, const char*>, "Calling operator<<(CSHA512, const 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::NONNEGATIVE_SIGNED || std::is_signed<I>::value, "Signed type required with mode NONNEGATIVE_SIGNED.");
+        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_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);