Introducing: Common Concepts

As Dolphin Emulator upgrades to C++20, concepts ought to be applied around the codebase to clean up static assertions and primitive SFINAE.  Also, a clang-format rule for concepts has been added.

Unfortunately, the Build-bot infrastructure currently has outdated C++ Standard Libraries despite supporting C++20 features.  We can work around this issue for the time being by wielding the other new header file introduced by this commit: 'Common/Future/CppLibConcepts.h'.

Finally, TypeUtils.h has been re-licensed under the CC0-1.0 public-domain-equivalent license with permission from Pokechu22, its original author and only contributor to it thus far.

Source/.clang-format

@@ -34,6 +34,7 @@ BraceWrapping:
 BreakBeforeBinaryOperators: None
 BreakBeforeBraces: Custom
 BreakBeforeTernaryOperators: false
+BreakBeforeConceptDeclarations: true
 BreakConstructorInitializersBeforeComma: false
 ColumnLimit:     100
 CommentPragmas:  '^ (IWYU pragma:|NOLINT)'

Source/Core/Common/Align.h

@@ -3,21 +3,20 @@
 #pragma once
 
 #include <cstddef>
-#include <type_traits>
+
+#include "Common/Future/CppLibConcepts.h"
 
 namespace Common
 {
-template <typename T>
+template <std::unsigned_integral T>
 constexpr T AlignUp(T value, size_t size)
 {
-  static_assert(std::is_unsigned<T>(), "T must be an unsigned value.");
   return static_cast<T>(value + (size - value % size) % size);
 }
 
-template <typename T>
+template <std::unsigned_integral T>
 constexpr T AlignDown(T value, size_t size)
 {
-  static_assert(std::is_unsigned<T>(), "T must be an unsigned value.");
   return static_cast<T>(value - value % size);
 }
 

Source/Core/Common/BitSet.h

@@ -9,6 +9,8 @@
 
 #include "Common/CommonTypes.h"
 
+#include "Common/Future/CppLibConcepts.h"
+
 namespace Common
 {
 // Similar to std::bitset, this is a class which encapsulates a bitset, i.e.
@@ -29,11 +31,9 @@ namespace Common
 //   operation.)
 // - Counting set bits using .Count() - see comment on that method.
 
-template <typename IntTy>
+template <std::unsigned_integral IntTy>
 class BitSet
 {
-  static_assert(!std::is_signed<IntTy>::value, "BitSet should not be used with signed types");
-
 public:
   // A reference to a particular bit, returned from operator[].
   class Ref

Source/Core/Common/BitUtils.h

@@ -11,6 +11,10 @@
 #include <initializer_list>
 #include <type_traits>
 
+#include "Common/Concepts.h"
+
+#include "Common/Future/CppLibConcepts.h"
+
 namespace Common
 {
 ///
@@ -113,11 +117,10 @@ constexpr Result ExtractBits(const T src) noexcept
 ///
 /// @return A bool indicating whether the mask is valid.
 ///
-template <typename T>
+template <std::unsigned_integral T>
 constexpr bool IsValidLowMask(const T mask) noexcept
 {
-  static_assert(std::is_integral<T>::value, "Mask must be an integral type.");
-  static_assert(std::is_unsigned<T>::value, "Signed masks can introduce hard to find bugs.");
+  // Signed masks can introduce hard to find bugs.
 
   // Can be efficiently determined without looping or bit counting. It's the counterpart
   // to https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
@@ -143,38 +146,28 @@ constexpr bool IsValidLowMask(const T mask) noexcept
 /// @pre Both To and From types must be the same size
 /// @pre Both To and From types must satisfy the TriviallyCopyable concept.
 ///
-template <typename To, typename From>
+template <TriviallyCopyable To, TriviallyCopyable From>
 inline To BitCast(const From& source) noexcept
 {
   static_assert(sizeof(From) == sizeof(To),
                 "BitCast source and destination types must be equal in size.");
-  static_assert(std::is_trivially_copyable<From>(),
-                "BitCast source type must be trivially copyable.");
-  static_assert(std::is_trivially_copyable<To>(),
-                "BitCast destination type must be trivially copyable.");
 
   alignas(To) std::byte storage[sizeof(To)];
   std::memcpy(&storage, &source, sizeof(storage));
   return reinterpret_cast<To&>(storage);
 }
 
-template <typename T, typename PtrType>
+template <TriviallyCopyable T, TriviallyCopyable PtrType>
 class BitCastPtrType
 {
 public:
-  static_assert(std::is_trivially_copyable<PtrType>(),
-                "BitCastPtr source type must be trivially copyable.");
-  static_assert(std::is_trivially_copyable<T>(),
-                "BitCastPtr destination type must be trivially copyable.");
-
   explicit BitCastPtrType(PtrType* ptr) : m_ptr(ptr) {}
 
   // Enable operator= only for pointers to non-const data
-  template <typename S>
-  inline typename std::enable_if<std::is_same<S, T>() && !std::is_const<PtrType>()>::type
-  operator=(const S& source)
+  inline BitCastPtrType& operator=(const T& source) requires NotConst<PtrType>
   {
     std::memcpy(m_ptr, &source, sizeof(source));
+    return *this;
   }
 
   inline operator T() const
@@ -199,46 +192,34 @@ inline auto BitCastPtr(PtrType* ptr) noexcept -> BitCastPtrType<T, PtrType>
 }
 
 // Similar to BitCastPtr, but specifically for aliasing structs to arrays.
-template <typename ArrayType, typename T,
-          typename Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
+template <typename ArrayType, TriviallyCopyable T,
+          TriviallyCopyable Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
 inline auto BitCastToArray(const T& obj) noexcept -> Container
 {
   static_assert(sizeof(T) % sizeof(ArrayType) == 0,
                 "Size of array type must be a factor of size of source type.");
-  static_assert(std::is_trivially_copyable<T>(),
-                "BitCastToArray source type must be trivially copyable.");
-  static_assert(std::is_trivially_copyable<Container>(),
-                "BitCastToArray array type must be trivially copyable.");
 
   Container result;
   std::memcpy(result.data(), &obj, sizeof(T));
   return result;
 }
 
-template <typename ArrayType, typename T,
-          typename Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
+template <typename ArrayType, TriviallyCopyable T,
+          TriviallyCopyable Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
 inline void BitCastFromArray(const Container& array, T& obj) noexcept
 {
   static_assert(sizeof(T) % sizeof(ArrayType) == 0,
                 "Size of array type must be a factor of size of destination type.");
-  static_assert(std::is_trivially_copyable<Container>(),
-                "BitCastFromArray array type must be trivially copyable.");
-  static_assert(std::is_trivially_copyable<T>(),
-                "BitCastFromArray destination type must be trivially copyable.");
 
   std::memcpy(&obj, array.data(), sizeof(T));
 }
 
-template <typename ArrayType, typename T,
-          typename Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
+template <typename ArrayType, TriviallyCopyable T,
+          TriviallyCopyable Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
 inline auto BitCastFromArray(const Container& array) noexcept -> T
 {
   static_assert(sizeof(T) % sizeof(ArrayType) == 0,
                 "Size of array type must be a factor of size of destination type.");
-  static_assert(std::is_trivially_copyable<Container>(),
-                "BitCastFromArray array type must be trivially copyable.");
-  static_assert(std::is_trivially_copyable<T>(),
-                "BitCastFromArray destination type must be trivially copyable.");
 
   T obj;
   std::memcpy(&obj, array.data(), sizeof(T));
@@ -304,11 +285,9 @@ class Flags
 
 // Left-shift a value and set new LSBs to that of the supplied LSB.
 // Converts a value from a N-bit range to an (N+X)-bit range. e.g. 0x101 -> 0x10111
-template <typename T>
+template <std::unsigned_integral T>
 T ExpandValue(T value, size_t left_shift_amount)
 {
-  static_assert(std::is_unsigned<T>(), "ExpandValue is only sane on unsigned types.");
-
   return (value << left_shift_amount) |
          (T(-ExtractBit<0>(value)) >> (BitSize<T>() - left_shift_amount));
 }

Source/Core/Common/CMakeLists.txt

@@ -15,6 +15,7 @@ add_library(common
   CommonFuncs.h
   CommonPaths.h
   CommonTypes.h
+  Concepts.h
   Config/Config.cpp
   Config/Config.h
   Config/ConfigInfo.cpp
@@ -58,6 +59,7 @@ add_library(common
   FloatUtils.h
   FormatUtil.h
   FPURoundMode.h
+  Future/CppLibConcepts.h
   GekkoDisassembler.cpp
   GekkoDisassembler.h
   Hash.cpp

Source/Core/Common/ChunkFile.h

@@ -21,14 +21,14 @@
 #include <optional>
 #include <set>
 #include <string>
-#include <type_traits>
 #include <utility>
 #include <vector>
 
 #include <fmt/format.h>
 
 #include "Common/Assert.h"
 #include "Common/CommonTypes.h"
+#include "Common/Concepts.h"
 #include "Common/EnumMap.h"
 #include "Common/Flag.h"
 #include "Common/Inline.h"
@@ -195,13 +195,13 @@ class PointerWrap
     DoArray(x.data(), static_cast<u32>(x.size()));
   }
 
-  template <typename T, typename std::enable_if_t<std::is_trivially_copyable_v<T>, int> = 0>
+  template <Common::TriviallyCopyable T>
   void DoArray(T* x, u32 count)
   {
     DoVoid(x, count * sizeof(T));
   }
 
-  template <typename T, typename std::enable_if_t<!std::is_trivially_copyable_v<T>, int> = 0>
+  template <Common::NotTriviallyCopyable T>
   void DoArray(T* x, u32 count)
   {
     for (u32 i = 0; i < count; ++i)
@@ -262,10 +262,9 @@ class PointerWrap
       atomic.store(temp, std::memory_order_relaxed);
   }
 
-  template <typename T>
+  template <Common::TriviallyCopyable T>
   void Do(T& x)
   {
-    static_assert(std::is_trivially_copyable_v<T>, "Only sane for trivially copyable types");
     // Note:
     // Usually we can just use x = **ptr, etc.  However, this doesn't work
     // for unions containing BitFields (long story, stupid language rules)

Source/Core/Common/Concepts.h

@@ -0,0 +1,68 @@
+// 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: CC0-1.0
+
+#pragma once
+
+#include <cstddef>
+#include <type_traits>
+
+#include "Common/TypeUtils.h"
+
+#include "Common/Future/CppLibConcepts.h"
+
+namespace Common
+{
+template <class T>
+concept TriviallyCopyable = std::is_trivially_copyable<T>::value;
+
+template <class T>
+concept NotTriviallyCopyable = !TriviallyCopyable<T>;
+
+template <class T>
+concept Const = std::is_const<T>::value;
+
+template <class T>
+concept NotConst = !Const<T>;
+
+template <class T>
+concept Enumerated = std::is_enum<T>::value;
+
+template <class T>
+concept NotEnumerated = !Enumerated<T>;
+
+template <class T>
+concept Class = std::is_class<T>::value;
+
+template <class T>
+concept Union = std::is_union<T>::value;
+
+template <class T>
+concept Arithmetic = std::is_arithmetic<T>::value;
+
+template <class T>
+concept Pointer = std::is_pointer<T>::value;
+
+template <class T>
+concept Function = std::is_function<T>::value;
+
+template <class T>
+concept FunctionPointer = Function<std::remove_pointer_t<T>>;
+
+template <class T>
+concept IntegralOrEnum = std::integral<T> || Enumerated<T>;
+
+template <class T, class U>
+concept UnderlyingSameAs = std::same_as<std::underlying_type_t<T>, U>;
+
+template <class T, class U>
+concept SameAsOrUnderlyingSameAs = std::same_as<T, U> || UnderlyingSameAs<T, U>;
+
+template <size_t N, class... Ts>
+concept CountOfTypes = IsCountOfTypes<N, Ts...>::value;
+
+template <class T, class... Ts>
+concept ConvertibleFromAllOf = IsConvertibleFromAllOf<T, Ts...>::value;
+
+template <class T, class... Ts>
+concept SameAsAnyOf = IsSameAsAnyOf<T, Ts...>::value;
+};  // namespace Common

Source/Core/Common/Config/ConfigInfo.h

@@ -10,17 +10,11 @@
 #include <utility>
 
 #include "Common/CommonTypes.h"
+#include "Common/Concepts.h"
 #include "Common/Config/Enums.h"
 
 namespace Config
 {
-namespace detail
-{
-// std::underlying_type may only be used with enum types, so make sure T is an enum type first.
-template <typename T>
-using UnderlyingType = typename std::enable_if_t<std::is_enum<T>{}, std::underlying_type<T>>::type;
-}  // namespace detail
-
 struct Location
 {
   System system{};
@@ -55,12 +49,8 @@ class Info
 
   // Make it easy to convert Info<Enum> into Info<UnderlyingType<Enum>>
   // so that enum settings can still easily work with code that doesn't care about the enum values.
-  template <typename Enum,
-            std::enable_if_t<std::is_same<T, detail::UnderlyingType<Enum>>::value>* = nullptr>
-  Info(const Info<Enum>& other)
-  {
-    *this = other;
-  }
+  template <Common::Enumerated Enum>
+  requires Common::UnderlyingSameAs<Enum, T> Info(const Info<Enum>& other) { *this = other; }
 
   Info<T>& operator=(const Info<T>& other)
   {
@@ -81,9 +71,9 @@ class Info
 
   // Make it easy to convert Info<Enum> into Info<UnderlyingType<Enum>>
   // so that enum settings can still easily work with code that doesn't care about the enum values.
-  template <typename Enum,
-            std::enable_if_t<std::is_same<T, detail::UnderlyingType<Enum>>::value>* = nullptr>
-  Info<T>& operator=(const Info<Enum>& other)
+  template <Common::Enumerated Enum>
+  requires Common::UnderlyingSameAs<Enum, T> Info<T>
+  &operator=(const Info<Enum>& other)
   {
     m_location = other.GetLocation();
     m_default_value = static_cast<T>(other.GetDefaultValue());

Source/Core/Common/Config/Layer.h

@@ -10,6 +10,7 @@
 #include <type_traits>
 #include <vector>
 
+#include "Common/Concepts.h"
 #include "Common/Config/ConfigInfo.h"
 #include "Common/Config/Enums.h"
 #include "Common/StringUtil.h"
@@ -18,7 +19,7 @@ namespace Config
 {
 namespace detail
 {
-template <typename T, std::enable_if_t<!std::is_enum<T>::value>* = nullptr>
+template <Common::NotEnumerated T>
 std::optional<T> TryParse(const std::string& str_value)
 {
   T value;
@@ -27,7 +28,7 @@ std::optional<T> TryParse(const std::string& str_value)
   return value;
 }
 
-template <typename T, std::enable_if_t<std::is_enum<T>::value>* = nullptr>
+template <Common::Enumerated T>
 std::optional<T> TryParse(const std::string& str_value)
 {
   const auto result = TryParse<std::underlying_type_t<T>>(str_value);