Everywhere: Remove redundant inequality comparison operators

C++20 can automatically synthesize `operator!=` from `operator==`, so
there is no point in writing such functions by hand if all they do is
call through to `operator==`.

This fixes a compile error with compilers that implement P2468 (Clang
16 currently). This paper restores the C++17 behavior that if both
`T::operator==(U)` and `T::operator!=(U)` exist, `U == T` won't be
rewritten in reverse to call `T::operator==(U)`. Removing `!=` operators
makes the rewriting possible again.
See https://reviews.llvm.org/D134529#3853062

AK/ByteBuffer.h

@@ -102,8 +102,6 @@ class ByteBuffer {
  return !__builtin_memcmp(data(), other.data(), size());
  }
 
- bool operator!=(ByteBuffer const& other) const { return !(*this == other); }
-
  [[nodiscard]] u8& operator[](size_t i)
  {
  VERIFY(i < m_size);

AK/Complex.h

@@ -211,12 +211,6 @@ class [[gnu::packed]] Complex {
  return (this->real() == a.real()) && (this->imag() == a.imag());
  }
 
- template<AK::Concepts::Arithmetic U>
- constexpr bool operator!=(Complex<U> const& a) const
- {
- return !(*this == a);
- }
-
  constexpr Complex<T> operator+()
  {
  return *this;

AK/DistinctNumeric.h

@@ -67,10 +67,6 @@ class DistinctNumeric {
  {
  return this->m_value == other.m_value;
  }
- constexpr bool operator!=(Self const& other) const
- {
- return this->m_value != other.m_value;
- }
 
  // Only implemented when `Incr` is true:
  constexpr Self& operator++()

AK/FlyString.h

@@ -53,16 +53,12 @@ class FlyString {
  bool is_null() const { return !m_impl; }
 
  bool operator==(FlyString const& other) const { return m_impl == other.m_impl; }
- bool operator!=(FlyString const& other) const { return m_impl != other.m_impl; }
 
  bool operator==(String const&) const;
- bool operator!=(String const& string) const { return !(*this == string); }
 
  bool operator==(StringView) const;
- bool operator!=(StringView string) const { return !(*this == string); }
 
  bool operator==(char const*) const;
- bool operator!=(char const* string) const { return !(*this == string); }
 
  StringImpl const* impl() const { return m_impl; }
  char const* characters() const { return m_impl ? m_impl->characters() : nullptr; }

AK/IntrusiveList.h

@@ -80,7 +80,6 @@ class IntrusiveList {
  T& operator*() { return *m_value; }
  auto operator->() { return m_value; }
  bool operator==(Iterator const& other) const { return other.m_value == m_value; }
- bool operator!=(Iterator const& other) const { return !(*this == other); }
  Iterator& operator++()
  {
  m_value = IntrusiveList<T, Container, member>::next(m_value);
@@ -108,7 +107,6 @@ class IntrusiveList {
  T& operator*() { return *m_value; }
  auto operator->() { return m_value; }
  bool operator==(ReverseIterator const& other) const { return other.m_value == m_value; }
- bool operator!=(ReverseIterator const& other) const { return !(*this == other); }
  ReverseIterator& operator++()
  {
  m_value = IntrusiveList<T, Container, member>::prev(m_value);
@@ -134,7 +132,6 @@ class IntrusiveList {
  T const& operator*() const { return *m_value; }
  auto operator->() const { return m_value; }
  bool operator==(ConstIterator const& other) const { return other.m_value == m_value; }
- bool operator!=(ConstIterator const& other) const { return !(*this == other); }
  ConstIterator& operator++()
  {
  m_value = IntrusiveList<T, Container, member>::next(m_value);

AK/JsonPath.h

@@ -75,10 +75,6 @@ class JsonPathElement {
  }
  return false;
  }
- bool operator!=(JsonPathElement const& other) const
- {
- return !(*this == other);
- }
 
 private:
  Kind m_kind;

AK/NonnullRefPtr.h

@@ -216,10 +216,8 @@ class [[nodiscard]] NonnullRefPtr {
  }
 
  bool operator==(NonnullRefPtr const& other) const { return m_ptr == other.m_ptr; }
- bool operator!=(NonnullRefPtr const& other) const { return m_ptr != other.m_ptr; }
 
  bool operator==(NonnullRefPtr& other) { return m_ptr == other.m_ptr; }
- bool operator!=(NonnullRefPtr& other) { return m_ptr != other.m_ptr; }
 
  // clang-format off
 private:

AK/RefPtr.h

@@ -260,29 +260,20 @@ class [[nodiscard]] RefPtr {
  ALWAYS_INLINE operator bool() { return !is_null(); }
 
  bool operator==(std::nullptr_t) const { return is_null(); }
- bool operator!=(std::nullptr_t) const { return !is_null(); }
 
  bool operator==(RefPtr const& other) const { return as_ptr() == other.as_ptr(); }
- bool operator!=(RefPtr const& other) const { return as_ptr() != other.as_ptr(); }
 
  bool operator==(RefPtr& other) { return as_ptr() == other.as_ptr(); }
- bool operator!=(RefPtr& other) { return as_ptr() != other.as_ptr(); }
 
  template<typename U>
  bool operator==(NonnullRefPtr<U> const& other) const { return as_ptr() == other.m_ptr; }
- template<typename U>
- bool operator!=(NonnullRefPtr<U> const& other) const { return as_ptr() != other.m_ptr; }
 
  template<typename U>
  bool operator==(NonnullRefPtr<U>& other) { return as_ptr() == other.m_ptr; }
- template<typename U>
- bool operator!=(NonnullRefPtr<U>& other) { return as_ptr() != other.m_ptr; }
 
  bool operator==(T const* other) const { return as_ptr() == other; }
- bool operator!=(T const* other) const { return as_ptr() != other; }
 
  bool operator==(T* other) { return as_ptr() == other; }
- bool operator!=(T* other) { return as_ptr() != other; }
 
  ALWAYS_INLINE bool is_null() const { return !m_ptr; }
 

AK/String.h

@@ -203,13 +203,10 @@ class String {
  [[nodiscard]] bool ends_with(char) const;
 
  bool operator==(String const&) const;
- bool operator!=(String const& other) const { return !(*this == other); }
 
  bool operator==(StringView) const;
- bool operator!=(StringView other) const { return !(*this == other); }
 
  bool operator==(FlyString const&) const;
- bool operator!=(FlyString const& other) const { return !(*this == other); }
 
  bool operator<(String const&) const;
  bool operator<(char const*) const;
@@ -222,7 +219,6 @@ class String {
  bool operator<=(char const* other) const { return !(*this > other); }
 
  bool operator==(char const* cstring) const;
- bool operator!=(char const* cstring) const { return !(*this == cstring); }
 
  [[nodiscard]] String isolated_copy() const;
 

AK/StringUtils.h

@@ -62,10 +62,6 @@ struct MaskSpan {
  {
  return start == other.start && length == other.length;
  }
- bool operator!=(MaskSpan const& other) const
- {
- return !(*this == other);
- }
 };
 
 namespace StringUtils {

AK/StringView.h

@@ -245,11 +245,6 @@ class StringView {
  return m_length == 1 && *m_characters == c;
  }
 
- constexpr bool operator!=(char const* cstring) const
- {
- return !(*this == cstring);
- }
-
 #ifndef KERNEL
  bool operator==(String const&) const;
 #endif

AK/Time.h

@@ -223,7 +223,6 @@ class Time {
  [[nodiscard]] bool is_negative() const { return m_seconds < 0; }
 
  bool operator==(Time const& other) const { return this->m_seconds == other.m_seconds && this->m_nanoseconds == other.m_nanoseconds; }
- bool operator!=(Time const& other) const { return !(*this == other); }
  Time operator+(Time const& other) const;
  Time& operator+=(Time const& other);
  Time operator-(Time const& other) const;

AK/UUID.cpp

@@ -113,15 +113,6 @@ String UUID::to_string() const
 }
 #endif
 
-bool UUID::operator==(const UUID& other) const
-{
- for (size_t index = 0; index < 16; index++) {
- if (m_uuid_buffer[index] != other.m_uuid_buffer[index])
- return false;
- }
- return true;
-}
-
 bool UUID::is_zero() const
 {
  return all_of(m_uuid_buffer, [](auto const octet) { return octet == 0; });

AK/UUID.h

@@ -31,12 +31,7 @@ class UUID {
  UUID(StringView, Endianness endianness = Endianness::Little);
  ~UUID() = default;
 
- bool operator==(const UUID&) const;
- bool operator!=(const UUID& other) const { return !(*this == other); }
- bool operator<=(const UUID&) const = delete;
- bool operator>=(const UUID&) const = delete;
- bool operator<(const UUID&) const = delete;
- bool operator>(const UUID&) const = delete;
+ bool operator==(const UUID&) const = default;
 
 #ifdef KERNEL
  ErrorOr<NonnullOwnPtr<Kernel::KString>> to_string() const;

AK/Utf16View.h

@@ -35,11 +35,6 @@ class Utf16CodePointIterator {
  return (m_ptr == other.m_ptr) && (m_remaining_code_units == other.m_remaining_code_units);
  }
 
- bool operator!=(Utf16CodePointIterator const& other) const
- {
- return !(*this == other);
- }
-
  Utf16CodePointIterator& operator++();
  u32 operator*() const;
 

AK/Utf32View.h

@@ -25,10 +25,6 @@ class Utf32CodePointIterator {
  {
  return m_ptr == other.m_ptr && m_length == other.m_length;
  }
- bool operator!=(Utf32CodePointIterator const& other) const
- {
- return !(*this == other);
- }
  Utf32CodePointIterator& operator++()
  {
  VERIFY(m_length > 0);

Userland/Applications/Spreadsheet/Position.h

@@ -37,11 +37,6 @@ struct Position {
  return row == other.row && column == other.column;
  }
 
- bool operator!=(Position const& other) const
- {
- return !(other == *this);
- }
-
  String to_cell_identifier(Sheet const& sheet) const;
  URL to_url(Sheet const& sheet) const;
 

Userland/Libraries/LibDebug/DebugInfo.h

@@ -50,7 +50,6 @@ class DebugInfo {
  }
 
  bool operator==(SourcePosition const& other) const { return file_path == other.file_path && line_number == other.line_number; }
- bool operator!=(SourcePosition const& other) const { return !(*this == other); }
 
  static SourcePosition from_line_info(Dwarf::LineProgram::LineInfo const&);
  };

Userland/Libraries/LibDeviceTree/FlattenedDeviceTree.h

@@ -34,7 +34,6 @@ struct FlattenedDeviceTreeReserveEntry {
  BigEndian<u64> size;
 
  bool operator==(FlattenedDeviceTreeReserveEntry const& other) const { return other.address == address && other.size == size; }
- bool operator!=(FlattenedDeviceTreeReserveEntry const& other) const { return !(operator==(other)); }
 };
 static_assert(sizeof(FlattenedDeviceTreeReserveEntry) == 16, "FDT Memory Reservation entry size must match specification");
 

Userland/Libraries/LibGUI/ModelIndex.h

@@ -33,11 +33,6 @@ class ModelIndex {
  return m_model == other.m_model && m_row == other.m_row && m_column == other.m_column && m_internal_data == other.m_internal_data;
  }
 
- bool operator!=(ModelIndex const& other) const
- {
- return !(*this == other);
- }
-
  Model const* model() const { return m_model; }
 
  Variant data(ModelRole = ModelRole::Display) const;

Userland/Libraries/LibGfx/Color.h

@@ -350,11 +350,6 @@ class Color {
  return m_value == other.m_value;
  }
 
- constexpr bool operator!=(Color const& other) const
- {
- return m_value != other.m_value;
- }
-
  String to_string() const;
  String to_string_without_alpha() const;
  static Optional<Color> from_string(StringView);

Userland/Libraries/LibGfx/Point.h

@@ -132,12 +132,6 @@ class Point {
  return x() == other.x() && y() == other.y();
  }
 
- template<class U>
- [[nodiscard]] bool operator!=(Point<U> const& other) const
- {
- return !(*this == other);
- }
-
  [[nodiscard]] Point<T> operator+(Point<T> const& other) const { return { m_x + other.m_x, m_y + other.m_y }; }
 
  Point<T>& operator+=(Point<T> const& other)

Userland/Libraries/LibGfx/Rect.h

@@ -477,12 +477,6 @@ class Rect {
  return location() == other.location() && size() == other.size();
  }
 
- template<class U>
- [[nodiscard]] bool operator!=(Rect<U> const& other) const
- {
- return !(*this == other);
- }
-
  [[nodiscard]] Rect<T> operator*(T factor) const { return { m_location * factor, m_size * factor }; }
 
  Rect<T>& operator*=(T factor)

Userland/Libraries/LibGfx/Size.h

@@ -99,12 +99,6 @@ class Size {
  return width() == other.width() && height() == other.height();
  }
 
- template<class U>
- [[nodiscard]] constexpr bool operator!=(Size<U> const& other) const
- {
- return !(*this == other);
- }
-
  constexpr Size<T>& operator-=(Size<T> const& other)
  {
  m_width -= other.m_width;

Userland/Libraries/LibJS/Runtime/PropertyAttributes.h

@@ -59,7 +59,6 @@ class PropertyAttributes {
  }
 
  bool operator==(PropertyAttributes const& other) const { return m_bits == other.m_bits; }
- bool operator!=(PropertyAttributes const& other) const { return m_bits != other.m_bits; }
 
  [[nodiscard]] u8 bits() const { return m_bits; }
 

Userland/Libraries/LibLine/KeyCallbackMachine.h

@@ -38,11 +38,6 @@ struct Key {
  {
  return other.key == key && other.modifiers == modifiers;
  }
-
- bool operator!=(Key const& other) const
- {
- return !(*this == other);
- }
 };
 
 struct KeyCallback {