AK: Ensure Utf16FlyString is hash-compatible with Utf16View/Utf16String

Author: trflynn89

AK/Utf16FlyString.h

@@ -165,6 +165,22 @@ struct Formatter<Utf16FlyString> : Formatter<Utf16String> {
     }
 };
 
+namespace Detail {
+
+template<>
+inline constexpr bool IsHashCompatible<Utf16View, Utf16FlyString> = true;
+
+template<>
+inline constexpr bool IsHashCompatible<Utf16FlyString, Utf16View> = true;
+
+template<>
+inline constexpr bool IsHashCompatible<Utf16String, Utf16FlyString> = true;
+
+template<>
+inline constexpr bool IsHashCompatible<Utf16FlyString, Utf16String> = true;
+
+}
+
 }
 
 [[nodiscard]] ALWAYS_INLINE AK::Utf16FlyString operator""_utf16_fly_string(char const* string, size_t length)

Tests/AK/TestUtf16FlyString.cpp

@@ -8,6 +8,12 @@
 
 #include <AK/Utf16FlyString.h>
 
+static_assert(AK::Concepts::HashCompatible<Utf16String, Utf16FlyString>);
+static_assert(AK::Concepts::HashCompatible<Utf16FlyString, Utf16String>);
+
+static_assert(AK::Concepts::HashCompatible<Utf16View, Utf16FlyString>);
+static_assert(AK::Concepts::HashCompatible<Utf16FlyString, Utf16View>);
+
 TEST_CASE(empty_string)
 {
     Utf16FlyString fly {};

Tests/AK/TestUtf16String.cpp

@@ -14,6 +14,9 @@
 #include <AK/Utf16String.h>
 #include <AK/Utf32View.h>
 
+static_assert(AK::Concepts::HashCompatible<Utf16String, Utf16View>);
+static_assert(AK::Concepts::HashCompatible<Utf16View, Utf16String>);
+
 static Utf16String make_copy(Utf16String const& string)
 {
     return string.has_ascii_storage()