AK+Kernel: Unify Traits<T>::equals()'s argument order on different types

There was a small mishmash of argument order, as seen on the table:

                 | Traits<T>::equals(U, T) | Traits<T>::equals(T, U)
   ============= | ======================= | =======================
   uses equals() | HashMap                 | Vector, HashTable
defines equals() | *String[^1]             | ByteBuffer

[^1]: String, DeprecatedString, their Fly-type equivalents and KString.

This mostly meant that you couldn't use a StringView for finding a value
in Vector<String>.

I'm changing the order of arguments to make the trait type itself first
(`Traits<T>::equals(T, U)`), as I think it's more expected and makes us
more consistent with the rest of the functions that put the stored type
first (like StringUtils functions and binary_serach). I've also renamed
the variable name "other" in find functions to "entry" to give more
importance to the value.

With this change, each of the following lines will now compile
successfully:

    Vector<String>().contains_slow("WHF!"sv);
    HashTable<String>().contains("WHF!"sv);
    HashMap<ByteBuffer, int>().contains("WHF!"sv.bytes());

AK/Find.h

@@ -26,6 +26,7 @@ template<typename TEndIterator, IteratorPairWith<TEndIterator> TIterator, typena
 template<typename TEndIterator, IteratorPairWith<TEndIterator> TIterator, typename T>
 [[nodiscard]] constexpr TIterator find(TIterator first, TEndIterator last, T const& value)
 {
+    // FIXME: Use the iterator's trait type, and swap arguments in equals call.
     return find_if(first, last, [&](auto const& v) { return Traits<T>::equals(value, v); });
 }
 
@@ -33,6 +34,7 @@ template<typename TEndIterator, IteratorPairWith<TEndIterator> TIterator, typena
 [[nodiscard]] constexpr size_t find_index(TIterator first, TEndIterator last, T const& value)
 requires(requires(TIterator it) { it.index(); })
 {
+    // FIXME: Use the iterator's trait type, and swap arguments in equals call.
     return find_if(first, last, [&](auto const& v) { return Traits<T>::equals(value, v); }).index();
 }
 

AK/HashMap.h

@@ -98,7 +98,7 @@ public:
     [[nodiscard]] IteratorType end() { return m_table.end(); }
     [[nodiscard]] IteratorType find(K const& key)
     {
-        return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(key, entry.key); });
+        return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(entry.key, key); });
     }
     template<typename TUnaryPredicate>
     [[nodiscard]] IteratorType find(unsigned hash, TUnaryPredicate predicate)
@@ -110,7 +110,7 @@ public:
     [[nodiscard]] ConstIteratorType end() const { return m_table.end(); }
     [[nodiscard]] ConstIteratorType find(K const& key) const
     {
-        return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(key, entry.key); });
+        return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(entry.key, key); });
     }
     template<typename TUnaryPredicate>
     [[nodiscard]] ConstIteratorType find(unsigned hash, TUnaryPredicate predicate) const
@@ -121,13 +121,13 @@ public:
     template<Concepts::HashCompatible<K> Key>
     requires(IsSame<KeyTraits, Traits<K>>) [[nodiscard]] IteratorType find(Key const& key)
     {
-        return m_table.find(Traits<Key>::hash(key), [&](auto& entry) { return Traits<K>::equals(key, entry.key); });
+        return m_table.find(Traits<Key>::hash(key), [&](auto& entry) { return Traits<K>::equals(entry.key, key); });
     }
 
     template<Concepts::HashCompatible<K> Key>
     requires(IsSame<KeyTraits, Traits<K>>) [[nodiscard]] ConstIteratorType find(Key const& key) const
     {
-        return m_table.find(Traits<Key>::hash(key), [&](auto& entry) { return Traits<K>::equals(key, entry.key); });
+        return m_table.find(Traits<Key>::hash(key), [&](auto& entry) { return Traits<K>::equals(entry.key, key); });
     }
 
     ErrorOr<void> try_ensure_capacity(size_t capacity) { return m_table.try_ensure_capacity(capacity); }

AK/HashTable.h

@@ -317,7 +317,7 @@ public:
 
     [[nodiscard]] Iterator find(T const& value)
     {
-        return find(TraitsForT::hash(value), [&](auto& other) { return TraitsForT::equals(value, other); });
+        return find(TraitsForT::hash(value), [&](auto& entry) { return TraitsForT::equals(entry, value); });
     }
 
     template<typename TUnaryPredicate>
@@ -328,14 +328,14 @@ public:
 
     [[nodiscard]] ConstIterator find(T const& value) const
     {
-        return find(TraitsForT::hash(value), [&](auto& other) { return TraitsForT::equals(value, other); });
+        return find(TraitsForT::hash(value), [&](auto& entry) { return TraitsForT::equals(entry, value); });
     }
     // FIXME: Support for predicates, while guaranteeing that the predicate call
     //        does not call a non trivial constructor each time invoked
     template<Concepts::HashCompatible<T> K>
     requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] Iterator find(K const& value)
     {
-        return find(Traits<K>::hash(value), [&](auto& other) { return Traits<T>::equals(other, value); });
+        return find(Traits<K>::hash(value), [&](auto& entry) { return Traits<T>::equals(entry, value); });
     }
 
     template<Concepts::HashCompatible<T> K, typename TUnaryPredicate>
@@ -347,7 +347,7 @@ public:
     template<Concepts::HashCompatible<T> K>
     requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] ConstIterator find(K const& value) const
     {
-        return find(Traits<K>::hash(value), [&](auto& other) { return Traits<T>::equals(other, value); });
+        return find(Traits<K>::hash(value), [&](auto& entry) { return Traits<T>::equals(entry, value); });
     }
 
     template<Concepts::HashCompatible<T> K, typename TUnaryPredicate>

AK/SinglyLinkedList.h

@@ -224,12 +224,12 @@ public:
 
     ConstIterator find(T const& value) const
     {
-        return find_if([&](auto& other) { return Traits<T>::equals(value, other); });
+        return find_if([&](auto& entry) { return Traits<T>::equals(entry, value); });
     }
 
     Iterator find(T const& value)
     {
-        return find_if([&](auto& other) { return Traits<T>::equals(value, other); });
+        return find_if([&](auto& entry) { return Traits<T>::equals(entry, value); });
     }
 
     template<typename U = T>

AK/Traits.h

@@ -22,7 +22,7 @@ struct GenericTraits {
     static constexpr bool is_trivially_serializable() { return false; }
     static constexpr bool equals(T const& a, T const& b) { return a == b; }
     template<Concepts::HashCompatible<T> U>
-    static bool equals(U const& a, T const& b) { return a == b; }
+    static bool equals(T const& self, U const& other) { return self == other; }
 };
 
 template<typename T>

Kernel/Library/KString.h

@@ -91,7 +91,7 @@ struct Traits<NonnullOwnPtr<Kernel::KString>> : public GenericTraits<NonnullOwnP
     using ConstPeekType = Kernel::KString const*;
     static unsigned hash(NonnullOwnPtr<Kernel::KString> const& p) { return string_hash(p->characters(), p->length()); }
     static bool equals(NonnullOwnPtr<Kernel::KString> const& a, NonnullOwnPtr<Kernel::KString> const& b) { return a->view() == b->view(); }
-    static bool equals(StringView a, NonnullOwnPtr<Kernel::KString> const& b) { return a == b->view(); }
+    static bool equals(NonnullOwnPtr<Kernel::KString> const& a, StringView b) { return a->view() == b; }
 };
 
 template<>
@@ -113,11 +113,11 @@ struct Traits<OwnPtr<Kernel::KString>> : public GenericTraits<OwnPtr<Kernel::KSt
 
         return a->view() == b->view();
     }
-    static bool equals(StringView a, OwnPtr<Kernel::KString> const& b)
+    static bool equals(OwnPtr<Kernel::KString> const& a, StringView b)
     {
-        if (!b)
-            return a.is_null();
-        return a == b->view();
+        if (!a)
+            return b.is_null();
+        return a->view() == b;
     }
 };
 

Tests/AK/TestVector.cpp

@@ -9,6 +9,7 @@
 #include <AK/DeprecatedString.h>
 #include <AK/OwnPtr.h>
 #include <AK/ReverseIterator.h>
+#include <AK/String.h>
 #include <AK/Vector.h>
 
 TEST_CASE(construct)
@@ -431,6 +432,13 @@ TEST_CASE(should_find_predicate_index)
     EXPECT(!v.find_first_index_if([](auto const v) { return v == 123; }).has_value());
 }
 
+TEST_CASE(should_find_using_a_hashcompatible_value)
+{
+    // Tests whether a hash-compatible value can be used to compare (Strings cannot be impliticly constructed from a StringView.)
+    Vector v { "hello!"_string };
+    EXPECT(v.contains_slow("hello!"sv));
+}
+
 TEST_CASE(should_contain_start)
 {
     // Tests whether value is found if at the start of the range.