LibJS: Integrate Symbols into objects as valid keys

This allows objects properties to be created for symbol keys in addition
to just plain strings/numbers

Libraries/LibJS/Runtime/StringOrSymbol.h

@@ -0,0 +1,152 @@
+/*
+ * Copyright (c) 2020, Matthew Olsson <matthewcolsson@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/PrimitiveString.h>
+#include <LibJS/Runtime/Symbol.h>
+#include <LibJS/Runtime/Value.h>
+
+namespace JS {
+
+class StringOrSymbol {
+public:
+    static StringOrSymbol from_value(Interpreter& interpreter, Value value)
+    {
+        if (value.is_symbol())
+            return &value.as_symbol();
+        if (!value.is_empty())
+            return value.to_string(interpreter);
+        return {};
+    }
+
+    StringOrSymbol() = default;
+
+    StringOrSymbol(const char* chars)
+        : m_ptr(StringImpl::create(chars).leak_ref())
+    {
+    }
+
+    StringOrSymbol(const String& string)
+        : m_ptr(StringImpl::create(string.characters(), string.length()).leak_ref())
+    {
+    }
+
+    StringOrSymbol(const Symbol* symbol)
+        : m_ptr(symbol)
+    {
+        set_symbol_flag();
+    }
+
+    StringOrSymbol(const StringOrSymbol& other)
+    {
+        m_ptr = other.m_ptr;
+    }
+
+    ALWAYS_INLINE bool is_valid() const { return m_ptr != nullptr; }
+    ALWAYS_INLINE bool is_symbol() const { return is_valid() && (bits() & 1ul); }
+    ALWAYS_INLINE bool is_string() const { return is_valid() && !(bits() & 1ul); }
+
+    ALWAYS_INLINE String as_string() const
+    {
+        ASSERT(is_string());
+        return reinterpret_cast<const StringImpl*>(m_ptr);
+    }
+
+    ALWAYS_INLINE const Symbol* as_symbol() const
+    {
+        ASSERT(is_symbol());
+        return reinterpret_cast<const Symbol*>(bits() & ~1ul);
+    }
+
+    String to_display_string() const
+    {
+        if (is_string())
+            return as_string();
+        if (is_symbol())
+            return as_symbol()->to_string();
+        ASSERT_NOT_REACHED();
+    }
+
+    Value to_value(Interpreter& interpreter) const
+    {
+        if (is_string())
+            return js_string(interpreter, as_string());
+        if (is_symbol())
+            return const_cast<Symbol*>(as_symbol());
+        return {};
+    }
+
+    void visit_children(Cell::Visitor& visitor)
+    {
+        if (is_symbol())
+            visitor.visit(const_cast<Symbol*>(as_symbol()));
+    }
+
+    ALWAYS_INLINE bool operator==(const StringOrSymbol& other) const
+    {
+        if (is_string())
+            return other.is_string() && as_string() == other.as_string();
+        if (is_symbol())
+            return other.is_symbol() && as_symbol() == other.as_symbol();
+        return true;
+    }
+
+    StringOrSymbol& operator=(const StringOrSymbol& other)
+    {
+        if (this == &other)
+            return *this;
+        m_ptr = other.m_ptr;
+        return *this;
+    }
+
+private:
+    ALWAYS_INLINE u64 bits() const
+    {
+        return reinterpret_cast<uintptr_t>(m_ptr);
+    }
+
+    ALWAYS_INLINE void set_symbol_flag()
+    {
+        m_ptr = reinterpret_cast<const void*>(bits() | 1ul);
+    }
+
+    const void* m_ptr { nullptr };
+};
+
+}
+
+template<>
+struct AK::Traits<JS::StringOrSymbol> : public GenericTraits<JS::StringOrSymbol> {
+    static unsigned hash(const JS::StringOrSymbol& key)
+    {
+        if (key.is_string())
+            return key.as_string().hash();
+        if (key.is_symbol())
+            return ptr_hash(key.as_symbol());
+        return 0;
+    }
+};