AK+LibWasm+LibJS: Disallow Variant.has() on types that aren't contained

Checking for this (and get()'ing it) is always invalid, so let's just
disallow it.
This also finds two bugs where the code is checking for types that can
never actually be in the variant (which was actually a refactor
artifact).

AK/Variant.h

@@ -201,6 +201,12 @@ private:
     static constexpr IndexType index_of() { return Detail::index_of<T, IndexType, Ts...>(); }
 
 public:
+    template<typename T>
+    static constexpr bool can_contain()
+    {
+        return index_of<T>() != invalid_index;
+    }
+
     template<typename... NewTs>
     friend struct Variant;
 
@@ -246,7 +252,7 @@ public:
     using Detail::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>::MergeAndDeduplicatePacks;
 
     template<typename T, typename StrippedT = RemoveCV<RemoveReference<T>>>
-    void set(T&& t) requires(index_of<StrippedT>() != invalid_index)
+    void set(T&& t) requires(can_contain<StrippedT>())
     {
         constexpr auto new_index = index_of<StrippedT>();
         Helper::delete_(m_index, m_data);
@@ -255,7 +261,7 @@ public:
     }
 
     template<typename T, typename StrippedT = RemoveCV<RemoveReference<T>>>
-    void set(T&& t, Detail::VariantNoClearTag) requires(index_of<StrippedT>() != invalid_index)
+    void set(T&& t, Detail::VariantNoClearTag) requires(can_contain<StrippedT>())
     {
         constexpr auto new_index = index_of<StrippedT>();
         new (m_data) StrippedT(forward<T>(t));
@@ -263,7 +269,7 @@ public:
     }
 
     template<typename T>
-    T* get_pointer()
+    T* get_pointer() requires(can_contain<T>())
     {
         if (index_of<T>() == m_index)
             return bit_cast<T*>(&m_data);
@@ -271,14 +277,14 @@ public:
     }
 
     template<typename T>
-    T& get()
+    T& get() requires(can_contain<T>())
     {
         VERIFY(has<T>());
         return *bit_cast<T*>(&m_data);
     }
 
     template<typename T>
-    const T* get_pointer() const
+    const T* get_pointer() const requires(can_contain<T>())
     {
         if (index_of<T>() == m_index)
             return bit_cast<const T*>(&m_data);
@@ -286,14 +292,14 @@ public:
     }
 
     template<typename T>
-    const T& get() const
+    const T& get() const requires(can_contain<T>())
     {
         VERIFY(has<T>());
         return *bit_cast<const T*>(&m_data);
     }
 
     template<typename T>
-    [[nodiscard]] bool has() const
+    [[nodiscard]] bool has() const requires(can_contain<T>())
     {
         return index_of<T>() == m_index;
     }
@@ -336,12 +342,6 @@ public:
         return instance;
     }
 
-    template<typename T>
-    static constexpr bool can_contain()
-    {
-        return index_of<T>() != invalid_index;
-    }
-
 private:
     static constexpr auto data_size = integer_sequence_generate_array<size_t>(0, IntegerSequence<size_t, sizeof(Ts)...>()).max();
     static constexpr auto data_alignment = integer_sequence_generate_array<size_t>(0, IntegerSequence<size_t, alignof(Ts)...>()).max();

Userland/Libraries/LibJS/Parser.cpp

@@ -1609,7 +1609,7 @@ NonnullRefPtr<VariableDeclaration> Parser::parse_variable_declaration(bool for_l
             init = parse_expression(2);
         } else if (!for_loop_variable_declaration && declaration_kind == DeclarationKind::Const) {
             syntax_error("Missing initializer in 'const' variable declaration");
-        } else if (target.has<BindingPattern>()) {
+        } else if (target.has<NonnullRefPtr<BindingPattern>>()) {
             syntax_error("Missing initializer in destructuring assignment");
         }
 

Userland/Libraries/LibWasm/AbstractMachine/Interpreter.cpp

@@ -482,12 +482,12 @@ void BytecodeInterpreter::interpret(Configuration& configuration, InstructionPoi
             return;
         }
         auto element = table_instance->elements()[index.value()];
-        if (!element.has_value() || !element->ref().has<FunctionAddress>()) {
+        if (!element.has_value() || !element->ref().has<Reference::Func>()) {
             dbgln("LibWasm: call_indirect attempted with invalid address element (not a function)");
             m_do_trap = true;
             return;
         }
-        auto address = element->ref().get<FunctionAddress>();
+        auto address = element->ref().get<Reference::Func>().address;
         dbgln_if(WASM_TRACE_DEBUG, "call_indirect({} -> {})", index.value(), address.value());
         call_address(configuration, address);
         return;