LibJS: Add using declaration support, RAII like operation in js

In this patch only top level and not the more complicated for loop using
statements are supported. Also, as noted in the latest meeting of tc39
async parts of the spec are not stage 3 thus not included.

Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp

@@ -31,6 +31,7 @@
 #include <LibJS/Runtime/PropertyKey.h>
 #include <LibJS/Runtime/ProxyObject.h>
 #include <LibJS/Runtime/Reference.h>
+#include <LibJS/Runtime/SuppressedError.h>
 
 namespace JS {
 
@@ -1316,4 +1317,160 @@ ThrowCompletionOr<String> get_substitution(VM& vm, Utf16View const& matched, Utf
     return TRY_OR_THROW_OOM(vm, Utf16View { result }.to_utf8());
 }
 
+// 2.1.2 AddDisposableResource ( disposable, V, hint [ , method ] ), https://tc39.es/proposal-explicit-resource-management/#sec-adddisposableresource-disposable-v-hint-disposemethod
+ThrowCompletionOr<void> add_disposable_resource(VM& vm, Vector<DisposableResource>& disposable, Value value, Environment::InitializeBindingHint hint, FunctionObject* method)
+{
+    // NOTE: For now only sync is a valid hint
+    VERIFY(hint == Environment::InitializeBindingHint::SyncDispose);
+
+    Optional<DisposableResource> resource;
+
+    // 1. If method is not present then,
+    if (!method) {
+        // a. If V is null or undefined, return NormalCompletion(empty).
+        if (value.is_nullish())
+            return {};
+
+        // b. If Type(V) is not Object, throw a TypeError exception.
+        if (!value.is_object())
+            return vm.throw_completion<TypeError>(ErrorType::NotAnObject, value.to_string_without_side_effects());
+
+        // c. Let resource be ? CreateDisposableResource(V, hint).
+        resource = TRY(create_disposable_resource(vm, value, hint));
+    }
+    // 2. Else,
+    else {
+        // a. If V is null or undefined, then
+        if (value.is_nullish()) {
+            // i. Let resource be ? CreateDisposableResource(undefined, hint, method).
+            resource = TRY(create_disposable_resource(vm, js_undefined(), hint, method));
+        }
+        // b. Else,
+        else {
+            // i. If Type(V) is not Object, throw a TypeError exception.
+            if (!value.is_object())
+                return vm.throw_completion<TypeError>(ErrorType::NotAnObject, value.to_string_without_side_effects());
+
+            // ii. Let resource be ? CreateDisposableResource(V, hint, method).
+            resource = TRY(create_disposable_resource(vm, value, hint, method));
+        }
+    }
+
+    // 3. Append resource to disposable.[[DisposableResourceStack]].
+    VERIFY(resource.has_value());
+    disposable.append(resource.release_value());
+
+    // 4. Return NormalCompletion(empty).
+    return {};
+}
+
+// 2.1.3 CreateDisposableResource ( V, hint [ , method ] ), https://tc39.es/proposal-explicit-resource-management/#sec-createdisposableresource
+ThrowCompletionOr<DisposableResource> create_disposable_resource(VM& vm, Value value, Environment::InitializeBindingHint hint, FunctionObject* method)
+{
+    // 1. If method is not present, then
+    if (!method) {
+        // a. If V is undefined, throw a TypeError exception.
+        if (value.is_undefined())
+            return vm.throw_completion<TypeError>(ErrorType::IsUndefined, "value");
+
+        // b. Set method to ? GetDisposeMethod(V, hint).
+        method = TRY(get_dispose_method(vm, value, hint));
+
+        // c. If method is undefined, throw a TypeError exception.
+        if (!method)
+            return vm.throw_completion<TypeError>(ErrorType::NoDisposeMethod, value.to_string_without_side_effects());
+    }
+    // 2. Else,
+    // a. If IsCallable(method) is false, throw a TypeError exception.
+    // NOTE: This is guaranteed to never occur from the type.
+    VERIFY(method);
+
+    // 3. Return the DisposableResource Record { [[ResourceValue]]: V, [[Hint]]: hint, [[DisposeMethod]]: method }.
+    // NOTE: Since we only support sync dispose we don't store the hint for now.
+    VERIFY(hint == Environment::InitializeBindingHint::SyncDispose);
+    return DisposableResource {
+        value,
+        *method
+    };
+}
+
+// 2.1.4 GetDisposeMethod ( V, hint ), https://tc39.es/proposal-explicit-resource-management/#sec-getdisposemethod
+ThrowCompletionOr<GCPtr<FunctionObject>> get_dispose_method(VM& vm, Value value, Environment::InitializeBindingHint hint)
+{
+    // NOTE: We only have sync dispose for now which means we ignore step 1.
+    VERIFY(hint == Environment::InitializeBindingHint::SyncDispose);
+
+    // 2. Else,
+    // a. Let method be ? GetMethod(V, @@dispose).
+    return GCPtr<FunctionObject> { TRY(value.get_method(vm, *vm.well_known_symbol_dispose())) };
+}
+
+// 2.1.5 Dispose ( V, hint, method ), https://tc39.es/proposal-explicit-resource-management/#sec-dispose
+Completion dispose(VM& vm, Value value, NonnullGCPtr<FunctionObject> method)
+{
+    // 1. Let result be ? Call(method, V).
+    [[maybe_unused]] auto result = TRY(call(vm, *method, value));
+
+    // NOTE: Hint can only be sync-dispose so we ignore step 2.
+    // 2. If hint is async-dispose and result is not undefined, then
+    //    a. Perform ? Await(result).
+
+    // 3. Return undefined.
+    return js_undefined();
+}
+
+// 2.1.6 DisposeResources ( disposable, completion ), https://tc39.es/proposal-explicit-resource-management/#sec-disposeresources-disposable-completion-errors
+Completion dispose_resources(VM& vm, Vector<DisposableResource> const& disposable, Completion completion)
+{
+    // 1. If disposable is not undefined, then
+    // NOTE: At this point disposable is always defined.
+
+    // a. For each resource of disposable.[[DisposableResourceStack]], in reverse list order, do
+    for (auto const& resource : disposable.in_reverse()) {
+        // i. Let result be Dispose(resource.[[ResourceValue]], resource.[[Hint]], resource.[[DisposeMethod]]).
+        auto result = dispose(vm, resource.resource_value, resource.dispose_method);
+
+        // ii. If result.[[Type]] is throw, then
+        if (result.is_error()) {
+            // 1. If completion.[[Type]] is throw, then
+            if (completion.is_error()) {
+                // a. Set result to result.[[Value]].
+
+                // b. Let suppressed be completion.[[Value]].
+                auto suppressed = completion.value().value();
+
+                // c. Let error be a newly created SuppressedError object.
+                auto error = SuppressedError::create(*vm.current_realm());
+
+                // d. Perform ! DefinePropertyOrThrow(error, "error", PropertyDescriptor { [[Configurable]]: true, [[Enumerable]]: false, [[Writable]]: true, [[Value]]: result }).
+                MUST(error->define_property_or_throw(vm.names.error, { .value = result.value(), .writable = true, .enumerable = true, .configurable = true }));
+
+                // e. Perform ! DefinePropertyOrThrow(error, "suppressed", PropertyDescriptor { [[Configurable]]: true, [[Enumerable]]: false, [[Writable]]: true, [[Value]]: suppressed }).
+                MUST(error->define_property_or_throw(vm.names.suppressed, { .value = suppressed, .writable = true, .enumerable = false, .configurable = true }));
+
+                // f. Set completion to ThrowCompletion(error).
+                completion = throw_completion(error);
+            }
+            // 2. Else,
+            else {
+                // a. Set completion to result.
+                completion = result;
+            }
+        }
+    }
+
+    // 2. Return completion.
+    return completion;
+}
+
+Completion dispose_resources(VM& vm, GCPtr<DeclarativeEnvironment> disposable, Completion completion)
+{
+    // 1. If disposable is not undefined, then
+    if (disposable)
+        return dispose_resources(vm, disposable->disposable_resource_stack(), completion);
+
+    // 2. Return completion.
+    return completion;
+}
+
 }