LibJS: Convert 'possible instants' AOs to MarkedVector<Instant*>

Resolve TODOs suggesting the use of a strongly typed MarkedValueList
(a.k.a. MarkedVector<T>) in the following AOs:

- get_possible_instants_for()
- disambiguate_possible_instants()

3 files changed, 20 insertions, 29 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
index 37a68e0224..71da4456bb 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
@@ -529,10 +529,8 @@ ThrowCompletionOr<Instant*> builtin_time_zone_get_instant_for(GlobalObject& glob
 }
 
 // 11.6.15 DisambiguatePossibleInstants ( possibleInstants, timeZone, dateTime, disambiguation ), https://tc39.es/proposal-temporal/#sec-temporal-disambiguatepossibleinstants
-ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject& global_object, Vector<Value> const& possible_instants, Value time_zone, PlainDateTime& date_time, StringView disambiguation)
+ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject& global_object, MarkedVector<Instant*> const& possible_instants, Value time_zone, PlainDateTime& date_time, StringView disambiguation)
 {
-    // TODO: MarkedValueList<T> would be nice, then we could pass a Vector<Instant*> here and wouldn't need the casts...
-
     auto& vm = global_object.vm();
 
     // 1. Assert: dateTime has an [[InitializedTemporalDateTime]] internal slot.
@@ -543,8 +541,7 @@ ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject& global_
     // 3. If n = 1, then
     if (n == 1) {
         // a. Return possibleInstants[0].
-        auto& instant = possible_instants[0];
-        return &static_cast<Instant&>(const_cast<Object&>(instant.as_object()));
+        return possible_instants[0];
     }
 
     // 4. If n ≠ 0, then
@@ -552,15 +549,13 @@ ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject& global_
         // a. If disambiguation is "earlier" or "compatible", then
         if (disambiguation.is_one_of("earlier"sv, "compatible"sv)) {
             // i. Return possibleInstants[0].
-            auto& instant = possible_instants[0];
-            return &static_cast<Instant&>(const_cast<Object&>(instant.as_object()));
+            return possible_instants[0];
         }
 
         // b. If disambiguation is "later", then
         if (disambiguation == "later"sv) {
             // i. Return possibleInstants[n − 1].
-            auto& instant = possible_instants[n - 1];
-            return &static_cast<Instant&>(const_cast<Object&>(instant.as_object()));
+            return possible_instants[n - 1];
         }
 
         // c. Assert: disambiguation is "reject".
@@ -606,15 +601,14 @@ ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject& global_
         auto* earlier_date_time = MUST(create_temporal_date_time(global_object, earlier.year, earlier.month, earlier.day, earlier.hour, earlier.minute, earlier.second, earlier.millisecond, earlier.microsecond, earlier.nanosecond, date_time.calendar()));
 
         // c. Set possibleInstants to ? GetPossibleInstantsFor(timeZone, earlierDateTime).
-        auto possible_instants_mvl = TRY(get_possible_instants_for(global_object, time_zone, *earlier_date_time));
+        auto possible_instants_ = TRY(get_possible_instants_for(global_object, time_zone, *earlier_date_time));
 
         // d. If possibleInstants is empty, throw a RangeError exception.
-        if (possible_instants_mvl.is_empty())
+        if (possible_instants_.is_empty())
             return vm.throw_completion<RangeError>(global_object, ErrorType::TemporalDisambiguatePossibleInstantsEarlierZero);
 
         // e. Return possibleInstants[0].
-        auto& instant = possible_instants_mvl[0];
-        return &static_cast<Instant&>(const_cast<Object&>(instant.as_object()));
+        return possible_instants_[0];
     }
 
     // 14. Assert: disambiguation is "compatible" or "later".
@@ -627,22 +621,21 @@ ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject& global_
     auto* later_date_time = MUST(create_temporal_date_time(global_object, later.year, later.month, later.day, later.hour, later.minute, later.second, later.millisecond, later.microsecond, later.nanosecond, date_time.calendar()));
 
     // 17. Set possibleInstants to ? GetPossibleInstantsFor(timeZone, laterDateTime).
-    auto possible_instants_mvl = TRY(get_possible_instants_for(global_object, time_zone, *later_date_time));
+    auto possible_instants_ = TRY(get_possible_instants_for(global_object, time_zone, *later_date_time));
 
     // 18. Set n to possibleInstants's length.
-    n = possible_instants_mvl.size();
+    n = possible_instants_.size();
 
     // 19. If n = 0, throw a RangeError exception.
     if (n == 0)
         return vm.throw_completion<RangeError>(global_object, ErrorType::TemporalDisambiguatePossibleInstantsZero);
 
     // 20. Return possibleInstants[n − 1].
-    auto& instant = possible_instants_mvl[n - 1];
-    return &static_cast<Instant&>(const_cast<Object&>(instant.as_object()));
+    return possible_instants_[n - 1];
 }
 
 // 11.6.16 GetPossibleInstantsFor ( timeZone, dateTime ), https://tc39.es/proposal-temporal/#sec-temporal-getpossibleinstantsfor
-ThrowCompletionOr<MarkedValueList> get_possible_instants_for(GlobalObject& global_object, Value time_zone, PlainDateTime& date_time)
+ThrowCompletionOr<MarkedVector<Instant*>> get_possible_instants_for(GlobalObject& global_object, Value time_zone, PlainDateTime& date_time)
 {
     auto& vm = global_object.vm();
 
@@ -655,7 +648,7 @@ ThrowCompletionOr<MarkedValueList> get_possible_instants_for(GlobalObject& globa
     auto iterator = TRY(get_iterator(global_object, possible_instants, IteratorHint::Sync));
 
     // 4. Let list be a new empty List.
-    auto list = MarkedValueList { vm.heap() };
+    auto list = MarkedVector<Instant*> { vm.heap() };
 
     // 5. Let next be true.
     Object* next = nullptr;
@@ -680,7 +673,7 @@ ThrowCompletionOr<MarkedValueList> get_possible_instants_for(GlobalObject& globa
             }
 
             // iii. Append nextValue to the end of the List list.
-            list.append(next_value);
+            list.append(static_cast<Instant*>(&next_value.as_object()));
         }
     } while (next != nullptr);
 
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.h b/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.h
index cc932facec..2b800e87ca 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/TimeZone.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Optional.h>
+#include <LibJS/Heap/MarkedVector.h>
 #include <LibJS/Runtime/MarkedValueList.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
@@ -53,8 +54,8 @@ ThrowCompletionOr<double> get_offset_nanoseconds_for(GlobalObject&, Value time_z
 ThrowCompletionOr<String> builtin_time_zone_get_offset_string_for(GlobalObject&, Value time_zone, Instant&);
 ThrowCompletionOr<PlainDateTime*> builtin_time_zone_get_plain_date_time_for(GlobalObject&, Value time_zone, Instant&, Object& calendar);
 ThrowCompletionOr<Instant*> builtin_time_zone_get_instant_for(GlobalObject&, Value time_zone, PlainDateTime&, StringView disambiguation);
-ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject&, Vector<Value> const& possible_instants, Value time_zone, PlainDateTime&, StringView disambiguation);
-ThrowCompletionOr<MarkedValueList> get_possible_instants_for(GlobalObject&, Value time_zone, PlainDateTime&);
+ThrowCompletionOr<Instant*> disambiguate_possible_instants(GlobalObject&, MarkedVector<Instant*> const& possible_instants, Value time_zone, PlainDateTime&, StringView disambiguation);
+ThrowCompletionOr<MarkedVector<Instant*>> get_possible_instants_for(GlobalObject&, Value time_zone, PlainDateTime&);
 ThrowCompletionOr<bool> time_zone_equals(GlobalObject&, Object& one, Object& two);
 
 bool is_valid_time_zone_numeric_utc_offset_syntax(String const&);
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
index cc5fd3f0cb..66a9eeef45 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
@@ -79,17 +79,14 @@ ThrowCompletionOr<BigInt const*> interpret_iso_date_time_offset(GlobalObject& gl
     auto possible_instants = TRY(get_possible_instants_for(global_object, time_zone, *date_time));
 
     // 9. For each element candidate of possibleInstants, do
-    for (auto& candidate_value : possible_instants) {
-        // TODO: As per the comment in disambiguate_possible_instants, having a MarkedValueList<T> would allow us to remove this cast.
-        auto& candidate = static_cast<Instant&>(candidate_value.as_object());
-
+    for (auto* candidate : possible_instants) {
         // a. Let candidateNanoseconds be ? GetOffsetNanosecondsFor(timeZone, candidate).
-        auto candidate_nanoseconds = TRY(get_offset_nanoseconds_for(global_object, time_zone, candidate));
+        auto candidate_nanoseconds = TRY(get_offset_nanoseconds_for(global_object, time_zone, *candidate));
 
         // b. If candidateNanoseconds = offsetNanoseconds, then
         if (candidate_nanoseconds == offset_nanoseconds) {
             // i. Return candidate.[[Nanoseconds]].
-            return &candidate.nanoseconds();
+            return &candidate->nanoseconds();
         }
 
         // c. If matchBehaviour is match minutes, then
@@ -100,7 +97,7 @@ ThrowCompletionOr<BigInt const*> interpret_iso_date_time_offset(GlobalObject& gl
             // ii. If roundedCandidateNanoseconds = offsetNanoseconds, then
             if (rounded_candidate_nanoseconds == offset_nanoseconds) {
                 // 1. Return candidate.[[Nanoseconds]].
-                return &candidate.nanoseconds();
+                return &candidate->nanoseconds();
             }
         }
     }