LibJS: Add Temporal.Instant.from()

Userland/Libraries/LibJS/Runtime/Temporal/InstantConstructor.cpp

@@ -27,6 +27,7 @@ void InstantConstructor::initialize(GlobalObject& global_object)
     define_direct_property(vm.names.prototype, global_object.temporal_instant_prototype(), 0);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.from, from, 1, attr);
     define_native_function(vm.names.fromEpochSeconds, from_epoch_seconds, 1, attr);
     define_native_function(vm.names.fromEpochMilliseconds, from_epoch_milliseconds, 1, attr);
     define_native_function(vm.names.fromEpochMicroseconds, from_epoch_microseconds, 1, attr);
@@ -68,6 +69,21 @@ Value InstantConstructor::construct(FunctionObject& new_target)
     return create_temporal_instant(global_object, *epoch_nanoseconds, &new_target);
 }
 
+// 8.2.2 Temporal.Instant.from ( item ), https://tc39.es/proposal-temporal/#sec-temporal.instant.from
+JS_DEFINE_NATIVE_FUNCTION(InstantConstructor::from)
+{
+    auto item = vm.argument(0);
+
+    // 1. If Type(item) is Object and item has an [[InitializedTemporalInstant]] internal slot, then
+    if (item.is_object() && is<Instant>(item.as_object())) {
+        // a. Return ? CreateTemporalInstant(item.[[Nanoseconds]]).
+        return create_temporal_instant(global_object, *js_bigint(vm.heap(), static_cast<Instant&>(item.as_object()).nanoseconds().big_integer()));
+    }
+
+    // 2. Return ? ToTemporalInstant(item).
+    return to_temporal_instant(global_object, item);
+}
+
 // 8.2.3 Temporal.Instant.fromEpochSeconds ( epochSeconds ), https://tc39.es/proposal-temporal/#sec-temporal.instant.fromepochseconds
 JS_DEFINE_NATIVE_FUNCTION(InstantConstructor::from_epoch_seconds)
 {

Userland/Libraries/LibJS/Runtime/Temporal/InstantConstructor.h

@@ -24,6 +24,7 @@ public:
 private:
     virtual bool has_constructor() const override { return true; }
 
+    JS_DECLARE_NATIVE_FUNCTION(from);
     JS_DECLARE_NATIVE_FUNCTION(from_epoch_seconds);
     JS_DECLARE_NATIVE_FUNCTION(from_epoch_milliseconds);
     JS_DECLARE_NATIVE_FUNCTION(from_epoch_microseconds);

Userland/Libraries/LibJS/Tests/builtins/Temporal/Instant/Instant.from.js

@@ -0,0 +1,17 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Instant.from).toHaveLength(1);
+    });
+
+    test("Instant instance argument", () => {
+        const instant = new Temporal.Instant(123n);
+        expect(Temporal.Instant.from(instant).epochNanoseconds).toBe(123n);
+    });
+
+    // Un-skip once ParseISODateTime & ParseTemporalTimeZoneString are implemented
+    test.skip("Instant string argument", () => {
+        expect(Temporal.Instant.from("1975-02-02T14:25:36.123456789Z").epochNanoseconds).toBe(
+            160583136123456789n
+        );
+    });
+});