LibJS: Add missing check in ParseTemporalInstant

This is an editorial change in the Temporal spec.

See: baead4d

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

@@ -127,8 +127,17 @@ ThrowCompletionOr<BigInt*> parse_temporal_instant(GlobalObject& global_object, S
     // 7. Let offsetNanoseconds be ? ParseTimeZoneOffsetString(offsetString).
     auto offset_nanoseconds = TRY(parse_time_zone_offset_string(global_object, *offset_string));
 
-    // 8. Return utc − offsetNanoseconds.
-    return js_bigint(vm, utc->big_integer().minus(Crypto::SignedBigInteger::create_from(offset_nanoseconds)));
+    // 8. Let result be utc − offsetNanoseconds.
+    auto* result_ns = js_bigint(vm, utc->big_integer().minus(Crypto::SignedBigInteger::create_from(offset_nanoseconds)));
+
+    // 9. If ! IsValidEpochNanoseconds(ℤ(result)) is false, then
+    if (!is_valid_epoch_nanoseconds(*result_ns)) {
+        // a. Throw a RangeError exception.
+        return vm.throw_completion<RangeError>(global_object, ErrorType::TemporalInvalidEpochNanoseconds);
+    }
+
+    // 10. Return result.
+    return result_ns;
 }
 
 // 8.5.5 CompareEpochNanoseconds ( epochNanosecondsOne, epochNanosecondsTwo ), https://tc39.es/proposal-temporal/#sec-temporal-compareepochnanoseconds

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

@@ -32,4 +32,20 @@ describe("errors", () => {
             Temporal.Instant.from("foo");
         }).toThrowWithMessage(RangeError, "Invalid instant string 'foo'");
     });
+
+    test("invalid epoch nanoseconds", () => {
+        // Test cases from https://github.com/tc39/proposal-temporal/commit/baead4d85bc3e9ecab1e9824c3d3fe4fdd77fc3a
+        expect(() => {
+            Temporal.Instant.from("-271821-04-20T00:00:00+00:01");
+        }).toThrowWithMessage(
+            RangeError,
+            "Invalid epoch nanoseconds value, must be in range -86400 * 10^17 to 86400 * 10^17"
+        );
+        expect(() => {
+            Temporal.Instant.from("+275760-09-13T00:00:00-00:01");
+        }).toThrowWithMessage(
+            RangeError,
+            "Invalid epoch nanoseconds value, must be in range -86400 * 10^17 to 86400 * 10^17"
+        );
+    });
 });