LibJS: Require that NanosecondsToDays doesn't flip sign

This is an normative change in the Temporal spec.
See: https://github.com/tc39/proposal-temporal/commit/e13c52d

2 files changed, 21 insertions, 1 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
index 53e2f28d22..d70cbd8a5b 100644
--- a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
+++ b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
@@ -269,6 +269,10 @@
     M(TemporalMissingOptionsObject, "Required options object is missing or undefined")                                                  \
     M(TemporalMissingStartingPoint, "A starting point is required for balancing {}")                                                    \
     M(TemporalMissingUnits, "One or both of smallestUnit or largestUnit is required")                                                   \
+    M(TemporalNanosecondsConvertedToDaysWithOppositeSign, "Time zone or calendar converted nanoseconds into a number of days with "     \
+                                                          "the opposite sign")                                                          \
+    M(TemporalNanosecondsConvertedToRemainderOfNanosecondsWithOppositeSign, "Time zone or calendar ended up with a remainder of "       \
+                                                                            "nanoseconds with the opposite sign")                       \
     M(TemporalObjectMustHaveOneOf, "Object must have at least one of the following properties: {}")                                     \
     M(TemporalObjectMustNotHave, "Object must not have a defined {} property")                                                          \
     M(TemporalPropertyMustBeFinite, "Property must not be Infinity")                                                                    \
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
index 4507b78ecc..da795b75dc 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
@@ -538,7 +538,23 @@ ThrowCompletionOr<NanosecondsToDaysResult> nanoseconds_to_days(VM& vm, Crypto::S
         }
     }
 
-    // 19. Return the Record { [[Days]]: days, [[Nanoseconds]]: nanoseconds, [[DayLength]]: abs(dayLengthNs) }.
+    // 19. If days < 0 and sign = 1, throw a RangeError exception.
+    if (days < 0 && sign == 1)
+        return vm.throw_completion<RangeError>(ErrorType::TemporalNanosecondsConvertedToDaysWithOppositeSign);
+
+    // 20. If days > 0 and sign = -1, throw a RangeError exception.
+    if (days > 0 && sign == -1)
+        return vm.throw_completion<RangeError>(ErrorType::TemporalNanosecondsConvertedToDaysWithOppositeSign);
+
+    // 21. If nanoseconds < 0 and sign = 1, throw a RangeError exception.
+    if (nanoseconds.is_negative() && sign == 1)
+        return vm.throw_completion<RangeError>(ErrorType::TemporalNanosecondsConvertedToRemainderOfNanosecondsWithOppositeSign);
+
+    // 22. If nanoseconds > 0 and sign = -1, throw a RangeError exception.
+    if (nanoseconds.is_positive() && sign == -1)
+        return vm.throw_completion<RangeError>(ErrorType::TemporalNanosecondsConvertedToRemainderOfNanosecondsWithOppositeSign);
+
+    // 23. Return the Record { [[Days]]: days, [[Nanoseconds]]: nanoseconds, [[DayLength]]: abs(dayLengthNs) }.
     return NanosecondsToDaysResult { .days = days, .nanoseconds = move(nanoseconds), .day_length = fabs(day_length_ns.to_double()) };
 }