LibWeb: Restore flags to prevent formatting timestamps as local time

The flag to stringify these timestamps as UTC was errantly dropped in
6fb2be96bf. This was causing test-web to
fail in time zones other than GMT+0.

Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -2326,7 +2326,7 @@ static String convert_number_to_date_string(double input)
     // date string that represents the date that, in UTC, is current input milliseconds after midnight UTC
     // on the morning of 1970-01-01 (the time represented by the value "1970-01-01T00:00:00.0Z").
     auto date = AK::UnixDateTime::from_seconds_since_epoch(input / 1000.);
-    return MUST(date.to_string("%Y-%m-%d"sv));
+    return MUST(date.to_string("%Y-%m-%d"sv, AK::UnixDateTime::LocalTime::No));
 }
 
 // https://html.spec.whatwg.org/multipage/input.html#time-state-(type=time):concept-input-value-number-string

Libraries/LibWeb/Internals/Internals.cpp

@@ -4,7 +4,9 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibJS/Runtime/Date.h>
 #include <LibJS/Runtime/VM.h>
+#include <LibUnicode/TimeZone.h>
 #include <LibWeb/Bindings/InternalsPrototype.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/DOM/Document.h>
@@ -53,6 +55,17 @@ void Internals::gc()
     vm().heap().collect_garbage();
 }
 
+WebIDL::ExceptionOr<String> Internals::set_time_zone(StringView time_zone)
+{
+    auto current_time_zone = Unicode::current_time_zone();
+
+    if (auto result = Unicode::set_current_time_zone(time_zone); result.is_error())
+        return vm().throw_completion<JS::InternalError>(MUST(String::formatted("Could not set time zone: {}", result.error())));
+
+    JS::clear_system_time_zone_cache();
+    return current_time_zone;
+}
+
 JS::Object* Internals::hit_test(double x, double y)
 {
     auto& active_document = window().associated_document();

Libraries/LibWeb/Internals/Internals.h

@@ -23,6 +23,8 @@ public:
     void signal_test_is_done(String const& text);
     void set_test_timeout(double milliseconds);
 
+    WebIDL::ExceptionOr<String> set_time_zone(StringView time_zone);
+
     void gc();
     JS::Object* hit_test(double x, double y);
 

Libraries/LibWeb/Internals/Internals.idl

@@ -8,6 +8,8 @@ interface Internals {
     undefined signalTestIsDone(DOMString text);
     undefined setTestTimeout(double milliseconds);
 
+    DOMString setTimeZone(DOMString timeZone);
+
     undefined gc();
     object hitTest(double x, double y);
 

Libraries/LibWeb/Loader/ResourceLoader.cpp

@@ -146,7 +146,7 @@ static HTTP::HeaderMap response_headers_for_file(StringView path, Optional<time_
 
     if (modified_time.has_value()) {
         auto const datetime = AK::UnixDateTime::from_seconds_since_epoch(modified_time.value());
-        response_headers.set("Last-Modified"sv, datetime.to_byte_string("%a, %d %b %Y %H:%M:%S GMT"sv));
+        response_headers.set("Last-Modified"sv, datetime.to_byte_string("%a, %d %b %Y %H:%M:%S GMT"sv, AK::UnixDateTime::LocalTime::No));
     }
 
     return response_headers;

Tests/LibWeb/Text/expected/input-date.txt

@@ -4,11 +4,13 @@
 4. "1970-01-01T19:46:19.000Z"
 5. null
 6. "1970-01-01"
-7. "2023-12-11"
-8. Exception: TypeError
-9. ""
-10. "18:47:37"
-11. "18:47:37.100"
-12. "18:47:37.864"
-13. Exception: TypeError
-14. ""
+7. "1970-01-01"
+8. "2023-12-11"
+9. "2023-12-11"
+10. Exception: TypeError
+11. ""
+12. "18:47:37"
+13. "18:47:37.100"
+14. "18:47:37.864"
+15. Exception: TypeError
+16. ""

Tests/LibWeb/Text/input/input-date.html

@@ -60,7 +60,20 @@
             return input.value;
         });
 
-        // 7. Input date set value as date
+        // 7. Input date set value as date (non-UTC time zone)
+        testPart(() => {
+            const originalTimeZone = internals.setTimeZone('America/New_York');
+
+            const input = document.createElement('input');
+            input.type = 'date';
+            input.valueAsDate = new Date(0);
+            const result = input.value;
+
+            internals.setTimeZone(originalTimeZone);
+            return result;
+        });
+
+        // 8. Input date set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'date';
@@ -68,7 +81,20 @@
             return input.value;
         });
 
-        // 8. Input date invalid set value as date
+        // 9. Input date set value as date (non-UTC time zone)
+        testPart(() => {
+            const originalTimeZone = internals.setTimeZone('Europe/Paris');
+
+            const input = document.createElement('input');
+            input.type = "date";
+            input.valueAsDate = new Date(1702320457860);
+            const result = input.value;
+
+            internals.setTimeZone(originalTimeZone);
+            return result;
+        });
+
+        // 10. Input date invalid set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'date';
@@ -76,7 +102,7 @@
             return input.value;
         });
 
-        // 9. Input date null set value as date
+        // 11. Input date null set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'date';
@@ -84,7 +110,7 @@
             return input.value;
         });
 
-        // 10. Input time set value as date
+        // 12. Input time set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'time';
@@ -92,7 +118,7 @@
             return input.value;
         });
 
-        // 11. Input time set value as date
+        // 13. Input time set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'time';
@@ -100,7 +126,7 @@
             return input.value;
         });
 
-        // 12. Input time set value as date
+        // 14. Input time set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'time';
@@ -108,7 +134,7 @@
             return input.value;
         });
 
-        // 13. Input time invalid set value as date
+        // 15. Input time invalid set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'time';
@@ -116,7 +142,7 @@
             return input.value;
         });
 
-        // 14. Input time null set value as date
+        // 16. Input time null set value as date
         testPart(() => {
             const input = document.createElement('input');
             input.type = 'time';