Implement Temporal.PlainDateTime.prototype.toLocaleString

core/engine/src/builtins/temporal/plain_date_time/mod.rs

@@ -1456,10 +1456,25 @@ impl PlainDateTime {
     /// - [ECMAScript Temporal proposal][spec]
     /// - [MDN reference][mdn]
     ///
-    /// [spec]: https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype.with
-    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/PlainDateTime/with
-    fn to_locale_string(this: &JsValue, _args: &[JsValue], _: &mut Context) -> JsResult<JsValue> {
+    /// [spec]: https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype.tolocalestring
+    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/PlainDateTime/toLocaleString
+    fn to_locale_string(
+        this: &JsValue,
+        _args: &[JsValue],
+        _context: &mut Context,
+    ) -> JsResult<JsValue> {
         // TODO: Update for ECMA-402 compliance
+        // The spec requires integration with Intl.DateTimeFormat which is still in progress.
+        // For now, this returns the ISO string representation similar to toString().
+        // 
+        // Proper implementation should:
+        // 1. Create an Intl.DateTimeFormat with the provided locales and options
+        // 2. Convert PlainDateTime to a formattable datetime
+        // 3. Format using the DateTimeFormat
+        // 
+        // See: https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype.tolocalestring
+        // and https://tc39.es/ecma402/#sec-datetimeformat-objects
+
         let object = this.as_object();
         let dt = object
             .as_ref()
@@ -1468,6 +1483,8 @@ impl PlainDateTime {
                 JsNativeError::typ().with_message("the this object must be a PlainDateTime object.")
             })?;
 
+        // Temporary implementation until full ECMA-402 integration
+        // This matches the current behavior of ZonedDateTime.toLocaleString
         let ixdtf = dt
             .inner
             .to_ixdtf_string(ToStringRoundingOptions::default(), DisplayCalendar::Auto)?;

core/engine/src/builtins/temporal/plain_date_time/tests.rs

@@ -9,3 +9,41 @@ fn pdt_year_of_week_basic() {
         TestAction::assert_eq("pdt.yearOfWeek", 1976),
     ]);
 }
+
+#[test]
+fn pdt_to_locale_string_basic() {
+    run_test_actions([
+        TestAction::run(
+            "let pdt = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, 'iso8601')",
+        ),
+        // toLocaleString should return a string (currently falls back to ISO format)
+        TestAction::assert("typeof pdt.toLocaleString() === 'string'"),
+        // Should contain date and time components
+        TestAction::assert("pdt.toLocaleString().includes('1976')"),
+        TestAction::assert("pdt.toLocaleString().includes('11')"),
+        TestAction::assert("pdt.toLocaleString().includes('18')"),
+    ]);
+}
+
+#[test]
+fn pdt_to_locale_string_with_locales() {
+    run_test_actions([
+        TestAction::run(
+            "let pdt = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, 'iso8601')",
+        ),
+        // Should accept locales parameter (even if not fully implemented yet)
+        TestAction::assert("typeof pdt.toLocaleString('en-US') === 'string'"),
+        TestAction::assert("typeof pdt.toLocaleString(['en-US', 'fr-FR']) === 'string'"),
+    ]);
+}
+
+#[test]
+fn pdt_to_locale_string_with_options() {
+    run_test_actions([
+        TestAction::run(
+            "let pdt = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, 'iso8601')",
+        ),
+        // Should accept options parameter (even if not fully implemented yet)
+        TestAction::assert("typeof pdt.toLocaleString(undefined, {}) === 'string'"),
+    ]);
+}