Fix timezone issue when add/sub with overflow

src/Carbon/Traits/Cast.php

@@ -36,7 +36,8 @@ public function cast(string $className): mixed
     {
         if (!method_exists($className, 'instance')) {
             if (is_a($className, DateTimeInterface::class, true)) {
-                return new $className($this->rawFormat('Y-m-d H:i:s.u'), $this->getTimezone());
+                return $className::createFromFormat('U.u', $this->rawFormat('U.u'))
+                    ->setTimezone($this->getTimezone());
             }
 
             throw new InvalidCastException("$className has not the instance() method needed to cast the date.");

src/Carbon/Traits/Converter.php

@@ -475,7 +475,8 @@ public function toJSON(): ?string
      */
     public function toDateTime(): DateTime
     {
-        return new DateTime($this->rawFormat('Y-m-d H:i:s.u'), $this->getTimezone());
+        return DateTime::createFromFormat('U.u', $this->rawFormat('U.u'))
+            ->setTimezone($this->getTimezone());
     }
 
     /**
@@ -488,7 +489,8 @@ public function toDateTime(): DateTime
      */
     public function toDateTimeImmutable(): DateTimeImmutable
     {
-        return new DateTimeImmutable($this->rawFormat('Y-m-d H:i:s.u'), $this->getTimezone());
+        return DateTimeImmutable::createFromFormat('U.u', $this->rawFormat('U.u'))
+            ->setTimezone($this->getTimezone());
     }
 
     /**

src/Carbon/Traits/Creator.php

@@ -146,7 +146,8 @@ public static function instance(DateTimeInterface $date): static
             return clone $date;
         }
 
-        $instance = new static($date->format('Y-m-d H:i:s.u'), $date->getTimezone());
+        $instance = parent::createFromFormat('U.u', $date->format('U.u'))
+            ->setTimezone($date->getTimezone());
 
         if ($date instanceof CarbonInterface) {
             $settings = $date->getSettings();

src/Carbon/Traits/Date.php

@@ -1709,9 +1709,11 @@ public function setUnitNoOverflow(string $valueUnit, int $value, string $overflo
             $end = $original->avoidMutation()->endOf($overflowUnit);
 
             if ($date < $start) {
-                $date = $date->setDateTimeFrom($start);
-            } elseif ($date > $end) {
-                $date = $date->setDateTimeFrom($end);
+                return $date->mutateIfMutable($start);
+            }
+
+            if ($date > $end) {
+                return $date->mutateIfMutable($end);
             }
 
             return $date;
@@ -2953,4 +2955,18 @@ private static function floorZeroPad(int|float $value, int $length): string
     {
         return str_pad((string) floor($value), $length, '0', STR_PAD_LEFT);
     }
+
+    /**
+     * @template T of CarbonInterface
+     *
+     * @param T $date
+     *
+     * @return T
+     */
+    private function mutateIfMutable(CarbonInterface $date): CarbonInterface
+    {
+        return $this instanceof DateTimeImmutable
+            ? $this
+            : $this->modify('@'.$date->rawFormat('U.u'))->setTimezone($date->getTimezone());
+    }
 }

src/Carbon/Traits/IntervalStep.php

@@ -70,7 +70,7 @@ public function convertDate(DateTimeInterface $dateTime, bool $negated = false):
         if ($this->step) {
             $carbonDate = Callback::parameter($this->step, $carbonDate->avoidMutation());
 
-            return $carbonDate->setDateTimeFrom(($this->step)($carbonDate, $negated));
+            return $carbonDate->modify(($this->step)($carbonDate, $negated)->format('Y-m-d H:i:s.u e O'));
         }
 
         if ($negated) {

src/Carbon/Traits/Units.php

@@ -266,7 +266,7 @@ public function add($unit, $value = 1, ?bool $overflow = null): static
             $result = $this->resolveCarbon($unit($this, false));
 
             if ($this !== $result && $this->isMutable()) {
-                return $this->setDateTimeFrom($result);
+                return $this->modify($result->rawFormat('Y-m-d H:i:s.u e O'));
             }
 
             return $result;
@@ -415,7 +415,7 @@ public function sub($unit, $value = 1, ?bool $overflow = null): static
             $result = $this->resolveCarbon($unit($this, true));
 
             if ($this !== $result && $this->isMutable()) {
-                return $this->setDateTimeFrom($result);
+                return $this->modify($result->rawFormat('Y-m-d H:i:s.u e O'));
             }
 
             return $result;

tests/Carbon/ObjectsTest.php

@@ -84,6 +84,17 @@ public function testToDateTime()
         $this->assertNotInstanceOf(CarbonInterface::class, $date);
 
         $this->assertSame('2000-03-26', $date->format('Y-m-d'));
+
+        // Check it keeps timezone offset during DST
+        $date = Carbon::create(2290, 11, 2, 1, 10, 10 + 888480 / 1000000, 'America/Toronto');
+        $this->assertSame(
+            '2290-11-02 01:10:10.888480 America/Toronto -0400',
+            $date->toDateTime()->format('Y-m-d H:i:s.u e O'),
+        );
+        $this->assertSame(
+            '2290-11-02 01:10:10.888480 America/Toronto -0500',
+            $date->copy()->addHour()->toDateTime()->format('Y-m-d H:i:s.u e O'),
+        );
     }
 
     public function testToDateTimeImmutable()