Make TimeZoneRegion::utc() return a TimeZoneRegion not an TimeZoneOffset

src/Instant.php

@@ -333,6 +333,6 @@ public function jsonSerialize() : string
 
     public function __toString() : string
     {
-        return (string) ZonedDateTime::ofInstant($this, TimeZone::utc());
+        return (string) ZonedDateTime::ofInstant($this, TimeZoneOffset::utc());
     }
 }

src/LocalDateTime.php

@@ -723,7 +723,7 @@ public function isPast(TimeZone $timeZone, ?Clock $clock = null) : bool
      */
     public function toDateTime() : \DateTime
     {
-        return $this->atTimeZone(TimeZone::utc())->toDateTime();
+        return $this->atTimeZone(TimeZoneOffset::utc())->toDateTime();
     }
 
     /**

src/TimeZone.php

@@ -36,10 +36,7 @@ public static function parse(string $text) : TimeZone
         return TimeZoneRegion::parse($text);
     }
 
-    public static function utc() : TimeZoneOffset
-    {
-        return TimeZoneOffset::utc();
-    }
+    abstract public static function utc(): self;
 
     /**
      * Returns the unique time-zone ID.

src/TimeZoneRegion.php

@@ -57,6 +57,11 @@ public static function from(DateTimeParseResult $result) : TimeZoneRegion
         return TimeZoneRegion::of($region);
     }
 
+    public static function utc() : TimeZoneRegion
+    {
+        return TimeZoneRegion::of('UTC');
+    }
+
     /**
      * Returns all the available time-zone identifiers.
      *

tests/InstantTest.php

@@ -9,6 +9,7 @@
 use Brick\DateTime\Duration;
 use Brick\DateTime\Instant;
 use Brick\DateTime\TimeZone;
+use Brick\DateTime\TimeZoneOffset;
 
 /**
  * Unit tests for class Instant.
@@ -641,7 +642,7 @@ public function providerToString() : array
 
     public function testAtTimeZone(): void
     {
-        $timeZone = TimeZone::utc();
+        $timeZone = TimeZoneOffset::utc();
         $instant = Instant::of(1000000000);
         $result = $instant->atTimeZone($timeZone);
         $this->assertSame(1000000000, $result->getInstant()->getEpochSecond());

tests/TimeZoneOffsetTest.php

@@ -8,6 +8,7 @@
 use Brick\DateTime\Instant;
 use Brick\DateTime\Parser\DateTimeParseException;
 use Brick\DateTime\TimeZoneOffset;
+use Brick\DateTime\TimeZoneRegion;
 
 /**
  * Units tests for class TimeZoneOffset.

tests/TimeZoneRegionTest.php

@@ -168,4 +168,11 @@ public function testToString(): void
     {
         $this->assertSame('America/Los_Angeles', (string) TimeZoneRegion::of('America/Los_Angeles'));
     }
+
+    public function testUTC(): void
+    {
+        $utcTimeZoneRegion = TimeZoneRegion::utc();
+        $this->assertInstanceOf(TimeZoneRegion::class, $utcTimeZoneRegion);
+        $this->assertSame('UTC', $utcTimeZoneRegion->getId());
+    }
 }

tests/TimeZoneTest.php

@@ -61,13 +61,13 @@ public function providerParseInvalidStringThrowsException() : array
 
     public function testUtc(): void
     {
-        $this->assertTimeZoneOffsetIs(0, TimeZone::utc());
+        $this->assertTimeZoneOffsetIs(0, TimeZoneOffset::utc());
     }
 
     public function testIsEqualTo(): void
     {
-        $this->assertTrue(TimeZone::utc()->isEqualTo(TimeZoneOffset::ofTotalSeconds(0)));
-        $this->assertFalse(TimeZone::utc()->isEqualTo(TimeZoneOffset::ofTotalSeconds(3600)));
+        $this->assertTrue(TimeZoneOffset::utc()->isEqualTo(TimeZoneOffset::ofTotalSeconds(0)));
+        $this->assertFalse(TimeZoneOffset::utc()->isEqualTo(TimeZoneOffset::ofTotalSeconds(3600)));
     }
 
     /**