Make string padding UTF-8 safe

The pad string could be truncated in the middle of a unicode code point.
This is now fixed.

Also updated unittest to test UTF-8 padding strings.

Author: martenkoetsier

src/Illuminate/Support/Str.php

@@ -608,7 +608,13 @@ public static function matchAll($pattern, $subject)
      */
     public static function padBoth($value, $length, $pad = ' ')
     {
-        return str_pad($value, strlen($value) - mb_strlen($value) + $length, $pad, STR_PAD_BOTH);
+        $short = max(0, $length - mb_strlen($value));
+        $short_left = floor($short / 2);
+        $short_right = ceil($short / 2);
+        return
+            mb_substr(str_repeat($pad, $short_left), 0, $short_left) .
+            $value .
+            mb_substr(str_repeat($pad, $short_right), 0, $short_right);
     }
 
     /**
@@ -621,7 +627,8 @@ public static function padBoth($value, $length, $pad = ' ')
      */
     public static function padLeft($value, $length, $pad = ' ')
     {
-        return str_pad($value, strlen($value) - mb_strlen($value) + $length, $pad, STR_PAD_LEFT);
+        $short = max(0, $length - mb_strlen($value));
+        return mb_substr(str_repeat($pad, $short), 0, $short) . $value;
     }
 
     /**
@@ -634,7 +641,8 @@ public static function padLeft($value, $length, $pad = ' ')
      */
     public static function padRight($value, $length, $pad = ' ')
     {
-        return str_pad($value, strlen($value) - mb_strlen($value) + $length, $pad, STR_PAD_RIGHT);
+        $short = max(0, $length - mb_strlen($value));
+        return $value . mb_substr(str_repeat($pad, $short), 0, $short);
     }
 
     /**

tests/Support/SupportStrTest.php

@@ -781,20 +781,23 @@ public function testPadBoth()
         $this->assertSame('__Alien___', Str::padBoth('Alien', 10, '_'));
         $this->assertSame('  Alien   ', Str::padBoth('Alien', 10));
         $this->assertSame('  ❤MultiByte☆   ', Str::padBoth('❤MultiByte☆', 16));
+        $this->assertSame('❤☆❤MultiByte☆❤☆❤', Str::padBoth('❤MultiByte☆', 16, '❤☆'));
     }
 
     public function testPadLeft()
     {
         $this->assertSame('-=-=-Alien', Str::padLeft('Alien', 10, '-='));
         $this->assertSame('     Alien', Str::padLeft('Alien', 10));
         $this->assertSame('     ❤MultiByte☆', Str::padLeft('❤MultiByte☆', 16));
+        $this->assertSame('❤☆❤☆❤❤MultiByte☆', Str::padLeft('❤MultiByte☆', 16, '❤☆'));
     }
 
     public function testPadRight()
     {
-        $this->assertSame('Alien-----', Str::padRight('Alien', 10, '-'));
+        $this->assertSame('Alien-=-=-', Str::padRight('Alien', 10, '-='));
         $this->assertSame('Alien     ', Str::padRight('Alien', 10));
         $this->assertSame('❤MultiByte☆     ', Str::padRight('❤MultiByte☆', 16));
+        $this->assertSame('❤MultiByte☆❤☆❤☆❤', Str::padRight('❤MultiByte☆', 16, '❤☆'));
     }
 
     public function testSwapKeywords(): void