Merge branch '6.1' into 6.2

* 6.1:
  [Mime] Fix TextPart broken after being serialized
  [String] CamelCase/SnakeCase on uppercase word

Author: fabpot

AbstractUnicodeString.php

@@ -159,7 +159,7 @@ public function ascii(array $rules = []): self
     public function camel(): static
     {
         $str = clone $this;
-        $str->string = str_replace(' ', '', preg_replace_callback('/\b./u', static function ($m) use (&$i) {
+        $str->string = str_replace(' ', '', preg_replace_callback('/\b.(?![A-Z]{2,})/u', static function ($m) use (&$i) {
             return 1 === ++$i ? ('İ' === $m[0] ? 'i̇' : mb_strtolower($m[0], 'UTF-8')) : mb_convert_case($m[0], \MB_CASE_TITLE, 'UTF-8');
         }, preg_replace('/[^\pL0-9]++/u', ' ', $this->string)));
 

ByteString.php

@@ -103,7 +103,10 @@ public function append(string ...$suffix): static
     public function camel(): static
     {
         $str = clone $this;
-        $str->string = lcfirst(str_replace(' ', '', ucwords(preg_replace('/[^a-zA-Z0-9\x7f-\xff]++/', ' ', $this->string))));
+
+        $parts = explode(' ', trim(ucwords(preg_replace('/[^a-zA-Z0-9\x7f-\xff]++/', ' ', $this->string))));
+        $parts[0] = 1 !== \strlen($parts[0]) && ctype_upper($parts[0]) ? $parts[0] : lcfirst($parts[0]);
+        $str->string = implode('', $parts);
 
         return $str;
     }

Tests/AbstractAsciiTestCase.php

@@ -1042,11 +1042,13 @@ public static function provideCamel()
         return [
             ['', ''],
             ['xY', 'x_y'],
+            ['xuYo', 'xu_yo'],
             ['symfonyIsGreat', 'symfony_is_great'],
             ['symfony5IsGreat', 'symfony_5_is_great'],
             ['symfonyIsGreat', 'Symfony is great'],
             ['symfonyIsAGreatFramework', 'Symfony is a great framework'],
             ['symfonyIsGREAT', '*Symfony* is GREAT!!'],
+            ['SYMFONY', 'SYMFONY'],
         ];
     }
 
@@ -1066,13 +1068,15 @@ public static function provideSnake()
             ['', ''],
             ['x_y', 'x_y'],
             ['x_y', 'X_Y'],
+            ['xu_yo', 'xu_yo'],
             ['symfony_is_great', 'symfonyIsGreat'],
             ['symfony5_is_great', 'symfony5IsGreat'],
             ['symfony5is_great', 'symfony5isGreat'],
             ['symfony_is_great', 'Symfony is great'],
             ['symfony_is_a_great_framework', 'symfonyIsAGreatFramework'],
             ['symfony_is_great', 'symfonyIsGREAT'],
             ['symfony_is_really_great', 'symfonyIsREALLYGreat'],
+            ['symfony', 'SYMFONY'],
         ];
     }