[String] fix slicing in UnicodeString

Author: nicolas-grekas

Tests/AbstractAsciiTestCase.php

@@ -597,6 +597,37 @@ public static function provideSlice()
             ['awesome', 'Symfony is awesome', 11, 7],
             ['awesome', 'Symfony is awesome', -7, null],
             ['awe', 'Symfony is awesome', -7, -4],
+            ['S', 'Symfony is awesome', -42, 1],
+            ['', 'Symfony is awesome', 42, 1],
+            ['', 'Symfony is awesome', 0, -42],
+        ];
+    }
+
+    /**
+     * @dataProvider provideSplice
+     */
+    public function testSplice(string $expected, int $start, int $length = null)
+    {
+        $this->assertEquals(
+            static::createFromString($expected),
+            static::createFromString('Symfony is awesome')->splice('X', $start, $length)
+        );
+    }
+
+    public static function provideSplice()
+    {
+        return [
+            ['X is awesome', 0, 7],
+            ['SymfonyXis awesome', 7, 1],
+            ['Symfony X awesome', 8, 2],
+            ['Symfony X', 8, null],
+            ['Symfony isXawesome', 10, 1],
+            ['Symfony is X', 11, 7],
+            ['Symfony is X', -7, null],
+            ['Symfony is Xsome', -7, -4],
+            ['Xymfony is awesome', -42, 1],
+            ['Symfony is awesomeX', 42, 1],
+            ['XSymfony is awesome', 0, -42],
         ];
     }
 

UnicodeString.php

@@ -267,18 +267,22 @@ public function replaceMatches(string $fromRegexp, $to): AbstractString
     public function slice(int $start = 0, int $length = null): AbstractString
     {
         $str = clone $this;
-        try {
-            $str->string = (string) grapheme_substr($this->string, $start, $length ?? 2147483647);
-        } catch (\ValueError $e) {
-            $str->string = '';
+
+        if (\PHP_VERSION_ID < 80000 && 0 > $start && grapheme_strlen($this->string) < -$start) {
+            $start = 0;
         }
+        $str->string = (string) grapheme_substr($this->string, $start, $length ?? 2147483647);
 
         return $str;
     }
 
     public function splice(string $replacement, int $start = 0, int $length = null): AbstractString
     {
         $str = clone $this;
+
+        if (\PHP_VERSION_ID < 80000 && 0 > $start && grapheme_strlen($this->string) < -$start) {
+            $start = 0;
+        }
         $start = $start ? \strlen(grapheme_substr($this->string, 0, $start)) : 0;
         $length = $length ? \strlen(grapheme_substr($this->string, $start, $length ?? 2147483647)) : $length;
         $str->string = substr_replace($this->string, $replacement, $start, $length ?? 2147483647);