bug symfony#60975 [Form] Fix precision loss when rounding large integers in NumberToLocalizedStringTransformer (OskarStark)

This PR was merged into the 6.4 branch.

Discussion
----------

[Form] Fix precision loss when rounding large integers in `NumberToLocalizedStringTransformer`

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix symfony#60947
| License       | MIT

Commits
-------

bf312d3 Fix precision loss when rounding large integers in `NumberToLocalizedStringTransformer`

Author: nicolas-grekas

src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php

@@ -189,6 +189,10 @@ protected function castParsedValue(int|float $value): int|float
      */
     private function round(int|float $number): int|float
     {
+        if (\is_int($number)) {
+            return $number;
+        }
+
         if (null !== $this->scale && null !== $this->roundingMode) {
             // shift number to maintain the correct scale during rounding
             $roundingCoef = 10 ** $this->scale;

src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php

@@ -726,4 +726,33 @@ public static function eNotationProvider(): array
             [1232.0, '1.232e3'],
         ];
     }
+
+    public function testReverseTransformDoesNotCauseIntegerPrecisionLoss()
+    {
+        $transformer = new NumberToLocalizedStringTransformer();
+
+        // Test a large integer that causes actual precision loss when cast to float
+        $largeInt = \PHP_INT_MAX - 1; // This value loses precision when cast to float
+        $result = $transformer->reverseTransform((string) $largeInt);
+
+        $this->assertSame($largeInt, $result);
+        $this->assertIsInt($result);
+    }
+
+    public function testRoundMethodKeepsIntegersAsIntegers()
+    {
+        $transformer = new NumberToLocalizedStringTransformer(2); // scale=2 triggers rounding
+        
+        // Use reflection to test the private round() method directly
+        $reflection = new \ReflectionClass($transformer);
+        $roundMethod = $reflection->getMethod('round');
+        $roundMethod->setAccessible(true);
+        
+        $int = \PHP_INT_MAX - 1;
+        $result = $roundMethod->invoke($transformer, $int);
+        
+        // With the fix, integers should stay as integers, not be converted to floats
+        $this->assertSame($int, $result);
+        $this->assertIsInt($result);
+    }
 }