Handling of User-supplied Decimal and Thousands Separators

Fix #3900. The code to adjust Decimal and Thousands separators to user-specified choices expects to convert periods to commas and vice versa - hard-coded without taking the user specification into account. This is likely to be the only significant use case, however, as the issue demonstrates, it is not the only possibility. In particular, it will mess up Csv output if decimal separator is kept as period, but thousands separator is set to null string. The code is altered to replace period with the user-selected decimal separator, and comma with the user-selected thousands separator. No existing tests broke as a result of this change in behavior.

src/PhpSpreadsheet/Style/NumberFormat/BaseFormatter.php

@@ -17,7 +17,7 @@ abstract class BaseFormatter
         $thousandsSeparator = StringHelper::getThousandsSeparator();
         $decimalSeparator = StringHelper::getDecimalSeparator();
         if ($thousandsSeparator !== ',' || $decimalSeparator !== '.') {
-            $value = str_replace(['.', ',', "\u{fffd}"], ["\u{fffd}", '.', ','], $value);
+            $value = str_replace(['.', ',', "\u{fffd}"], ["\u{fffd}", $thousandsSeparator, $decimalSeparator], $value);
         }
 
         return $value;

tests/PhpSpreadsheetTests/Shared/StringHelperTest.php

@@ -5,6 +5,8 @@ declare(strict_types=1);
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Csv;
 use PHPUnit\Framework\TestCase;
 
 class StringHelperTest extends TestCase
@@ -98,4 +100,24 @@ class StringHelperTest extends TestCase
 
         self::assertEquals($expectedResult, $result);
     }
+
+    public function testIssue3900(): void
+    {
+        StringHelper::setDecimalSeparator('.');
+        StringHelper::setThousandsSeparator('');
+
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->setCellValue('A1', 1.4);
+        $sheet->setCellValue('B1', 1004.5);
+        $sheet->setCellValue('C1', 1000000.5);
+
+        ob_start();
+        $ioWriter = new Csv($spreadsheet);
+        $ioWriter->setDelimiter(';');
+        $ioWriter->save('php://output');
+        $output = ob_get_clean();
+        $spreadsheet->disconnectWorksheets();
+        self::assertSame('"1.4";"1004.5";"1000000.5"' . PHP_EOL, $output);
+    }
 }