Possible fix for issue #3337

src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php

@@ -1231,7 +1231,7 @@ private function writeCellFormula(XMLWriter $objWriter, string $cellValue, Cell
             $objWriter->writeAttribute('ref', $cell->getCoordinate());
             $objWriter->writeAttribute('aca', '1');
             $objWriter->writeAttribute('ca', '1');
-            $objWriter->text(substr($cellValue, 1));
+            $objWriter->text(FunctionPrefix::addFunctionPrefixStripEquals($cellValue));
             $objWriter->endElement();
         } else {
             $objWriter->writeElement('f', FunctionPrefix::addFunctionPrefixStripEquals($cellValue));

tests/PhpSpreadsheetTests/Writer/Xlsx/ArrayFormulaPrefixTest.php

@@ -0,0 +1,88 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\Cell\DataType;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
+use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
+
+class ArrayFormulaPrefixTest extends AbstractFunctional
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+    }
+
+    /**
+     * Test to ensure that xlfn prefix is being added to functions
+     * included in an array formula, if appropriate.
+     *
+     * @throws \PhpOffice\PhpSpreadsheet\Exception
+     */
+    public function testWriteArrayFormulaTextJoin(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $worksheet = $spreadsheet->getActiveSheet();
+
+        //Write data
+        $worksheet->getCell('A1')->setValue('Some Text');
+        $worksheet->getCell('A2')->setValue('Some More Text');
+        $worksheet->getCell('A3')->setValue(14.56);
+        $worksheet->getCell('A4')->setValue(17.24);
+        $worksheet->getCell('A5')->setValue(9.4);
+        $worksheet->getCell('A6')->setValue(5);
+
+        //Write formula
+        $cell = $worksheet->getCell('A7');
+        $cell->setValueExplicit('=TEXTJOIN("",TRUE,IF(ISNUMBER(A1:A6), A1:A6,""))', DataType::TYPE_FORMULA);
+        $attrs = $cell->getFormulaAttributes();
+        $attrs['t'] = 'array';
+        $cell->setFormulaAttributes($attrs);
+
+        $writer = new Xlsx($spreadsheet);
+        $writerWorksheet = new Xlsx\Worksheet($writer);
+        $data = $writerWorksheet->writeWorksheet($worksheet, []);
+
+        $expected = <<<XML
+            <f t="array" ref="A7" aca="1" ca="1">_xlfn.TEXTJOIN(&quot;&quot;,TRUE,IF(ISNUMBER(A1:A6), A1:A6,&quot;&quot;))</f>
+            XML;
+        self::assertStringContainsString($expected, $data);
+    }
+
+    /**
+     * Certain functions do not have the xlfn prefix applied.  Test an array formula
+     * that includes those functions to see if they are written properly.
+     *
+     * @throws \PhpOffice\PhpSpreadsheet\Exception
+     */
+    public function testWriteArrayFormulaWithoutPrefix(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $worksheet = $spreadsheet->getActiveSheet();
+
+        //Write data
+        $worksheet->getCell('A1')->setValue('orange');
+        $worksheet->getCell('A2')->setValue('green');
+        $worksheet->getCell('A3')->setValue('blue');
+        $worksheet->getCell('A4')->setValue('yellow');
+        $worksheet->getCell('A5')->setValue('pink');
+        $worksheet->getCell('A6')->setValue('red');
+
+        //Write formula
+        $cell = $worksheet->getCell('A7');
+        $cell->setValueExplicit('=SUM(LEN(A1:A6))', DataType::TYPE_FORMULA);
+        $attrs = $cell->getFormulaAttributes();
+        $attrs['t'] = 'array';
+        $cell->setFormulaAttributes($attrs);
+
+        $writer = new Xlsx($spreadsheet);
+        $writerWorksheet = new Xlsx\Worksheet($writer);
+        $data = $writerWorksheet->writeWorksheet($worksheet, []);
+
+        $expected = <<<XML
+            <f t="array" ref="A7" aca="1" ca="1">SUM(LEN(A1:A6))</f>
+            XML;
+        self::assertStringContainsString($expected, $data);
+    }
+}