Add excel shorthand for Excel-friendly UTF-8 exports.

Microsoft Excel on Windows does not recognise a UTF-8 CSV unless
it has a byte-order mark, CRLF line endings, and an explicit
UTF-8 declaration. Users have had to remember and set all three
options individually each time. This is a recurring source of
"opens as mojibake" reports.

Add a single `excel` config key (default false). When enabled, the
view forces `bom => true`, `eol => "\r\n"`, and `csvEncoding =>
'UTF-8'` at serialize time. The preset wins for those three keys;
other CSV options (delimiter, enclosure, header, extract,
setSeparator, etc.) are independent and behave normally.

The preset runs in `_serialize()` rather than `initialize()` so
it takes effect regardless of when `excel` is set, including the
common test pattern of constructing the view and then calling
`setConfig()`.

README documents the new option under a new "Excel-friendly
UTF-8 export" heading in the Usage section.

Author: dereuromark

README.md

@@ -263,6 +263,36 @@ The currently supported encoding extensions are as follows:
 - `iconv`
 - `mbstring`
 
+#### Excel-friendly UTF-8 export
+
+Microsoft Excel on Windows does not recognise a UTF-8 CSV unless it has a
+byte-order mark, CRLF line endings, and an explicit UTF-8 declaration. Setting
+all three options individually each time is repetitive and easy to get wrong.
+
+The `excel` shorthand sets the right defaults in one go:
+
+```php
+$this->viewBuilder()
+    ->setClassName('CsvView.Csv')
+    ->setOptions([
+        'serialize' => 'data',
+        'excel' => true,
+    ]);
+```
+
+`excel => true` is equivalent to:
+
+```php
+'bom' => true,
+'eol' => "\r\n",
+'csvEncoding' => 'UTF-8',
+```
+
+The shorthand always wins for the three keys it controls; if you need a
+different combination (e.g. UTF-16, no BOM) do not enable `excel` and set the
+individual keys yourself instead. Other CSV options (`delimiter`, `enclosure`,
+`setSeparator`, `header`, `extract`, etc.) are independent and behave normally.
+
 #### Setting the downloaded file name
 
 By default, the downloaded file will be named after the last segment of the URL

src/View/CsvView.php

@@ -144,6 +144,10 @@ class CsvView extends SerializedView
      * - 'csvEncoding': (default 'UTF-8') CSV file encoding
      * - 'dataEncoding': (default 'UTF-8') Encoding of data to be serialized
      * - 'transcodingExtension': (default 'iconv') PHP extension to use for character encoding conversion
+     * - 'excel': (default false)  Shorthand for an Excel-friendly UTF-8 export.
+     *     When true, sets `bom => true`, `eol => "\r\n"`, and `csvEncoding => 'UTF-8'`.
+     *     These specific keys are forced; if you need a different combination
+     *     do not enable `excel` and set them individually instead.
      *
      * @var array<string, mixed>
      */
@@ -163,6 +167,7 @@ class CsvView extends SerializedView
         'csvEncoding' => 'UTF-8',
         'dataEncoding' => 'UTF-8',
         'transcodingExtension' => self::EXTENSION_ICONV,
+        'excel' => false,
     ];
 
     /**
@@ -210,6 +215,7 @@ public static function contentType(): string
     protected function _serialize(array|string $serialize): string
     {
         $this->resetState();
+        $this->_applyExcelPreset();
 
         $this->_renderRow($this->getConfig('header'));
         $this->_renderContent();
@@ -246,6 +252,29 @@ public function __destruct()
         }
     }
 
+    /**
+     * Apply the `excel` shorthand if enabled: BOM + CRLF EOL + UTF-8 encoding,
+     * the three options Excel needs to open a UTF-8 CSV correctly on Windows.
+     *
+     * Applied at serialize-time (rather than `initialize()`) so the preset
+     * takes effect regardless of when `excel` is set — including the test
+     * pattern of constructing the view and then calling `setConfig()`.
+     *
+     * @return void
+     */
+    protected function _applyExcelPreset(): void
+    {
+        if (!$this->getConfig('excel')) {
+            return;
+        }
+
+        $this->setConfig([
+            'bom' => true,
+            'eol' => "\r\n",
+            'csvEncoding' => 'UTF-8',
+        ]);
+    }
+
     /**
      * Renders the body of the data to the csv
      *

tests/TestCase/View/CsvViewTest.php

@@ -597,4 +597,48 @@ public function testRenderViaExtractArrayValueThrows()
             );
         }
     }
+
+    /**
+     * `excel => true` is a shorthand that forces the three options Excel
+     * needs to open a UTF-8 CSV correctly on Windows: BOM, CRLF line
+     * endings, and UTF-8 encoding.
+     *
+     * @return void
+     */
+    public function testExcelPresetEmitsBomCrlfAndUtf8()
+    {
+        $data = [['Möhre', 'café'], ['ü', 'ß']];
+        $this->view->set(['data' => $data])
+            ->setConfig(['serialize' => 'data', 'excel' => true]);
+
+        $bom = chr(0xEF) . chr(0xBB) . chr(0xBF);
+        $expected = $bom . 'Möhre,café' . "\r\n" . 'ü,ß' . "\r\n";
+
+        $this->assertSame($expected, $this->view->render());
+    }
+
+    /**
+     * The Excel preset wins for the three keys it controls even when the
+     * user has explicitly set them to other values. `excel => true` is a
+     * single switch; for a different combination set the individual keys
+     * yourself instead of enabling the preset.
+     *
+     * @return void
+     */
+    public function testExcelPresetOverridesIndividualKeys()
+    {
+        $data = [['a', 'b']];
+        $this->view->set(['data' => $data])
+            ->setConfig([
+                'serialize' => 'data',
+                'excel' => true,
+                'bom' => false,
+                'eol' => "\n",
+            ]);
+
+        $output = $this->view->render();
+        $bom = chr(0xEF) . chr(0xBB) . chr(0xBF);
+        $this->assertStringStartsWith($bom, $output);
+        $this->assertStringEndsWith("\r\n", $output);
+    }
 }