Issue #3489538 by mondrake, daffie, alexpott:...

Issue #3489538 by mondrake, daffie, alexpott: StatementPrefetchIterator::fetchField fails silently if the column index is out of range

core/lib/Drupal/Core/Database/FetchModeTrait.php

@@ -99,11 +99,17 @@ protected function assocToClass(array $rowAssoc, string $className, array $const
    * @param int $columnIndex
    *   The index of the column to fetch the value of.
    *
-   * @return string|false
-   *   The value of the column, or FALSE if the column is not defined.
+   * @return string
+   *   The value of the column.
+   *
+   * @throws \ValueError
+   *   If the column index is not defined.
    */
   protected function assocToColumn(array $rowAssoc, array $columnNames, int $columnIndex): mixed {
-    return $rowAssoc[$columnNames[$columnIndex]] ?? FALSE;
+    if (!isset($columnNames[$columnIndex])) {
+      throw new \ValueError('Invalid column index');
+    }
+    return $rowAssoc[$columnNames[$columnIndex]];
   }
 
 }

core/lib/Drupal/Core/Database/StatementInterface.php

@@ -108,6 +108,9 @@ public function fetch($mode = NULL, $cursor_orientation = NULL, $cursor_offset =
    *
    * @return mixed
    *   A single field from the next record, or FALSE if there is no next record.
+   *
+   * @throws \ValueError
+   *   If there is a record and the column index is not defined.
    */
   public function fetchField($index = 0);
 

core/lib/Drupal/Core/Database/StatementPrefetchIterator.php

@@ -260,7 +260,7 @@ public function fetch($fetch_style = NULL, $cursor_orientation = \PDO::FETCH_ORI
    */
   public function fetchColumn($index = 0) {
     if ($row = $this->fetch(\PDO::FETCH_ASSOC)) {
-      return $row[$this->columnNames[$index]];
+      return $this->assocToColumn($row, $this->columnNames, $index);
     }
     return FALSE;
   }

core/tests/Drupal/KernelTests/Core/Database/FetchTest.php

@@ -230,6 +230,69 @@ public function testQueryFetchField(): void {
     $this->assertSame($expectedResults, $actualResults);
   }
 
+  /**
+   * Tests ::fetchField() for edge values returned.
+   */
+  public function testQueryFetchFieldEdgeCases(): void {
+    $this->connection->insert('test_null')
+      ->fields([
+        'name' => 'Foo',
+        'age' => 0,
+      ])
+      ->execute();
+
+    $this->connection->insert('test_null')
+      ->fields([
+        'name' => 'Bar',
+        'age' => NULL,
+      ])
+      ->execute();
+
+    $this->connection->insert('test_null')
+      ->fields([
+        'name' => 'Qux',
+        'age' => (int) FALSE,
+      ])
+      ->execute();
+
+    $statement = $this->connection->select('test_null')
+      ->fields('test_null', ['age'])
+      ->orderBy('id')
+      ->execute();
+
+    // First fetch returns '0' since an existing value is always a string.
+    $this->assertSame('0', $statement->fetchField());
+
+    // Second fetch returns NULL since NULL was inserted.
+    $this->assertNull($statement->fetchField());
+
+    // Third fetch returns '0' since a FALSE bool cast to int was inserted.
+    $this->assertSame('0', $statement->fetchField());
+
+    // Fourth fetch returns FALSE since no row was available.
+    $this->assertFalse($statement->fetchField());
+  }
+
+  /**
+   * Confirms that an out of range index throws an error.
+   */
+  public function testQueryFetchFieldIndexOutOfRange(): void {
+    $this->expectException(\ValueError::class);
+    $this->expectExceptionMessage('Invalid column index');
+    $this->connection
+      ->query('SELECT [name] FROM {test} WHERE [age] = :age', [':age' => 25])
+      ->fetchField(200);
+  }
+
+  /**
+   * Confirms that empty result set prevails on out of range index.
+   */
+  public function testQueryFetchFieldIndexOutOfRangeOnEmptyResultSet(): void {
+    $this->assertFalse($this->connection
+      ->query('SELECT [name] FROM {test} WHERE [age] = :age', [':age' => 255])
+      ->fetchField(200));
+  }
+
   /**
    * Tests that rowCount() throws exception on SELECT query.
    */