From 5f01161095c4e6fefa702f1da64bca6698a19d10 Mon Sep 17 00:00:00 2001
From: Tim Hunt <T.J.Hunt@open.ac.uk>
Date: Fri, 12 Apr 2024 12:08:05 +0100
Subject: [PATCH] MDL-82308 forms: set a nice default size for multi-selects

This is a backport of MDL-81515.
---
 lib/form/select.php            |  7 +++
 lib/form/tests/select_test.php | 79 ++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 lib/form/tests/select_test.php

diff --git a/lib/form/select.php b/lib/form/select.php
index 7195401151d..b4e0bd8ab2b 100644
--- a/lib/form/select.php
+++ b/lib/form/select.php
@@ -198,6 +198,13 @@ class MoodleQuickForm_select extends HTML_QuickForm_select implements templatabl
     }
 
     public function export_for_template(renderer_base $output) {
+        // For multi-selects, if there is not already a size set, then set a sensible default.
+        if ($this->getMultiple()) {
+            if (!isset($this->_attributes['size'])) {
+                $this->_attributes['size'] = min(count($this->_options), 10);
+            }
+        }
+
         $context = $this->export_for_template_base($output);
 
         $options = [];
diff --git a/lib/form/tests/select_test.php b/lib/form/tests/select_test.php
new file mode 100644
index 00000000000..c12df378fce
--- /dev/null
+++ b/lib/form/tests/select_test.php
@@ -0,0 +1,79 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+namespace core_form;
+
+use MoodleQuickForm_select;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/form/select.php');
+
+/**
+ * Unit tests for MoodleQuickForm_select
+ *
+ * @package   core_form
+ * @category  test
+ * @copyright 2024 the Open University
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @covers    \MoodleQuickForm_select
+ */
+final class select_test extends \advanced_testcase {
+
+    /**
+     * Testcase to check generated timestamp
+     */
+    public function test_multi_select_uses_sensible_default_size(): void {
+        global $OUTPUT;
+
+        // With fewer than 10 choices, default the size to that number (3 here).
+        $element = new MoodleQuickForm_select('testel', 'Label',
+            ['Choice 1', 'Choice 2', 'Choice 3'], ['id' => 'testel_id', 'multiple' => true]);
+
+        $html = $OUTPUT->mform_element($element, false, false, '', false);
+        $this->assertStringContainsString(' size="3"', $html);
+        $this->assertEquals(3, $element->_attributes['size']);
+
+        // With more than 10 choices, set to size 10.
+        $element = new MoodleQuickForm_select('testel', 'Label', [
+                'Choice 1', 'Choice 2', 'Choice 3',
+                'Choice 4', 'Choice 5', 'Choice 6',
+                'Choice 7', 'Choice 8', 'Choice 9',
+                'Choice 10', 'Choice 11', 'Choice 12',
+            ], ['id' => 'testel_id', 'multiple' => true]);
+
+        $html = $OUTPUT->mform_element($element, false, false, '', false);
+        $this->assertStringContainsString(' size="10"', $html);
+        $this->assertEquals(10, $element->_attributes['size']);
+
+        // If a size is already set, don't change in.
+        $element = new MoodleQuickForm_select('testel', 'Label',
+            ['Choice 1', 'Choice 2', 'Choice 3'], ['id' => 'testel_id', 'multiple' => true, 'size' => 7]);
+
+        $html = $OUTPUT->mform_element($element, false, false, '', false);
+        $this->assertStringContainsString(' size="7"', $html);
+        $this->assertEquals(7, $element->_attributes['size']);
+
+        // Don't set a size for single selects.
+        $element = new MoodleQuickForm_select('testel', 'Label',
+            ['Choice 1', 'Choice 2', 'Choice 3'], ['id' => 'testel_id']);
+
+        $html = $OUTPUT->mform_element($element, false, false, '', false);
+        $this->assertStringNotContainsString('size', $html);
+        $this->assertArrayNotHasKey('size', $element->_attributes);
+    }
+}