From 9b085ae35e44540aabf64eeb0e32793e2f92896e Mon Sep 17 00:00:00 2001
From: "Eloy Lafuente (stronk7)" <stronk7@moodle.org>
Date: Mon, 7 Feb 2022 15:48:42 +0100
Subject: [PATCH] MDL-72762 backup: Accept empty and whitespace-only UI labels.

This was causing problems when sections or activity names where
set to be empty or whitespace-only, with the PARAM_CLEANHTML
leading to exception.

Now they are supported and handled like &nbsp; (0xc2a0) to
allow the process to continue.

Added a few extra tests to confirm the behaviour.
---
 backup/upgrade.txt                            |  4 ++++
 backup/util/ui/backup_ui_setting.class.php    |  7 +++++-
 backup/util/ui/tests/base_setting_ui_test.php | 24 ++++++++++++-------
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/backup/upgrade.txt b/backup/upgrade.txt
index a07e0b4e2b5..d07cc39886b 100644
--- a/backup/upgrade.txt
+++ b/backup/upgrade.txt
@@ -1,6 +1,10 @@
 This files describes API changes in /backup/*,
 information provided here is intended especially for developers.
 
+=== 3.10.10 ===
+
+* Backup UI labels now accept empty/whitespace-only contents.
+
 === 3.10 ===
  * Local plugins can now hook into a backup and restore process of grade items by
    using define_grade_item_plugin_structure method (See MDL-69418).
diff --git a/backup/util/ui/backup_ui_setting.class.php b/backup/util/ui/backup_ui_setting.class.php
index da74cfec88e..d5f8287f01e 100644
--- a/backup/util/ui/backup_ui_setting.class.php
+++ b/backup/util/ui/backup_ui_setting.class.php
@@ -146,7 +146,12 @@ class base_setting_ui {
      * @throws base_setting_ui_exception when the label is not valid.
      * @param string $label
      */
-    public function set_label(string $label) :void {
+    public function set_label(string $label): void {
+        // Let's avoid empty/whitespace-only labels, so the html clean (that makes trim()) doesn't fail.
+        if (trim($label) === '') {
+            $label = '&nbsp;'; // Will be converted to non-breaking utf-8 char 0xc2a0 by PARAM_CLEANHTML.
+        }
+
         $label = clean_param($label, PARAM_CLEANHTML);
 
         if ($label === '') {
diff --git a/backup/util/ui/tests/base_setting_ui_test.php b/backup/util/ui/tests/base_setting_ui_test.php
index 6aa3da6c09b..61960023ca1 100644
--- a/backup/util/ui/tests/base_setting_ui_test.php
+++ b/backup/util/ui/tests/base_setting_ui_test.php
@@ -58,13 +58,21 @@ class base_setting_ui_test extends advanced_testcase {
         $bsui->set_label(123);
         $this->assertSame('123', $bsui->get_label());
 
-        // Should raise an exception when label is empty.
-        try {
-            $bsui->set_label('');
-            $this->assertTrue(false, 'base_setting_ui_exception');
-        } catch (Exception $exception) {
-            $this->assertTrue($exception instanceof base_setting_ui_exception);
-            $this->assertEquals($exception->errorcode, 'setting_invalid_ui_label');
-        }
+        // Should be converted to non-breaking space (U+00A0) when label is empty.
+        $bsui->set_label('');
+        $this->assertSame("\u{00A0}", $bsui->get_label());
+
+        // Should be converted to non-breaking space (U+00A0) when the trimmed label is empty.
+        $bsui->set_label("  \t\t\n\n\t\t  ");
+        $this->assertSame("\u{00A0}", $bsui->get_label());
+
+        // Should clean partially the wrong bits.
+        $bsui->set_label('<b onmouseover=alert("test")>label</b>');
+        $this->assertSame('<b>label</b>', $bsui->get_label());
+
+        // Should raise an exception when cleaning ends with 100% empty.
+        $this->expectException(base_setting_ui_exception::class);
+        $this->expectExceptionMessage('error/setting_invalid_ui_label');
+        $bsui->set_label('<script>alert("test")</script>');
     }
 }