PHP Warning: Undefined array key "alt" in theme_icon()

[jenlampton]

Description of the bug

When running on_the_web module I'm seeing a handful of PHP warnings, one for each icon:

Warning: Undefined array key "alt" in theme_icon() (line 327 of /var/www/html/docroot/core/includes/icon.inc).

Line 327 is as follows:

if (isset($variables['alt']) {

The warning comes because in hook_theme() we are not specifying alt as an allowed value:

  'icon' => array(
      'variables' => array(
        'name' => NULL,
        'path' => NULL,
        'attributes' => array('class' => array()),
        'wrapper_attributes' => array('class' => array()),
      ),
    ),

But when you call the icon() function to display an icon, we are passing the alt in as though it should were defined in hook_theme():

    return theme('icon', array(
      'name' => $icon_name,
      'path' => $icon_path,
      'alt' => $options['alt'],
      'attributes' => $options['attributes'],
    ));

Steps To Reproduce

To reproduce the behavior:

1. Write some code that calls icon() to render one of the new core icons:

$svg_options = array(
    'alt' => 'alt-test',
    'attributes' => array('class' => array('test-class)),
  );
icon('envelope', $svg_options);

3. See the warning.

Actual behavior

Warning

Expected behavior

No warning

Additional information

Add any other information that could help, such as:

• Backdrop CMS version: 1.29.2
• Web server and its version:
• PHP version:
• Database sever (MySQL or MariaDB?) and its version:
• Operating System and its version:
• Browser(s) and their versions:

[jenlampton]

PR at backdrop/backdrop#4910.