Infinite Inheritance for theme.xml Layout Updates

In his soon to be referenced widely Magento Infinite Theme Fallback Fix, Eric Wiese notes that layout update XML files added via theme.xml are ignored by the parent/child theme inheritance. An XML file added to a parent’s theme.xml will not be added automatically to the child theme’s layout.

Eric’s solution is a custom module that makes theme inheritance consider these files.

If installing a module isn’t a solution available to you, here’s another option. Just specify the file from the parent theme you’d like in the child’s theme.xml.

In Eric’s example his US theme’s theme.xml

<?xml version="1.0"?>
<theme>
    <parent>mycompany/corporate-base</parent>
    <layout>
        <updates>
            <us_default>
                <file>us/default.xml</file>
            </us_default>
        </updates>
    </layout>
</theme>

Could be changed to the following

<?xml version="1.0"?>
<theme>
    <parent>mycompany/corporate-base</parent>
    <layout>
        <updates>
            <us_default>
                <file>us/default.xml</file>
            </us_default>

            <corporate_base_default>
                <file>corporate-base/default.xml</file>
            </corporate_base_default>

        </updates>
    </layout>
</theme>

With this in place, his new theme would pickup the corporate-base updates. Notice we haven’t added corporate-base/default.xml to the US theme — all we’ve done is configure its name in theme.xml. The fallback system takes care of the rest.

If you’re curious why this works, my longer Magento 1.9 Infinite Theme Fallback article may be of interest.