After upgrading to Magento 1.9.3+ I get a 404 error when creating configurable product

Question

When I create a new configurable product this sometimes results in a 404 error after selecting the attributes to use for configuring the product and clicking Next. It doesn't always happen but only with certain attributes and / or attribute sets.

Note: Today I ran into this issue with a customer's installation of Magento 1.9.3.1 and after tracking it down I found out it's due to a change in Magento 1.9.3.0. I will answer this question myself to document the fix for future reference for others.

Answer 1

This is caused by a double URL encoding problem introduced in Magento 1.9.3.0. This update of Magento changed the following function in /js/mage/adminhtml/tools.js

function setLocation(url){
    window.location.href = url;
}

to

function setLocation(url){
    window.location.href = encodeURI(url);
}

Thus it now URI encodes the entire URL.

However, the /app/design/adminhtml/default/default/template/catalog/product/edit.phtml template for the product edit page already contains a (poor) implementation to encode the parameters. Because these parameters are base64 encoded it's not unlikely that a / or = ends up in the parameters. It seems a bit unnecessary as the values are just integers (ID's) but anyway.

The code is in the setSuperSettings function:

 function setSuperSettings(urlTemplate, attributesClass, validateField) {
    var attributesFields = $$('.' + attributesClass);
    var attributes = Form.serializeElements(attributesFields, true).attribute;
    if(typeof attributes == 'string') {
        attributes = [attributes];
    }

    if(!attributes) {
        $(validateField).value = 'no-attributes';
    } else {
        $(validateField).value = 'has-attributes';
    }

    if (productForm.validator.validate()) {
        var template = new Template(urlTemplate, productTemplateSyntax);
        var url = template.evaluate({
            attributes: encode_base64(attributes.join(',')).replace(new RegExp('/','g'),'%2F').replace(new RegExp('=','g'),'%3D')
        });
        setLocation(url);
    }
}

Specifically this line:

    attributes: encode_base64(attributes.join(',')).replace(new RegExp('/','g'),'%2F').replace(new RegExp('=','g'),'%3D')

The problem can be fixed by removing the last two replace functions. Thus resulting in:

        attributes: encode_base64(attributes.join(','))

You should now be able to create configurable products again for all attributes / attribute sets.