Cannot use Catalog ImageBuilder for custom product image attribute

[erfanimani]

Preconditions

1. Magento 2.1.7

Steps to reproduce

1. Create product attribute with input type media image, and attribute code "side_image" for example
2. Create a new product, add a few images, and select the role of one of the images to be the "side_image"
3. In our template we want to show the side image (using the block \Magento\Catalog\Block\Product\View). Therefore we're adding the following code:

<?php /** @var $block \Magento\Catalog\Block\Product\View */ ?>
<?php
    $product = $block->getProduct();

    $image = $block->getImage(
        $product,
        'product_page_image_medium',
        ['type' => 'side_image']
    );
?>

<img src="<?php echo $image->getImageUrl() ?>" />

Expected result

1. Product side image shows up

Actual result

1. Product base image shows up

A stack exchange question related to this bug can be found here: https://magento.stackexchange.com/questions/102498/extending-the-complextype-named-imagetype-with-a-custom-image-type

Essentially, without having to specify the third parameter, one would expect to create new image types by adding them into the view.xml, like this:

    $image = $block->getImage(
        $product,
        'my_custom_image_id_with_custom_product_image_type'
    );

.. however, that's not possible given XSD validation, and hence devs are trying to overwrite the core XSD to simply add their own image types.

The problem here, however, is that the third parameter gets discarded along the way, and that definitely seems like a bug to me.

On top of that, the fact that it's not possible to add image types definitely seems like a design flaw, and maybe the XSD shouldn't be this strict.

[erfanimani]

Actually, I found out that attributes is for custom HTML attributes on the img tag, not for image processing. The problem still stands - there is actually no way we can add our own custom image types.

[koenner01]

Definitely a major flaw in the system. We are allowed to create image attributes but can't use them...

[koenner01]

There might be some hope in this commit 7fa3789 . It allows for the constructor to take in a path different from the default.

[koenner01]

Ok after experimenting with the commit I referenced in the previous post, I can confirm that it simplifies the whole need to plugin the system. After patching in the commit, you can set the argument directly in your di.xml now.

Example view.xml

<?xml version="1.0"?>
<view xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/view.xsd">
    <media>
        <images module="Magento_Catalog">
            <image id="fetch_my_new_fancy_type" type="some_fancy_new_image_type">
                <width>600</width>
                <height>600</height>
            </image>
        </images>
    </media>
</view>

Example di.xml

<type name="Magento\Framework\Config\SchemaLocator">
    <arguments>
        <argument name="realPath" xsi:type="string">urn:magento:module:Vendor_MyModule:etc/view.xsd</argument>
    </arguments>
</type>

This is still not the right fix for the problem.
If only the noNamespaceSchemaLocation file would be used correctly if we filled in our own view.xsd. That would solve all these workarounds..