Extra generated cache images when a product is saved in admin

[miquelcoma]

When saving a product in admin, extra images are generated in pub/media/catalog/product/cache.

the sizes are coming from the view.xml file defined in the luma and blank themes in the vendor core folder.

Preconditions

1. A custom theme with a custom image sizes defined in the view.xml file.
2. Magento 2.1.7 C.E., in development or production mode.
3. Running in ngingx with php 7.0.

Steps to reproduce

1. Have a look at pub/media/catalog/product/cache
2. Go to admin
3. Go to Product -> Catalog -> select an article.
4. Save the product (is not necessary any modification)
5. Have a look again to the cache folder.

Expected result

1. In the cache image folder, only the image sizes defined in our custom theme view.xml file exists plus the sizes defined in magento backend theme view.xml file.

Actual result

1. In the images cache folder appears extra images that have no relation with our theme or magento backend theme etc/view.xml file.
2. Those extra sizes are coming from the view.xml file defined in the luma and blank themes in the vendor core folder.

How I can avoid those extra images generated in the cache folder?

[orlangur]

Looks like #3650 is related to me. Some workarounds are available in comments there.

[hostep]

This is more a duplicate of #8145, although being able to remove/disable a theme should probably also work around this issue.
There is also a closed PR which you can maybe turn into a module which should solve this problem (haven't tested this for a couple of months, so no idea if this is still relevant for the latest Magento version): #8142

[miquelcoma]

Thanks @orlangur and @hostep,

I have tested the proposed solution from @vrann and works fine!

I have created a temporary module (waiting for the next update of magento 2.x) that implements the fix without changing anything in the vendor core folder:

di.xml:

<preference for="Magento\Catalog\Model\Product\Image\Cache" type="VENDOR\MagentoFix\Model\Product\Image\Cache"/>

app\code\VENDOR\MagentoFix\Model\Product\Image\Cache.php:

With the contents of: @vrann fix

with the namespace changed to VENDOR.

[magento-engcom-team]

@miquelcoma, thank you for your report.
We've created internal ticket(s) MAGETWO-80436 to track progress on the issue.