\Magento\Framework\View\Model\Layout\Merge stores the theme at construct time

[ericmorand]

Preconditions (*)

Magento 2.3.5

Steps to reproduce (*)

1. Set a specific theme for a Product
2. Add a widget expected to be displayed on all the product pages using the specific theme above
3. Load the page of the Product that you set a specific theme at step 1

Expected result (*)

The specific theme is used and the widget is displayed.

Actual result (*)

The specific theme is used but the widget is not displayed.

Explanation

\Magento\Framework\View\Model\Layout\Merge stores the theme at construct time.

This creates a major issue with the rendering process, when one of the actor wants to change the theme - like for example the Magento_Catalog module. Since the theme is stored at construct time, would it be changed later, the Merge instance would always use the former theme stored at construct time to fetch layout updates.

The most spectacuar issues it creates is when trying to assign widgets for catalog layout handles (like catalog_product_view). Since the Merge instance always uses the default theme to fetch the layout updates, it never gets the chance to fetch the ones that are assigned to the widget if the theme of the product is not set to the default theme of the website. The only way for the widget to get grabbed is for it to be assigned to the default theme of the website, whatever the custom theme applied to the products.

Fortunately it should be easy to write a plugin that intercepts getTheme from the Merge instance to return the current theme instead of the one set at construct time.

---

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[m2-assistant]

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[ericmorand]

I confirm that a plugin solves the issue:

<?php

namespace {Vendor}\{Module}\Plugin\Framework\View\Model\Layout;

use Magento\Framework\View\DesignInterface;

class Merge
{
    /** @var DesignInterface */
    protected $_design;

    public function __construct(DesignInterface $design)
    {
        $this->_design = $design;
    }

    public function afterGetTheme(\Magento\Framework\View\Model\Layout\Merge $subject) {
        return $this->_design->getDesignTheme();
    }
}

[mrtuvn]

Hi
This class seem only have responsible to merge all xml files across code base (themes, magento core modules, 3rd-party modules) follow order in app/etc/config.php
base xml will always load first then follow by specific area (frontend, adminhtml) then follow modules . Current theme active will have load priority at last, parent will load first

[ericmorand]

It is also responsible to load handle updates stored in database - for example widgets set in the back office, through this function:

    public function getDbUpdateString($handle)
    {
        return null;
    }

This function is intercepted by a plugin (Magento\Widget\Model\ResourceModel\Layout\Plugin) to actually retrieve the widget updates from the database.

The issue here is that at that point, the theme has already been loaded by the Merge singleton , and thus when the updates are fetched from the database, they are fetched using the id of the theme that was loaded at construct time - i.e. the default theme of the website. Even if the theme is changed later, the DB updates for that theme won't be grabbed.

You end up with the following situation:

• You set a specific theme named "MyProductTheme" for the Product 123456
• You add a widget expected to be displayed on all the product pages using the theme "MyProductTheme"
• You load the product 123456 page, the "MyProductTheme" is used but the widget is not displayed

It is expected since when Merge singleton is created, it is created with the default theme of your website. The Catalog controller later set the custom theme of the Product 123456 but the theme used by Merge singleton to fetch the database updates will always be the default theme.

It's what my plugin above fixes. But it should be fixed in the core code base.

[mrtuvn]

Widget dynamic type such as (list, link..) only visible after clean cache. If after setup widget we don't clear cache widget will never show. Widget type block will show without need clean cache
Test in Open source 2.4.0 similar your case. But no use any customises (clean setup) No varnish setup only default magento cache

Interesting use case! So in your specific case widget will not show ? have try clear cache ? @ericmorand

[m2-assistant]

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[mrtuvn]

Maybe we should target on widget plugin ? Obviously that widget should get current theme instead singleton instance
CC: @ihor-sviziev maybe he know this

[engcom-Delta]

Hi @ericmorand thank you for your report.
If set Schedule Design Update->New Theme=Magento Luma for product and Design Package/Theme=Magento Luma for widget withType=Catalog Product List, widget is correctly displayed on product page

Could you clarify how you set specific theme for the Product ?

[mrtuvn]

@engcom-Delta Have you check the test case specific product set for schedule update theme luma and widget set for all product display at blank theme for example.? Expected result widget should not visible when we visit product

[mrtuvn]

This issue may can reproducible in latest codebase

[mrtuvn]

Reproducible case with luma theme setup with default sampledata

Pre-config
Setup theme config default for store => luma theme

Product named "Joust Duffle Bag"
1.Go to admin -> Change Schedule Design Update : New theme: Choose blank theme
2.Create widget show products list type for blank theme and display only in product detail for "Joust Duffle Bag"
2.1 Type: Catalog Products List
2.2 Design Package/Theme: Blank theme
2.3 Assign to Store Views: All Store Views
2.4 Layout Updates: All product types
Specific Products: choose "Joust Duffle Bag"
Contianer: Main Container Bottom
Widget options: Choose default to make sure all critieria meet and valid widget to show
3. Save widget
4. Clear cache
5. Go to homepage first (Verify theme luma applied) OK it's work fine
6. Go to frontend visit page product "Joust Duffle Bag". Theme blank applied ok and expect widget created previously should visible
7.After page loaded see results. Theme blank show but widget not visible

Actual
Widget not show (because magento still get theme luma default from initialized, Actually in the update layout theme applied use should be blank)
Theme blank applied (Correct display)

Expected
Widget should show and
Theme blank applied (Correct display)

cc: @engcom-Delta @engcom-Oscar

[mrtuvn]

Seem issue fixed in this commit 76ff97e#diff-d036d544db88cf91738bb3b56dbe89e156d4043e4cb7062af1eda9d20911d672R196 (lastest recently merged 2.4-develop)
Can you verify it again ? @ericmorand
Not sure this fix satisfied you or not (for your specific case)

[m2-assistant]

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[mrtuvn]

Hi @engcom-Echo can you help re-verify this case ?

[mrtuvn]

based on update from 2.4-develop as i mentioned previously above message

[mrtuvn]

#30656 (comment)
@ericmorand can you re-verify your use cases one more time ? At latest 2.4-develop branch. Or add new test case that you believe can reproduce problem