Less compilation problems in Magento/backend theme

[hostep]

Description

This is similar issue as what was being reported in #23619
But this time it's for the Magento/backend theme.
The fact that there are errors in the less code might indicate that certain things aren't getting outputted in css properly. But without deeper research I can't confirm this yet.

Preconditions (*)

1. Magento 2.3-develop branch (or any older released version)
2. NodeJs (I'm using v8.16.0)
3. PHP 7.2

Steps to reproduce (*)

1. Setup a vanilla Magento installation
2. Run npm install less@3.9.0
3. Run rm -R var/view_preprocessed/* pub/static/*; bin/magento setup:static-content:deploy -f --theme=Magento/backend en_US
4. Run node_modules/.bin/lessc -l var/view_preprocessed/pub/static/adminhtml/Magento/backend/en_US/css/styles-old.less

Expected result (*)

1. Linting of the styles-old.less file shouldn't show any errors

Actual result (*)

1. Linting of the styles-old.less file shows the following errors:

extend ' .data-table tbody tr:nth-child(odd) td' has no matches
extend ' .grid-actions .export .label' has no matches
extend ' .grid-actions .export .action-' has no matches
extend ' .col-570' has no matches

[m2-assistant]

Hi @hostep. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• Summary of the issue
• Information on your environment
• Steps to reproduce
• Expected and actual results

Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento give me 2.3-develop instance - upcoming 2.3.x release

For more details, please, review the Magento Contributor Assistant documentation.

@hostep do you confirm that you were able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

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[m2-assistant]

Hi @engcom-Charlie. Thank you for working on this issue.
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[magento-engcom-team]

@engcom-Charlie Thank you for verifying the issue.

Unfortunately, not enough information was provided to acknowledge ticket. Please consider adding the following:

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[magento-engcom-team]

✅ Confirmed by @engcom-Charlie
Thank you for verifying the issue. Based on the provided information internal tickets MC-18940 were created

Issue Available: @engcom-Charlie, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.

[magento-engcom-team]

Hi @hostep. Thank you for your report.
The issue has been fixed in #28895 by @mrtuvn in 2.4-develop branch
Related commit(s):

• e715fdcea41e821441ff17ee360b352f91f3248a

The fix will be available with the upcoming 2.4.1 release.