Less SourceMaps Path is not corret

[gizmocn]

Summary (*)

Grunt generate wrong less sourceMaps path, both Chrome and Firefox can not find sourceMaps files

Environment

OS: Ubuntu 18.04 with apache and php 7.1.x
Magento Version: 2.3.0

How to Reproduce

1. Download Magento 2.3.0 Open Source with Sample from Official Site.
2. Install it on local server.
3. Install and configure grunt according to https://devdocs.magento.com/guides/v2.3/frontend-dev-guide/css-topics/css_debug.html
4. Run: grunt clean, grunt exec, grunt less:luma.
5. Browser can not find less sourceMaps files.

It is very difficult to reproduce on on vanilla Magento instance, as the issue need a lot of CLI operations to install node.js, npm etc.

Examples (*)

Use Grunt to compile Less file, and Grunt add sourceMaps path is:
/*# sourceMappingURL=pub/static/frontend/Magento/luma/en_US/css/styles-l.css.map */
In order to let browser to find the sourceMpas file, it should be
/*# sourceMappingURL=styles-l.css.map */

Proposed solution

Try to change less.js but failed.

[magento-engcom-team]

Hi @gizmocn. 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-engcom-team give me 2.3-develop instance - upcoming 2.3.x release

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

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

• yes
• no

[gizmocn]

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

[magento-engcom-team]

Hi @gizmocn. Thank you for your request. I'm working on Magento 2.3-develop instance for you

[magento-engcom-team]

Hi @gizmocn, here is your Magento instance.
Admin access: https://i-20952-2-3-develop.instances.magento-community.engineering/admin
Login: admin Password: 123123q
Instance will be terminated in up to 3 hours.

[gizmocn]

I have tried vanilla Magento instance, but I have no idea about how to run CLI command on it, the issue need to install node.js npm and grunt etc.

[amol2jcommerce]

@magento-engcom-team give me 2.3-develop instance

[magento-engcom-team]

Hi @amol2jcommerce. Thank you for your request. I'm working on Magento 2.3-develop instance for you

[magento-engcom-team]

Hi @amol2jcommerce, here is your Magento instance.
Admin access: https://i-20952-2-3-develop.instances.magento-community.engineering/admin
Login: admin Password: 123123q
Instance will be terminated in up to 3 hours.

[magento-engcom-team]

Hi @engcom-backlog-nazar. Thank you for working on this issue.
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