Hello I am new in developing in Magento, I have Magento CE. When I set the Front End development workflow to type client side less compilation shows me an error

Fatal error: Uncaught TypeError: Argument 4 passed to Magento\Developer \Model\View\Asset\PreProcessor\FrontendCompilation::processContent() must be an instance of Magento\Framework\View\Asset\File\FallbackContext, instance of Magento\Framework\View\Asset\File\Context given, called in C:\xampp\htdocs\magento\vendor\magento\module-developer\Model\View\Asset\PreProcessor\FrontendCompilation.php on line 90 and defined in C:\xampp\htdocs\magento\vendor\magento\module-developer\Model\View\Asset\PreProcessor\FrontendCompilation.php:107 Stack trace: #0 C:\xampp\htdocs\magento\vendor\magento\module-developer\Model\View\Asset\PreProcessor\FrontendCompilation.php(90): Magento\Developer\Model\View\Asset\PreProcessor\FrontendCompilation->processContent('e6a662994948b56...', '@import 'source...', '', Object(Magento\Framework\View\Asset\File\Context)) #1 C:\xampp\htdocs\magento\vendor\magento\module-developer\Model\View\Asset\PreProcessor\PreprocessorStrategy.php(74): Magento\Developer\Model\View\Asset\PreProcessor\FrontendCompilation-> in C:\xampp\htdocs\magento\vendor\magento\module-developer\Model\View\Asset\PreProcessor\FrontendCompilation.php on line 107

My mode is set it to developer mode. Any consideration for that?

  • did you try setup upgrade command?
    – Ashish Raj
    Commented Oct 18, 2018 at 8:56
  • yes I try it. It doesn't work !! Commented Oct 18, 2018 at 9:08
  • try after delete files from generated folder.
    – kunj
    Commented Oct 18, 2018 at 9:55

2 Answers 2


Just check if you have "CSS Settings" -> "Merge CSS Files" set to No, and then try switching to Client side

Use this command to set css minification to NO

php bin/magento config:set dev/css/merge_css_files 0

Thanks for this @s-adamson answer it saved many times.

  • 3
    If developer mode is crashing, then you can't reach these settings using the front end (the section is hidden in production mode) so you'll need to use the command line: php bin/magento config:set dev/css/merge_css_files 0
    – S Adamson
    Commented Aug 20, 2019 at 17:51
  • @SAdamson Thanks it saved Commented Nov 6, 2019 at 15:04

Remove the content of : var/view_preprocessed/

Remove the content of : pub/static/

run : php bin/magento cache:clean

run : php bin/magento setup:di:compile

run : php bin/magento setup:static-content:deploy -f

  • when I try php bin/magento setup:di:compile it shows The directory "C:/xampp/htdocs/magento/generated/code/Temando/Shipping/Model" cannot be deleted Warning!rmdir(C:/xampp/htdocs/magento/generated/code/Temando/Shipping/Model): Directory not empty Commented Oct 18, 2018 at 11:40
  • clean the content of generated/ then restart the steps
    – PЯINCƎ
    Commented Oct 18, 2018 at 13:12
  • Well, it works but I loose the front end and I see only a blank page. After that I try the setup:upgrade and it shows me again the same problem.. How I can restart magento ? It was a fresh install. Commented Oct 19, 2018 at 5:47
  • I don't know if there is some way to retart Magento, you need to remove your custom modules, theme. otherwise you reinstall a new Magento
    – PЯINCƎ
    Commented Oct 19, 2018 at 7:58
  • 1
    It 's seems so difficult to develop in magneto I do one change and crash for ever.. Commented Oct 19, 2018 at 9:27

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