The generate-theme command puts quotes around the 'base theme' YAML key in the generated theme's info.yml file, because it has spaces in it:
'base theme': stable9
Do
$ php core/scripts/drupal generate-theme my_theme
and inspect the generated code.
AFAIK from my work on Module Builder, this is caused by Symfony's YAML dumper component.
Active
11.0 🔥
Last updated
Yes, these single quotes are not needed, tested by removing these from the themes .info.yml file, these still work properly.
However, guidance is needed to determine the source of this addition.
Thank you.