After reinstalling Eclipse lately I was having trouble setting up a proper code formatting for tabs. Despite setting 'Preferences | General | Editors | Text Editor | Insert Spaces for Tabs' I still got tabs in my code. You can check that by enable 'Preferences | General | Editors | Text Editor | Show whitespace characters'. I really couldn't figure out why this happened and it was driving me nuts. It turns out that there is another setting in the code formatter options that overrides this setting. The Descent (D programming language plugin) default code formatter setting 'Preferences | D | Code style | Formatter | Indentation | General option | Tab policy' was set to 'tabs only'. It needs to be set to 'spaces only'.