The default Gedit text editor on GNOME has this bug. The alternatives, including Mousepad, don't have auto-completion and/or don't support visualising just trailing spaces in text (e.g., both Mousepad and Geany have all-or-nothing visualisation for whitespace, but not for trailing spaces only).
I'm looking for a (preferably native GTK3) text editor that has these two features (like Gedit) but I don't want to install "heavyweights" like Atom/Sublime, nor do I want to pull in a lot of extraneous dependencies, as when installing Kwrite or Kate in a non-Qt, mostly pure-GTK environment such as GNOME.
Is there any such editor?
I did find CodeEditor (spun off from Qt Creator) but it too doesn't seem to have general (plain text) auto-completion.