Hi,
Semantic speedbar provides a nice outline view for buffers parsed by
semantic. I've got it working for C, Elisp, Java, build files (Makefile,
Ant build.xml and Maven pom.xml), HTML, CSS, Latex and SQL. See screenshots
https://lifeofpenguin.blogspot.com/2021/04/gnu-emacs-as-lightweight-ide-outline.html

However, I had to make some non-trivial changes to get it working. So I'm
wondering if it ever worked for anyone. If you happen to use it for
anything other than browsing folders, can you help me test my changes and
let me know if anything is breaking? You can either use my fork or add
specific files in your setup.

Additional feature: You can press '-' on a leaf to collapse the parent.

Code https://gitlab.com/atamariya/emacs/tree/dev
Changed files:
lisp/cedet/semantic/sb.el
lisp/speedbar.el

Thanks,
Anand