outline-indent

The outline-indent.el Emacs package provides a minor mode that enables code
folding based on indentation levels.

The outline-indent.el package is a fast and reliable alternative to the
origami.el and yafolding.el packages. (origami.el and yafolding.el are no
longer maintained, slow, and known to have bugs that impact their reliability
and performance.)

In addition to code folding, outline-indent allows:
- Moving indented subtrees up and down,
- indent/unindent sections to adjust indentation levels,
- customizing the ellipsis,
- inserting a new line with the same indentation level as the current line,
- and other features.

The outline-indent.el package uses the built-in outline-minor-mode, which is
maintained by the Emacs developers and is less likely to be abandoned like
origami.el or yafolding.el. Since outline-indent.el is based on
outline-minor-mode, it's also much much faster than origami.el and
yafolding.el.

Installation from MELPA:
------------------------
(use-package outline-indent
  :commands outline-indent-minor-mode
  :custom
  (outline-indent-ellipsis " ▼"))

Activation:
-----------
Once installed, the minor mode can be activated using:
  (outline-indent-minor-mode)

Activation using a hook:
------------------------
The minor mode can also be automatically activated for a certain mode. For
example for Python and YAML:
  ;; Python
  (add-hook 'python-mode-hook #'outline-indent-minor-mode)
  (add-hook 'python-ts-mode-hook #'outline-indent-minor-mode)

  ;; YAML
  (add-hook 'yaml-mode-hook #'outline-indent-minor-mode)
  (add-hook 'yaml-ts-mode-hook #'outline-indent-minor-mode)

Links:
------
- More information about outline-indent (Frequently asked questions, usage...):
  https://github.com/jamescherti/outline-indent.el