riju/doc/tutorial/formatter.md

Tutorial: add a code formatter

Not all languages have code formatters, but if they exist, we like to add them. You'll need to update the install recipe in your language's configuration to install the code formatter as well. Then add a format.run key with a shell command that will read a program on stdin and write the formatted version to stdout.

You'll also want to add a format.input key which is equivalent to the template code, but formatted incorrectly. This can be used to verify that the formatter is working as expected.

Here's an example:

install:
  apt:
    - black

template: |
  print("Hello, world!")  

format:
  run: |
    black -    
  input: |
    print('Hello, world!')