How do I make the yaml indent not indent lists?

Question

OK so I would like to change the way that my yaml gets indented.

Right now my vim indents a yaml list like this:

list:
  - this
  - is
  - a list
dict:
  this: is a dict

I would like it to indent like this:

test:
- this
- is
- a list
dict:
  this: is a dict

Answer 1

Python module ruamel.yaml as equalprg

Installation of ruamel.yaml is possible with pip

$ pip install ruamel.yaml

ruamel.yaml is python3 compatible, i.e. pip3 install ruamel.yaml works as well. If you want to install it only in your home directory, use pip install --user ruamel.yaml.

Ensure that import ruamel.yaml works for the python version vim sees.

Configure equalprg of vim for yaml files with

augroup myequalprograms
  autocmd!
  autocmd FileType yaml setlocal equalprg=python\ -c\ \'import\ sys;\ from\ ruamel.yaml\ import\ YAML;yaml=YAML();yaml.dump(yaml.load(sys.stdin),sys.stdout)\'
augroup END

Alternatively, place following line in ~/.vim/after/ftplugin/yaml.vim

setlocal equalprg=python\ -c\ \'import\ sys;\ from\ ruamel.yaml\ import\ YAML;yaml=YAML();yaml.dump(yaml.load(sys.stdin),sys.stdout)\'

Now you should be able to press =ip for your example to get the desired output. I have tried it on my machine with python3 and it works.

---

• Note you could also use pyyaml with

  setlocal equalprg=python\ -c\ \'import\ yaml,sys;print(yaml.dump(yaml.safe_load(sys.stdin),default_flow_style=False))\'
  

  However, pyyaml changes order, removes comments and other things. ruamel.yaml explicitly tries to support the roundtrip of parsing and emitting without modifying these things.

• There is also the project pretty-yaml with a convenient command line interface

  $ python -m pyaml demo.yaml
  

  Note the unfortunate similarity of the name pyaml to pyyaml. The author has made the decision that lists should be indented and therefore does not help you:

  • List items get indented, as they should be.

• Finally, you could contact the maintainer of $VIMRUNTIME/indent/yaml.vim to ask him whether he would consider to add an option to achieve your style:

  " Vim indent file
  " Language:         YAML
  " Maintainer:       Nikolai Pavlov <zyx.vim@gmail.com>
  " Last Change:      2017 Jun 13
  

Answer 2

A solution that's more internal to vim, is to override indentexpr with a custom indent expression (most likely just overriding the builtin indentexpr for your specific instance).

The steps:

• define a filetype override, either in an autocmd (group) or in a ftplugin override (preferred).
• define a new (global, i.e. starting with a capital letter) function, say MyYamlIndent(lnum)
• Add logic that detects the dash led entries. The main workhorse is likely getline(v:lnum) andgetline(v:lnum-1). The goal:
• find the indent count (in spaces) for the previous line.
• check if the current line contains a dash, if not, return the default (GetYAMLIndent(v:lnum))
• If there is a leading dash, return the previous line's leading indent (in count of spaces)