Bad indentation in list comprehension

[brand17]

Issue created from fantomas-online

Code

[ for x in [] do yield 1 ]

Result

[ for x in [] do
      yield 1 ]

Problem description

Getting two excessive spaces added before yield - there are six instead of four.

Extra information

• The formatted result breaks my code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.
• I would like a release if this problem is solved.

Options

Fantomas main branch at 1/8/2025

Default Fantomas configuration

[nojaf]

There are four spaces in regards to the for keyword.
I'm pretty sure this is a can of worms if we want to respect this from the opening [.
For your small example there is no problem, but for larger expressions I can imagine it can lead to indentation problems.

Are you interested to send a PR to investigate this?

[brand17]

@nojaf Sorry, I am not a professional developer. What does your last question mean?

Do you want me to investigate the scale of this problem? Not sure I can help with it because I just don't understand what should I do. But I actually had a large expression with two nested list comprehensions where such indents were a real trouble.

Or you want me to propose the changes to Fantomas source code? If so I think I can participate - I did similar things a couple of times in other open source projects.

[nojaf]

I cannot definitively say whether it is safe to preserve indentation relative to the [ for each expression. My assumption is that we currently do so to ensure formatted code remains valid.

A developer should investigate by changing the code and running the test suite to observe the effects; each test verifies whether the formatted code is still valid.

If this proves not to be a problem, we should raise the matter with the style-guide maintainers to determine whether the behavior can be formalized.

Do you want to do some digging?

[brand17]

ok, will do

[nojaf]

Thank you! Comprehensive documentation is available at https://fsprojects.github.io/fantomas/docs/contributors/Getting%20Started.html. Please do not hesitate to ask if you have any questions.