Add range formatting to the ruby-lsp

[vinistock]

Range formatting is a request very similar to formatting, but it applies only to the selected range and not the entire document.

Currently, trying to format ranges with either RuboCop or SyntaxTree fails, because both believe they are always looking at whole files instead of ranges.

For RuboCop, this will be difficult to overcome, given that trying to format a range in the middle of the document will even add # frozen_string_literal comments.

However, we may be able to use SyntaxTree for this if we add the ability of informing the formatter about the current indentation (or nesting) level. In the current behaviour, the code inside the range will be considered as a whole file and everything is pushed to indentation level zero.

Documentation: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_rangeFormatting

[bsgreenb]

This would be big! Can't use formatOnSaveMode until this is introduced!

[choosen]

would it be easier for VSCode addon to send whole file to language server and then filter response linter errors for modified only lines ?

// I don't know how it works under the hood.

Overcommit + rubocop had option problem_on_unmodified_line: warn to skip others

[vinistock]

@choosen RuboCop has no API to get corrections for only a portion of the file. Filtering diagnostics for a section of the file is relatively straight forward, but that's unrelated to formatting. Since in formatting we only get the formatted string back, it would not be possible to know which corrections have to be excluded.

RuboCop would need an API that allows for partial formatting and cops would need to know if they are operating on the entire file or not.

For example, if you're auto-correcting only a section of a file, you don't want the # frozen_string_literal: true comment to be added. And you would like the indentation of that section to be considered as the starting point for all corrections, otherwise it would bring all code to zero indentation even when applying formatting in the middle of a class.

Consider this example, which is what would currently happen without a new API being introduced to RuboCop.

# Example: before formatting
# frozen_string_literal: true

class Foo
  def initialize
  end
end

# ----
# Example: after formatting
# frozen_string_literal: true

class Foo
# frozen_string_literal: true
def initialize
end
end

For reference, I added support for this to Syntax Tree, but it's easier because Syntax Tree is a pure formatter and doesn't perform linting like RuboCop does.

[choosen]

@vinistock use case of modifying # frozen_string_literal: true

is about sending par of the inspected file to rubocop.

I said that you send whole file , parse rubocop output and keep only modified lines.
then frozen string literal will not be a problem as it would be added on top of the file and will be ignored as you did not change file top (it will work only on new files)

Maybe some problems will be with whole function definition indentation, but also better to have partial rubocop rules setup of linter in terms of modification range than nothing or whole file ?

[vinistock]

My concern is whether that approach will be brittle or not and the performance of doing more work on top of the formatting (which is already not very fast).

Additionally, RuboCop allows for extensions (rubocop-performance, rubocop-rails, ...) and it's not clear to me that we can ensure all of the corrections will be only what's relevant for the selected range.

I put up #2657 to add the request implementation for Syntax Tree, which I added the bits needed for range formatting myself.

If you have an idea of how to make it work for RuboCop, then please propose a PR that will implement run_range_formatting in lib/ruby_lsp/requests/support/rubocop_formatter.rb.

Maybe some problems will be with whole function definition indentation, but also better to have partial rubocop rules setup of linter in terms of modification range than nothing or whole file ?

Based on my experience working on the Ruby LSP for over 2 years, I can tell you with confidence that if we format the files incorrectly people will be a lot more upset than if we simply don't provide the feature 😅. My concern is applying incorrect edits to the range, which I couldn't find a general solution for.