Introduce line-breaks in multiline arguments

[IndrajeetPatil]

cf. tidyverse/style#209

styler::style_text("
list(
  x, y,
  c(
    a
  ), c(
    b
  )
)
")
#> list(
#>   x, y,
#>   c(
#>     a
#>   ),
#>   c(
#>     b
#>   )
#> )

^{Created on 2024-12-20 with reprex v2.1.1}

[IndrajeetPatil]

Wow, that's quite the slowdown. Need to figure out what's causing it once the scope is clear.

[IndrajeetPatil]

@lorenzwalthert Any thoughts?

I am blocked here without any further feedback from the team.

[lorenzwalthert]

Maybe we should talk about the abstract rule first. What is it exactly that we try to achieve?
As for the code, I just wanted to say that you can easily figure out if there are line-breaks in a nest by looking at the respective column. To figure out if there are line breaks hidden in one of the children, consier the is_multi_line column. That will save you a lot of computations I think.

Also important: in the example you gave, all line breaks should simply be removed if we had #247.

[IndrajeetPatil]

What is it exactly that we try to achieve?

This is where I need some clarity.

I am interpreting the discussion in tidyverse/style#209 to mean that the style guide recommends "one line per argument" rule.

Elsewhere, the style guide carves out an exception to put multiple arguments per line, but the intent of clubbing similar arguments is not something {styler} can understand:

Therefore, I opted to just always follow the stated rule and if users wish to retain multiple arguments per like, they will just have to add ignore directives.

[lorenzwalthert]

as it is evident from the test cases, enforcing one argument per line is quite a change to the current behaviour I'd discourage this, at least at this point. Also, sometimes you want more than one argument per line when named arguments are involved:

map(x, f
  y = 2
)

So I suggest to just focus on a small interesting scope first and then maybe extend it gradually. And in my view, a small improvement involves the focus of multi-line arguments and it is to enforce a line-break between two multi-line arguments using the is_multi_line argument.

c(
 c(
  'b'
 ), fun(
  f = 2
 )
)
# becomes 
c(
 c(
  'b'
 ), 
 fun(
  f = 2
 )
)

Or even slightly more rigid, each multi-line expression has to be on its own line:

c(
 a, c(
  'b'
 ), fun(
  f = 2
 )
)
# becomes 
c(
 a, 
 c(
  'b'
 ), 
 fun(
  f = 2
 )
)

Comments should probably be ignored in that logic, i.e. token after or before comma should be defined as in skip the comments. Do you want to adapt your PR to that effect? I can also tell you how I'd solve the puzzle in abstract terms first, but I don't want to take away the fun of figuring it out, so you can go ahead if you want.

[IndrajeetPatil]

@lorenzwalthert I am not sure how to fix the performance issues here, and I no longer have time to work on this, at least not in the forseeable future.

I can either close the PR, or let you take it over from here. Up to you.

[lorenzwalthert]

@IndrajeetPatil ok, let's leave it open. I might implement the above outlined solution at some point, God knows when 🤔

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 99b9681 is merged into main:

• ✔️cache_applying: 26.8ms -> 26.7ms [-2.43%, +2%]
• ❗🐌cache_recording: 404ms -> 957ms [+135.29%, +137.88%]
• ❗🐌without_cache: 949ms -> 2.28s [+138.55%, +141.47%]

Further explanation regarding interpretation and methodology can be found in the documentation.

[Copilot]

Pull Request Overview

This PR introduces automatic line-break formatting for multiline arguments in function calls, improving code readability when some arguments span multiple lines. The main implementation adds a new transformer function set_line_breaks_for_multiline_args that ensures consistent formatting by placing line breaks after commas when at least one argument is multiline.

Key changes:

• New transformer set_line_breaks_for_multiline_args that detects multiline arguments and adds appropriate line breaks
• Integration into the tidyverse style guide as a strict-mode transformer
• Test cases updated to reflect the new formatting behavior, including removal of FIXME comments that are now addressed
• Incidental typo fix changing prin(x) to print(x) across test files

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
R/rules-line-breaks.R	Implements new set_line_breaks_for_multiline_args transformer function that adds line breaks for function calls with multiline arguments
R/style-guides.R	Integrates the new transformer into tidyverse_style as a strict-mode line break manipulator
tests/testthat/test-transformers-drop.R	Adds the new transformer name to the expected list of line break transformers
tests/testthat/line_breaks_fun_call/named_arguments-*.R	Test cases demonstrating the new formatting behavior for function calls with mixed single-line and multiline arguments
tests/testthat/line_breaks_fun_call/unindent-out.R	Updated expected output showing proper line breaks after opening parentheses and commas when multiline arguments are present
tests/testthat/line_breaks_fun_call/token_dependent_complex_strict-out.R	Updated expected output for complex nested function calls with multiline arguments
tests/testthat/roxygen-examples-complete/*-out.R	Updated expected output for roxygen examples showing the new line-break formatting
tests/testthat/line_breaks_and_other/pipe-line-breaks-.R	Removes FIXME comments now addressed by the new formatting; shows proper line breaks for piped expressions as function arguments
tests/testthat/indention_multiple/overall-*.R	Updated to reflect new formatting and incidental typo fix (prin → print)
tests/testthat/scope-/scope_none-.R	Incidental typo fix changing prin(x) to print(x)
tests/testthat/cache-with-r-cache/mlflow-1-in.R	Updated expected formatting for multiline argument in paste function
styler.Rproj	ProjectId regenerated (auto-generated RStudio project setting)

---

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[Copilot]

The new function set_line_breaks_for_multiline_args lacks documentation. Consider adding a roxygen2 comment block explaining:

• The purpose of the function
• The logic/rules it implements
• Example input/output (similar to set_line_break_before_curly_opening at line 1)
• @keywords internal tag to match the pattern of other internal functions in this file

Suggested change

	#' Set line breaks for multiline function arguments
	#'
	#' Rule:
	#' If any argument in a function call is multiline, ensure a line break after the opening parenthesis
	#' and after each comma separating arguments. This improves readability for calls with complex or
	#' multiline arguments.
	#'
	#' Example:
	#' # Before:
	#' fun(arg1, arg2,
	#' long_expr +
	#' more_stuff, arg4)
	#'
	#' # After:
	#' fun(
	#' arg1,
	#' arg2,
	#' long_expr +
	#' more_stuff,
	#' arg4
	#' )
	#'
	#' @keywords internal