Theory

Here are the steps required to deactivate a rule you don’t like

• Figure out which transformer function in the transformers returned by tidyerse_style() corresponds to the rule you want to remove.

• Set that element in the list to NULL, which is equivalent to removing it.

• Pass the list to style_text as a transformer.

Practice

Lets assume you want to remove the rule that turns = into <- for assignment. That means you want

string = "hi there" 

to remain unchanged after applying styler. This is not the case if you use the default style guide of styler:

library(styler)
style_text("string = 'hi there'")
string <- "hi there"

So you need to figure out which rule is responsible for this. Let’s check the transformer categories used with the tidyverse style guide.

transformers <- tidyverse_style()
names(transformers)
#>  [1] "initialize"             "line_break"             "space"                 
#>  [4] "token"                  "indention"              "use_raw_indention"     
#>  [7] "reindention"            "style_guide_name"       "style_guide_version"   
#> [10] "more_specs_style_guide" "transformers_drop"      "indent_character"

From the aforementioned vignette:

We note that there are different types of transformer functions. initialize initializes some variables in the nested parse table (so it is not actually a transformer), and the other elements modify either spacing, line breaks or tokens. use_raw_indention is not a function, it is just an option.

Now, we can look at the names of the rules that are sub-elements of the transformer categories.

library(magrittr)
levels <- c("space", "line_break", "indention", "token")
purrr::map(
  levels,
  ~ names(transformers[[.x]])
) %>%
  purrr::set_names(levels)
#> $space
#>  [1] "remove_space_before_closing_paren"  "remove_space_before_opening_paren" 
#>  [3] "add_space_after_for_if_while"       "remove_space_before_comma"         
#>  [5] "style_space_around_math_token"      "style_space_around_tilde"          
#>  [7] "spacing_around_op"                  "remove_space_after_opening_paren"  
#>  [9] "remove_space_after_excl"            "set_space_after_bang_bang"         
#> [11] "remove_space_before_dollar"         "remove_space_after_fun_dec"        
#> [13] "remove_space_around_colons"         "start_comments_with_space"         
#> [15] "remove_space_after_unary_pm_nested" "spacing_before_comments"           
#> [17] "set_space_between_levels"           "set_space_between_eq_sub_and_comma"
#> [19] "set_space_in_curly"                
#> 
#> $line_break
#>  [1] "remove_empty_lines_after_opening_and_before_closing_braces"
#>  [2] "set_line_break_around_comma_and_or"                        
#>  [3] "set_line_break_after_assignment"                           
#>  [4] "set_line_break_before_curly_opening"                       
#>  [5] "remove_line_break_before_round_closing_after_curly"        
#>  [6] "remove_line_breaks_in_fun_dec"                             
#>  [7] "style_line_break_around_curly"                             
#>  [8] "set_line_break_around_curly_curly"                         
#>  [9] "set_line_break_before_closing_call"                        
#> [10] "set_line_break_after_opening_if_call_is_multi_line"        
#> [11] "remove_line_break_in_fun_call"                             
#> [12] "add_line_break_after_pipe"                                 
#> [13] "set_line_break_after_ggplot2_plus"                         
#> 
#> $indention
#> [1] "indent_braces"                "unindent_fun_dec"            
#> [3] "indent_op"                    "indent_eq_sub"               
#> [5] "indent_without_paren"         "update_indention_ref_fun_dec"
#> 
#> $token
#> [1] "fix_quotes"                                    
#> [2] "force_assignment_op"                           
#> [3] "resolve_semicolon"                             
#> [4] "add_brackets_in_pipe"                          
#> [5] "wrap_if_else_while_for_fun_multi_line_in_curly"

Spotted the rule we want to get rid of? It’s under token and it’s called force_assignment_op. I agree, we could have chosen a better name. If you are not sure if you can guess from the name of the rule what it does you can also have a look at the function declaration of this (unexported) function.

styler:::force_assignment_op
#> function (pd) 
#> {
#>     to_replace <- pd$token == "EQ_ASSIGN"
#>     pd$token[to_replace] <- "LEFT_ASSIGN"
#>     pd$text[to_replace] <- "<-"
#>     pd
#> }
#> <bytecode: 0x558eeb74d7b0>
#> <environment: namespace:styler>

Next, you simply set that element to NULL.

transformers$token$force_assignment_op <- NULL

And you can use the modified transformer list as input to style_text()

style_text("string = 'hi there'", transformers = transformers)
#> string = "hi there"

If you want to use it the same way as tidyverse_style(), here’s the last step:

eq_assign_style <- function(...) {
  transformers <- tidyverse_style(...)
  transformers$token$force_assignment_op <- NULL
  transformers
}

style_text("string = 'hi there'", style = eq_assign_style)
#> string = "hi there"

That’s it. Note that the transformer functions and how they are returned by tidyverse_style() is not part of the exposed API. This means that the order, the naming etc. may change. Also, remember we did not add a rule to replace <- with =, but we only removed a rule to replace = with <-, so <- won’t be touched:

style_text("string <- 'hi there'", style = eq_assign_style)
#> string <- "hi there"

If you want to turn <- into =, you need to add a rule as described in vignette("customizing_styler").

If you have trouble identifying a rule based on rule names,

• First write an example whose results is not the one you wanted, e.g.

code <- "
f <- function () {

return (1)
}"

is code that will have the first empty line in the function body removed by styler.

• Then pinpoint the probable rule type (e.g. line breaks if you want less new lines).
• In a local styler clone, add e.g. a return(pd) at the top of the body to deactivate the rule quickly, or add a print(pd) or browser() call in the functions of that type (e.g. the different functions of R/rules-line-breaks.R), load_all(), run your example, see if that function made the change. move the print(pd) or browser() call to another function if not.
• Once you’ve identified the culprit (in this case style_line_break_around_curly), set it to NULL as shown earlier.

Some other rules and their transformers

• You don’t like multi-line ifelse statements getting wrapped around curly braces: transformers$token$wrap_if_else_multi_line_in_curly.

• You don’t like multi-line calls to be broken before the first named argument: transformers$line_break$set_line_break_after_opening_if_call_is_multi_line (interacting with transformers$line_break$set_line_break_before_closing_call).

• You don’t like the line being broken after the pipe: transformers$line_break$add_line_break_after_pipe

• You don’t like single quotes to be replaced by double quotes: transformers$space$fix_quotes.

• You don’t like comments to start with one space: transformers$space$start_comments_with_space

I think you get the idea. I nevertheless recommend using the tidyverse style guide as is since

• it is a well-established, thought-through style.

• using a consistent style (no matter which) reduces friction in the community.

If you have questions, don’t hesitate to create an issue in the GitHub repo.