Customizing styler - the quick way

Jul 16, 2018 00:00 · 924 words · 5 minute read styler

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One cool thing that happens if you work resonates in the community is that you see other people using it. In this blog post I am going to address a typical question people have when they want to use a source code formatter - in particular styler:

I don’t like rule xyz of the tidyverse style guide, which is the default style guide implemented in styler. How can I tell styler not to apply it?


First, I think reading the docs would be a good approach. There are two resources:

  • The help file for the function tidyverse_style(), which returns the transformer functions that prettify your code. It has a few interesting arguments, some of which are rather complex.1

  • If you can’t get styler behaving the way you want using the arguments of tidyverse_style(), you have another option, which is described in a vignette: Creating your own style guide. Yes, I admit, it’s pretty long and if you don’t want to become a styler expert, it may be a little bit overwhelming.

If you don’t care about how to create new rules but you simply want to remove a rule, I have good news for you: There is a quick way to do it. These are the steps you need to complete in order to do it:

  • 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.


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:

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()
#>  [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"

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.

levels <- c("space", "line_break", "indention", "token")
  ~ names(transformers[[.x]])
) %>%
#> $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_curly"          
#> $line_break
#>  [1] "set_line_break_around_comma_and_or"                
#>  [2] "set_line_break_after_assignment"                   
#>  [3] "set_line_break_before_curly_opening"               
#>  [4] "remove_line_break_before_round_closing_after_curly"
#>  [5] "remove_line_breaks_in_fun_dec"                     
#>  [6] "style_line_break_around_curly"                     
#>  [7] "set_line_break_around_curly_curly"                 
#>  [8] "set_line_break_before_closing_call"                
#>  [9] "set_line_break_after_opening_if_call_is_multi_line"
#> [10] "remove_line_break_in_fun_call"                     
#> [11] "add_line_break_after_pipe"                         
#> [12] "set_linebreak_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.

#> function(pd) {
#>   to_replace <- pd$token == "EQ_ASSIGN"
#>   pd$token[to_replace] <- "LEFT_ASSIGN"
#>   pd$text[to_replace] <- "<-"
#>   pd
#> }
#> <bytecode: 0x7fd3a29c58d0>
#> <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"

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. For example, I only recently spotted that the rule to remove quotes (fix_quotes)is in the category space, which is clearly wrong and I think I will move it over to token in a future release of styler.

Some other rules and their tranformers

  • 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 mutli-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.

In case you want to add a custom rule, the vignette Customizing styler is still the way to go. If you have questions, don’t hesitate to post on Stackoverflow or leave a comment below.

  1. One example is math_token_spacing. It requires an input that is typically easiest created with another function, e.g. specify_math_token_spacing() ↩︎

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