Uses the {styler} package to automatically format R sources.
Details
The code is formatted according to the styler::tidyverse_style guide with one adjustment:
spacing around math operators is not modified to avoid conflicts with box::use() statements.
Examples
if (interactive()) {
  # Format a single file.
  format_r("app/main.R")
  # Format all files in a directory.
  format_r("app/view")
}