pipe_continuation_linter.R

#' Pipe continuation linter
#'
#' Check that each step in a pipeline is on a new line, or the entire pipe fits on one line.
#'
#' @evalRd rd_tags("pipe_continuation_linter")
#' @seealso
#'   [linters] for a complete list of linters available in lintr. \cr
#'   <https://style.tidyverse.org/pipes.html#long-lines-2>
#' @export
pipe_continuation_linter <- function() {
  # For pipelines, either the whole expression should fit on a single line, or,
  # each pipe symbol within the expression should be on a separate line

  # Where a single-line pipeline is nested inside a larger expression (eg,
  # inside a function definition), the outer expression can span multiple lines
  # without a pipe-continuation lint being thrown.

  multiline_pipe_test <- paste(
    # In xml derived from the expression `E1 %>% E2`:
    # `E1`, the pipe and `E2` are sibling expressions of the parent expression

    # We only consider expressions where E1 contains a pipe character somewhere
    # and we split these expressions based on whether E2 starts on the same
    # line, or on a subsequent line to that where E1 ended.

    # We only consider the parent expression of the pipe under consideration,
    # rather than all ancestors.

    # select all pipes
    "//SPECIAL[text() = '%>%'",
    # that are nested in a parent-expression that spans multiple lines
    "and parent::expr[@line1 < @line2]",
    # where the parent contains pipes that precede the pipe under scrutiny
    "and preceding-sibling::*/descendant-or-self::SPECIAL[text() = '%>%']",
    "and (",
    # where a preceding sibling 'expr' [...] ends on the same line that a
    # succeeding 'expr' starts {...}
    # either "[a %>%\n b()] %>% {c(...)}"
    # or     "[a %>% b(...\n)] %>% {c(...)}"
    "(preceding-sibling::*/descendant-or-self::expr/@line2 = ",
    "  following-sibling::*/descendant-or-self::expr/@line1)",

    # or, (if the post-pipe expression starts on a subsequent line) where a
    # preceding sibling 'expr' [...] contains a pipe character on the
    # same line as the original pipe character |...|
    # [a %>% b] |%>%| \n c
    "or (@line1 = preceding-sibling::*/descendant-or-self::SPECIAL[text() = '%>%']/@line1)",
    ")",
    "]"
  )

  Linter(function(source_expression) {
    if (!is_lint_level(source_expression, "file")) {
      return(list())
    }
    x <- source_expression$full_xml_parsed_content

    pipe_exprs <- xml_find_all(x, multiline_pipe_test)

    xml_nodes_to_lints(
      pipe_exprs,
      source_expression = source_expression,
      lint_message = paste(
        "`%>%` should always have a space before it and a new line after it,",
        "unless the full pipeline fits on one line."
      ),
      type = "style"
    )
  })
}