Block unreachable code and comments following return statements

Code after e.g. a return() or stop() or in deterministically false conditional loops like if (FALSE) can't be reached; typically this is vestigial code left after refactoring or sandboxing code, which is fine for exploration, but shouldn't ultimately be checked in. Comments meant for posterity should be placed before the final return().

Usage

unreachable_code_linter(
  allow_comment_regex = getOption("covr.exclude_end", "# nocov end")
)

Arguments

allow_comment_regex

Character vector of regular expressions which identify comments to exclude when finding unreachable terminal comments. By default, this includes the default "skip region" end marker for {covr} (option "covr.exclude_end", or "# nocov end" if unset). The end marker for {lintr} (settings$exclude_end) is always included. Note that the regexes should include the initial comment character #.

See also

linters for a complete list of linters available in lintr.

Tags

best_practices, configurable, readability

Examples

# will produce lints
code_lines <- "f <- function() {\n  return(1 + 1)\n  2 + 2\n}"
writeLines(code_lines)
#> f <- function() {
#>   return(1 + 1)
#>   2 + 2
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> <text>:3:3: warning: [unreachable_code_linter] Remove code and comments coming after return() or stop().
#>   2 + 2
#>   ^~~~~

code_lines <- "if (FALSE) {\n 2 + 2\n}"
writeLines(code_lines)
#> if (FALSE) {
#>  2 + 2
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> <text>:1:1: warning: [unreachable_code_linter] Remove code inside a conditional loop with a deterministically false condition.
#> if (FALSE) {
#> ^~~~~~~~~~~~

code_lines <- "while (FALSE) {\n 2 + 2\n}"
writeLines(code_lines)
#> while (FALSE) {
#>  2 + 2
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> <text>:1:1: warning: [unreachable_code_linter] Remove code inside a conditional loop with a deterministically false condition.
#> while (FALSE) {
#> ^~~~~~~~~~~~~~~

code_lines <- "f <- function() {\n  return(1)\n  # end skip\n}"
writeLines(code_lines)
#> f <- function() {
#>   return(1)
#>   # end skip
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> <text>:3:3: warning: [unreachable_code_linter] Remove code and comments coming after return() or stop().
#>   # end skip
#>   ^~~~~~~~~~

# okay
code_lines <- "f <- function() {\n  return(1 + 1)\n}"
writeLines(code_lines)
#> f <- function() {
#>   return(1 + 1)
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> ℹ No lints found.

code_lines <- "if (foo) {\n 2 + 2\n}"
writeLines(code_lines)
#> if (foo) {
#>  2 + 2
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> ℹ No lints found.

code_lines <- "while (foo) {\n 2 + 2\n}"
writeLines(code_lines)
#> while (foo) {
#>  2 + 2
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter()
)
#> ℹ No lints found.

code_lines <- "f <- function() {\n  return(1)\n  # end skip\n}"
writeLines(code_lines)
#> f <- function() {
#>   return(1)
#>   # end skip
#> }
lint(
  text = code_lines,
  linters = unreachable_code_linter(allow_comment_regex = "# end skip")
)
#> ℹ No lints found.