lint-switch-arg.R

library(lintr)

test_file <- tempfile(fileext = ".txt")
cat(
"
1 + 1
switch('x', a = (1 + 1), b = 10, 12) # this is fine
x <- 20
switch('x', b = 20, a = 12) # should find this one
print('foo')
",
file = test_file
)

my_linter <- function(x) {
  
  # Report no lints when expression doesn't have a switch statement
  xml_calls <- x$xml_find_function_calls("switch")
  if (length(xml_calls) == 0) {
    return(list())
  }

  content <- x$parsed_content
  
  # Deliniate which part of the expression is part of the 'switch()' call
  switch_hit <- which(content$token == "SYMBOL_FUNCTION_CALL" & content$text == "switch")
  
  # Find first open '(' after switch
  open  <- which(content$token == "'('")
  open  <- min(open[open > switch_hit])
  
  # Find matching close ')' with same parent as open '('
  close <- which(content$token == "')'")
  close <- close[which(content$parent[close] == content$parent[open])[1]]
  
  # Find the last comma in the call
  commas <- which(content$token == "','")
  commas <- max(commas[commas > open & commas < close])
  
  # After this comma, do we have an argument symbol?
  names <- which(content$token == "SYMBOL_SUB")
  names <- names[names > commas & names < close]
  
  # If we do have an unnamed last argument, return without lints
  if (length(names) == 0) {
    return(list())
  }
  
  # Report lint
  xml_nodes_to_lints(
    xml_calls,
    source_expression = x,
    lint_message = "switch without last unnamed argument",
    type = "warning"
  )
}

lint(
  test_file,
  linters = Linter(my_linter, linter_level = "expression")
)