add option to ignore blank lines to trailing_whitespace_linter()

supersedes #165

Author: AshesITR

NEWS.md

@@ -137,6 +137,8 @@ function calls. (#850, #851, @renkun-ken)
   This prevents false positive lints in the case of long generic names, e.g. 
   `very_very_very_long_generic_name.short_class` no longer produces a lint (#871, @AshesITR)
 * `object_name_linter()` now correctly detects assignment generics (#843, @jonkeane)
+* `trailing_whitespace_linter()` now also lints completely blank lines by default. This can be disabled by setting the
+  new argument `allow_empty_lines = TRUE` (#1033, @AshesITR)
 
 # lintr 2.0.1
 

R/trailing_whitespace_linter.R

@@ -2,41 +2,40 @@
 #'
 #' Check that there are no space characters at the end of source lines.
 #'
+#' @param allow_empty_lines Suppress lints for lines that only contain whitespace.
+#'
 #' @evalRd rd_tags("trailing_whitespace_linter")
 #' @seealso [linters] for a complete list of linters available in lintr.
 #' @export
-trailing_whitespace_linter <- function() {
+trailing_whitespace_linter <- function(allow_empty_lines = FALSE) {
   Linter(function(source_file) {
+    if (is.null(source_file$file_lines)) return(list())
+
     res <- re_matches(
-      source_file$lines,
-      rex(capture(name = "space", some_of(" ", regex("\\t"))), or(newline, end)),
-      global = TRUE,
+      source_file$file_lines,
+      rex(blanks, end),
       locations = TRUE
     )
 
-    lapply(seq_along(source_file$lines), function(itr) {
-
-      mapply(
-        FUN = function(start, end) {
-          if (is.na(start)) {
-            return()
-          }
-          line_number <- names(source_file$lines)[itr]
-          Lint(
-            filename = source_file$filename,
-            line_number = line_number,
-            column_number = start,
-            type = "style",
-            message = "Trailing whitespace is superfluous.",
-            line = source_file$lines[as.character(line_number)],
-            ranges = list(c(start, end))
-          )
-        },
-        start = res[[itr]]$space.start,
-        end = res[[itr]]$space.end,
-        SIMPLIFY = FALSE
-      )
-    })
+    if (isTRUE(allow_empty_lines)) {
+      bad_lines <- which(res$start > 1L)
+    } else {
+      bad_lines <- which(!is.na(res$start))
+    }
 
+    lapply(
+      bad_lines,
+      function(line) {
+        Lint(
+          filename = source_file$filename,
+          line_number = line,
+          column_number = res$start[[line]],
+          type = "style",
+          message = "Trailing whitespace is superfluous.",
+          line = source_file$file_lines[[line]],
+          ranges = list(c(res$start[[line]], res$end[[line]]))
+        )
+      }
+    )
   })
 }

man/trailing_whitespace_linter.Rd

@@ -2,7 +2,8 @@ regexes <- list(
   assign = rex("Use <-, not =, for assignment."),
   local_var = rex("local variable"),
   quotes = rex("Only use double-quotes."),
-  trailing = rex("Trailing blank lines are superfluous.")
+  trailing = rex("Trailing blank lines are superfluous."),
+  trailws = rex("Trailing whitespace is superfluous.")
 )
 
 test_that("it handles dir", {
@@ -72,7 +73,12 @@ test_that("it handles tex", {
       list(regexes[["assign"]], line_number = 11),
       list(regexes[["local_var"]], line_number = 23),
       list(regexes[["assign"]], line_number = 23),
-      list(regexes[["trailing"]], line_number = 25)
+      list(regexes[["trailing"]], line_number = 25),
+      list(regexes[["trailws"]], line_number = 25)
+      # FIXME(AshesITR)
+      # file_lines contains a whitespace on the final line for Rtex, because that is used to mark the Rtex escape char
+      # "%" as well.
+      # cf. get_source_expressions("tests/testthat/knitr_formats/test.Rtex")$lines[[25]]
     ),
     default_linters,
     parse_settings = FALSE

tests/testthat/test-knitr_formats.R

@@ -20,4 +20,22 @@ test_that("returns the correct linting", {
     list(message = rex("Trailing whitespace is superfluous."), line_number = 3),
     linter
   )
+
+  expect_lint(
+    "blah <- 1\n  \n'hi'\na <- 2",
+    list(message = rex("Trailing whitespace is superfluous."), line_number = 2),
+    linter
+  )
+
+  expect_lint(
+    "blah <- 1  ",
+    list(message = rex("Trailing whitespace is superfluous."), column_number = 10),
+    trailing_whitespace_linter(allow_empty_lines = TRUE)
+  )
+
+  expect_lint(
+    "blah <- 1\n  \n'hi'\na <- 2",
+    NULL,
+    trailing_whitespace_linter(allow_empty_lines = TRUE)
+  )
 })