Add "list" to S3 class of lint(), Lint() output

NEWS.md

@@ -68,6 +68,8 @@
 
   Thanks to Yihui and other developers for their helpful discussions around this issue (#797, @IndrajeetPatil).
 
+* The output of `lint()` and `Lint()` gain S3 class `"list"` to assist with S3 dispatch (#1494, @MichaelChirico)
+
 # lintr 3.0.1
 
 * Skip multi-byte tests in non UTF-8 locales (#1504)

R/lint.R

@@ -25,7 +25,7 @@
 #'
 #' @aliases lint_file
 # TODO(next release after 3.0.0): remove the alias
-#' @return A list of lint objects.
+#' @return An object of class `c("lints", "list")`, each element of which is a `"list"` object.
 #'
 #' @examples
 #' \dontrun{
@@ -97,7 +97,8 @@ lint <- function(filename, linters = NULL, ..., cache = FALSE, parse_settings =
   }
 
   lints <- maybe_append_error_lint(lints, source_expressions$error, lint_cache, filename)
-  lints <- structure(reorder_lints(flatten_lints(lints)), class = "lints")
+  lints <- reorder_lints(flatten_lints(lints))
+  class(lints) <- c("lints", "list")
 
   cache_file(lint_cache, filename, linters, lints)
   save_cache(lint_cache, filename, cache_path)
@@ -439,7 +440,7 @@ pkg_name <- function(path = find_package()) {
 #' @param line code source where the lint occurred
 #' @param ranges a list of ranges on the line that should be emphasized.
 #' @param linter deprecated. No longer used.
-#' @return an object of class 'lint'.
+#' @return an object of class `c("lint", "list")`.
 #' @name lint-s3
 #' @export
 Lint <- function(filename, line_number = 1L, column_number = 1L, # nolint: object_name.
@@ -455,18 +456,18 @@ Lint <- function(filename, line_number = 1L, column_number = 1L, # nolint: objec
 
   type <- match.arg(type)
 
-  structure(
-    list(
-      filename = filename,
-      line_number = as.integer(line_number),
-      column_number = as.integer(column_number),
-      type = type,
-      message = message,
-      line = line,
-      ranges = ranges,
-      linter = NA_character_
-    ),
-    class = "lint")
+  obj <- list(
+    filename = filename,
+    line_number = as.integer(line_number),
+    column_number = as.integer(column_number),
+    type = type,
+    message = message,
+    line = line,
+    ranges = ranges,
+    linter = NA_character_
+  )
+  class(obj) <- c("lint", "list")
+  obj
 }
 
 rstudio_source_markers <- function(lints) {

tests/testthat/test-lint_file.R

@@ -1,12 +1,12 @@
 # The lints for a given file should be the same regardless of the working
 # directory
 
-# Helper function: run assignment_linter on a given file
-lint_assignments <- function(filename) {
-  lint(filename, linters = list(assignment_linter()))
-}
-
 test_that("lint() results do not depend on the working directory", {
+  # Helper function: run assignment_linter on a given file
+  lint_assignments <- function(filename) {
+    lint(filename, linters = list(assignment_linter()))
+  }
+
   # a dummy package for use in the test
   pkg_path <- test_path("dummy_packages", "assignmentLinter")
 
@@ -63,7 +63,7 @@ test_that("lint() results do not depend on the position of the .lintr", {
   lint_with_config <- function(config_path, config_string, filename) {
     cat(config_string, file = config_path)
     on.exit(unlink(config_path))
-    lint_assignments(filename)
+    lint(filename, linters = assignment_linter())
   }
 
   # a dummy package for use in the test

tests/testthat/test-methods.R

@@ -31,6 +31,7 @@ test_that("as.data.frame.lints", {
     ),
     "lint"
   )
+  expect_type(l1, "list")
 
   # A larger lint
   expect_s3_class(
@@ -147,3 +148,9 @@ test_that("split.lint works as intended", {
   l <- lint(tmp, seq_linter())
   expect_true(all(vapply(split(l), inherits, logical(1L), "lints")))
 })
+
+test_that("within.list is dispatched", {
+  l <- lint(text = "a=1\nb=2", linters = infix_spaces_linter())
+  expect_silent(l <- lapply(l, within, line_number <- line_number + 1L))
+  expect_identical(vapply(l, `[[`, integer(1L), "line_number"), 2L:3L)
+})