test_that("missing_argument_linter skips allowed usages", {
  linter <- missing_argument_linter()

  expect_lint("fun(x, a = 1)", NULL, linter)
  expect_lint("fun(x = 1, a = 1)", NULL, linter)
  expect_lint("dt[, 1]", NULL, linter)
  expect_lint("dt[, 'col']", NULL, linter)
  expect_lint("array[, , 1]", NULL, linter)
  expect_lint("switch(a =, b =, c = 1, 0)", NULL, linter)
  expect_lint("alist(a =, b =, c = 1, 0)", NULL, linter)
  expect_lint("pairlist(path = quote(expr = ))", NULL, linter) # 1889

  # always allow this missing usage
  expect_lint("foo()", NULL, linter)
})

test_that("missing_argument_linter blocks disallowed usages", {
  linter <- missing_argument_linter()
  lint_msg <- "Missing argument in function call."

  expect_lint("fun(, a = 1)", lint_msg, linter)
  expect_lint(
    "f <- function(x, y) x\nf(, y = 1)\n",
    lint_msg,
    linter
  )
  expect_lint("fun(a = 1,, b = 2)", lint_msg, linter)
  expect_lint("fun(b = 1, a =)", lint_msg, linter)
  expect_lint("fun(a = 1,)", lint_msg, linter)
  expect_lint("fun(a = )", lint_msg, linter)

  expect_lint(
    trim_some(
      "
      list(
        a = 1,
        b = 2,
      )
    "
    ),
    lint_msg,
    linter
  )

  expect_lint("stats::median(1:10, a =)", lint_msg, linter)
  expect_lint("env$get(1:10, a =)", lint_msg, linter)

  # TODO
  # Fixes https://github.com/r-lib/lintr/issues/906
  # Comments should be ignored so that missing arguments could be
  # properly identified in these cases.
  # expect_lint(
  #   trim_some("
  #     fun(
  #       1,
  #       2,
  #       # comment
  #     )
  #   "),
  #   lint_msg,
  #   linter
  # )

  # expect_lint(
  #   trim_some("
  #     fun(
  #       # comment
  #       ,
  #       1
  #     )
  #   "),
  #   lint_msg,
  #   linter
  # )

  # expect_lint(
  #   trim_some("
  #     fun(
  #       a = # comment
  #       ,
  #       1
  #     )
  #   "),
  #   lint_msg,
  #   linter
  # )
})

test_that("except list can be empty", {
  linter <- missing_argument_linter()

  expect_lint("switch(a =, b = 1, 0)", NULL, linter)
  expect_lint("alist(a =)", NULL, linter)
})

# test_that("allow_trailing can allow trailing empty args also for non-excepted functions", {
#   linter <- missing_argument_linter(allow_trailing = TRUE)
#
#   expect_lint("fun(a = 1,)", NULL, linter)
#   expect_lint(
#     trim_some("
#       fun(
#         a = 1,
#         # comment
#       )
#     "),
#     NULL,
#     linter
#   )
#   # ... but not if the final argument is named
#   expect_lint(
#     "fun(a = 1, b = )",
#     rex::rex("Missing argument 'b' in function call."),
#     linter
#   )
# })