Documentation issue in `exclusions`

[jabenninghoff]

Even after the documentation fix for #1401, when using the 3.0.0 CRAN release of lintr, implementing the example in https://lintr.r-lib.org/articles/lintr.html#excluding-lines-via-the-config-file results in an unexpected error:

linters: linters_with_defaults(
    line_length_linter(100) 
  )
exclusions: list(
    "bad.R" = list(
      1, # global exclusions are unnamed
      line_length_linter = 4:6
    )
  )

Error message when running lint_dir():

$ Rscript -e 'lintr::lint_dir(".")'
Error in file_exclusion[[names2(file_exclusion) == ""]] : 
  attempt to select less than one element in integerOneIndex
Calls: <Anonymous> ... drop_excluded -> vapply -> FUN -> is_excluded_file -> %in%
Execution halted

To reproduce: run Rscript -e 'lintr::lint_dir(".")' from a directory containing the .lintr file above, and the following bad.R:

tmp = "value"

# regular comment
# really long comment ............................................................................................................
# really long comment ............................................................................................................
# really long comment ............................................................................................................
# regular comment

[jabenninghoff]

This appears to be a bug specific to lint_dir(). The following command works with no issues:

$ Rscript -e 'lintr::lint("bad.R")'

[AshesITR]

Thanks for your testing. The bug you found is triggered whenever exclusions: in the .lintr config contains more than one instruction for a single file.
The only workaround I see is to put some of the exclusion directives directly into the file using nolint comments.