available_linters(tags = "deprecated") should "just work"

[MichaelChirico]

I find the current behavior a bit strange:

available_linters(tags = "deprecated")
# [1] linter  package tags   
# <0 rows> (or 0-length row.names)

Almost surely, that's not what the user wanted. The problem is exclude_tags = "deprecated" by default, so we need to also specify exclude_tags = NULL:

nrow(available_linters(tags = "deprecated", exclude_tags = NULL))
# [1] 7

I see two options:

1. Special case "deprecated" with an if (missing(exclude_tags) && identical(tags, "deprecated")) exclude_tags <- NULL
2. Always run exclude_tags <- setdiff(exclude_tags, tags), i.e., exclude_tags takes priority over tags if there's any collision

Either way, it will simplify the implementation for #1958.

Any thoughts?

[AshesITR]

I think option 2 is a more elegant solution (what the code says, not the description; i.e. tags should take priority).

[MichaelChirico]

hmm it looks like we've already declared the opposite prioritization for linters_with_tags():

lintr/tests/testthat/test-with.R

Line 47 in 9038957

expect_length(linters_with_tags("default", exclude_tags = "default"), 0L)

[AshesITR]

The change in behavior makes sense to me -- we should find another way to produce a zero-row output.