topics cannot be excluded from reference index sections

[bastistician]

The documentation on topic matching says:

Use a leading '-' to remove topics from a section, e.g. '-topic_name', '-starts_with("foo")'.

AFAIK, this is to allow for exclusion of specific topics in one set of references, for example:

- contents:
  - has_keyword("datasets")
  - -foodata

This has worked in version 1.6.1 but it no longer does as from 2.0.0 -- most likely because of the changes in #1664. Topics are no longer selected based on the whole pattern vector (select_topics(section$contents, pkg$topics), but one-by-one (purrr::imap(section$contents, content_info, pkg = pkg, section = index)). The above exclusion pattern actually leads to the inclusion of all topics.

Test code:

ref <- list(
  list(contents = c("matches('[ab]')", "-b")),  # only a
  list(contents = c("b", "c", "?", "e"))        # all but a
)
meta <- list(reference = ref)
pkg <- as_pkgdown(test_path("assets/reference"), override = meta)
lapply(data_reference_index(pkg)$rows, `[[`, "names")

Observed result (in 2.0.2):

[[1]]
   a.Rd    b.Rd    c.Rd    e.Rd help.Rd 
    "a"     "b"     "c"     "e"     "?" 

[[2]]
   b.Rd    c.Rd help.Rd    e.Rd 
    "b"     "c"     "?"     "e" 

Expected result (as in 1.6.1):

[[1]]
a.Rd 
 "a" 

[[2]]
   b.Rd    c.Rd help.Rd    e.Rd 
    "b"     "c"     "?"     "e" 

[maelle]

Thanks for catching & reporting this @bastistician! There is a draft PR in #2041 (however with no expected time of completion at the moment).