`build_home_license()` interaction with `usethis::use_*_license(include_future = TRUE)`

[stephenashton-dhsc]

If a call to usethis::use_*_license() is made with the include_future = TRUE argument to apply a GPL, AGPL, LGPL or Apache licence to a package, this will set the Licence field in the description file to be something along the lines of GPL (>=3).

Whilst this versioning is picked up by pkgdown, where it isn't doesn't exactly match any version in license.db it is just displayed as a text string. Would it be better for build_home_license() to identify where a future provision is included in a package license, then proceed as if the user had used a strict version of the license, before appending the term "or later"?

[hadley]

I think this is a good idea in principle, but if we start down this path, I think we'd need to support the full R license specification, and that's going to be complicated. The code that base R uses is at https://github.com/wch/r-source/blob/d35cfa99425da7f9d57928efa1961dc5f9caaef2/src/library/tools/R/license.R#L83. We could maybe do something like tools:::expand_license_spec_component_from_db("GPL (>=3)"), but the output from that is not super easy to work with.

...

Hmmmm, actually, maybe we could just special case the most common uses of >=:

library(dplyr, warn.conflicts = FALSE)
library(stringr)

packages <- as_tibble(available.packages())

parsed <- packages |> 
  select(package = Package, license = License) |> 
  mutate(
    or_file = str_detect(license, fixed("| file LICEN[CS]E")),
    plus_file = str_detect(license, fixed("+ file LICEN[CS]E")),
    license = str_remove(license, " [+|] file LICEN[CS]E")
  )

parsed |> count(license, sort = TRUE)
#> # A tibble: 121 × 2
#>    license                n
#>    <chr>              <int>
#>  1 GPL-3               4804
#>  2 MIT                 4369
#>  3 GPL (>= 2)          4270
#>  4 GPL-2               2454
#>  5 GPL (>= 3)          1816
#>  6 GPL                  446
#>  7 GPL-2 | GPL-3        343
#>  8 CC0                  232
#>  9 LGPL-3               170
#> 10 Apache License 2.0   160
#> # ℹ 111 more rows

^{Created on 2024-04-17 with reprex v2.1.0}

Looks like if we just handled GPL (>= 2) and GPL (>= 3) that'd get us support for an extra ~6000 packages, which is ~30% of CRAN.

Given this scope, I think this would be a good issue for TDD — it's just a matter of manually writing the HTML for these three cases and then making a named character vector which is used in autolink_license().