function for checking for unused dependencies

Here is a function for checking if we have unused dependencies in a package.

Throwing it here in circus might be a good home for it.

find_unused_dependencies <- function(
  dependencies = c("Depends", "Imports", "LinkingTo"),
  include_supp_files = FALSE,
  path = getwd(),
  root = NULL,
  ...,
  progress = TRUE,
  errors = c("reported", "fatal", "ignored"),
  dev = FALSE
) {
  deps <- renv::dependencies(path = path, root = root, ...,
                             progress = progress, errors = errors, dev = dev)
  if (isFALSE(include_supp_files)) {
    deps <- dplyr::filter(
      deps, 
      stringr::str_detect(Source, "DESCRIPTION") |
        stringr::str_detect(Source, "/R/")
    )
  }
  deps <- dplyr::filter(deps, Package != "R")
  deps_desc <- data.frame(Package = remotes::local_package_deps(
    pkgdir = path, 
    dependencies = dependencies
  ))
  deps_used <- dplyr::filter(deps, ! stringr::str_detect(Source, "DESCRIPTION"))
  deps_orphan <- dplyr::anti_join(deps_desc, deps_used, by = "Package")
  return(deps_orphan)
}

find_unused_dependencies()
# Finding R package dependencies ... Done!
#   Package
# 1 poorman

dependencies says which dependencies fields to check. See ?remotes::local_package_deps.
include_supp_files: If FALSE, only check for dependencies in DESCRIPTION and files in /R/ (excluding tests, vignettes, /WIP/, README, etc.). If TRUE, all files are checked.

Originally posted by @bwiernik in https://github.com/easystats/correlation/pull/192#discussion_r657094308

Start by inspecting the circus package structure and existing dependency-related utilities to determine where this function belongs. Compare the proposed behavior and example output with the package's conventions, then add the dependency check and verify that declared but unused packages are reported as shown.