bs_dependency_defer() factory-built closures collide on the memoise cache

[AleKoure]

bs_dependency_defer(func)  memoises  func  against a shared cache keyed on  formals(f)  +  body(f)  + call args. Closures produced by a factory (the pattern from the "Dynamically themeable component" vignette) only differ in captured variables, so they all hash to the same key and every dependency after the first is served the first one's compiled output.

library(bslib)

mk_dep <- function(name, css) {
  bs_dependency_defer(function(theme) {
    if (!is_bs_theme(theme)) theme <- bs_theme(version = 5)
    tmp <- tempfile(fileext = ".scss"); writeLines(css, tmp)
    bs_dependency(input = sass::sass_file(tmp), theme = theme,
                  name = paste0("test-", name), version = "0.0.0")
  })
}

mk_dep("red",  ".x{color:red}")()$name
mk_dep("blue", ".x{color:blue}")()$name
#> [1] "test-red"
#> [1] "test-red"   # expected "test-blue"

Today's viable workarounds are either  memoise = FALSE or the one-liner in the docs suggestion below.

Suggested fixes:

1. Code: add an optional  cache_key  to  bs_dependency_defer()  folded into the memoise key:  bs_dependency_defer(func, memoise = TRUE, cache_key = NULL) . Callers pass a stable per-component id and the collision is gone. Happy to PR.
2. Docs: update the "Dynamically themeable component" vignette +  ?bs_dependency_defer  to warn about the shared-cache collision when  func  is factory-built, and show the caller-side one-liner, give the sole  theme  formal a per-component default so  formals(f)  differs per component:

build <- function(theme) { ... }
formals(build)$theme <- "unique-per-component-id"
bs_dependency_defer(build)

Happy to PR either.

[cpsievert]

Sorry about this and those suggestions seem pretty reasonable. Feel free to submit a PR.