Make check_encoding() more relaxed, as in readr

Closes #559

Author: jennybc

NEWS.md

@@ -1,5 +1,7 @@
 # vroom (development version)
 
+* `locale(encoding =)` now warns, instead of errors, when the encoding cannot be found in `iconvlist()` return value. This removes an unnecessary blocker on platforms like Alpine Linux where the output doesn't reflect actual capabilities.
+
 * vroom no longer uses `STDVEC_DATAPTR()` and takes the recommended approach for phasing out usage of `DATAPTR()` (#561).
 
 # vroom 1.6.6

R/locale.R

@@ -130,12 +130,29 @@ check_tz <- function(x) {
     stop("Unknown TZ ", x, call. = FALSE)
   }
 }
+
+# see https://github.com/tidyverse/readr/pull/1537 for why this more relaxed
+# than you might expect (and than it used to be)
 check_encoding <- function(x) {
   stopifnot(is.character(x), length(x) == 1)
 
-  if (tolower(x) %in% tolower(iconvlist())) {
+  # portable encoding names
+  if (x %in% c("latin1", "UTF-8")) {
     return(TRUE)
   }
 
-  stop("Unknown encoding ", x, call. = FALSE)
+  # 'iconvlist' could be incomplete (musl) or even unavailable
+  known <- tryCatch(iconvlist(), error = identity)
+  if (inherits(known, "error")) {
+    warning("Could not check `encoding` against `iconvlist()`.", call. = FALSE)
+  } else if (tolower(x) %in% tolower(known)) {
+    TRUE
+  } else {
+    warning(
+      "Unknown encoding ",
+      encodeString(x, quote = '"'),
+      ".",
+      call. = FALSE
+    )
+  }
 }