Use vec-last for length-2 vecs if no vec-sep2

Another fix for #681.

R/glue.R

@@ -79,7 +79,8 @@ drop_null <- function(x) {
 #' to collapse.
 #' @param sep Separator. A character string.
 #' @param sep2 Separator for the special case that `x` contains only two
-#' elements. A character string.
+#' elements. A character string. Defaults to the value of `last` without the
+#' serial comma.
 #' @param last Last separator, if there is no truncation. E.g. use
 #' `", and "` for the [serial
 #' comma](https://en.wikipedia.org/wiki/Serial_comma). A character string.
@@ -112,7 +113,7 @@ drop_null <- function(x) {
 #' # head style
 #' ansi_collapse(letters, trunc = 5, style = "head")
 
-ansi_collapse <- function(x, sep = ", ", sep2 = " and ", last = ", and ",
+ansi_collapse <- function(x, sep = ", ", sep2 = sub("^,", "", last), last = ", and ",
                           trunc = Inf, width = Inf, ellipsis = symbol$ellipsis,
                           style = c("both-ends", "head")) {
 

R/inline.R

@@ -43,9 +43,9 @@ inline_generic <- function(app, x, style) {
 }
 
 inline_collapse <- function(x, style = list()) {
-  sep <- style[["vec-sep"]] %||% style[["vec_sep"]] %||% ", "
-  sep2 <- style[["vec-sep2"]] %||% style[["vec_sep2"]] %||% " and "
   last <- style[["vec-last"]] %||% style[["vec_last"]] %||% ", and "
+  sep <- style[["vec-sep"]] %||% style[["vec_sep"]] %||% ", "
+  sep2 <- style[["vec-sep2"]] %||% style[["vec_sep2"]] %||% sub("^,", "", last)
 
   trunc <- style[["vec-trunc"]] %||% style[["vec_trunc"]] %||% 20L
   col_style <- style[["vec-trunc-style"]] %||% "both-ends"

tests/testthat/test-collapsing.R

@@ -200,9 +200,13 @@ test_that("ansi_collapse uses `sep2` for length-two inputs", {
 
 
 test_that("Issue #681", {
-  expect_equal(ansi_collapse(1:2, last = " or "), "1 or 2")
-  expect_equal(ansi_collapse(1:2, sep2 = " and ", last = " or "), "1 or 2")
+  # sep2 takes precedence
+  expect_equal(ansi_collapse(1:2, sep2 = " and ", last = " or "), "1 and 2")
   expect_equal(ansi_collapse(1:2, sep2 = " xor ", last = " or "), "1 xor 2")
+  # default for sep2 is last without the Oxford comma
+  expect_equal(ansi_collapse(1:3, last = ", or "), "1, 2, or 3")
+  expect_equal(ansi_collapse(1:2, last = ", or "), "1 or 2")
+  expect_equal(ansi_collapse(1:2, last = " or "), "1 or 2")
 
   expect_snapshot({
     v <- cli::cli_vec(