ansi_collapse(): fix trunc behavior

Now it is as documented.

NEWS.md

@@ -1,5 +1,8 @@
 # cli (development version)
 
+* `ansi_collapse(x, trunc = 1, style = "head")` now indeed show one element
+  if `length(x) == 2`, as documented (@salim-b, #572).
+
 # cli 3.6.0
 
 * The progressr progress handler now reports progress correctly

R/glue.R

@@ -112,10 +112,6 @@ ansi_collapse <- function(x, sep = ", ", last = ", and ", trunc = Inf,
                           width = Inf, ellipsis = symbol$ellipsis,
                           style = c("both-ends", "head")) {
 
-  # does not make sense to show ... instead of an element
-  trunc <- max(trunc, 1L)
-  if (trunc == length(x) - 1L) trunc <- trunc + 1L
-
   style <- match.arg(style)
   switch(
     style,
@@ -147,6 +143,7 @@ collapse_head_notrim <- function(x, trunc, sep, last, ellipsis) {
 collapse_head <- function(x, sep = ", ", last = ", and ", trunc = Inf,
                           width = Inf, ellipsis = symbol$ellipsis) {
 
+  trunc <- max(trunc, 1L)
   x <- as.character(x)
   lnx <- length(x)
 

tests/testthat/_snaps/collapsing.md

@@ -81,7 +81,7 @@
     Code
       cli_text("{v(2,1)}")
     Message
-      1 and 2
+      1, ...
     Code
       cli_text("{v(3,1)}")
     Message
@@ -105,7 +105,7 @@
     Code
       cli_text("{v(3,2)}")
     Message
-      1, 2, and 3
+      1, 2, ...
     Code
       cli_text("{v(4,2)}")
     Message
@@ -129,7 +129,7 @@
     Code
       cli_text("{v(4,3)}")
     Message
-      1, 2, 3, and 4
+      1, 2, 3, ...
     Code
       cli_text("{v(0,4)}")
     Message
@@ -263,7 +263,7 @@
     Code
       cli_text("{.val {v(11,10)}}")
     Message
-      1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11
+      1, 2, 3, 4, 5, 6, 7, 8, ..., 10, and 11
 
 # both-ends with formatting [ansi]
 
@@ -314,7 +314,7 @@
     Code
       cli_text("{.val {v(11,10)}}")
     Message
-      [34m1[39m, [34m2[39m, [34m3[39m, [34m4[39m, [34m5[39m, [34m6[39m, [34m7[39m, [34m8[39m, [34m9[39m, [34m10[39m, and [34m11[39m
+      [34m1[39m, [34m2[39m, [34m3[39m, [34m4[39m, [34m5[39m, [34m6[39m, [34m7[39m, [34m8[39m, ..., [34m10[39m, and [34m11[39m
 
 # ansi_collapse