In combine_words, when words vector is length 2 and and is blank, use sep

NEWS.md

@@ -1,5 +1,6 @@
 # CHANGES IN knitr VERSION 1.35
 
+- In `knitr::combine_words()`, when `words` is length 2 and `and = ""`, `sep` will now be used (thanks, @eitsupi, #2044).
 
 # CHANGES IN knitr VERSION 1.34
 

R/utils.R

@@ -842,9 +842,10 @@ create_label = function(..., latex = FALSE) {
 #'
 #' If the length of the input \code{words} is smaller than or equal to 1,
 #' \code{words} is returned. When \code{words} is of length 2, the first word
-#' and second word are combined using the \code{and} string. When the length is
-#' greater than 2, \code{sep} is used to separate all words, and the \code{and}
-#' string is prepended to the last word.
+#' and second word are combined using the \code{and} string, or if blank,
+#' \code{sep} if is used. When the length is greater than 2, \code{sep} is used
+#' to separate all words, and the \code{and} string is prepended to the last
+#' word.
 #' @param words A character vector.
 #' @param sep Separator to be inserted between words.
 #' @param and Character string to be prepended to the last word.
@@ -866,7 +867,7 @@ combine_words = function(
   if (n == 0) return(words)
   words = paste0(before, words, after)
   if (n == 1) return(rs(words))
-  if (n == 2) return(rs(paste(words, collapse = and)))
+  if (n == 2) return(rs(paste(words, collapse = if (is_blank(and)) sep else and)))
   if (oxford_comma && grepl('^ ', and) && grepl(' $', sep)) and = gsub('^ ', '', and)
   words[n] = paste0(and, words[n])
   # combine the last two words directly without the comma

tests/testit/test-utils.R

@@ -123,6 +123,7 @@ assert('combine_words() combines multiple words into a single string', {
   (cw(NULL) %==% NULL)
   (cw(c('a')) %==% 'a')
   (cw(c('a', 'b')) %==% 'a and b')
+  (cw(c('a', 'b'), and = "") %==% 'a, b')
   (cw(c('a', 'b', 'c')) %==% 'a, b, and c')
   (cw(c('a', 'b', 'c'), and = '') %==% 'a, b, c')
   (cw(c('a', 'b', 'c'), ' / ', '') %==% 'a / b / c')