Add parameter to account for empty vector inputs like character(0)

R/glue.R

@@ -28,6 +28,10 @@
 #'   NULL values with. If `character()` whole output is `character()`. If
 #'   `NULL` all NULL values are dropped (as in `paste0()`). Otherwise the
 #'   value is replaced by the value of `.null`.
+#' @param .empty \[`character(1)`: \sQuote{character()}]\cr Value to replace
+#'   vectors of length 0 with. If `NULL` empty vectors are treated as NULL and
+#'   the behaviours specified in `.null` applies. If `character()` whole output is
+#'  `character()`. Otherwise the value is replaced by the value of `.empty`.
 #' @param .comment \[`character(1)`: \sQuote{#}]\cr Value to use as the comment
 #'   character.
 #' @param .literal \[`boolean(1)`: \sQuote{FALSE}]\cr Whether to treat single or
@@ -87,7 +91,7 @@
 #' @name glue
 #' @export
 glue_data <- function(.x, ..., .sep = "", .envir = parent.frame(),
-  .open = "{", .close = "}", .na = "NA", .null = character(),
+  .open = "{", .close = "}", .na = "NA", .null = character(), .empty = character(),
   .comment = "#", .literal = FALSE, .transformer = identity_transformer, .trim = TRUE) {
 
   if (is.null(.envir)) {
@@ -120,7 +124,12 @@ glue_data <- function(.x, ..., .sep = "", .envir = parent.frame(),
       # - If `.null == NULL` then it is allowed and any such argument will be
       # silently dropped.
       # - In other cases output is treated as it was evaluated to `.null`.
-      eval(call("force", as.symbol(paste0("..", x)))) %||% .null
+      eval_func <- eval(call("force", as.symbol(paste0("..", x))))
+      if (length(eval_func) == 0 & !is.null(eval_func)) {
+        .empty
+      } else {
+        eval_func %||% .null
+      }
     }
   )
   unnamed_args <- drop_null(unnamed_args)
@@ -151,7 +160,11 @@ glue_data <- function(.x, ..., .sep = "", .envir = parent.frame(),
   }
 
   f <- function(expr){
-    eval_func <- .transformer(expr, env) %||% .null
+    eval_func <- .transformer(expr, env)
+    if (length(eval_func) == 0 & !is.null(eval_func)) {
+      eval_func <- .empty
+    }
+    eval_func <- eval_func %||% .null
 
     # crayon functions *can* be used, so we use tryCatch()
     # to give as.character() a chance to work

tests/testthat/test-glue.R

@@ -457,6 +457,76 @@ test_that("glue replaces NULL input if `.null` is not NULL or character()", {
     "x: foo")
 })
 
+test_that("glue always returns character() if given any empty input if `.empty` == character()", {
+  expect_equal(
+    glue("{character()}", .empty = character()),
+    character())
+
+  expect_equal(
+    glue("{numeric()}", .empty = character()),
+    character())
+
+  expect_equal(
+    glue("{logical()}", .empty = character()),
+    character())
+
+  expect_equal(
+    glue("{integer()}", 1, .empty = character()),
+    character())
+
+  expect_equal(
+    glue("{double()}", 1, .empty = character()),
+    character())
+
+  expect_equal(
+    glue("{complex()}", 1, .empty = character()),
+    character())
+
+  expect_equal(
+    glue("{raw()}", 1, .empty = character()),
+    character())
+})
+
+test_that("glue always defaults to .null if given any empty input if `.empty` == 'NULL'", {
+  expect_equal(
+    glue("{character()}", .empty = NULL, .null = "foo"),
+    "foo")
+
+  expect_equal(
+    glue("{character()}", .empty = NULL, .null = NULL),
+    character())
+
+  expect_equal(
+    glue("{character()}", .empty = NULL, .null = character()),
+    character())
+
+  expect_equal(
+    glue("{character()}foo", .empty = NULL, .null = NULL),
+    "foo")
+})
+
+test_that("glue always returns character() if given any empty input if `.empty` == character()", {
+  expect_equal(
+    glue("{character()}", .empty = "foo"),
+    "foo")
+
+  expect_equal(
+    glue(character(), .empty = "foo"),
+    "foo")
+
+  expect_equal(
+    glue(character(), 1, .empty = "foo"),
+    "foo1")
+
+  expect_equal(
+    glue(1, character(), 2, .empty = "foo"),
+    "1foo2")
+
+  expect_equal(
+    glue("x: {character()}", .empty = "foo"),
+    "x: foo")
+})
+
 test_that("glue works within functions", {
   x <- 1
   f <- function(msg) glue(msg, .envir = parent.frame())