theme() supports splicing arguments

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* `theme()` now supports splicing a list of arguments (#5542).
+
 * Contour functions will not fail when `options("OutDec")` is not `.` (@eliocamp, #5555).
 
 * The `legend.key` theme element is set to inherit from the `panel.background`

R/theme.R

@@ -281,7 +281,8 @@
 #' p3 + theme(strip.text.x.top = element_text(colour = "white", face = "bold"))
 #' p3 + theme(panel.spacing = unit(1, "lines"))
 #' }
-theme <- function(line,
+theme <- function(...,
+                  line,
                   rect,
                   text,
                   title,
@@ -388,7 +389,6 @@ theme <- function(line,
                   strip.text.y.right,
                   strip.switch.pad.grid,
                   strip.switch.pad.wrap,
-                  ...,
                   complete = FALSE,
                   validate = TRUE) {
   elements <- find_args(..., complete = NULL, validate = NULL)

R/utilities.R

@@ -320,7 +320,7 @@ find_args <- function(...) {
   vals <- mget(args, envir = env)
   vals <- vals[!vapply(vals, is_missing_arg, logical(1))]
 
-  modify_list(vals, list(..., `...` = NULL))
+  modify_list(vals, list2(..., `...` = NULL))
 }
 
 # Used in annotations to ensure printed even when no

tests/testthat/test-theme.R

@@ -6,6 +6,13 @@ test_that("dollar subsetting the theme does no partial matching", {
   expect_equal(t$foobar, 12)
 })
 
+test_that("theme argument splicing works", {
+  l <- list(a = 10, b = "c", d = c("foo", "bar"))
+  test <- theme(!!!l)
+  ref  <- theme(a = 10, b = "c", d = c("foo", "bar"))
+  expect_equal(test, ref)
+})
+
 test_that("modifying theme element properties with + operator works", {
 
   # Changing a "leaf node" works