Support splicing in named arguments of aes() (#4802)

Closes #2675

Author: lionel-

NEWS.md

@@ -1,5 +1,9 @@
 # ggplot2 (development version)
 
+* `aes()` now supports the `!!!` operator in its first two arguments
+  (#2675). Thanks to @yutannihilation and @teunbrand for draft
+  implementations.
+
 * Require rlang >= 1.0.0 (@billybarc, #4797)
 
 * `geom_violin()` no longer issues "collapsing to unique 'x' values" warning

R/aes.r

@@ -79,8 +79,21 @@ NULL
 #' cut3 <- function(x) cut_number(x, 3)
 #' scatter_by(mtcars, cut3(disp), drat)
 aes <- function(x, y, ...) {
-  exprs <- enquos(x = x, y = y, ..., .ignore_empty = "all")
-  aes <- new_aes(exprs, env = parent.frame())
+  xs <- arg_enquos("x")
+  ys <- arg_enquos("y")
+  dots <- enquos(...)
+
+  args <- c(xs, ys, dots)
+  args <- Filter(Negate(quo_is_missing), args)
+
+  # Pass arguments to helper dummy to throw an error when duplicate
+  # `x` and `y` arguments are passed through dots
+  local({
+    aes <- function(x, y, ...) NULL
+    inject(aes(!!!args))
+  })
+
+  aes <- new_aes(args, env = parent.frame())
   rename_aes(aes)
 }
 
@@ -426,3 +439,26 @@ extract_target_is_likely_data <- function(x, data, env) {
     identical(data_eval, data)
   }, error = function(err) FALSE)
 }
+
+# Takes a quosure and returns a named list of quosures, expanding
+# `!!!` expressions as needed
+arg_enquos <- function(name, frame = caller_env()) {
+  # First start with `enquo0()` which does not process injection
+  # operators
+  quo <- inject(enquo0(!!sym(name)), frame)
+  expr <- quo_get_expr(quo)
+
+  if (!is_missing(expr) && is_triple_bang(expr)) {
+    # Evaluate `!!!` operand and create a list of quosures
+    env <- quo_get_env(quo)
+    xs <- eval_bare(expr[[2]][[2]][[2]], env)
+    xs <- lapply(xs, as_quosure, env = env)
+  } else {
+    # Redefuse `x` to process injection operators, then store in a
+    # length-1 list of quosures
+    quo <- inject(enquo(!!sym(name)), frame)
+    xs <- set_names(list(quo), name)
+  }
+
+  new_quosures(xs)
+}

R/utilities.r

@@ -604,3 +604,25 @@ split_with_index <- function(x, f, n = max(f)) {
   attributes(f) <- list(levels = as.character(seq_len(n)), class = "factor")
   unname(split(x, f))
 }
+
+is_bang <- function(x) {
+  is_call(x, "!", n = 1)
+}
+
+is_triple_bang <- function(x) {
+  if (!is_bang(x)) {
+    return(FALSE)
+  }
+
+  x <- x[[2]]
+  if (!is_bang(x)) {
+    return(FALSE)
+  }
+
+  x <- x[[2]]
+  if (!is_bang(x)) {
+    return(FALSE)
+  }
+
+  TRUE
+}

tests/testthat/_snaps/aes.md

@@ -0,0 +1,7 @@
+# aes() supports `!!!` in named arguments (#2675)
+
+    Code
+      (expect_error(aes(y = 1, !!!list(y = 2))))
+    Output
+      <simpleError in aes(y = 1, y = 2): formal argument "y" matched by multiple actual arguments>
+

tests/testthat/test-aes.r

@@ -152,6 +152,22 @@ test_that("Warnings are issued when plots use discouraged extract usage within a
   expect_warning(ggplot_build(p), "Use of `df\\$x` is discouraged")
 })
 
+test_that("aes() supports `!!!` in named arguments (#2675)", {
+  expect_equal(
+    aes(!!!list(y = 1)),
+    aes(y = 1)
+  )
+  expect_equal(
+    aes(!!!list(x = 1), !!!list(y = 2)),
+    aes(x = 1, y = 2)
+  )
+  expect_equal(
+    aes(, , !!!list(y = 1)),
+    aes(y = 1)
+  )
+  expect_snapshot((expect_error(aes(y = 1, !!!list(y = 2)))))
+})
+
 # Visual tests ------------------------------------------------------------
 
 test_that("aesthetics are drawn correctly", {