Ensure that quasi_label() doesn't error for missing inputs (#2248)

Author: hadley

R/quasi-label.R

@@ -59,10 +59,11 @@ quasi_label <- function(quo, label = NULL, arg = NULL) {
 }
 
 labelled_value <- function(value, label) {
-  list(
-    val = value,
-    lab = label
-  )
+  if (missing(value)) {
+    list(val = missing_arg(), lab = label)
+  } else {
+    list(val = value, lab = label)
+  }
 }
 
 quasi_capture <- function(.quo, .label, .capture, ...) {

tests/testthat/_snaps/quasi-label.md

@@ -1,3 +1,14 @@
+# missing arguments are propagated
+
+    Code
+      expect_null(x$missing)
+    Condition
+      Error:
+      ! Expected `x$missing` to be NULL.
+      Differences:
+      `actual` is absent
+      `expected` is NULL
+
 # produces useful summaries for long calls
 
     Code

tests/testthat/test-quasi-label.R

@@ -10,6 +10,10 @@ test_that("symbols are quoted", {
   expect_equal(expr_label(quote(a)), "`a`")
 })
 
+test_that("missing arguments are propagated", {
+  x <- list(missing = missing_arg())
+  expect_snapshot_failure(expect_null(x$missing))
+})
 
 test_that("is_call_infix() handles complex calls (#1472)", {
   expect_false(is_call_infix(quote(