From 285981cbcb6508ab973af289209e8ecae7cb7697 Mon Sep 17 00:00:00 2001
From: Nic Crane <thisisnic@gmail.com>
Date: Sat, 12 Sep 2026 08:32:00 -0400
Subject: [PATCH 1/2] Error on empty column names

---
 r/R/dplyr-eval.R                   |  9 +++++++++
 r/tests/testthat/test-dplyr-eval.R | 25 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/r/R/dplyr-eval.R b/r/R/dplyr-eval.R
index 1282f171878d..5ed95c7646d7 100644
--- a/r/R/dplyr-eval.R
+++ b/r/R/dplyr-eval.R
@@ -252,6 +252,15 @@ abandon_ship <- function(err, env) {
 arrow_mask <- function(.data) {
   f_env <- new_environment(.cache$functions)
 
+  # Empty column names can't be bound into an environment (GH-40303).
+  # Like dplyr, refuse to transform such data rather than repairing names.
+  if (!all(nzchar(names(.data$selected_columns)))) {
+    abort(c(
+      "Can't transform data with empty (`\"\"`) column names.",
+      i = "Rename or drop the unnamed columns first, e.g. with `rename()` or `select()`."
+    ))
+  }
+
   # Assign the schema to the expressions
   schema <- .data$.data$schema
   walk(.data$selected_columns, ~ (.$schema <- schema))
diff --git a/r/tests/testthat/test-dplyr-eval.R b/r/tests/testthat/test-dplyr-eval.R
index 0b0b9f98f432..50ab3a6c3834 100644
--- a/r/tests/testthat/test-dplyr-eval.R
+++ b/r/tests/testthat/test-dplyr-eval.R
@@ -59,3 +59,28 @@ test_that("try_arrow_dplyr/abandon_ship adds the right message about collect()",
     expect_snapshot(tester(ds, i), error = TRUE)
   }
 })
+
+test_that("dplyr verbs error clearly on empty column names", {
+  # GH-40303
+  tbl <- example_data
+  names(tbl)[1] <- ""
+
+  # dplyr also refuses these ("Can't transform a data frame with `NA` or
+  # `""` names."), but our wording differs since the input isn't a data frame
+  tab <- arrow_table(tbl)
+  msg <- "Can't transform data with empty"
+  expect_error(tab |> mutate(z = dbl + 1), msg)
+  expect_error(tab |> filter(dbl > 4), msg)
+  expect_error(tab |> arrange(dbl), msg)
+  expect_error(tab |> group_by(dbl), msg)
+
+  # select() and rename() still work as an escape hatch, as in dplyr
+  compare_dplyr_binding(
+    .input |> select(-1) |> mutate(z = dbl + 1) |> collect(),
+    tbl
+  )
+  compare_dplyr_binding(
+    .input |> rename(int = 1) |> mutate(z = dbl + 1) |> collect(),
+    tbl
+  )
+})

From 92ae85b891ac0fba7fcafc57ceaec02c16463ccc Mon Sep 17 00:00:00 2001
From: Nic Crane <thisisnic@gmail.com>
Date: Wed, 16 Sep 2026 11:30:44 -0500
Subject: [PATCH 2/2] Add test for empty column names in dplyr verbs

Add test for dplyr verbs handling empty column names.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
---
 r/tests/testthat/test-dplyr-eval.R | 1 +
 1 file changed, 1 insertion(+)

diff --git a/r/tests/testthat/test-dplyr-eval.R b/r/tests/testthat/test-dplyr-eval.R
index 50ab3a6c3834..78bd84eb6d21 100644
--- a/r/tests/testthat/test-dplyr-eval.R
+++ b/r/tests/testthat/test-dplyr-eval.R
@@ -61,6 +61,7 @@ test_that("try_arrow_dplyr/abandon_ship adds the right message about collect()",
 })
 
 test_that("dplyr verbs error clearly on empty column names", {
+  skip_if_not_available("acero")
   # GH-40303
   tbl <- example_data
   names(tbl)[1] <- ""