feat: vertices() errors on duplicate attribute names (#2430)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: krlmlr <[email protected]>
Co-authored-by: Kirill Müller <[email protected]>

Author: Copilot

R/operators.R

@@ -967,7 +967,21 @@ edges <- edge
 #' g
 #' plot(g)
 vertex <- function(...) {
-  structure(list(...), class = "igraph.vertex")
+  args <- list(...)
+  arg_names <- names(args)
+
+  # Check for duplicate named arguments
+  if (!is.null(arg_names)) {
+    named_args <- arg_names[arg_names != ""]
+    if (anyDuplicated(named_args)) {
+      duplicates <- unique(named_args[duplicated(named_args)])
+      cli::cli_abort(
+        "Duplicate attribute {cli::qty(duplicates)}name{?s} in {.fn vertices}: {.val {duplicates}}."
+      )
+    }
+  }
+
+  structure(args, class = "igraph.vertex")
 }
 
 #' @export

tests/testthat/_snaps/operators.md

@@ -2,3 +2,19 @@
 
     Can't recycle `name` (size 2) to match `foo` (size 3).
 
+# vertices() errors on duplicate attribute names
+
+    Duplicate attribute name in `vertices()`: "name".
+
+---
+
+    Duplicate attribute name in `vertices()`: "blop".
+
+---
+
+    Duplicate attribute name in `vertices()`: "name".
+
+---
+
+    Duplicate attribute names in `vertices()`: "foo" and "bar".
+

tests/testthat/test-operators.R

@@ -252,6 +252,28 @@ test_that("vertices() works", {
   expect_snapshot_error(make_empty_graph(1) + vertices("a", "b", foo = 5:7))
 })
 
+test_that("vertices() errors on duplicate attribute names", {
+  # Test case from issue: vertices("a", name = "c")
+  expect_snapshot_error(
+    vertices("a", name = "c", name = "d")
+  )
+
+  # Test case from issue: vertices("a", blop = "c", blop = 1)
+  expect_snapshot_error(
+    vertices("a", blop = "c", blop = 1)
+  )
+
+  # Test with graph addition
+  expect_snapshot_error(
+    make_empty_graph(1) + vertices("a", "b", name = "c", name = "d")
+  )
+
+  # Test multiple duplicates
+  expect_snapshot_error(
+    vertices(foo = 1, foo = 2, bar = 3, bar = 4)
+  )
+})
+
 test_that("infix operators work", {
   g <- make_ring(10)
   V(g)$name <- letters[1:10]