From 625f057d35fa7920e27fc0aef584033b0744fcd3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kirill=20M=C3=BCller?= <kirill@cynkra.com>
Date: Sun, 25 Jan 2026 19:53:32 +0100
Subject: [PATCH 1/5] feat: Check that exactly one vertex is passed

---
 R/aaa-auto.R                 | 262 +++++++++++++++++------------------
 tools/stimulus/types-RR.yaml |  10 +-
 2 files changed, 133 insertions(+), 139 deletions(-)

diff --git a/R/aaa-auto.R b/R/aaa-auto.R
index 23226656712..6726e86cbbb 100644
--- a/R/aaa-auto.R
+++ b/R/aaa-auto.R
@@ -189,9 +189,9 @@ neighbors_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   vid <- as_igraph_vs(graph, vid)
-  if (length(vid) == 0) {
+  if (length(vid) != 1) {
     cli::cli_abort(
-      "{.arg vid} must specify at least one vertex",
+      "{.arg vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -339,16 +339,16 @@ get_all_eids_between_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -377,9 +377,9 @@ incident_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   vid <- as_igraph_vs(graph, vid)
-  if (length(vid) == 0) {
+  if (length(vid) != 1) {
     cli::cli_abort(
-      "{.arg vid} must specify at least one vertex",
+      "{.arg vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2439,16 +2439,16 @@ are_adjacent_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   v1 <- as_igraph_vs(graph, v1)
-  if (length(v1) == 0) {
+  if (length(v1) != 1) {
     cli::cli_abort(
-      "{.arg v1} must specify at least one vertex",
+      "{.arg v1} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   v2 <- as_igraph_vs(graph, v2)
-  if (length(v2) == 0) {
+  if (length(v2) != 1) {
     cli::cli_abort(
-      "{.arg v2} must specify at least one vertex",
+      "{.arg v2} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2473,16 +2473,16 @@ are_connected_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   v1 <- as_igraph_vs(graph, v1)
-  if (length(v1) == 0) {
+  if (length(v1) != 1) {
     cli::cli_abort(
-      "{.arg v1} must specify at least one vertex",
+      "{.arg v1} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   v2 <- as_igraph_vs(graph, v2)
-  if (length(v2) == 0) {
+  if (length(v2) != 1) {
     cli::cli_abort(
-      "{.arg v2} must specify at least one vertex",
+      "{.arg v2} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2716,16 +2716,16 @@ get_shortest_path_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2765,16 +2765,16 @@ get_shortest_path_bellman_ford_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2823,16 +2823,16 @@ get_shortest_path_dijkstra_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2882,16 +2882,16 @@ get_shortest_path_astar_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2940,9 +2940,9 @@ get_shortest_paths_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -2982,9 +2982,9 @@ get_all_shortest_paths_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3110,9 +3110,9 @@ get_shortest_paths_dijkstra_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3162,9 +3162,9 @@ get_shortest_paths_bellman_ford_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3214,9 +3214,9 @@ get_all_shortest_paths_dijkstra_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3426,9 +3426,9 @@ get_all_simple_paths_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3480,16 +3480,16 @@ get_k_shortest_paths_impl <- function(
   }
   k <- as.numeric(k)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3531,16 +3531,16 @@ get_widest_path_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3589,9 +3589,9 @@ get_widest_paths_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -3752,9 +3752,9 @@ subcomponent_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   vid <- as_igraph_vs(graph, vid)
-  if (length(vid) == 0) {
+  if (length(vid) != 1) {
     cli::cli_abort(
-      "{.arg vid} must specify at least one vertex",
+      "{.arg vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -6192,9 +6192,9 @@ pseudo_diameter_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   start_vid <- as_igraph_vs(graph, start_vid)
-  if (length(start_vid) == 0) {
+  if (length(start_vid) != 1) {
     cli::cli_abort(
-      "{.arg start_vid} must specify at least one vertex",
+      "{.arg start_vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -6232,9 +6232,9 @@ pseudo_diameter_dijkstra_impl <- function(
     weights <- NULL
   }
   start_vid <- as_igraph_vs(graph, start_vid)
-  if (length(start_vid) == 0) {
+  if (length(start_vid) != 1) {
     cli::cli_abort(
-      "{.arg start_vid} must specify at least one vertex",
+      "{.arg start_vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -6305,9 +6305,9 @@ random_walk_impl <- function(
     weights <- NULL
   }
   start <- as_igraph_vs(graph, start)
-  if (length(start) == 0) {
+  if (length(start) != 1) {
     cli::cli_abort(
-      "{.arg start} must specify at least one vertex",
+      "{.arg start} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -6360,9 +6360,9 @@ random_edge_walk_impl <- function(
     weights <- NULL
   }
   start <- as_igraph_vs(graph, start)
-  if (length(start) == 0) {
+  if (length(start) != 1) {
     cli::cli_abort(
-      "{.arg start} must specify at least one vertex",
+      "{.arg start} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -6621,9 +6621,9 @@ bfs_simple_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   root <- as_igraph_vs(graph, root)
-  if (length(root) == 0) {
+  if (length(root) != 1) {
     cli::cli_abort(
-      "{.arg root} must specify at least one vertex",
+      "{.arg root} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -7670,9 +7670,9 @@ layout_star_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   center <- as_igraph_vs(graph, center)
-  if (length(center) == 0) {
+  if (length(center) != 1) {
     cli::cli_abort(
-      "{.arg center} must specify at least one vertex",
+      "{.arg center} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -10313,16 +10313,16 @@ write_graph_dimacs_flow_impl <- function(
   check_string(outstream)
 
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11125,9 +11125,9 @@ rooted_product_impl <- function(
   ensure_igraph(g1)
   ensure_igraph(g2)
   root <- as_igraph_vs(g2, root)
-  if (length(root) == 0) {
+  if (length(root) != 1) {
     cli::cli_abort(
-      "{.arg root} must specify at least one vertex",
+      "{.arg root} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11179,16 +11179,16 @@ maxflow_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11231,16 +11231,16 @@ maxflow_value_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11393,16 +11393,16 @@ st_mincut_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11445,16 +11445,16 @@ st_mincut_value_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11489,16 +11489,16 @@ st_vertex_connectivity_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11550,16 +11550,16 @@ st_edge_connectivity_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11603,16 +11603,16 @@ edge_disjoint_paths_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11637,16 +11637,16 @@ vertex_disjoint_paths_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11709,9 +11709,9 @@ dominator_tree_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   root <- as_igraph_vs(graph, root)
-  if (length(root) == 0) {
+  if (length(root) != 1) {
     cli::cli_abort(
-      "{.arg root} must specify at least one vertex",
+      "{.arg root} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11745,16 +11745,16 @@ all_st_cuts_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -11785,16 +11785,16 @@ all_st_mincuts_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   source <- as_igraph_vs(graph, source)
-  if (length(source) == 0) {
+  if (length(source) != 1) {
     cli::cli_abort(
-      "{.arg source} must specify at least one vertex",
+      "{.arg source} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   target <- as_igraph_vs(graph, target)
-  if (length(target) == 0) {
+  if (length(target) != 1) {
     cli::cli_abort(
-      "{.arg target} must specify at least one vertex",
+      "{.arg target} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -13204,9 +13204,9 @@ fundamental_cycles_impl <- function(
   ensure_igraph(graph)
   if (!is.null(start)) {
     start <- as_igraph_vs(graph, start)
-    if (length(start) == 0) {
+    if (length(start) != 1) {
       cli::cli_abort(
-        "{.arg start} must specify at least one vertex",
+        "{.arg start} must specify exactly one vertex",
         call = rlang::caller_env()
       )
     }
@@ -13485,9 +13485,9 @@ random_spanning_tree_impl <- function(
   ensure_igraph(graph)
   if (!is.null(vid)) {
     vid <- as_igraph_vs(graph, vid)
-    if (length(vid) == 0) {
+    if (length(vid) != 1) {
       cli::cli_abort(
-        "{.arg vid} must specify at least one vertex",
+        "{.arg vid} must specify exactly one vertex",
         call = rlang::caller_env()
       )
     }
@@ -13636,9 +13636,9 @@ deterministic_optimal_imitation_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   vid <- as_igraph_vs(graph, vid)
-  if (length(vid) == 0) {
+  if (length(vid) != 1) {
     cli::cli_abort(
-      "{.arg vid} must specify at least one vertex",
+      "{.arg vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -13720,9 +13720,9 @@ roulette_wheel_imitation_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   vid <- as_igraph_vs(graph, vid)
-  if (length(vid) == 0) {
+  if (length(vid) != 1) {
     cli::cli_abort(
-      "{.arg vid} must specify at least one vertex",
+      "{.arg vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -13762,9 +13762,9 @@ stochastic_imitation_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   vid <- as_igraph_vs(graph, vid)
-  if (length(vid) == 0) {
+  if (length(vid) != 1) {
     cli::cli_abort(
-      "{.arg vid} must specify at least one vertex",
+      "{.arg vid} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
@@ -13916,9 +13916,9 @@ vertex_path_from_edge_path_impl <- function(
   ensure_igraph(graph)
   if (!is.null(start)) {
     start <- as_igraph_vs(graph, start)
-    if (length(start) == 0) {
+    if (length(start) != 1) {
       cli::cli_abort(
-        "{.arg start} must specify at least one vertex",
+        "{.arg start} must specify exactly one vertex",
         call = rlang::caller_env()
       )
     }
@@ -13981,7 +13981,6 @@ cliques_callback_closure_impl <- function(
     )
   }
 
-
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
@@ -14015,7 +14014,6 @@ maximal_cliques_callback_closure_impl <- function(
     )
   }
 
-
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
@@ -14091,7 +14089,6 @@ get_isomorphisms_vf2_callback_closure_impl <- function(
     )
   }
 
-
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
@@ -14170,7 +14167,6 @@ get_subisomorphisms_vf2_callback_closure_impl <- function(
     )
   }
 
-
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
@@ -14215,7 +14211,6 @@ simple_cycles_callback_closure_impl <- function(
     )
   }
 
-
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
@@ -14252,7 +14247,6 @@ motifs_randesu_callback_closure_impl <- function(
     )
   }
 
-
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
diff --git a/tools/stimulus/types-RR.yaml b/tools/stimulus/types-RR.yaml
index 628d59afb30..5146785bf73 100644
--- a/tools/stimulus/types-RR.yaml
+++ b/tools/stimulus/types-RR.yaml
@@ -196,9 +196,9 @@ VERTEX:
     CALL: '%I% - 1'
     INCONV: |-
         %I% <- as_igraph_vs(%I1%, %I%)
-        if (length(%I%) == 0) {
+        if (length(%I%) != 1) {
           cli::cli_abort(
-            "{.arg %I%} must specify at least one vertex",
+            "{.arg %I%} must specify exactly one vertex",
             call = rlang::caller_env()
           )
         }
@@ -212,9 +212,9 @@ VERTEX_ROOT:
     CALL: '%I% - 1'
     INCONV: |-
         %I% <- as_igraph_vs(%I1%, %I%)
-        if (length(%I%) == 0) {
+        if (length(%I%) != 1) {
           cli::cli_abort(
-            "{.arg %I%} must specify at least one vertex",
+            "{.arg %I%} must specify exactly one vertex",
             call = rlang::caller_env()
           )
         }
@@ -379,7 +379,7 @@ EXTRA:
 
 CLOSURE:
     CALL: '%I%_wrapped'
-    INCONV: |
+    INCONV: |-
         if (!is.function(%I%)) {
           cli::cli_abort("{.arg callback} must be a function")
         }

From 3720d5fcf8f1ac15ffd64bd3cb103d42d80041f5 Mon Sep 17 00:00:00 2001
From: krlmlr <krlmlr@users.noreply.github.com>
Date: Sun, 25 Jan 2026 19:02:11 +0000
Subject: [PATCH 2/5] chore: Auto-update from GitHub Actions

Run: https://github.com/igraph/rigraph/actions/runs/21337783921
---
 tests/testthat/_snaps/flow.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/testthat/_snaps/flow.md b/tests/testthat/_snaps/flow.md
index add2f35391b..61e2886e0f3 100644
--- a/tests/testthat/_snaps/flow.md
+++ b/tests/testthat/_snaps/flow.md
@@ -4,7 +4,7 @@
       st_cuts(g_path, source = "a", target = NULL)
     Condition
       Error in `st_cuts()`:
-      ! `target` must specify at least one vertex
+      ! `target` must specify exactly one vertex
 
 ---
 
@@ -12,7 +12,7 @@
       st_cuts(g_path, source = NULL, target = "a")
     Condition
       Error in `st_cuts()`:
-      ! `source` must specify at least one vertex
+      ! `source` must specify exactly one vertex
 
 ---
 
@@ -20,7 +20,7 @@
       st_min_cuts(g_path, source = "a", target = NULL)
     Condition
       Error in `st_min_cuts()`:
-      ! `target` must specify at least one vertex
+      ! `target` must specify exactly one vertex
 
 ---
 
@@ -28,7 +28,7 @@
       st_min_cuts(g_path, source = NULL, target = "a")
     Condition
       Error in `st_min_cuts()`:
-      ! `source` must specify at least one vertex
+      ! `source` must specify exactly one vertex
 
 # vertex_connectivity error works
 

From 7cfc92121122338d6f46bead9e2754b7547998de Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kirill=20M=C3=BCller?= <kirill@cynkra.com>
Date: Mon, 26 Jan 2026 07:30:55 +0100
Subject: [PATCH 3/5] chore: Consistent checks

---
 R/aaa-auto.R | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/R/aaa-auto.R b/R/aaa-auto.R
index a2d976c29f0..db6e330dfc9 100644
--- a/R/aaa-auto.R
+++ b/R/aaa-auto.R
@@ -314,16 +314,16 @@ get_eid_impl <- function(
   # Argument checks
   ensure_igraph(graph)
   from <- as_igraph_vs(graph, from)
-  if (length(from) == 0) {
+  if (length(from) != 1) {
     cli::cli_abort(
-      "{.arg from} must specify at least one vertex",
+      "{.arg from} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }
   to <- as_igraph_vs(graph, to)
-  if (length(to) == 0) {
+  if (length(to) != 1) {
     cli::cli_abort(
-      "{.arg to} must specify at least one vertex",
+      "{.arg to} must specify exactly one vertex",
       call = rlang::caller_env()
     )
   }

From 388f803929ed6dce9bc7bad37b6dfa6b8427019e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kirill=20M=C3=BCller?= <kirill@cynkra.com>
Date: Mon, 26 Jan 2026 07:44:10 +0100
Subject: [PATCH 4/5] Induce conflict

---
 tests/testthat/test-aaa-auto.R | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/testthat/test-aaa-auto.R b/tests/testthat/test-aaa-auto.R
index c3a96cd35b2..7f982c3c13c 100644
--- a/tests/testthat/test-aaa-auto.R
+++ b/tests/testthat/test-aaa-auto.R
@@ -11795,6 +11795,7 @@ test_that("get_eid_impl errors", {
   ))
 
   # Test error when from or to is not exactly one vertex
+  # This is here to stay in f-exactly, merging with main will give a conflict at some point.
   expect_snapshot_igraph_error(get_eid_impl(
     graph = g,
     from = c(1, 2),

From 3f1a50aac0579935d5ba701378d4ddc0ef9addb2 Mon Sep 17 00:00:00 2001
From: krlmlr <krlmlr@users.noreply.github.com>
Date: Mon, 26 Jan 2026 14:33:42 +0000
Subject: [PATCH 5/5] chore: Auto-update from GitHub Actions

Run: https://github.com/igraph/rigraph/actions/runs/21361174078
---
 tests/testthat/_snaps/aaa-auto.md | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tests/testthat/_snaps/aaa-auto.md b/tests/testthat/_snaps/aaa-auto.md
index 754b76eac82..083602728f5 100644
--- a/tests/testthat/_snaps/aaa-auto.md
+++ b/tests/testthat/_snaps/aaa-auto.md
@@ -11711,13 +11711,21 @@
       Error in `ensure_igraph()`:
       ! Must provide a graph object (provided `NULL`).
 
+---
+
+    Code
+      get_eid_impl(graph = g, from = c(1, 2), to = 2)
+    Condition
+      Error:
+      ! `from` must specify exactly one vertex
+
 ---
 
     Code
       get_eid_impl(graph = g, from = 1, to = integer(0))
     Condition
       Error:
-      ! `to` must specify at least one vertex
+      ! `to` must specify exactly one vertex
 
 # community_voronoi_impl basic