refactor: move optional VERTEX subtraction to INCONV block

Move the `- 1` subtraction for optional VERTEX parameters from .Call() into the INCONV block (inside the NULL check) as requested by @maelle. This improves code clarity by keeping all parameter transformations together.

Changes:
- Modified Stimulus R generator to add subtraction inside optional_wrapper_r for VERTEX type
- Updated CALL handling to pass VERTEX name directly for optional parameters
- Regenerated R/aaa-auto.R with cleaner code structure

Co-authored-by: krlmlr <1741643+krlmlr@users.noreply.github.com>

Author: Copilot

R/aaa-auto.R

@@ -9730,6 +9730,7 @@ fundamental_cycles_impl <- function(
         call = rlang::caller_env()
       )
     }
+    start <- start - 1
   }
   bfs_cutoff <- as.numeric(bfs_cutoff)
   if (is.null(weights) && "weight" %in% edge_attr_names(graph)) {
@@ -9746,7 +9747,8 @@ fundamental_cycles_impl <- function(
   res <- .Call(
     R_igraph_fundamental_cycles,
     graph,
-    if (!is.null(start)) start - 1 else NULL,    bfs_cutoff,
+    start,
+    bfs_cutoff,
     weights
   )
   if (igraph_opt("return.vs.es")) {
@@ -9982,14 +9984,15 @@ random_spanning_tree_impl <- function(
         call = rlang::caller_env()
       )
     }
+    vid <- vid - 1
   }
 
   on.exit(.Call(R_igraph_finalizer))
   # Function call
   res <- .Call(
     R_igraph_random_spanning_tree,
     graph,
-    if (!is.null(vid)) vid - 1 else NULL
+    vid
   )
   if (igraph_opt("return.vs.es")) {
     res <- create_es(graph, res)
@@ -10315,6 +10318,7 @@ vertex_path_from_edge_path_impl <- function(
         call = rlang::caller_env()
       )
     }
+    start <- start - 1
   }
   edge_path <- as_igraph_es(graph, edge_path)
   mode <- switch_igraph_arg(
@@ -10330,7 +10334,8 @@ vertex_path_from_edge_path_impl <- function(
   res <- .Call(
     R_igraph_vertex_path_from_edge_path,
     graph,
-    if (!is.null(start)) start - 1 else NULL,    edge_path - 1,
+    start,
+    edge_path - 1,
     mode
   )
   if (igraph_opt("return.vs.es")) {

tools/py-stimulus/src/stimulus/generators/r.py

@@ -255,7 +255,15 @@ def handle_argument_check(param: ParamSpec) -> str:
 
             if param.is_optional and param.is_input and res:
                 res = optional_wrapper_r(res)
-
+                # For optional VERTEX parameters, add the subtraction inside the NULL check
+                if param.type == "VERTEX":
+                    # Add the subtraction at the end of the wrapped block
+                    name = get_r_parameter_name(param)
+                    res = res.rstrip()
+                    if res.endswith("}"):
+                        # Insert before the closing brace
+                        res = res[:-1] + f"  {name} <- {name} - 1\n}}"
+                    
             # Replace template placeholders
             res = indent(res).replace("%I%", get_r_parameter_name(param))
             for i, dep in enumerate(param.dependencies):
@@ -299,9 +307,13 @@ def handle_argument_check(param: ParamSpec) -> str:
             name = get_r_parameter_name(param)
             call = type.get("CALL", name)
             if call:
-                call_formatted = call.replace("%I%", name)
-                # Add spaces around arithmetic operators
-                call_formatted = re.sub(r'(\w+)(\+|\-|\*|/)(\d+)', r'\1 \2 \3', call_formatted)
+                # For optional VERTEX parameters, subtraction is done in INCONV, so just use the name
+                if param.is_optional and param.type == "VERTEX":
+                    call_formatted = name
+                else:
+                    call_formatted = call.replace("%I%", name)
+                    # Add spaces around arithmetic operators
+                    call_formatted = re.sub(r'(\w+)(\+|\-|\*|/)(\d+)', r'\1 \2 \3', call_formatted)
                 parts.append(call_formatted)
 
         # Format .Call() as multi-line with each argument on its own line