From ff57e5180a1f78e8f409791305182f52abf55faf Mon Sep 17 00:00:00 2001
From: James Mitchell <jdm3@st-andrews.ac.uk>
Date: Sat, 3 Oct 2026 19:36:22 +0100
Subject: [PATCH] Move error from gv -> dot

---
 gap/dot.gi   | 14 +++++++-------
 gap/gv.gi    |  4 +---
 tst/node.tst |  2 +-
 3 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/gap/dot.gi b/gap/dot.gi
index 0997734..403d3db 100644
--- a/gap/dot.gi
+++ b/gap/dot.gi
@@ -294,10 +294,15 @@ InstallMethod(GraphvizGetAttr, "for a graphviz (di)graph or context and string",
 # GraphvizAddNode
 #############################################################################
 
-InstallMethod(GraphvizAddNode, "for a graphviz (di)graph or context and string",
-[IsGraphvizGraphDigraphOrContext, IsString],
+InstallMethod(GraphvizAddNode, "for a graphviz (di)graph or context and object",
+[IsGraphvizGraphDigraphOrContext, IsObject],
 function(gv, val)
   local node;
+  val := String(val);
+
+  if Length(val) = 0 then
+    ErrorNoReturn("the argument <val> (the name of the node being added) cannot be empty");
+  fi;
 
   # Reuse existing node if available
   node := GraphvizNode(gv, val);
@@ -332,11 +337,6 @@ function(gv, name)  # gaplint: disable=unused-func-args
                 "the node's name instead");
 end);
 
-InstallMethod(GraphvizAddNode,
-"for a graphviz (di)graph or context and string",
-[IsGraphvizGraphDigraphOrContext, IsObject],
-{x, name} -> GraphvizAddNode(x, String(name)));
-
 #############################################################################
 # GraphvizAddEdge
 #############################################################################
diff --git a/gap/gv.gi b/gap/gv.gi
index 9db9dd4..fe12654 100644
--- a/gap/gv.gi
+++ b/gap/gv.gi
@@ -35,9 +35,7 @@ InstallMethod(GV_Node, "for a string",
 [IsGraphvizGraphDigraphOrContext, IsString],
 function(graph, name)
   local out;
-  if Length(name) = 0 then
-    ErrorNoReturn("the 2nd argument (string/node name) cannot be empty");
-  fi;
+  Assert(0, not IsEmpty(name));
   out := Objectify(GV_NodeType,
                   rec(
                     Name   := name,
diff --git a/tst/node.tst b/tst/node.tst
index 0df86ab..3d9b9d3 100644
--- a/tst/node.tst
+++ b/tst/node.tst
@@ -28,7 +28,7 @@ gap> n := GraphvizAddNode(GraphvizGraph(), "  ");
 
 # Test making a node with empty name fails
 gap> n := GraphvizAddNode(GraphvizGraph(), "");
-Error, the 2nd argument (string/node name) cannot be empty
+Error, the argument <val> (the name of the node being added) cannot be empty
 
 # Test whitespace in node names
 gap> n := GraphvizAddNode(GraphvizGraph(), "a  a   ");