feat: add ConcreteVariantEntry for non-SimpleGraph variant nodes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: GiggleLiu

src/rules/graph.rs

@@ -10,7 +10,7 @@
 
 use crate::graph_types::{GraphSubtypeEntry, WeightSubtypeEntry};
 use crate::rules::cost::PathCostFn;
-use crate::rules::registry::{ReductionEntry, ReductionOverhead};
+use crate::rules::registry::{ConcreteVariantEntry, ReductionEntry, ReductionOverhead};
 use crate::types::ProblemSize;
 use ordered_float::OrderedFloat;
 use petgraph::algo::all_simple_paths;
@@ -21,6 +21,13 @@ use std::any::TypeId;
 use std::cmp::Reverse;
 use std::collections::{BinaryHeap, HashMap, HashSet};
 
+// Register concrete variants for problems that support non-SimpleGraph graph types.
+// These generate additional nodes in the JSON export.
+inventory::submit! { ConcreteVariantEntry { name: "MaximumIndependentSet", variant: &[("graph", "GridGraph"), ("weight", "Unweighted")] } }
+inventory::submit! { ConcreteVariantEntry { name: "MaximumIndependentSet", variant: &[("graph", "UnitDiskGraph"), ("weight", "Unweighted")] } }
+inventory::submit! { ConcreteVariantEntry { name: "MaxCut", variant: &[("graph", "GridGraph"), ("weight", "Unweighted")] } }
+inventory::submit! { ConcreteVariantEntry { name: "SpinGlass", variant: &[("graph", "GridGraph"), ("weight", "f64")] } }
+
 /// JSON-serializable representation of the reduction graph.
 #[derive(Debug, Clone, Serialize)]
 pub struct ReductionGraphJson {
@@ -673,6 +680,14 @@ impl ReductionGraph {
             ));
         }
 
+        // Also collect nodes from ConcreteVariantEntry registrations
+        for entry in inventory::iter::<ConcreteVariantEntry> {
+            node_set.insert((
+                entry.name.to_string(),
+                Self::variant_to_map(entry.variant),
+            ));
+        }
+
         // Build nodes with categories and doc paths
         let mut nodes: Vec<NodeJson> = node_set
             .iter()

src/rules/registry.rs

@@ -89,6 +89,15 @@ impl std::fmt::Debug for ReductionEntry {
 
 inventory::collect!(ReductionEntry);
 
+/// A registered concrete problem variant (for JSON export nodes).
+/// Variants registered here appear as nodes even without explicit reduction rules.
+pub struct ConcreteVariantEntry {
+    pub name: &'static str,
+    pub variant: &'static [(&'static str, &'static str)],
+}
+
+inventory::collect!(ConcreteVariantEntry);
+
 #[cfg(test)]
 #[path = "../unit_tests/rules/registry.rs"]
 mod tests;

src/unit_tests/rules/graph.rs

@@ -813,3 +813,28 @@ fn test_json_variant_content() {
         "Edge involving MaximumIndependentSet should exist"
     );
 }
+
+#[test]
+fn test_concrete_variant_nodes_in_json() {
+    let graph = ReductionGraph::new();
+    let json = graph.to_json();
+
+    // GridGraph variants should appear as nodes
+    let mis_gridgraph = json.nodes.iter().any(|n| {
+        n.name == "MaximumIndependentSet"
+            && n.variant.get("graph") == Some(&"GridGraph".to_string())
+    });
+    assert!(mis_gridgraph, "MIS/GridGraph node should exist");
+
+    let mis_unitdisk = json.nodes.iter().any(|n| {
+        n.name == "MaximumIndependentSet"
+            && n.variant.get("graph") == Some(&"UnitDiskGraph".to_string())
+    });
+    assert!(mis_unitdisk, "MIS/UnitDiskGraph node should exist");
+
+    let maxcut_gridgraph = json.nodes.iter().any(|n| {
+        n.name == "MaxCut"
+            && n.variant.get("graph") == Some(&"GridGraph".to_string())
+    });
+    assert!(maxcut_gridgraph, "MaxCut/GridGraph node should exist");
+}