Change GraphMap to Graph

Author: pierwill

Cargo.lock

@@ -20,3 +20,4 @@ chalk-solve = { version = "0.76.0-dev.0", path = "../chalk-solve" }
 chalk-recursive = { version = "0.76.0-dev.0", path = "../chalk-recursive" }
 chalk-engine = { version = "0.76.0-dev.0", path = "../chalk-engine" }
 chalk-parse = { version = "0.76.0-dev.0", path = "../chalk-parse" }
+indexmap = "1.6.2"

chalk-integration/Cargo.toml

@@ -105,18 +105,21 @@ where
 
     // Build the forest of specialization relationships.
     fn build_specialization_forest(&self) -> Result<Graph<ImplId<I>, ()>, CoherenceError<I>> {
-        // The forest is returned as a graph but built as a GraphMap; this is
-        // so that we never add multiple nodes with the same ItemId.
-        let mut forest = DiGraphMap::new();
+        let mut forest = DiGraph::new();
+
+        let node_impls: Vec<ImplId<_>> = forest.raw_nodes().iter().map(|x| x.weight).collect();
 
-        // Find all specializations (implemented in coherence/solve)
-        // Record them in the forest by adding an edge from the less special
-        // to the more special.
         self.visit_specializations_of_trait(|less_special, more_special| {
-            forest.add_edge(less_special, more_special, ());
+            // Check so that we never add multiple nodes with the same ImplId.
+            if !node_impls.contains(&less_special) && !node_impls.contains(&more_special) {
+                let l = forest.add_node(less_special);
+                let m = forest.add_node(more_special);
+
+                forest.add_edge(l, m, ());
+            }
         })?;
 
-        Ok(forest.into_graph())
+        Ok(forest)
     }
 
     // Recursively set priorities for those node and all of its children.