fix: Don't panic if a borrow-checker error in the graph is caused by a mutable reference

Author: LukeMathWalker

compiler/pavexc/src/compiler/analyses/call_graph/borrow_checker/move_while_borrowed.rs

@@ -349,8 +349,7 @@ fn emit_ancestor_descendant_borrow_error(
     while let Some(node_id) = nodes_to_visit.pop_front() {
         let mut incoming_edges = call_graph.edges_directed(node_id, Direction::Incoming);
         if incoming_edges.clone().any(|edge_ref| {
-            edge_ref.weight() == &CallGraphEdgeMetadata::SharedBorrow
-                && edge_ref.source().id() == contended_node_id
+            edge_ref.weight().is_borrow() && edge_ref.source().id() == contended_node_id
         }) {
             downstream_borrow_node_id = Some(node_id);
             break;

compiler/pavexc/src/compiler/analyses/call_graph/core_graph.rs

@@ -781,6 +781,15 @@ pub(crate) enum CallGraphEdgeMetadata {
     HappensBefore,
 }
 
+impl CallGraphEdgeMetadata {
+    pub(crate) fn is_borrow(&self) -> bool {
+        matches!(
+            self,
+            CallGraphEdgeMetadata::SharedBorrow | CallGraphEdgeMetadata::ExclusiveBorrow
+        )
+    }
+}
+
 impl From<ConsumptionMode> for CallGraphEdgeMetadata {
     fn from(value: ConsumptionMode) -> Self {
         match value {