feat(ir): use petgraph

src/ir/graph.rs

@@ -0,0 +1,37 @@
+use hashbrown::HashMap;
+use petgraph::graph::{DiGraph, NodeIndex};
+use petgraph::algo::{condensation, toposort};
+
+use super::*;
+
+struct GraphBuilder<'ctx> {
+    ctx: &'ctx DowngradeContext,
+    graph: DiGraph<usize, ()>,
+    nodes: HashMap<usize, NodeIndex>
+}
+
+impl GraphBuilder<'_> {
+    fn connect(&mut self, idx: usize) {
+        let node = self.graph.add_node(idx);
+        self.nodes.insert(idx, node);
+        let deps = self.ctx.thunk_deps.get(idx).unwrap();
+        for (&refee, _) in deps {
+            if !self.nodes.contains_key(&refee) {
+                self.connect(refee);
+            }
+            self.graph.add_edge(node, *self.nodes.get(&refee).unwrap(), ());
+        }
+    }
+}
+
+pub fn sort_dependencies(ctx: &DowngradeContext) -> Vec<Vec<usize>> {
+    let mut builder = GraphBuilder {
+        ctx,
+        graph: DiGraph::new(),
+        nodes: HashMap::new(),
+    };
+    builder.connect(ctx.thunks.len() - 1);
+    let mut graph = condensation(builder.graph, false);
+    let sorted = toposort(&graph, None).unwrap();
+    sorted.into_iter().map(|idx| graph.remove_node(idx).unwrap()).collect_vec()
+}