1 files changed, 91 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_visualize.rs b/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_visualize.rs
new file mode 100644
index 000000000..c0a0bfe8e
--- /dev/null
+++ b/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_visualize.rs
@@ -0,0 +1,91 @@
+//! Implementation of GraphWalk for DropRanges so we can visualize the control
+//! flow graph when needed for debugging.
+
+use rustc_graphviz as dot;
+use rustc_middle::ty::TyCtxt;
+
+use super::{DropRangesBuilder, PostOrderId};
+
+/// Writes the CFG for DropRangesBuilder to a .dot file for visualization.
+///
+/// It is not normally called, but is kept around to easily add debugging
+/// code when needed.
+pub(super) fn write_graph_to_file(
+    drop_ranges: &DropRangesBuilder,
+    filename: &str,
+    tcx: TyCtxt<'_>,
+) {
+    dot::render(
+        &DropRangesGraph { drop_ranges, tcx },
+        &mut std::fs::File::create(filename).unwrap(),
+    )
+    .unwrap();
+}
+
+struct DropRangesGraph<'a, 'tcx> {
+    drop_ranges: &'a DropRangesBuilder,
+    tcx: TyCtxt<'tcx>,
+}
+
+impl<'a> dot::GraphWalk<'a> for DropRangesGraph<'_, '_> {
+    type Node = PostOrderId;
+
+    type Edge = (PostOrderId, PostOrderId);
+
+    fn nodes(&'a self) -> dot::Nodes<'a, Self::Node> {
+        self.drop_ranges.nodes.iter_enumerated().map(|(i, _)| i).collect()
+    }
+
+    fn edges(&'a self) -> dot::Edges<'a, Self::Edge> {
+        self.drop_ranges
+            .nodes
+            .iter_enumerated()
+            .flat_map(|(i, node)| {
+                if node.successors.len() == 0 {
+                    vec![(i, i + 1)]
+                } else {
+                    node.successors.iter().map(move |&s| (i, s)).collect()
+                }
+            })
+            .collect()
+    }
+
+    fn source(&'a self, edge: &Self::Edge) -> Self::Node {
+        edge.0
+    }
+
+    fn target(&'a self, edge: &Self::Edge) -> Self::Node {
+        edge.1
+    }
+}
+
+impl<'a> dot::Labeller<'a> for DropRangesGraph<'_, '_> {
+    type Node = PostOrderId;
+
+    type Edge = (PostOrderId, PostOrderId);
+
+    fn graph_id(&'a self) -> dot::Id<'a> {
+        dot::Id::new("drop_ranges").unwrap()
+    }
+
+    fn node_id(&'a self, n: &Self::Node) -> dot::Id<'a> {
+        dot::Id::new(format!("id{}", n.index())).unwrap()
+    }
+
+    fn node_label(&'a self, n: &Self::Node) -> dot::LabelText<'a> {
+        dot::LabelText::LabelStr(
+            format!(
+                "{n:?}: {}",
+                self.drop_ranges
+                    .post_order_map
+                    .iter()
+                    .find(|(_hir_id, &post_order_id)| post_order_id == *n)
+                    .map_or("<unknown>".into(), |(hir_id, _)| self
+                        .tcx
+                        .hir()
+                        .node_to_string(*hir_id))
+            )
+            .into(),
+        )
+    }
+}