1 files changed, 32 insertions, 0 deletions
diff --git a/compiler/rustc_mir_dataflow/src/framework/fmt.rs b/compiler/rustc_mir_dataflow/src/framework/fmt.rs
index 6a256fae3..e3a66bd95 100644
--- a/compiler/rustc_mir_dataflow/src/framework/fmt.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/fmt.rs
@@ -1,6 +1,7 @@
 //! Custom formatting traits used when outputting Graphviz diagrams with the results of a dataflow
 //! analysis.
 
+use super::lattice::MaybeReachable;
 use rustc_index::bit_set::{BitSet, ChunkedBitSet, HybridBitSet};
 use rustc_index::Idx;
 use std::fmt;
@@ -124,6 +125,37 @@ where
     }
 }
 
+impl<S, C> DebugWithContext<C> for MaybeReachable<S>
+where
+    S: DebugWithContext<C>,
+{
+    fn fmt_with(&self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            MaybeReachable::Unreachable => {
+                write!(f, "unreachable")
+            }
+            MaybeReachable::Reachable(set) => set.fmt_with(ctxt, f),
+        }
+    }
+
+    fn fmt_diff_with(&self, old: &Self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match (self, old) {
+            (MaybeReachable::Unreachable, MaybeReachable::Unreachable) => Ok(()),
+            (MaybeReachable::Unreachable, MaybeReachable::Reachable(set)) => {
+                write!(f, "\u{001f}+")?;
+                set.fmt_with(ctxt, f)
+            }
+            (MaybeReachable::Reachable(set), MaybeReachable::Unreachable) => {
+                write!(f, "\u{001f}-")?;
+                set.fmt_with(ctxt, f)
+            }
+            (MaybeReachable::Reachable(this), MaybeReachable::Reachable(old)) => {
+                this.fmt_diff_with(old, ctxt, f)
+            }
+        }
+    }
+}
+
 fn fmt_diff<T, C>(
     inserted: &HybridBitSet<T>,
     removed: &HybridBitSet<T>,