Graphviz output for new constraints

Author: amandasystems

compiler/rustc_borrowck/src/region_infer/graphviz.rs

@@ -12,6 +12,9 @@ use rustc_middle::ty::UniverseIndex;
 use super::*;
 
 fn render_outlives_constraint(constraint: &OutlivesConstraint<'_>) -> String {
+    if let ConstraintCategory::IllegalPlaceholder(from, to) = constraint.category {
+        return format!("b/c {from:?}: {to:?}");
+    }
     match constraint.locations {
         Locations::All(_) => "All(...)".to_string(),
         Locations::Single(loc) => format!("{loc:?}"),