From 8d91f66b8efc3ee82a56ea7da0d2893124f7fa5d Mon Sep 17 00:00:00 2001
From: Seyon Sivarajah <seyon.sivarajah@quantinuum.com>
Date: Mon, 6 Nov 2023 17:50:34 +0000
Subject: [PATCH] add test for non-dominating edge validation

---
 src/builder/cfg.rs | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/builder/cfg.rs b/src/builder/cfg.rs
index 275782906..7b87caff0 100644
--- a/src/builder/cfg.rs
+++ b/src/builder/cfg.rs
@@ -325,6 +325,8 @@ mod test {
     use crate::builder::build_traits::HugrBuilder;
     use crate::builder::{DataflowSubContainer, ModuleBuilder};
 
+    use crate::hugr::validate::InterGraphEdgeError;
+    use crate::hugr::ValidationError;
     use crate::{builder::test::NAT, type_row};
     use cool_asserts::assert_matches;
 
@@ -408,17 +410,52 @@ mod test {
 
             entry_b.finish_with_outputs(sum, [])?
         };
-        let exit = cfg_builder.exit_block();
         let mut middle_b =
             cfg_builder.simple_block_builder(FunctionType::new(type_row![], type_row![NAT]), 1)?;
         let middle = {
             let c = middle_b.load_const(&sum_tuple_const)?;
             middle_b.finish_with_outputs(c, [inw])?
         };
+        let exit = cfg_builder.exit_block();
         cfg_builder.branch(&entry, 0, &middle)?;
         cfg_builder.branch(&middle, 0, &exit)?;
         assert_matches!(cfg_builder.finish_prelude_hugr(), Ok(_));
 
         Ok(())
     }
+
+    #[test]
+    fn test_non_dom_edge() -> Result<(), BuildError> {
+        let mut cfg_builder = CFGBuilder::new(FunctionType::new(type_row![NAT], type_row![NAT]))?;
+        let sum_tuple_const =
+            cfg_builder.add_constant(ops::Const::unary_unit_sum(), ExtensionSet::new())?;
+        let sum_variants = vec![type_row![]];
+        let mut middle_b = cfg_builder
+            .simple_block_builder(FunctionType::new(type_row![NAT], type_row![NAT]), 1)?;
+        let [inw] = middle_b.input_wires_arr();
+        let middle = {
+            let c = middle_b.load_const(&sum_tuple_const)?;
+            middle_b.finish_with_outputs(c, [inw])?
+        };
+
+        let mut entry_b =
+            cfg_builder.entry_builder(sum_variants.clone(), type_row![NAT], ExtensionSet::new())?;
+        let entry = {
+            let sum = entry_b.load_const(&sum_tuple_const)?;
+            // entry block uses wire from middle block even though middle block
+            // does not dominate entry
+            entry_b.finish_with_outputs(sum, [inw])?
+        };
+        let exit = cfg_builder.exit_block();
+        cfg_builder.branch(&entry, 0, &middle)?;
+        cfg_builder.branch(&middle, 0, &exit)?;
+        assert_matches!(
+            cfg_builder.finish_prelude_hugr(),
+            Err(ValidationError::InterGraphEdgeError(
+                InterGraphEdgeError::NonDominatedAncestor { .. }
+            ))
+        );
+
+        Ok(())
+    }
 }