add tests for the rigid issue

compiler/constrain/src/pattern.rs

@@ -11,6 +11,7 @@ use roc_region::all::{Located, Region};
 use roc_types::subs::Variable;
 use roc_types::types::{Category, PReason, PatternCategory, Reason, RecordField, Type};
 
+#[derive(Default)]
 pub struct PatternState {
     pub headers: SendMap<Symbol, Located<Type>>,
     pub vars: Vec<Variable>,

compiler/gen/tests/gen_primitives.rs

@@ -1148,7 +1148,7 @@ mod gen_primitives {
 
                 ConsList a : [ Cons a (ConsList a), Nil ]
 
-                # isEmpty : ConsList a -> Bool
+                isEmpty : ConsList a -> Bool
                 isEmpty = \list ->
                     when list is
                         Cons _ _ ->

compiler/solve/tests/solve_expr.rs

@@ -3106,4 +3106,33 @@ mod solve_expr {
             "Dict Int Int",
         );
     }
+
+    #[test]
+    fn rbtree_insert() {
+        // exposed an issue where pattern variables were not introduced
+        // at the correct level in the constraint
+        //
+        // see 22592eff805511fbe1da63849771ee5f367a6a16
+        infer_eq_without_problem(
+            indoc!(
+                r#"
+                app Test provides [ main ] imports []
+
+                Dict k : [ Node k (Dict k), Empty ]
+
+                balance : Dict k -> Dict k
+                balance = \left ->
+                    when left is
+                      Node _ Empty -> Empty
+
+                      _ -> Empty
+
+                main : Dict {}
+                main =
+                    balance Empty
+                "#
+            ),
+            "Dict {}",
+        );
+    }
 }