fix recursion layout issue

cli/src/repl/eval.rs

@@ -140,6 +140,9 @@ fn jit_to_ast_help<'a>(
 
                     single_tag_union_to_ast(env, ptr, field_layouts, tag_name.clone(), payload_vars)
                 }
+                Content::Structure(FlatType::FunctionOrTagUnion(tag_name, _, _)) => {
+                    single_tag_union_to_ast(env, ptr, field_layouts, tag_name.clone(), &[])
+                }
                 other => {
                     unreachable!(
                         "Something had a Struct layout, but instead of a Record or TagUnion type, it had: {:?}",
@@ -313,6 +316,9 @@ fn ptr_to_ast<'a>(
                 let (tag_name, payload_vars) = tags.iter().next().unwrap();
                 single_tag_union_to_ast(env, ptr, field_layouts, tag_name.clone(), payload_vars)
             }
+            Content::Structure(FlatType::FunctionOrTagUnion(tag_name, _, _)) => {
+                single_tag_union_to_ast(env, ptr, field_layouts, tag_name.clone(), &[])
+            }
             Content::Structure(FlatType::EmptyRecord) => {
                 struct_to_ast(env, ptr, &[], &MutMap::default())
             }

compiler/mono/src/layout.rs

@@ -423,6 +423,12 @@ impl<'a, 'b> Env<'a, 'b> {
 
         self.seen.insert(var)
     }
+
+    fn remove_seen(&mut self, var: Variable) -> bool {
+        let var = self.subs.get_root_key_without_compacting(var);
+
+        self.seen.remove(&var)
+    }
 }
 
 impl<'a> Layout<'a> {
@@ -1248,6 +1254,8 @@ fn layout_from_flat_type<'a>(
                 UnionLayout::Recursive(tag_layouts.into_bump_slice())
             };
 
+            env.remove_seen(rec_var);
+
             Ok(Layout::Union(union_layout))
         }
         EmptyTagUnion => {

compiler/types/src/pretty_print.rs

@@ -595,6 +595,11 @@ pub fn chase_ext_tag_union(
 
             chase_ext_tag_union(subs, ext_var, fields)
         }
+        Content::Structure(FunctionOrTagUnion(tag_name, _, ext_var)) => {
+            fields.push((tag_name, vec![]));
+
+            chase_ext_tag_union(subs, ext_var, fields)
+        }
         Content::Alias(_, _, var) => chase_ext_tag_union(subs, var, fields),
 
         content => Err((var, content)),

compiler/unify/src/unify.rs

@@ -1051,13 +1051,14 @@ fn unify_flat_type(
         }
 
         (RecursiveTagUnion(recursion_var, tags1, ext1), FunctionOrTagUnion(tag_name, _, ext2)) => {
+            // this never happens in type-correct programs, but may happen if there is a type error
             debug_assert!(is_recursion_var(subs, *recursion_var));
 
-            let union1 = gather_tags(subs, tags1.clone(), *ext1);
-
             let mut tags2 = MutMap::default();
             tags2.insert(tag_name.clone(), vec![]);
-            let union2 = gather_tags(subs, tags2, *ext2);
+
+            let union1 = gather_tags(subs, tags1.clone(), *ext1);
+            let union2 = gather_tags(subs, tags2.clone(), *ext2);
 
             unify_tag_union(
                 subs,
@@ -1074,12 +1075,13 @@ fn unify_flat_type(
 
             let mut tags1 = MutMap::default();
             tags1.insert(tag_name.clone(), vec![]);
-            let union1 = gather_tags(subs, tags1, *ext1);
 
+            let union1 = gather_tags(subs, tags1.clone(), *ext1);
             let union2 = gather_tags(subs, tags2.clone(), *ext2);
 
             unify_tag_union_not_recursive_recursive(subs, pool, ctx, union1, union2, *recursion_var)
         }
+
         (other1, other2) => mismatch!(
             "Trying to unify two flat types that are incompatible: {:?} ~ {:?}",
             other1,