pending test for #528

unison-src/tests/fix528.uu

@@ -0,0 +1,36 @@
+-- needs Base.u
+
+use Trie tail head
+
+type Trie k v = { head : Optional v, tail : Map k (Trie k v) }
+
+Trie.empty = Trie None Map.empty
+
+Trie.toList : Trie k v -> [([k], v)]
+Trie.toList t =
+  go : [k] -> Trie k v -> [([k], v)]
+  go path t =
+    here = case Trie.head t of
+      Optional.None -> []
+      Optional.Some v -> [(path, v)]
+    tail t |> Map.toList
+           |> List.map (p -> go (path `snoc` at1 p) (at2 p))
+           |> List.join
+           |> (List.++) here
+  go [] t
+
+> toList Trie.empty
+
+---
+
+bombs with:
+
+  💔💥
+
+  I stopped evaluation after encountering an error:
+
+    user error (type error, expecting List, got: (Lam 1 FormClosure 5MQKGmyVUfJMTmaGyk8TBmLJMoZbUKGDE4fgKBhAMzMkmwpweM7gsPPUivFuY4PeMM1Qrt7e2RnAs2sw4QJzsqjJ Ref(##List.++) [[]] (Leaf External:ExternalFunction)))
+
+  I'm sorry this message doesn't have more detail
+  about the location of the failure. My makers plan to
+  fix this in a future release. 😢