Provide more informative error for dynamic.dict when key is a string

Author: sporto

src/gleam/dynamic.gleam

@@ -976,13 +976,17 @@ pub fn dict(
       |> dict.to_list
       |> list.try_map(fn(pair) {
         let #(k, v) = pair
+        let value_error = case string(k) {
+          Ok(k) -> "values[" <> k <> "]"
+          _ -> "values"
+        }
         use k <- result.try(
           key_type(k)
           |> map_errors(push_path(_, "keys")),
         )
         use v <- result.try(
           value_type(v)
-          |> map_errors(push_path(_, "values")),
+          |> map_errors(push_path(_, value_error)),
         )
         Ok(#(k, v))
       }),

test/gleam/dynamic_test.gleam

@@ -1138,6 +1138,13 @@ pub fn dict_test() {
   dict.from_list([#("a", 1), #("b", 2)])
   |> dynamic.from
   |> dynamic.dict(dynamic.string, dynamic.string)
+  |> should.equal(
+    Error([DecodeError(expected: "String", found: "Int", path: ["values[a]"])]),
+  )
+
+  dict.from_list([#(1, 1), #(2, 2)])
+  |> dynamic.from
+  |> dynamic.dict(dynamic.int, dynamic.string)
   |> should.equal(
     Error([DecodeError(expected: "String", found: "Int", path: ["values"])]),
   )