allow datetime as form option values (#468)

Author: ryanwinchester

lib/phoenix_html/form.ex

@@ -391,7 +391,8 @@ defmodule Phoenix.HTML.Form do
   end
 
   defp option(group_label, group_values, extra, value)
-       when is_list(group_values) or is_map(group_values) do
+       when is_list(group_values) or
+              (is_map(group_values) and not is_map_key(group_values, :__struct__)) do
     section_options = escaped_options_for_select(group_values, value, extra)
     option_tag("optgroup", [label: group_label], {:safe, section_options})
   end

test/phoenix_html/form_test.exs

@@ -293,6 +293,19 @@ defmodule Phoenix.HTML.FormTest do
                ~s(<option value="value">Label</option>) <>
                  ~s(<hr/>) <>
                  ~s(<option value="new">New</option>)
+
+      assert options_for_select(
+               [
+                 {"Open", ~U[2025-01-01 06:30:00.000000Z]},
+                 {"Close", ~U[2025-01-01 18:30:00.000000Z]}
+               ],
+               [
+                 ~U[2025-01-01 06:30:00.000000Z]
+               ]
+             )
+             |> safe_to_string() ==
+               ~s(<option selected value="2025-01-01T06:30:00.000000Z">Open</option>) <>
+                 ~s(<option value="2025-01-01T18:30:00.000000Z">Close</option>)
     end
 
     test "with custom option tag" do