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lib/elixir/lib/module/types/apply.ex

@@ -1328,6 +1328,9 @@ defmodule Module.Types.Apply do
   Computes the return type of an application.
   """
   def return(type, args_types, stack) do
+    # An argument being gradual does not imply the return type
+    # is gradual in static mode. However, we do wrap in dynamic
+    # in :dynamic / :gradual mode to avoid false positives.
     cond do
       stack.mode == :static -> type
       Enum.any?(args_types, &gradual?/1) -> dynamic(type)