Print out settings that will be removed when specifying the group and key for consistency

Fix error message when specified key doesn't exist

lib/mix/tasks/pleroma/config.ex

@@ -134,7 +134,18 @@ defmodule Mix.Tasks.Pleroma.Config do
     group = maybe_atomize(group)
     key = maybe_atomize(key)
 
+    with true <- key_exists?(group, key) do
+      shell_info("The following settings will be removed from ConfigDB:\n")
+
+      group
+      |> ConfigDB.get_by_group_and_key(key)
+      |> dump()
+
       delete_key(group, key)
+    else
+      _ ->
+        shell_error("No settings in ConfigDB for #{inspect(group)}, #{inspect(key)}. Aborting.")
+    end
   end
 
   def run(["delete", "--force", group]) do
@@ -157,11 +168,22 @@ defmodule Mix.Tasks.Pleroma.Config do
     group = maybe_atomize(group)
     key = maybe_atomize(key)
 
+    with true <- key_exists?(group, key) do
+      shell_info("The following settings will be removed from ConfigDB:\n")
+
+      group
+      |> ConfigDB.get_by_group_and_key(key)
+      |> dump()
+
       if shell_prompt("Are you sure you want to continue?", "n") in ~w(Yn Y y) do
         delete_key(group, key)
       else
         shell_error("No changes made.")
       end
+    else
+      _ ->
+        shell_error("No settings in ConfigDB for #{inspect(group)}, #{inspect(key)}. Aborting.")
+    end
   end
 
   def run(["delete", group]) do
@@ -315,6 +337,13 @@ defmodule Mix.Tasks.Pleroma.Config do
     |> Enum.any?()
   end
 
+  defp key_exists?(group, key) do
+    group
+    |> ConfigDB.get_by_group_and_key(key)
+    |> is_nil
+    |> Kernel.!()
+  end
+
   defp maybe_atomize(arg) when is_atom(arg), do: arg
 
   defp maybe_atomize(":" <> arg), do: maybe_atomize(arg)