Revert "Add support for :writable option on belongs_to (#4624)"

This reverts commit 576665f.

Author: josevalim

lib/ecto/schema.ex

@@ -1106,12 +1106,6 @@ defmodule Ecto.Schema do
     * `:where` - A filter for the association. See "Filtering associations"
       in `has_many/3`.
 
-    * `:writable` - Defines when the underlying field is allowed to modified, Must be
-      one of `:always`, `:insert`, or `:never`. If set to `:always`, the field can be
-      modified by any repo operation. If set to `:insert`, the field can be inserted
-      but cannot be further modified, even in an upsert. If set to `:never`, the field
-      becomes read only. Defaults to `:always`.
-
   ## Examples
 
       defmodule Comment do
@@ -2144,7 +2138,6 @@ defmodule Ecto.Schema do
     :defaults,
     :primary_key,
     :source,
-    :writable,
     :where
   ]
 

test/ecto/repo/belongs_to_test.exs

@@ -35,15 +35,6 @@ defmodule Ecto.Repo.BelongsToTest do
     end
   end
 
-  defmodule RestrictedSchema do
-    use Ecto.Schema
-
-    schema "restricted_schema" do
-      belongs_to :unwritable, MyAssoc, writable: :never
-      belongs_to :non_updatable, MyAssoc, writable: :insert
-    end
-  end
-
   test "handles assocs on insert" do
     sample = %MyAssoc{x: "xyz"}
 
@@ -505,29 +496,4 @@ defmodule Ecto.Repo.BelongsToTest do
     assert updated_schema.assoc_id == 2
     assert %Ecto.Association.NotLoaded{} = updated_schema.assoc
   end
-
-  test "handles writable: :never" do
-    schema =
-      %RestrictedSchema{}
-      |> Ecto.Changeset.cast(%{unwritable_id: 111}, [:unwritable_id])
-      |> TestRepo.insert!()
-
-    assert schema.unwritable_id == nil
-  end
-
-  test "handles writable: :insert" do
-    schema =
-      %RestrictedSchema{}
-      |> Ecto.Changeset.cast(%{non_updatable_id: 222}, [:non_updatable_id])
-      |> TestRepo.insert!()
-
-    assert schema.non_updatable_id == 222
-
-    schema =
-      schema
-      |> Ecto.Changeset.cast(%{non_updatable_id: 333}, [:non_updatable_id])
-      |> TestRepo.update!()
-
-    assert schema.non_updatable_id == 222
-  end
 end