Allow for specifying the :writable and :on_writable_violation option for :inserted_at in the timestamps macro

lib/ecto/schema.ex

@@ -167,8 +167,8 @@ defmodule Ecto.Schema do
       used by `belongs_to` associations. It must be set in the same
       module that defines the `belongs_to`. Defaults to `:id`;
 
-    * `@timestamps_opts` - configures the default timestamps type
-      used by `timestamps`. Defaults to `[type: :naive_datetime]`;
+    * `@timestamps_opts` - configures the default timestamps options
+      used by the [`timestamps`](`timestamps/1`) macro. Defaults to `[type: :naive_datetime]`;
 
     * `@derive` - the same as `@derive` available in `Kernel.defstruct/1`
       as the schema defines a struct behind the scenes;
@@ -730,6 +730,11 @@ defmodule Ecto.Schema do
     * `:inserted_at` - the Ecto schema name of the field for insertion times or `false`
     * `:updated_at` - the Ecto schema name of the field for update times or `false`
     * `:inserted_at_source` - the name of the database column for insertion times or `false`
+    * `:inserted_at_writable` - the value of the Ecto schema `:writable` option for the
+      `inserted_at` field generated by this macro. Raises if `:never` is provided,
+      as Ecto must be able to automatically set the field at insertion.
+    * `:inserted_at_on_writable_violation` - the value of the Ecto schema `:on_writable_violation`
+      option for the `inserted_at` field generated by this macro.
     * `:updated_at_source` - the name of the database column for update times or `false`
     * `:type` - the timestamps type, defaults to `:naive_datetime`.
     * `:autogenerate` - a module-function-args tuple used for generating
@@ -2110,6 +2115,23 @@ defmodule Ecto.Schema do
 
     if inserted_at do
       opts = if source = timestamps[:inserted_at_source], do: [source: source], else: []
+
+      opts = if writable = timestamps[:inserted_at_writable] do
+        if writable == :never do
+          raise ArgumentError, ":inserted_at_writable option cannot be set to :never as `inserted_at` will never be populated"
+        end
+
+        Keyword.put(opts, :writable, writable)
+      else
+        opts
+      end
+
+      opts = if on_writable_violation = timestamps[:inserted_at_on_writable_violation] do
+        Keyword.put(opts, :on_writable_violation, on_writable_violation)
+      else
+        opts
+      end
+
       Ecto.Schema.__field__(mod, inserted_at, type, opts)
     end
 

test/ecto/schema_test.exs

@@ -359,6 +359,40 @@ defmodule Ecto.SchemaTest do
              [{[:updated_at], {:m, :f, [:a]}}]
   end
 
+  defmodule TimestampsWritableDefault do
+    use Ecto.Schema
+
+    schema "timestamps" do
+      timestamps()
+    end
+  end
+
+  defmodule TimestampsWritableCustom do
+    use Ecto.Schema
+
+    schema "timestamps" do
+      timestamps(inserted_at_writable: :insert, inserted_at_on_writable_violation: :raise)
+    end
+  end
+
+  test "timestamps with writable options" do
+    assert TimestampsWritableDefault.__schema__(:updatable_fields) == {[:updated_at, :inserted_at, :id], []}
+    assert TimestampsWritableDefault.__schema__(:on_writable_violation, :inserted_at) == :nothing
+
+    assert TimestampsWritableCustom.__schema__(:updatable_fields) == {[:updated_at, :id], [:inserted_at]}
+    assert TimestampsWritableCustom.__schema__(:on_writable_violation, :inserted_at) == :raise
+
+    assert_raise ArgumentError, ":inserted_at_writable option cannot be set to :never as `inserted_at` will never be populated", fn ->
+      defmodule TimestampsWritableNever do
+        use Ecto.Schema
+
+        schema "timestamps" do
+          timestamps(inserted_at_writable: :never)
+        end
+      end
+    end
+  end
+
   defmodule TimestampsCustom do
     use Ecto.Schema