Feat/ensure constructor usage

.gitignore

@@ -23,3 +23,4 @@ erl_crash.dump
 struct_cop-*.tar
 
 .elixir_ls
+.DS_Store

lib/struct_cop.test.exs

@@ -3,12 +3,12 @@ defmodule StructCopTest do
 
   describe "cast!/2" do
     test "returns struct" do
-      assert %TestStruct{a: 4} = %TestStruct{} |> StructCop.cast!(a: 4)
+      assert %TestStruct{a: 4} = TestStruct.new!() |> StructCop.cast!(a: 4)
     end
 
     test "raises ArgumentError for invalid attrs" do
       assert_raise ArgumentError, fn ->
-        %TestStruct{}
+        TestStruct.new!()
         |> StructCop.cast!(a: 5)
       end
     end
@@ -28,16 +28,16 @@ defmodule StructCopTest do
 
   describe "cast/2" do
     test "returns {:ok, struct}" do
-      assert {:ok, %TestStruct{a: 4}} = %TestStruct{} |> StructCop.cast(a: 4)
+      assert {:ok, %TestStruct{a: 4}} = TestStruct.new!() |> StructCop.cast(a: 4)
     end
 
     test "handles struct as attrs" do
-      assert {:ok, %TestStruct{a: 4}} = %TestStruct{} |> StructCop.cast(%TestStruct{a: 4})
+      assert {:ok, %TestStruct{a: 4}} = TestStruct.new!() |> StructCop.cast(TestStruct.new!(a: 4))
     end
 
     test "returns {:error, %Ecto.Changeset{}} for invalid attrs" do
       assert {:error, %Ecto.Changeset{valid?: false, errors: errors}} =
-               %TestStruct{} |> StructCop.cast(a: 3)
+               TestStruct.new!() |> StructCop.cast(a: 3)
 
       assert :a in Keyword.keys(errors)
     end
@@ -56,21 +56,21 @@ defmodule StructCopTest do
   describe "cast/2 for compound fileds" do
     test "casts array field" do
       assert {:ok, %TestStruct{array: [1, 2, 3]}} =
-               %TestStruct{} |> StructCop.cast(array: [1, 2, 3])
+               TestStruct.new!() |> StructCop.cast(array: [1, 2, 3])
     end
 
     test "casts map field" do
       assert {:ok, %TestStruct{map: %{abc: 1, cde: 2}}} =
-               %TestStruct{} |> StructCop.cast(map: %{abc: 1, cde: 2})
+               TestStruct.new!() |> StructCop.cast(map: %{abc: 1, cde: 2})
     end
   end
 
   test "cast/2 for embeds_one with nested StructCop" do
     assert {:ok, %TestStruct{nested: %TestStruct.Nested{a: 1, b: 2}}} =
-             %TestStruct{} |> StructCop.cast(nested: %{a: 1, b: 2})
+             TestStruct.new!() |> StructCop.cast(nested: %{a: 1, b: 2})
 
     assert {:error, %Ecto.Changeset{valid?: false, changes: %{nested: nested_changeset}}} =
-             %TestStruct{} |> StructCop.cast(nested: %{b: 2})
+             TestStruct.new!() |> StructCop.cast(nested: %{b: 2})
 
     assert %Ecto.Changeset{valid?: false, errors: errors} = nested_changeset
 
@@ -79,10 +79,10 @@ defmodule StructCopTest do
 
   test "cast/2 for embeds_many with nested StructCop" do
     assert {:ok, %TestStruct{nesteds: [%TestStruct.Nested{a: 1, b: 2}]}} =
-             %TestStruct{} |> StructCop.cast(nesteds: [%{a: 1, b: 2}])
+             TestStruct.new!() |> StructCop.cast(nesteds: [%{a: 1, b: 2}])
 
     assert {:error, %Ecto.Changeset{valid?: false, changes: %{nesteds: [nested_changeset]}}} =
-             %TestStruct{} |> StructCop.cast(nesteds: [%{b: 2}])
+             TestStruct.new!() |> StructCop.cast(nesteds: [%{b: 2}])
 
     assert %Ecto.Changeset{valid?: false, errors: errors} = nested_changeset
 
@@ -93,18 +93,19 @@ defmodule StructCopTest do
     assert {:ok,
             %TestStruct{
               nesteds: [
-                %TestStruct.Nested{a: 1, b: 2, deeply_nesteds: [%TestStruct.DeeplyNested{a: 1}]}
+                %TestStruct.Nested{a: 1, b: 2, deeply_nesteds: [%TestStruct.MyStruct{a: 1}]}
               ]
             }} =
-             %TestStruct{} |> StructCop.cast(nesteds: [%{a: 1, b: 2, deeply_nesteds: [%{a: 1}]}])
+             TestStruct.new!()
+             |> StructCop.cast(nesteds: [%{a: 1, b: 2, deeply_nesteds: [%{a: 1}]}])
   end
 
   test "cast/2 for embeds_one with nested embedded_schema" do
     assert {:ok, %TestStruct{nested_ecto: %TestStruct.EctoSchema{a: 1}}} =
-             %TestStruct{} |> StructCop.cast(nested_ecto: %{a: 1})
+             TestStruct.new!() |> StructCop.cast(nested_ecto: %{a: 1})
 
     assert {:error, %Ecto.Changeset{valid?: false, changes: %{nested_ecto: nested_changeset}}} =
-             %TestStruct{} |> StructCop.cast(nested_ecto: %{b: 2})
+             TestStruct.new!() |> StructCop.cast(nested_ecto: %{b: 2})
 
     assert %Ecto.Changeset{valid?: false, errors: errors} = nested_changeset
 

lib/struct_cop/changeset.test.exs

@@ -6,14 +6,14 @@ defmodule StructCop.ChangesetTest do
   describe "cast_all/2" do
     test "works with %Ecto.Changeset{}" do
       assert %Ecto.Changeset{changes: %{b: 4, a: 4}} =
-               %TestStruct{}
+               TestStruct.new!()
                |> cast(%{a: 4}, [:a])
                |> Subject.cast_all(b: 4)
     end
 
     test "fallbacks to &cast_all/2 for embeds without changeset" do
       assert %Ecto.Changeset{changes: %{inline: %Ecto.Changeset{changes: %{c: 10}}}} =
-               %TestStruct{}
+               TestStruct.new!()
                |> Subject.cast_all(inline: %{c: 10})
     end
   end

lib/struct_cop/error_message.test.exs

@@ -6,7 +6,7 @@ defmodule StructCop.ErrorMessageTest do
   def changeset do
     import Ecto.Changeset
 
-    %TestStruct{}
+    TestStruct.new!()
     |> cast(%{a: 4}, [:a])
     |> validate_number(:a, greater_than: 5)
     |> validate_number(:a, less_than: 3)

lib/struct_cop/macro.ex

@@ -25,6 +25,7 @@ defmodule StructCop.Macro do
       end
 
       def __struct_cop__, do: true
+      def __struct_cop_enforce_constructor__, do: true
 
       defoverridable changeset: 2
       defoverridable validate: 1

lib/struct_cop/tracer.ex

@@ -0,0 +1,28 @@
+defmodule StructCop.Tracer do
+  def trace({:struct_expansion, _meta, _module, _keys}, %Macro.Env{context: :match}), do: :ok
+
+  def trace({:struct_expansion, _meta, module, _keys}, env) do
+    if function_exported?(module, :__struct_cop__, 0) &&
+         module.__struct_cop_enforce_constructor__() do
+      raise CompileError,
+        file: env.file,
+        line: env.line,
+        description: """
+
+          #{struct_label(module)} enforces constructors usage (new/1 & new!/1),
+          ordinary struct creation is not allowed:
+
+          * #{struct_label(module)}
+          * #{struct_label(module, "struct | arg: 123")}
+        """
+    else
+      :ok
+    end
+  end
+
+  def trace(_, _), do: :ok
+
+  defp struct_label(module, content \\ nil) do
+    "%#{inspect(module)}{#{content}}"
+  end
+end

lib/struct_cop/tracer.test.exs

@@ -0,0 +1,90 @@
+defmodule StructCop.TracerTest do
+  use ExUnit.Case, async: true
+
+  alias TestStruct.MyStruct
+  alias TestStruct.Ordinary
+
+  setup do
+    Code.put_compiler_option(:tracers, [StructCop.Tracer])
+
+    :ok
+  end
+
+  def compile(ast), do: Code.compile_quoted(ast)
+
+  test "raises CompileError for %MyStruct{}" do
+    assert_raise CompileError, fn ->
+      quote do
+        %MyStruct{}
+      end
+      |> compile()
+    end
+
+    assert_raise CompileError, fn ->
+      quote do
+        %MyStruct{} == %MyStruct{}
+      end
+      |> compile()
+    end
+
+    assert_raise CompileError, fn ->
+      quote do
+        struct = MyStruct.new!()
+        %MyStruct{struct | a: 2}
+      end
+      |> compile()
+    end
+
+    assert_raise CompileError, fn ->
+      quote do
+        defmodule MyMacroMod do
+          defmacro __using__(_) do
+            quote do
+              def call do
+                %MyStruct{}
+              end
+            end
+          end
+        end
+
+        defmodule MyClientMod do
+          use MyMacroMod
+        end
+      end
+      |> compile()
+    end
+  end
+
+  test "raises CompileError for struct!(MyStruct, attrs)" do
+    # TODO
+  end
+
+  test "doesn't raise CompileError for ordinary structs" do
+    quote do
+      %Ordinary{}
+    end
+    |> compile()
+
+    assert true
+  end
+
+  test "doesn't raise for LEFT side of pattern match" do
+    quote do
+      defmodule MyMod do
+        def call(%MyStruct{}) do
+        end
+      end
+    end
+    |> compile()
+
+    quote do
+      struct = MyStruct.new!(a: 2)
+
+      %MyStruct{a: a} = struct
+      %MyStruct{a: 2} = struct
+    end
+    |> compile()
+
+    assert true
+  end
+end

mix.exs

@@ -7,7 +7,7 @@ defmodule StructCop.MixProject do
     [
       app: :struct_cop,
       version: @version,
-      elixir: "~> 1.8",
+      elixir: "~> 1.10",
       elixirc_paths: elixirc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,
       test_coverage: [tool: ExCoveralls],

test/support/test_structs.ex

@@ -14,18 +14,16 @@ defmodule TestStruct.EctoSchema do
   end
 end
 
-defmodule TestStruct.DeeplyNested do
+defmodule TestStruct.Ordinary do
+  defstruct [:a, :b]
+end
+
+defmodule TestStruct.MyStruct do
   use StructCop
 
   contract do
     field :a, :integer
-  end
-
-  def validate(changeset) do
-    import Ecto.Changeset
-
-    changeset
-    |> validate_required([:a])
+    field :b, :integer
   end
 end
 
@@ -35,7 +33,7 @@ defmodule TestStruct.Nested do
   contract do
     field :a, :integer
     field :b, :integer
-    embeds_many :deeply_nesteds, TestStruct.DeeplyNested
+    embeds_many :deeply_nesteds, TestStruct.MyStruct
   end
 
   def validate(changeset) do