From 10900ca0f3b9bdf63c37cd41bc85e858d9fd7c21 Mon Sep 17 00:00:00 2001
From: Martin Schut <martin-gitlab@wommm.nl>
Date: Tue, 7 Feb 2023 15:29:25 +0100
Subject: [PATCH] Add opaque typespecs

---
 lib/strukt.ex   | 14 +++++++++-----
 lib/typespec.ex | 12 +++++++++---
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/lib/strukt.ex b/lib/strukt.ex
index 5d92d04..df26b6e 100644
--- a/lib/strukt.ex
+++ b/lib/strukt.ex
@@ -31,8 +31,8 @@ defmodule Strukt do
 
   NOTE: It is recommended that if you need to perform custom validations, that
   you use the `validation/1` and `validation/2` facility for performing custom
-  validations in a module or function, and if necessary, override `c:validate/1` 
-  instead of performing validations in this callback. If you need to override this 
+  validations in a module or function, and if necessary, override `c:validate/1`
+  instead of performing validations in this callback. If you need to override this
   callback specifically for some reason, make sure you call `super/2` at some point during
   your implementation to ensure that validations are run.
   """
@@ -242,9 +242,11 @@ defmodule Strukt do
           []
       end
 
+    opaque_fields = Enum.any?(special_attrs, fn {:@, _, [{attr, _, [value]}]} -> attr == :opaque_fields &&!!value end)
+
     fields = Strukt.Field.parse(fields)
 
-    define_struct(env, name, meta, moduledoc, derives, schema_attrs, fields, body)
+    define_struct(env, name, meta, moduledoc, derives, opaque_fields, schema_attrs, fields, body)
   end
 
   # This clause handles the edge case where the definition only contains
@@ -252,10 +254,10 @@ defmodule Strukt do
   defp define_struct(env, name, {type, _, _} = field) when is_supported(type) do
     fields = Strukt.Field.parse([field])
 
-    define_struct(env, name, [], nil, [], [], fields, [])
+    define_struct(env, name, [], nil, [], false, [], fields, [])
   end
 
-  defp define_struct(_env, name, meta, moduledoc, derives, schema_attrs, fields, body) do
+  defp define_struct(_env, name, meta, moduledoc, derives, opaque_fields, schema_attrs, fields, body) do
     # Extract macros which should be defined at the top of the module
     {macros, body} =
       Enum.split_with(body, fn
@@ -356,6 +358,7 @@ defmodule Strukt do
         end
 
         @schema_name Macro.underscore(__MODULE__)
+        @opaque_fields unquote(opaque_fields)
         @validated_fields unquote(validated_fields)
         @cast_embed_fields unquote(Macro.escape(cast_embed_fields))
 
@@ -491,6 +494,7 @@ defmodule Strukt do
       typespec_ast =
         Strukt.Typespec.generate(%Strukt.Typespec{
           caller: __MODULE__,
+          opaque: @opaque_fields,
           info: @validated_fields,
           fields: @cast_fields,
           embeds: @cast_embed_fields
diff --git a/lib/typespec.ex b/lib/typespec.ex
index 240b2ac..608bc32 100644
--- a/lib/typespec.ex
+++ b/lib/typespec.ex
@@ -1,11 +1,13 @@
 defmodule Strukt.Typespec do
   @moduledoc false
 
-  defstruct [:caller, :info, :fields, :embeds]
+  defstruct [:caller, :opaque, :info, :fields, :embeds]
 
   @type t :: %__MODULE__{
           # The module where the struct is being defined
           caller: module,
+          # Defines whether the typespec should be opaque or the default type
+          opaque: boolean,
           # Metadata about all fields in the struct
           info: %{optional(atom) => map},
           # A list of all non-embed field names
@@ -45,7 +47,7 @@ defmodule Strukt.Typespec do
   * `fields` - This is a list of all field names which are defined via `field/3`
   * `embeds` - This is a list of all field names which are defined via `embeds_one/3` or `embeds_many/3`
   """
-  def generate(%__MODULE__{caller: caller, info: info, fields: fields, embeds: embeds}) do
+  def generate(%__MODULE__{caller: caller, opaque: opaque, info: info, fields: fields, embeds: embeds}) do
     # Build up the AST for each field's type spec
     fields =
       fields
@@ -87,7 +89,11 @@ defmodule Strukt.Typespec do
     # Join all fields together
     struct_fields = fields ++ embeds
 
-    quote(context: caller, do: @type(t :: %__MODULE__{unquote_splicing(struct_fields)}))
+    if opaque do
+      quote(context: caller, do: @opaque(t :: %__MODULE__{unquote_splicing(struct_fields)}))
+    else
+      quote(context: caller, do: @type(t :: %__MODULE__{unquote_splicing(struct_fields)}))
+    end
   end
 
   defp primitive(atom, args \\ []) when is_atom(atom) and is_list(args),