Use @external_resource module attribute (#189)

* Use external_resource module attribute

* Fix helper tests for read_abi

* Fix read_abi spec

Author: alisinabh

CHANGELOG.md

@@ -10,6 +10,7 @@
 
 - Update `Ethers` module to RPCfy eth_call request params
 - Removed unnecessary hex decode/encodes in requests
+- Use `@external_resource` in generated contracts to track ABI changes and recompile if needed. (Thanks @sitch)
 
 ## v0.6.3 (2025-01-21)
 

lib/ethers/contract.ex

@@ -80,7 +80,7 @@ defmodule Ethers.Contract do
       |> Module.get_attribute(:_ethers_using_opts)
       |> Code.eval_quoted([], env)
 
-    {:ok, abi} = read_abi(opts)
+    {abi, abi_file} = read_abi(opts)
     contract_binary = maybe_read_contract_binary(opts)
     default_address = Keyword.get(opts, :default_address)
     skip_docs = Keyword.get(opts, :skip_docs, false)
@@ -124,11 +124,20 @@ defmodule Ethers.Contract do
     events_impl = Enum.map(events, &impl(&1, module, impl_opts))
     event_selectors = Enum.flat_map(events, & &1.selectors)
 
+    external_resource_ast =
+      if abi_file do
+        quote do
+          @external_resource unquote(abi_file)
+        end
+      end
+
     events_module_ast =
       quote context: module do
         defmodule unquote(events_mod_name) do
           @moduledoc "Events for `#{Macro.to_string(unquote(module))}`"
 
+          unquote(external_resource_ast)
+
           defdelegate __default_address__, to: unquote(module)
           unquote(events_impl)
 
@@ -150,6 +159,8 @@ defmodule Ethers.Contract do
         defmodule unquote(errors_mod_name) do
           @moduledoc false
 
+          unquote(external_resource_ast)
+
           unquote(error_modules_ast)
           unquote(errors_module_impl)
         end
@@ -164,6 +175,8 @@ defmodule Ethers.Contract do
 
     extra_ast =
       quote context: module do
+        unquote(external_resource_ast)
+
         def __contract_binary__, do: unquote(contract_binary)
 
         @doc """

lib/ethers/contract_helpers.ex

@@ -3,14 +3,14 @@ defmodule Ethers.ContractHelpers do
 
   require Logger
 
-  @spec read_abi(Keyword.t()) :: {:ok, [...]} | {:error, atom()}
+  @spec read_abi(Keyword.t()) :: {abi :: [...], file_path :: String.t() | nil}
   def read_abi(opts) do
     case Keyword.take(opts, [:abi, :abi_file]) do
       [{type, data}] ->
-        read_abi(type, data)
+        do_read_abi(type, data, nil)
 
       _ ->
-        {:error, :bad_argument}
+        raise ArgumentError, "Invalid arguments. Specify either `:abi` or `:abi_file` option"
     end
   end
 
@@ -389,21 +389,22 @@ defmodule Ethers.ContractHelpers do
     |> Enum.map(&elem(&1, 0))
   end
 
-  defp read_abi(:abi, abi) when is_list(abi), do: {:ok, abi}
-  defp read_abi(:abi, %{"abi" => abi}), do: read_abi(:abi, abi)
+  defp do_read_abi(:abi, abi, file_path) when is_list(abi), do: {abi, file_path}
+  defp do_read_abi(:abi, %{"abi" => abi}, file_path), do: do_read_abi(:abi, abi, file_path)
 
-  defp read_abi(:abi, abi) when is_atom(abi) do
-    read_abi(:abi_file, Path.join(:code.priv_dir(:ethers), "abi/#{abi}.json"))
+  defp do_read_abi(:abi, abi, _file_path) when is_atom(abi) do
+    file_path = Path.join(:code.priv_dir(:ethers), "abi/#{abi}.json")
+    do_read_abi(:abi_file, file_path, nil)
   end
 
-  defp read_abi(:abi, abi) when is_binary(abi) do
+  defp do_read_abi(:abi, abi, file_path) when is_binary(abi) do
     abi = Ethers.json_module().decode!(abi)
-    read_abi(:abi, abi)
+    do_read_abi(:abi, abi, file_path)
   end
 
-  defp read_abi(:abi_file, file) do
+  defp do_read_abi(:abi_file, file, _file_path) do
     abi = File.read!(file)
-    read_abi(:abi, abi)
+    do_read_abi(:abi, abi, file)
   end
 
   defp get_argument_name_ast({ast, name}) do

test/ethers/contract_helpers_test.exs

@@ -4,13 +4,19 @@ defmodule Ethers.ContractHelpersTest do
 
   describe "read_abi" do
     test "works with default abis" do
-      assert {:ok, abi_results} = ContractHelpers.read_abi(abi: :erc20)
+      assert {abi_results, abi_file} = ContractHelpers.read_abi(abi: :erc20)
       assert is_list(abi_results)
+      assert String.ends_with?(abi_file, "priv/abi/erc20.json")
     end
 
     test "returns error with invalid parameters" do
-      assert {:error, :bad_argument} = ContractHelpers.read_abi(abi: :erc20, abi_file: "file")
-      assert {:error, :bad_argument} = ContractHelpers.read_abi(bad_arg: true)
+      assert_raise ArgumentError, fn ->
+        ContractHelpers.read_abi(abi: :erc20, abi_file: "file")
+      end
+
+      assert_raise ArgumentError, fn ->
+        assert {:error, :bad_argument} = ContractHelpers.read_abi(bad_arg: true)
+      end
     end
   end