From 6a3d8b447f86a813d0c72ed29774a8e45c3904fa Mon Sep 17 00:00:00 2001
From: Eric Koslow <ekoslow@gmail.com>
Date: Wed, 2 Oct 2024 14:19:25 -0700
Subject: [PATCH] fix: Don't raise error when switch is missing default branch

Removed the compiler error when a `switch` statement was missing an
`default` branch. Now it will compile cleanly.
---
 lib/reactor/dsl/switch.ex        |  8 +++++++-
 test/reactor/dsl/switch_test.exs | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/lib/reactor/dsl/switch.ex b/lib/reactor/dsl/switch.ex
index bdb4833..a662d41 100644
--- a/lib/reactor/dsl/switch.ex
+++ b/lib/reactor/dsl/switch.ex
@@ -155,7 +155,13 @@ defmodule Reactor.Dsl.Switch do
     def verify(switch, dsl_state) do
       switch.matches
       |> Enum.flat_map(& &1.steps)
-      |> Enum.concat(switch.default.steps)
+      |> Enum.concat(
+        if is_nil(switch.default) do
+          []
+        else
+          switch.default.steps
+        end
+      )
       |> Enum.reduce_while(:ok, fn step, :ok ->
         case Build.verify(step, dsl_state) do
           :ok -> {:cont, :ok}
diff --git a/test/reactor/dsl/switch_test.exs b/test/reactor/dsl/switch_test.exs
index a643cd0..266ad1d 100644
--- a/test/reactor/dsl/switch_test.exs
+++ b/test/reactor/dsl/switch_test.exs
@@ -34,6 +34,21 @@ defmodule Reactor.Dsl.SwitchTest do
     return :is_truthy?
   end
 
+  defmodule SwitchNoDefaultReactor do
+    @moduledoc false
+    use Reactor
+
+    input :value
+
+    switch :is_nil? do
+      on input(:value)
+
+      matches? &is_nil/1 do
+        step :falsy, Noop
+      end
+    end
+  end
+
   test "when provided a falsy value it works" do
     assert {:ok, :falsy} = Reactor.run(SwitchReactor, value: nil)
   end
@@ -41,4 +56,8 @@ defmodule Reactor.Dsl.SwitchTest do
   test "when provided a truthy value it works" do
     assert {:ok, :truthy} = Reactor.run(SwitchReactor, value: :marty)
   end
+
+  test "it does not require a default" do
+    assert {:ok, nil} = Reactor.run(SwitchNoDefaultReactor, value: nil)
+  end
 end