electric-sql · magnetised · Jun 30, 2025 · Jun 5, 2025
diff --git a/config/test.exs b/config/test.exs
@@ -1,6 +1,6 @@
 import Config
 
-config :logger, level: :critical
+config :logger, level: :warning
 
 config :phoenix_sync, mode: :disabled
 

diff --git a/lib/phoenix/sync/application.ex b/lib/phoenix/sync/application.ex
@@ -9,14 +9,17 @@ defmodule Phoenix.Sync.Application do
 
   @impl true
   def start(_type, _args) do
-    case children() do
-      {:ok, children} ->
-        Supervisor.start_link(children, strategy: :one_for_one, name: Phoenix.Sync.Supervisor)
+    children =
+      case children() do
+        {:ok, children} ->
+          children
 
-      {:error, reason} ->
-        Logger.warning(reason)
-        Supervisor.start_link([], strategy: :one_for_one, name: Phoenix.Sync.Supervisor)
-    end
+        {:error, reason} ->
+          Logger.warning(reason)
+          []
+      end
+
+    Supervisor.start_link(children, strategy: :one_for_one, name: Phoenix.Sync.Supervisor)
   end
 
   @doc false
@@ -41,6 +44,8 @@ defmodule Phoenix.Sync.Application do
 
   @doc false
   def children(opts) when is_list(opts) do
+    warn_missing_env(opts)
+
     {adapter, env} = adapter_env(opts)
 
     apply(adapter, :children, [env, opts])
@@ -73,4 +78,23 @@ defmodule Phoenix.Sync.Application do
       :error -> {:error, "Missing required key #{inspect(key)}"}
     end
   end
+
+  defp warn_missing_env(config) do
+    if config[:mode] != :disabled && !config[:env] do
+      Logger.warning("""
+      No `env` specified for :phoenix_sync: defaulting to `:prod`.
+
+      Add the following to your config:
+
+      config :phoenix_sync,
+        env: config_env(),
+        # the rest of your config
+
+      In `:prod` mode, shapes are persisted between server restarts
+      which may cause problems in `:dev` or `:test` environments.
+      """)
+    end
+
+    config
+  end
 end
diff --git a/test/phoenix/sync/application_test.exs b/test/phoenix/sync/application_test.exs
@@ -3,6 +3,8 @@ defmodule Phoenix.Sync.ApplicationTest do
 
   alias Phoenix.Sync.Application, as: App
 
+  import ExUnit.CaptureLog
+
   Code.ensure_loaded!(Support.ConfigTestRepo)
 
   defp validate_repo_connection_opts!(opts, overrides \\ []) do
@@ -78,7 +80,20 @@ defmodule Phoenix.Sync.ApplicationTest do
     end
 
     test "disabled mode" do
-      assert {:ok, []} = App.children(mode: :disabled)
+      refute capture_log(fn ->
+               assert {:ok, []} = App.children(mode: :disabled)
+             end) =~ ~r/No `env` specified for :phoenix_sync: defaulting to `:prod`/
+    end
+
+    test "warns if env not set" do
+      config = [
+        mode: :embedded,
+        repo: Support.ConfigTestRepo
+      ]
+
+      assert capture_log(fn ->
+               assert {:ok, _} = App.children(config)
+             end) =~ ~r/No `env` specified for :phoenix_sync: defaulting to `:prod`/
     end
 
     test "embedded mode dev env" do