improvement: automatically set min_pg_version where possible

improvement: use a notice to suggest configuring `min_pg_version`

doing this instead of showing a prompt, to reduce initial sign-up friction

fixes #430

lib/igniter.ex

@@ -3,8 +3,8 @@ if Code.ensure_loaded?(Igniter) do
     @moduledoc "Codemods and utilities for working with AshPostgres & Igniter"
 
     @doc false
-    def default_repo_contents(otp_app, name, opts \\ []) do
-      min_pg_version = get_min_pg_version(name, opts)
+    def default_repo_contents(otp_app, opts \\ []) do
+      min_pg_version = opts[:min_pg_version] || Version.parse!("16.0.0")
 
       """
       use AshPostgres.Repo, otp_app: #{inspect(otp_app)}
@@ -88,12 +88,25 @@ if Code.ensure_loaded?(Igniter) do
             otp_app = Igniter.Project.Application.app_name(igniter)
 
             igniter =
-              Igniter.Project.Module.create_module(
-                igniter,
-                repo,
-                default_repo_contents(otp_app, repo, opts),
-                opts
-              )
+              if opts[:min_pg_version] do
+                igniter
+              else
+                Igniter.add_notice(igniter, """
+                A `min_pg_version/0` function has been defined 
+                in `#{inspect(repo)}` as `16.0.0`.
+
+                You may wish to update this configuration. It should 
+                be set to the lowest version that your application 
+                expects to be run against.
+                """)
+              end
+
+            Igniter.Project.Module.create_module(
+              igniter,
+              repo,
+              default_repo_contents(otp_app, opts),
+              opts
+            )
 
             {igniter, repo}
           else

lib/mix/tasks/ash_postgres.install.ex

@@ -362,11 +362,40 @@ if Code.ensure_loaded?(Igniter) do
           end
         )
       else
+        min_pg_version = get_min_pg_version()
+
+        notice =
+          if min_pg_version do
+            """
+            A `min_pg_version/0` function has been defined 
+            in `#{inspect(repo)}` as `#{min_pg_version}`.
+
+            This was based on running `postgres -V`.
+
+            You may wish to update this configuration. It should 
+            be set to the lowest version that your application 
+            expects to be run against.
+            """
+          else
+            """
+            A `min_pg_version/0` function has been defined in 
+            `#{inspect(repo)}` automatically.
+
+            You may wish to update this configuration. It should 
+            be set to the lowest version that your application 
+            expects to be run against.
+            """
+          end
+
         Igniter.Project.Module.create_module(
           igniter,
           repo,
-          AshPostgres.Igniter.default_repo_contents(otp_app, repo, opts)
+          AshPostgres.Igniter.default_repo_contents(
+            otp_app,
+            Keyword.put(opts, :min_pg_version, min_pg_version)
+          )
         )
+        |> Igniter.add_notice(notice)
       end
       |> Igniter.Project.Module.find_and_update_module!(
         repo,
@@ -382,6 +411,28 @@ if Code.ensure_loaded?(Igniter) do
       )
     end
 
+    def get_min_pg_version do
+      case System.cmd("postgres", ["-V"]) do
+        {"postgres (PostgreSQL) " <> version_and_text, 0} ->
+          version_and_text
+          |> String.split(~r/\s+/, parts: 2, trim: true)
+          |> Enum.at(0)
+          |> String.split(".", trim: true)
+          |> case do
+            [major, minor, patch | _] -> Version.parse!("#{major}.#{minor}.#{patch}")
+            [major, minor] -> Version.parse!("#{major}.#{minor}.0")
+            [major] -> Version.parse!("#{major}.0.0")
+            _ -> nil
+          end
+
+        _ ->
+          nil
+      end
+    rescue
+      _ ->
+        nil
+    end
+
     defp use_ash_postgres_instead_of_ecto(zipper) do
       with {:ok, zipper} <- Igniter.Code.Module.move_to_module_using(zipper, Ecto.Repo),
            {:ok, zipper} <- Igniter.Code.Module.move_to_use(zipper, Ecto.Repo),