fix: Run ppx as main, not standalone

bin/Bin.re

@@ -1 +1,17 @@
-let () = Ppxlib.Driver.standalone();
+let argv =
+  switch (Sys.argv |> Array.to_list) {
+  | [program, ...rest] =>
+    switch (List.rev(rest)) {
+    | [output_file, input_file, ...args] =>
+      List.concat([
+        [program],
+        List.rev(args),
+        [input_file, "-o", output_file, "--dump-ast"],
+      ])
+      |> Array.of_list
+    | _ => Sys.argv
+    }
+  | _ => Sys.argv
+  };
+
+let () = Migrate_parsetree.Driver.run_main(~argv, ());

test/dune

@@ -9,7 +9,7 @@
   ; expect the process to fail, capturing stderr
   (with-stderr-to
    %{targets}
-   (bash "! ./%{pp} -no-color -impl %{input}")
+   (bash "! ./%{pp} %{input}")
   )
  )
 )
@@ -36,7 +36,7 @@
   ; expect the process to fail, capturing stderr
   (with-stderr-to
    %{targets}
-   (bash "! ./%{pp} -no-color -impl %{input}")
+   (bash "! ./%{pp} %{input}")
   )
  )
 )
@@ -63,7 +63,7 @@
   ; expect the process to fail, capturing stderr
   (with-stderr-to
    %{targets}
-   (bash "! ./%{pp} -no-color -impl %{input}")
+   (bash "! ./%{pp} %{input}")
   )
  )
 )
@@ -90,7 +90,7 @@
   ; expect the process to fail, capturing stderr
   (with-stderr-to
    %{targets}
-   (bash "! ./%{pp} -no-color -impl %{input}")
+   (bash "! ./%{pp} %{input}")
   )
  )
 )