From 756429e9cf444230ffb9747025084f05e1936565 Mon Sep 17 00:00:00 2001
From: Nathan Rebours <nathan.p.rebours@gmail.com>
Date: Wed, 21 Feb 2024 15:30:13 +0100
Subject: [PATCH] Add merge visible and hidden load_path when migrating to 5.1

Signed-off-by: Nathan Rebours <nathan.p.rebours@gmail.com>
---
 astlib/migrate_501_502.ml                     | 33 +++++++++----------
 astlib/migrate_502_501.ml                     | 33 ++++++++++++++++---
 .../run.t                                     |  2 +-
 3 files changed, 44 insertions(+), 24 deletions(-)

diff --git a/astlib/migrate_501_502.ml b/astlib/migrate_501_502.ml
index e4a0d0fe..c48ba65e 100644
--- a/astlib/migrate_501_502.ml
+++ b/astlib/migrate_501_502.ml
@@ -17,26 +17,23 @@ let extract_attr name (attrs : Ast_501.Parsetree.attributes) =
 
 let migrate_ppx_context_load_path expr =
   let open Ast_501.Parsetree in
-  let visible = { expr with pexp_attributes = [] } in
   let payload, other_attrs =
-    extract_attr "ppxlib.migration.hidden_load_path" expr.pexp_attributes
+    extract_attr "ppxlib.migration.load_path" expr.pexp_attributes
   in
-  let hidden =
-    match payload with
-    | None ->
-        (* An empty list *)
-        let pexp_desc =
-          Pexp_construct ({ txt = Lident "[]"; loc = expr.pexp_loc }, None)
-        in
-        { expr with pexp_desc; pexp_attributes = [] }
-    | Some (PStr [ { pstr_desc = Pstr_eval (expr, []); _ } ]) -> expr
-    | Some _ -> invalid_arg "Invalid ppxlib.migration.hidden_load_path paylaod"
-  in
-  {
-    expr with
-    pexp_attributes = other_attrs;
-    pexp_desc = Pexp_tuple [ visible; hidden ];
-  }
+  match payload with
+  | None ->
+      let pexp_desc =
+        Pexp_construct ({ txt = Lident "[]"; loc = expr.pexp_loc }, None)
+      in
+      let hidden = { expr with pexp_desc; pexp_attributes = [] } in
+      let visible = expr in
+      {
+        expr with
+        pexp_attributes = other_attrs;
+        pexp_desc = Pexp_tuple [ visible; hidden ];
+      }
+  | Some (PStr [ { pstr_desc = Pstr_eval (expr, []); _ } ]) -> expr
+  | Some _ -> invalid_arg "Invalid ppxlib.migration.load_path paylaod"
 
 let migrate_ppx_context_fields fields =
   List.map
diff --git a/astlib/migrate_502_501.ml b/astlib/migrate_502_501.ml
index c7af15a8..fead8f70 100644
--- a/astlib/migrate_502_501.ml
+++ b/astlib/migrate_502_501.ml
@@ -13,21 +13,44 @@ let mk_ghost_attr name =
     attr_loc = Location.none;
   }
 
+let rec concat_list_lit left right =
+  let open Ast_502.Parsetree in
+  let open Ast_502.Asttypes in
+  match (left.pexp_desc, right.pexp_desc) with
+  | _, Pexp_construct ({ txt = Lident "[]"; _ }, _) -> left
+  | Pexp_construct ({ txt = Lident "[]"; _ }, _), _ -> right
+  | ( Pexp_construct
+        ( { txt = Lident "::"; loc },
+          Some ({ pexp_desc = Pexp_tuple [ hd; tl ]; _ } as arg_expr) ),
+      _ ) ->
+      {
+        left with
+        pexp_desc =
+          Pexp_construct
+            ( { txt = Lident "::"; loc },
+              Some
+                {
+                  arg_expr with
+                  pexp_desc = Pexp_tuple [ hd; concat_list_lit tl right ];
+                } );
+      }
+  | _ -> invalid_arg "Invalid ocaml.ppx.context's load_path"
+
 let migrate_ppx_context_load_path expr =
   let open Ast_502.Parsetree in
   let loc = Location.none in
   match expr.pexp_desc with
   | Pexp_tuple [ visible; hidden ] ->
-      let hidden_attr =
+      let migration_attr =
         {
-          attr_name =
-            { Location.txt = "ppxlib.migration.hidden_load_path"; loc };
+          attr_name = { Location.txt = "ppxlib.migration.load_path"; loc };
           attr_loc = loc;
           attr_payload =
-            PStr [ { pstr_loc = loc; pstr_desc = Pstr_eval (hidden, []) } ];
+            PStr [ { pstr_loc = loc; pstr_desc = Pstr_eval (expr, []) } ];
         }
       in
-      { visible with pexp_attributes = hidden_attr :: expr.pexp_attributes }
+      let expr' = concat_list_lit visible hidden in
+      { expr' with pexp_attributes = migration_attr :: expr.pexp_attributes }
   | _ -> expr
 
 let migrate_ppx_context_fields fields =
diff --git a/test/driver/ocaml-ppx-context-load-path-migration/run.t b/test/driver/ocaml-ppx-context-load-path-migration/run.t
index b3de2c03..2786f3b6 100644
--- a/test/driver/ocaml-ppx-context-load-path-migration/run.t
+++ b/test/driver/ocaml-ppx-context-load-path-migration/run.t
@@ -41,7 +41,7 @@ the one above.
       tool_name: "ocaml";
       include_dirs: ["foo"];
       hidden_include_dirs: [];
-      load_path: ["foo"; "bar"];
+      load_path: ["foo"; "bar"; "baz"];
       open_modules: [];
       for_package: None;
       debug: true;