Merge pull request #621 from patricoferris/encoding-505

Encode all structure items in 505 migration

Author: patricoferris

astlib/encoding_505.ml

@@ -0,0 +1,28 @@
+module Ext_name = struct
+  let pexp_struct_item = "ppxlib.migration.pexp_struct_item_505"
+end
+
+let invalid_encoding ~loc name =
+  Location.raise_errorf ~loc "Invalid %s encoding" name
+
+module To_504 = struct
+  open Ast_504.Asttypes
+  open Ast_504.Parsetree
+
+  let encode_pexp_struct_item ~loc ((si, e) : structure_item * expression) =
+    let expr_as_structure_item =
+      let pstr_desc = Pstr_eval (e, []) in
+      { pstr_desc; pstr_loc = loc }
+    in
+    let payload =
+      let items = [ si; expr_as_structure_item ] in
+      PStr items
+    in
+    let name = { txt = Ext_name.pexp_struct_item; loc } in
+    Pexp_extension (name, payload)
+
+  let decode_pexp_struct_item ~loc payload =
+    match payload with
+    | PStr [ si; { pstr_desc = Pstr_eval (e, []); _ } ] -> (si, e)
+    | _ -> invalid_encoding ~loc Ext_name.pexp_struct_item
+end

astlib/migrate_504_505.ml

@@ -495,6 +495,10 @@ and copy_expression_desc :
       Ast_505.Parsetree.Pexp_struct_item (opendecl, copy_expression x1)
   | Ast_504.Parsetree.Pexp_letop x0 ->
       Ast_505.Parsetree.Pexp_letop (copy_letop x0)
+  | Ast_504.Parsetree.Pexp_extension ({ txt; loc }, payload)
+    when String.equal txt Encoding_505.Ext_name.pexp_struct_item ->
+      let si, e = Encoding_505.To_504.decode_pexp_struct_item ~loc payload in
+      Pexp_struct_item (copy_structure_item si, copy_expression e)
   | Ast_504.Parsetree.Pexp_extension x0 ->
       Ast_505.Parsetree.Pexp_extension (copy_extension x0)
   | Ast_504.Parsetree.Pexp_unreachable -> Ast_505.Parsetree.Pexp_unreachable

astlib/migrate_505_504.ml

@@ -476,9 +476,9 @@ and copy_expression_desc :
               copy_module_expr mexpr,
               copy_expression x1 )
       | _ ->
-          Location.raise_errorf ~loc:x0.pstr_loc
-            "Only structure items [open M], [exception C] and [module B = T] \
-             are supported in [let SI in E].")
+          let item = copy_structure_item x0 in
+          Encoding_505.To_504.encode_pexp_struct_item ~loc:x0.pstr_loc
+            (item, copy_expression x1))
   | Ast_505.Parsetree.Pexp_assert x0 ->
       Ast_504.Parsetree.Pexp_assert (copy_expression x0)
   | Ast_505.Parsetree.Pexp_lazy x0 ->

astlib/stdlib0.ml

@@ -7,6 +7,8 @@ module Option = struct
 end
 
 module String = struct
+  include String
+
   let is_prefix t ~prefix =
     let rec is_prefix_from t ~prefix ~pos ~len =
       pos >= len

test/505_migrations/run.t

@@ -28,6 +28,26 @@ it should successfully roundtrip to 5.2 and print the source code unchanged:
   module T = struct let x = 1 end
   let f = let exception E of int  in let module X = T in let open X in x
 
+In addition to these items, the 5.5 AST can now encode pretty much any structure item
+locally, except for a few (e.g. [let let ...]). We have to handle these also during migration.
+
+  $ cat > extra.ml << EOF
+  > type e = ..
+  > 
+  > let f =
+  >   let type e += Hello in
+  >   let external id : 'a -> 'a = "identity" in 
+  >   let type t = int in
+  >   ()
+  > EOF
+
+  $ ./driver.exe extra.ml --use-compiler-pp
+  type e = ..
+  let f =
+    let type e +=  
+          | Hello  in
+      let external id : 'a -> 'a = "identity" in let type t = int in ()
+
 2. Ptyp_extension
 
 A new feature of OCaml 5.5 are external types (e.g. [type t = external "t"]).