5.3 effect syntax

Signed-off-by: Nathan Rebours <[email protected]>
ocaml-ppx · Jan 13, 2025 · 0a1fbc5 · 0a1fbc5
1 parent f06c16e
commit 0a1fbc5
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Showing 3 changed files with 17 additions and 10 deletions.
diff --git a/astlib/migrate_502_503.ml b/astlib/migrate_502_503.ml
@@ -325,6 +325,10 @@ and copy_pattern_desc :
         (copy_loc (fun x -> Option.map (fun x -> x) x) x0)
   | Ast_502.Parsetree.Ppat_exception x0 ->
       Ast_503.Parsetree.Ppat_exception (copy_pattern x0)
+  | Ast_502.Parsetree.Ppat_extension (
+     {txt = "ppxlib.effect_syntax"; _},
+     PPat ({ ppat_desc = Ppat_tuple [e; c ]; _}, None)) ->
+      Ast_503.Parsetree.Ppat_effect (copy_pattern e, copy_pattern c)
   | Ast_502.Parsetree.Ppat_extension x0 ->
       Ast_503.Parsetree.Ppat_extension (copy_extension x0)
   | Ast_502.Parsetree.Ppat_open (x0, x1) ->

diff --git a/astlib/migrate_503_502.ml b/astlib/migrate_503_502.ml
@@ -2,10 +2,6 @@ open Stdlib0
 module From = Ast_503
 module To = Ast_502
 
-let migration_error loc missing_feature =
-  Location.raise_errorf ~loc
-    "migration error: %s is not supported before OCaml 5.03" missing_feature
-
 let rec copy_toplevel_phrase :
     Ast_503.Parsetree.toplevel_phrase -> Ast_502.Parsetree.toplevel_phrase =
   function
@@ -330,7 +326,15 @@ and copy_pattern_desc loc :
         (copy_loc (fun x -> Option.map (fun x -> x) x) x0)
   | Ast_503.Parsetree.Ppat_exception x0 ->
       Ast_502.Parsetree.Ppat_exception (copy_pattern x0)
-  | Ast_503.Parsetree.Ppat_effect _ -> migration_error loc "effect pattern"
+  | Ast_503.Parsetree.Ppat_effect (e,c) ->
+     Ast_502.Parsetree.Ppat_extension (
+         Location.{txt = "ppxlib.effect_syntax"; loc = Location.none},
+         Ast_502.Parsetree.PPat (
+             {ppat_desc = Ppat_tuple [copy_pattern e; copy_pattern c];
+              ppat_attributes = [];
+              ppat_loc_stack = [];
+              ppat_loc = Location.none},
+             None))
   | Ast_503.Parsetree.Ppat_extension x0 ->
       Ast_502.Parsetree.Ppat_extension (copy_extension x0)
   | Ast_503.Parsetree.Ppat_open (x0, x1) ->

diff --git a/test/503_migrations/preserve-effect-downward/run.t b/test/503_migrations/preserve-effect-downward/run.t
@@ -18,8 +18,7 @@ If we run the driver on the following source file:
 it should successfully roundtrip to 5.2 and print the source code unchanged:
 
   $ ./driver.exe test.ml -o test.pp.ml
-  File "test.ml", line 4, characters 2-23:
-  4 | | effect Random_bits, k -> Effect.Deep.continue k (Random.bits ())
-        ^^^^^^^^^^^^^^^^^^^^^
-  Error: migration error: effect pattern is not supported before OCaml 5.03
-  [1]
+  let handler f =
+    match f () with
+    | x -> x
+    | effect Random_bits,  k -> Effect.Deep.continue k (Random.bits ())