unikernel/duniverse/ppxlib/test/migrations/driver.ml

@@ -0,0 +1,36 @@
+open Ppxlib
+
+module B = Ast_builder.Make (struct
+  let loc = Location.none
+end)
+
+let add_function =
+  let param v = B.pparam_val Nolabel None (B.ppat_var (B.Located.mk v)) in
+  let body =
+    B.pexp_function
+      [ param "b" ]
+      None
+      (Pfunction_body
+         (B.pexp_apply
+            (B.pexp_ident (B.Located.mk (Lident "+")))
+            [
+              (Nolabel, B.pexp_ident (B.Located.lident "a"));
+              (Nolabel, B.pexp_ident (B.Located.lident "b"));
+            ]))
+  in
+  let func = B.pexp_function [ param "a" ] None (Pfunction_body body) in
+  B.pstr_value Nonrecursive
+    [ B.value_binding ~pat:(B.ppat_var (B.Located.mk "f")) ~expr:func ]
+
+let generative_functor =
+  let empty_struct = B.pmod_structure [] in
+  B.pstr_module
+    (B.module_binding ~name:(B.Located.mk (Some "F"))
+       ~expr:(B.pmod_apply (B.pmod_ident (B.Located.lident "F")) empty_struct))
+
+let () =
+  Driver.register_transformation
+    ~impl:(fun impl -> add_function :: generative_functor :: impl)
+    "migrators"
+
+let () = Driver.standalone ()

unikernel/duniverse/ppxlib/test/migrations/dune

@@ -0,0 +1,9 @@
+(executable
+ (name driver)
+ (modules driver)
+ (libraries ppxlib))
+
+(cram
+ (enabled_if
+  (< %{ocaml_version} "5.2.0"))
+ (deps driver.exe))

unikernel/duniverse/ppxlib/test/migrations/run.t

@@ -0,0 +1,22 @@
+Ppxlib applies migrations to the AST. In some cases, especially when applying
+downward migrations, extra information must be encoded in the AST in order to
+be able to properly re-encode the AST when migrating back up.
+
+This means that sometimes the extra information is left in the AST especially
+when printing the code as source of the current compiler (where the current
+compiler is less than the internal AST version).
+
+Therefore we must clean the produced AST to remove ppxlib.migration attributes.
+
+  $ touch file.ml
+  $ ./driver.exe file.ml
+  let f a = fun b -> a + b
+  module F = (F)(struct  end)
+
+Now we ensure no attributes are left in the AST after we force a downard
+migration using the --use-compiler-pp flag.
+
+  $ ./driver.exe --use-compiler-pp file.ml
+  let f a b = a + b
+  module F = (F)(struct  end)
+