Fix #8769 (#8770)

* Don't generate illegal Pfield's when compiling alias coercions

* Simplify lambda code when compiling packs

* Add regression test for pr8769

* Add Changes entry

Changes

@@ -344,6 +344,9 @@ OCaml 4.09.0
 - #8701, #8725: Variance of constrained parameters causes principality issues
   (Jacques Garrigue, report by Leo White, review by Gabriel Scherer)
 
+- #8769, #8770: Fix assertion failure with -pack
+  (Leo White, review by Gabriel Scherer, report by Fabian @copy)
+
 OCaml 4.08.0
 ------------
 

asmcomp/asmpackager.ml

@@ -105,6 +105,7 @@ let make_package_object ~ppf_dump members targetobj targetname coercion
         let main_module_block_size, code =
           Translmod.transl_package_flambda components coercion
         in
+        let code = Simplif.simplify_lambda code in
         let program =
           { Lambda.
             code;
@@ -119,6 +120,7 @@ let make_package_object ~ppf_dump members targetobj targetname coercion
           Translmod.transl_store_package components
             (Ident.create_persistent targetname) coercion
         in
+        let code = Simplif.simplify_lambda code in
         let program =
           { Lambda.
             code;

bytecomp/bytepackager.ml

@@ -195,6 +195,7 @@ let build_global_target ~ppf_dump oc target_name members mapping pos coercion =
   let lam =
     Translmod.transl_package
       components (Ident.create_persistent target_name) coercion in
+  let lam = Simplif.simplify_lambda lam in
   if !Clflags.dump_lambda then
     Format.fprintf ppf_dump "%a@." Printlambda.lambda lam;
   let instrs =

lambda/translmod.ml

@@ -72,7 +72,10 @@ let rec apply_coercion loc strict restr arg =
       arg
   | Tcoerce_structure(pos_cc_list, id_pos_list) ->
       name_lambda strict arg (fun id ->
-        let get_field pos = Lprim(Pfield pos,[Lvar id], loc) in
+        let get_field pos =
+          if pos < 0 then lambda_unit
+          else Lprim(Pfield pos,[Lvar id], loc)
+        in
         let lam =
           Lprim(Pmakeblock(0, Immutable, None),
                 List.map (apply_coercion_field loc get_field) pos_cc_list,

testsuite/tests/regression/pr8769/nocrypto.mli

@@ -0,0 +1,3 @@
+module Rng : sig
+  module F : sig end
+end

testsuite/tests/regression/pr8769/ocamltests

@@ -0,0 +1 @@
+pr8769.ml

testsuite/tests/regression/pr8769/pr8769.ml

@@ -0,0 +1,32 @@
+(* TEST
+modules = "nocrypto.mli fortuna.ml rng.ml"
+
+* setup-ocamlc.byte-build-env
+** ocamlc.byte
+module = "nocrypto.mli"
+** ocamlc.byte
+flags = "-for-pack Nocrypto"
+module = "fortuna.ml"
+** ocamlc.byte
+flags = "-for-pack Nocrypto"
+module = "rng.ml"
+** ocamlc.byte
+program = "nocrypto.cmo"
+flags = "-pack"
+all_modules = "fortuna.cmo rng.cmo"
+
+* setup-ocamlopt.byte-build-env
+** ocamlopt.byte
+module = "nocrypto.mli"
+** ocamlopt.byte
+flags = "-for-pack Nocrypto"
+module = "fortuna.ml"
+** ocamlopt.byte
+flags = "-for-pack Nocrypto"
+module = "rng.ml"
+** ocamlopt.byte
+program = "nocrypto.cmx"
+flags = "-pack"
+all_modules = "fortuna.cmx rng.cmx"
+
+*)

testsuite/tests/regression/pr8769/rng.ml

@@ -0,0 +1 @@
+module F = Fortuna