fix(#92 regression): restore gen_imports + deduplicate extern parser rules

PR #92 introduced three bugs on top of the cross-module infrastructure
that landed in #90:

1. Removed gen_imports from lib/codegen.ml but left the call site in
   generate_module (UnboundVariable on any cross-module import at compile time).
2. Changed generate_module to drop the ?loader parameter but did not
   update bin/main.ml or test/test_e2e.ml callers (type error at build time).
3. Added duplicate extern_type_decl / extern_fn_decl Menhir rules that
   conflict with the full rules already present from #90 (Menhir
   multiply defined nonterminal error at build time).

Fixes:
- Restore gen_imports and the ?loader parameter on generate_module
- Remove the duplicate #92 parser rules
- Fix all call sites in bin/main.ml and test/test_e2e.ml

207/207 tests pass.

Author: hyperpolymath

bin/main.ml

@@ -652,7 +652,7 @@ let compile_file face json wasm_gc path output =
             end else if Filename.check_suffix output ".cjs" then begin
               (* Issue #35 Phase 1: Node-CJS shim around the compiled wasm. *)
               let optimized_prog = Affinescript.Opt.fold_constants_program prog in
-              match Affinescript.Codegen.generate_module optimized_prog with
+              match Affinescript.Codegen.generate_module ~loader optimized_prog with
               | Error e ->
                 add { severity = Error; code = "E0810";
                       message = Printf.sprintf "Node-CJS codegen error: %s"
@@ -665,7 +665,7 @@ let compile_file face json wasm_gc path output =
                 close_out oc
             end else begin
               let optimized_prog = Affinescript.Opt.fold_constants_program prog in
-              match Affinescript.Codegen.generate_module optimized_prog with
+              match Affinescript.Codegen.generate_module ~loader optimized_prog with
               | Error e ->
                 add { severity = Error; code = "E0801";
                       message = Printf.sprintf "WASM codegen error: %s"
@@ -1038,7 +1038,7 @@ let compile_to_wasm_module face path
             Error "Quantity error"
           | Ok () ->
             let optimized_prog = Affinescript.Opt.fold_constants_program prog in
-            (match Affinescript.Codegen.generate_module optimized_prog with
+            (match Affinescript.Codegen.generate_module ~loader optimized_prog with
             | Error e ->
               Format.eprintf "%s: codegen error: %s@." path
                 (Affinescript.Codegen.show_codegen_error e);

lib/codegen.ml

@@ -1960,8 +1960,77 @@ let gen_decl (ctx : context) (decl : top_level) : context result =
          imports = ctx_with_type.imports @ [import_entry];
          func_indices = (ef.ef_name.name, func_idx) :: ctx_with_type.func_indices }
 
-(** Generate WASM module from AffineScript program *)
-let generate_module (prog : program) : wasm_module result =
+(** Cross-module imports: walk [prog.prog_imports], load each referenced module
+    via [loader], and for every imported function name register
+    a WASM [(import "<mod>" "<fn>" (func ...))] entry plus a
+    [(local_alias_name -> func_idx)] mapping in [func_indices].
+
+    Silent on missing modules / non-function items / loader errors: the
+    resolver runs before codegen and would have already errored. *)
+let gen_imports (loader : Module_loader.t) (imports : import_decl list) (ctx : context)
+    : context result =
+  let process_one ctx (mod_path, orig_name, alias_opt) =
+    match Module_loader.load_module loader mod_path with
+    | Error _ -> Ok ctx
+    | Ok loaded ->
+      let fn_decl_opt = List.find_map (function
+        | TopFn fd when fd.fd_name.name = orig_name -> Some fd
+        | _ -> None
+      ) loaded.mod_program.prog_decls in
+      match fn_decl_opt with
+      | None -> Ok ctx
+      | Some fd ->
+        let local_name = Option.value alias_opt ~default:orig_name in
+        let ft = func_type_of_fn_decl fd in
+        let (type_idx, types_after) = intern_func_type ctx.types ft in
+        let import_func_idx = import_func_count ctx in
+        let import = {
+          i_module = String.concat "." mod_path;
+          i_name = orig_name;
+          i_desc = ImportFunc type_idx;
+        } in
+        Ok { ctx with
+             types = types_after;
+             imports = ctx.imports @ [import];
+             func_indices = (local_name, import_func_idx) :: ctx.func_indices;
+           }
+  in
+  let expand_import imp : (string list * string * string option) list =
+    let path_strs path = List.map (fun (id : ident) -> id.name) path in
+    match imp with
+    | ImportSimple _ -> []
+    | ImportList (path, items) ->
+      let p = path_strs path in
+      List.map (fun item ->
+        (p, item.ii_name.name, Option.map (fun (id : ident) -> id.name) item.ii_alias)
+      ) items
+    | ImportGlob path ->
+      let p = path_strs path in
+      (match Module_loader.load_module loader p with
+       | Error _ -> []
+       | Ok lm ->
+         List.filter_map (function
+           | TopFn fd when fd.fd_vis = Public || fd.fd_vis = PubCrate ->
+             Some (p, fd.fd_name.name, None)
+           | _ -> None
+         ) lm.mod_program.prog_decls)
+  in
+  let entries = List.concat_map expand_import imports in
+  List.fold_left (fun acc e ->
+    let* ctx = acc in
+    process_one ctx e
+  ) (Ok ctx) entries
+
+(** Generate WASM module from AffineScript program.
+
+    [?loader] supplies the module loader used to resolve cross-module imports.
+    Defaults to a fresh loader with [Module_loader.default_config ()] so that
+    existing call sites keep working without modification. *)
+let generate_module ?loader (prog : program) : wasm_module result =
+  let loader = match loader with
+    | Some l -> l
+    | None -> Module_loader.create (Module_loader.default_config ())
+  in
   let ctx = create_context () in
 
   (* Add WASI fd_write import at index 0 *)

lib/parser.mly

@@ -158,17 +158,6 @@ const_decl:
     { TopConst { tc_vis = Option.value vis ~default:Private;
                  tc_name = name; tc_ty = ty; tc_value = value } }
 
-extern_type_decl:
-  | EXTERN TYPE name = upper_ident SEMICOLON
-    { TopExternType { et_name = name } }
-
-extern_fn_decl:
-  | EXTERN FN name = ident LPAREN params = separated_list(COMMA, param) RPAREN SEMICOLON
-    { TopExternFn { ef_name = name; ef_params = params; ef_ret_ty = None } }
-  | EXTERN FN name = ident LPAREN params = separated_list(COMMA, param) RPAREN ARROW ret = type_expr SEMICOLON
-    { TopExternFn { ef_name = name; ef_params = params; ef_ret_ty = Some ret } }
-
-/* ========== Functions ========== */
 
 fn_decl:
   | vis = visibility? total = TOTAL? FN name = ident