feat(moc.js): add blob: import placeholder setting

src/js/moc_js.ml

@@ -28,6 +28,7 @@ let () =
       method setPublicMetadata entries = set_public_metadata entries
       method setRunStepLimit limit = js_set_run_step_limit limit
       method setTypecheckerCombineSrcs combineSrcs = Flags.typechecker_combine_srcs := combineSrcs
+      method setBlobImportPlaceholders placeholders = Flags.blob_import_placeholders := placeholders
       method gcFlags option = gc_flags option
       method run list s = Flags.compiled := false; wrap_output (fun _ -> js_run list s)
       method check s = Flags.compiled := false; js_check s

src/lowering/desugar.ml

@@ -1215,9 +1215,13 @@ and transform_import (i : S.import) : Ir.dec list =
     | S.IDLPath (fp, canister_id) ->
       primE (I.ActorOfIdBlob t) [blobE canister_id]
     | S.ImportedValuePath path ->
-       let contents = Lib.FilePath.contents path in
-       assert T.(t = Prim Blob);
-       blobE contents
+       if !Mo_config.Flags.blob_import_placeholders then
+         raise (Invalid_argument ("blob import placeholder"))
+       else begin
+         let contents = Lib.FilePath.contents path in
+         assert T.(t = Prim Blob);
+         blobE contents
+       end
   in [ letP (pat p) rhs ]
 
 type import_declaration = Ir.dec list

src/mo_config/flags.ml

@@ -80,6 +80,7 @@ let stable_memory_access_limit = ref stable_memory_access_limit_default
 let experimental_stable_memory_default = 0 (* _ < 0: error; _ = 0: warn, _ > 0: allow *)
 let experimental_stable_memory = ref experimental_stable_memory_default
 let typechecker_combine_srcs = ref false (* useful for the language server *)
+let blob_import_placeholders = ref false (* when enabled, blob:file imports resolve as empty blobs *)
 
 let default_warning_levels = M.empty
   |> M.add "M0223" Allow (* don't report redundant instantions *)

src/mo_interpreter/interpret.ml

@@ -459,9 +459,13 @@ and interpret_exp_mut env exp (k : V.value V.cont) =
     | LibPath {path; _} ->
       k (find path env.libs)
     | ImportedValuePath path ->
-      let contents = Lib.FilePath.contents path in
-      assert T.(exp.note.note_typ = Prim Blob);
-      k (V.Blob contents)
+      if !Mo_config.Flags.blob_import_placeholders then
+        trap exp.at "blob import placeholder"
+      else begin
+        let contents = Lib.FilePath.contents path in
+        assert T.(exp.note.note_typ = Prim Blob);
+        k (V.Blob contents)
+      end
     | IDLPath _ -> trap exp.at "actor import"
     | PrimPath -> k (find "@prim" env.libs)
     )

src/pipeline/resolve_import.ml

@@ -156,15 +156,22 @@ let add_idl_import msgs imported ri_ref at full_path bytes =
     err_file_does_not_exist msgs at full_path
 
 let add_value_import msgs imported ri_ref at path =
-  let add_no_extension _file_exists f = f in
-  match resolve_lib_import at path add_no_extension with
-  | Ok full_path -> begin
-      let ri = ImportedValuePath full_path in
-      ri_ref := ri;
-      imported := RIM.add ri at !imported
-    end
-  | Error err ->
-    Diag.add_msg msgs err
+  if !Mo_config.Flags.blob_import_placeholders then begin
+    (* When placeholders are enabled, skip file existence check *)
+    let ri = ImportedValuePath path in
+    ri_ref := ri;
+    imported := RIM.add ri at !imported
+  end else begin
+    let add_no_extension _file_exists f = f in
+    match resolve_lib_import at path add_no_extension with
+    | Ok full_path -> begin
+        let ri = ImportedValuePath full_path in
+        ri_ref := ri;
+        imported := RIM.add ri at !imported
+      end
+    | Error err ->
+      Diag.add_msg msgs err
+  end
 
 let add_prim_import imported ri_ref at =
   ri_ref := PrimPath;

test/test-moc.js

@@ -245,3 +245,12 @@ assert(Motoko.parseMotokoTypedWithScopeCache(/*enable_recovery=*/false, ["bad.mo
 // TODO: This requires avoid dropping 'code' field in all checks though all pipeline e.g. infer_prog
 // assert(Motoko.parseMotokoTypedWithScopeCache(/*enable_recovery=*/true, ["bad.mo"], new Map()).code != null);
 
+// `blob:` import placeholders
+Motoko.setBlobImportPlaceholders(true);
+Motoko.saveFile("blob.mo", 'import MyBlob "blob:file:path/to/blob.txt"; MyBlob.size();');
+assert(Motoko.parseMotoko(/*enable_recovery=*/true, "blob.mo").code != null);
+assert.deepStrictEqual(Motoko.run([], "blob.mo"), {
+  stdout: "",
+  stderr: "blob.mo:1.1-1.43: execution error, blob import placeholder\n",
+  result: { error: {} },
+});