Is there a way to ignore option map_entry = true; for schemas downloaded from Confluent Schema Registry?

[guga4ka]

I'm using Confluent Schema Registry (CSR) to store and distribute Protobuf schemas, along with the Buf CLI to lint and check for breaking changes in service schemas.

Problem

When a schema containing a map is registered in CSR, the map field is transformed into a map_entry message with option map_entry = true;. If a service later imports this schema, Buf flags it as an issue.

For example, a schema like this:

syntax = "proto3";
package events.v1;

option java_multiple_files = true;
option java_outer_classname = "EventsProto";

message Event{
  map<string, string> data = 1;
}

After registration in CSR, it transforms into:

syntax = "proto3";
package events.v1;

option java_outer_classname = "EventsProto";
option java_multiple_files = true;

message Event {
  repeated .events.v1.Event.DataEntry data = 1;

  message DataEntry {
    option map_entry = true;
  
    string key = 1;
    string value = 2;
  }
}

When another schema imports this transformed version, Buf fails any lint or breaking command due to the modification.

Question

Is there a way to ignore the map_entry option for downloaded schemas?

[doriable]

The map_entry option is a restricted option, so the build is failing because it's a compiler restriction (it would fail with protoc also). There appears to be a fix in the CSR for schemas to emit a proper map type, even when normalization is not enabled: confluentinc/schema-registry#3444

So in this particular case, I would suggest not depending on any schemas that are being pulled from a version of the CSR that emits the map entry messages with the map_entry option set and checking your CSR versions and configurations.

To address the broader use-case of excluding options when working with schemas, we are currently working on a feature to configure excluding options when generating code with buf generate.

[guga4ka]

Thanks for your answer, @doriable. It seems like these changes were reverted, but thank you for pointing me in this direction