Feature description:

I would be happy if cel expression validation is supported.

Problem it solves or use case:

When I buf lint the following proto, the second mistake is caught by buf lint proto/xxx/greeting/v1/greeting.proto:35:79:field xxx.greeting.v1.SayHelloResponse.request_time: option (buf.validate.field).timestamp.lt_nowwww: field lt_nowwww of buf.validate.TimestampRules does not exist, but the first one (cel expression) is not. I'd like to know if the expression is valid or not.

message SayHelloResponse {
  string message_id = 1;

  string message = 2 [(buf.validate.field).cel = {
    id: "sayHelloResponse.message",
    message: "message must start with 'Hello, ' and shorter than 1024",
    expression: "(this.startsWith('Hello, ') && this.string.max_lennnn "
  }];

  google.protobuf.Timestamp request_time = 3  [(buf.validate.field).timestamp.lt_nowwwwwww = true];
}

Proposed implementation or solution:

Is it possible to validate expression like other tools like linting IAM condition that checks cel validity?
https://cloud.google.com/iam/docs/linting-policies

Contribution:

Examples or references:

Additional context: