[Feature Request] Bitwise operation support in predefined CEL rules

[KeXiangWang]

Feature description: Support bitwise operations in predefined CEL rules.

For example,

extend buf.validate.Int32Rules {
  optional bool power_of_two = 100000 [(buf.validate.predefined).cel = {
    id: "int32.power_of_two"
    message: "value must be a power of two"
    expression: "this >= 0 && (this & (this - 1)) == 0"
  }];
}

although the above rules can be successfully complied by protoc, when execute, I got this error:

compilation error: failed to compile standard rule "xxxxx.power_of_two": compilation error: failed to compile expression int32.power_of_two: ERROR: <input>:1:20: Syntax error: token recognition error at: '& '
 | this >= 0 && (this & (this - 1)) == 0

I think CEL itself support bitwise operations? I'm not sure whether protovalidate disable it or there's some reason it doesn't work.

My toolchain version: protoc: libprotoc 3.21.9 validate.proto: https://github.com/bufbuild/protovalidate/blob/51ee9b3a85ed11c19a2b8023aa2520cca82f431e/proto/protovalidate/buf/validate/validate.proto protovalidate-go: buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go v1.36.6-20250425153114-8976f5be98c1.1

Problem it solves or use case: When predefining some more complicated rules.

Proposed implementation or solution: Although cel-spec hasn't support bitwise operations. They provide go-implenmation for this as an extension. See https://github.com/google/cel-go/blob/f6d3c92171c2c8732a8d0a4b24d6729df4261520/ext/math.go#L95. It should not be hard to support this new operations just like other extension rules.

Contribution: Willing to contribute, if I can get necessary guidance.

Examples or references: None

Additional context: None

[nicksnyder]

Just as a note to folks who come across this issue, updating protovalidate-go is blocked on the spec itself being updated (https://github.com/bufbuild/protovalidate/issues/362), and then we will want to land a similar change to all other supported protovalidate implementations at the same time.

[KeXiangWang]

Hi @nicksnyder I'm interested in your repo and planning to implement bitwise operations in this repo. @smaye81 told me you would welcome the PR. https://github.com/bufbuild/protovalidate/issues/362#issuecomment-2864869153 However, before kicking off, I still want to confirm one thing: would you consider merging my PR to your main branch? This will break your consistency between different languages.

[nicksnyder]

I'm sorry there was some confusion caused by that comment. We can't merge features into this repo (or any Protovalidate repo) until:

1. The CEL spec itself supports those features, and
2. We have PRs ready to add support to all protovalidate implementations

We need to maintain consistency across all Protovalidate implementations.