Implement Filter interface

[jchadwick-buf]

Adds ValidationOption for options passed to the Validate function rather than on creation of a validator.

Adds WithFilter option for setting a filter to control which fields are validated.

Adds Filter interface:

type Filter interface {
	ShouldValidate(message protoreflect.Message, descriptor protoreflect.Descriptor) bool
}

• ShouldValidate is called once for a message, once for each of its oneofs, and once for each of its fields. The message value is the message itself, and the descriptor value is the descriptor of the element being operated on.
• ShouldValidate will be called for every oneof and field even if it returns false for any message, field or oneof.
• Sub-messages nested under fields will not be checked if ShouldValidate returns false.

This is to satisfy the following usecases

• For buf lint, we want to be able to single out an individual field to check examples. This can be done by using descriptor == fieldDescriptor as a filter. This can also filter oneof and message constraints, which is desirable.
• For field masking, it is possible for a stateful filter to perform field masking using this interface. The only important behavioral detail for that is that we nest depth-first into submessages. This would allow a user to implement out-of-band field masks.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / validate-protos (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Feb 11, 2025, 6:25 PM