Signing event with self-referencing p tag discards the tag

[xeruf]

Describe the bug
When creating an EventBuilder with a "p"-tag that contains the public key of the key that the event is signed with, the "p"-tag is discarded

To Reproduce

    let keys = Keys::generate();
    let builder = EventBuilder::new(Kind::from(1234), "test").tags([Tag::public_key(keys.public_key)]);
    println!("{:?}", builder);
    println!("{:?}", builder.sign_with_keys(&keys));

example output:

EventBuilder { kind: Custom(1234), tags: [Tag(["p", "258884c3e5e1433731654c6f7c604e0f2176a7c144a42ea1e2575b981fff40bb"])], content: "test", custom_created_at: None, pow: None }
Ok(Event { id: EventId(fc1a6dc2117ef31a7d16644c343a49b9fb880f2cd01e4ce3b56b0d36af03ca76), pubkey: PublicKey(258884c3e5e1433731654c6f7c604e0f2176a7c144a42ea1e2575b981fff40bb), created_at: Timestamp(1738187545), kind: Custom(1234), tags: [], content: "test", sig: Signature(cb5dbcb56fcf5156027fa0bddae53d48f3cd70f13a8696a6ed9a895ab292cae5765b4f609c540d0307950d6d0b602bc0da6d087f871e6d8cacb35424de135c86) })

Expected behavior
No discarding, unless that is something that may be in the spec?

Build environment

• Library:
• Language: Rust
• Language version:
• Tag/commit: 0.38

[yukibtc]

It's not a bug, it's a feature added at commit 27c656b, suggested by @dluvian here #657.
I'm going to write this also in the doc.

What is the purpose of tagging yourself?

[dluvian]

Maybe it should be allowed to be included when using EventBuilder::tags, but EventBuilder::comment and similar functions should not add your own p-tag.

[xeruf]

The purpose is that I use an own event kind for tracking tasks, and use the p-tag to assign somebody to the task.
I can also assign myself.

[yukibtc]

This is from NIP01: "The p tag, used to refer to another user"

https://github.com/nostr-protocol/nips/blob/f440eac3dccefa5c0ec9d3964e1d08357fd31e09/01.md?plain=1#L79

What if by default the self-tagging is not allowed, but enabling an option, it's allowed. Or the opposite?

Allow self-tagging only if explicitly enabled:

let event = builder.allow_self_tagging().sign(signer).await?;

The opposite, allow self-tagging by default and prevent it by calling a method:

let event = builder.prevent_self_tagging().sign(signer).await?;

@xeruf @dluvian