Do not include satisfaction in policy id calculation

[afilini]

Currently every node in the Policy tree has an id which is calculated as a checksum on the string of the json-serialized object:

bdk/crates/bdk/src/descriptor/policy.rs

Lines 174 to 178 in d6a0cf0

	/// Returns a unique id for the [`SatisfiableItem`]
	pub fn id(&self) -> String {
	calc_checksum(&serde_json::to_string(self).expect("Failed to serialize a SatisfiableItem"))
	.expect("Failed to compute a SatisfiableItem id")
	}

The object includes details about whether the current wallet can satisfy the policy in some ways (aka contribution), and these are also included in the checksum. The same is true for what in a psbt is currently satisfied, which is the satisfaction field of Policy.

This causes the id of the nodes to change from wallet to wallet, depending on which private keys a wallet has or depending on which psbt you are looking at. Ideally if both wallets have the same public descriptor, they should also have the same id for the nodes, which makes sharing policy_paths much easier.

I would recommend changing the way the id is calculated, if you have any ideas let me know. I could also try working on it myself.

[notmandatory]

@matthiasdebernardini I believe your project uses this feature pretty heavily, any thoughts?

[LLFourn]

I was going to suggest simply removing the policy module in favor of pointing people to the planning module in miniscript. Thoughts?

[afilini]

Yeah that would be better, but as far as I know it still hasn't been released, right?

[LLFourn]

It's still not released yeah :\

[matthiasdebernardini]

@LLFourn I was gonna ask, where can I see this module? I can't find it.

[LLFourn]

Here you go:

https://github.com/rust-bitcoin/rust-miniscript/blob/c94deab5bd16b42da53ab38afcc521ae8c8bf024/src/plan.rs

It needs feedback and iterations but this is the way of the future.