Get keychain for script

[vladimirfomene]

Description

This PR fixes #1042.

Notes to the reviewers

Changelog notice

It adds a method which_keychain_derived that tells us which keychain derived a particular script. This is helpful when trying to figure out if a particular script belongs to our wallet.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[ValuedMammal]

In addition to checking the keychain, we could possibly also check the correct spk index is returned from which_keychain_derived.

diff

 fn test_which_keychain_derived_script() {
     let (mut segwit_wallet, _) = get_funded_wallet(get_test_wpkh());
     let addr = segwit_wallet.get_address(New);
     let script = addr.script_pubkey();
     let keychain = segwit_wallet.which_keychain_derived(&script).unwrap();
     assert_eq!(keychain.0, KeychainKind::External);
 
     let (mut taproot_wallet, _) = get_funded_wallet(get_test_tr_single_sig());
     let addr = taproot_wallet.get_address(New);
     let script = addr.script_pubkey();
     let keychain = segwit_wallet.which_keychain_derived(&script);
     assert!(keychain.is_none());
+
+    // find correct derivation index from spk
+    let desc = get_test_tr_single_sig_xprv();
+    let mut wallet = Wallet::new_no_persist(desc, None, Network::Testnet).unwrap();
+    let spk = wallet.get_address(New).address.script_pubkey();
+    let (_k, i) = wallet.which_keychain_derived(&spk).unwrap();
+    assert_eq!(i, &0);
+
+    // reveal more addresses. the last revealed index should now be 10.
+    for _ in 0..10 {
+        let _ = wallet.get_address(New);
+    }
+    let spk = wallet.get_address(Peek(10)).address.script_pubkey();
+    let (_k, i) = wallet.which_keychain_derived(&spk).unwrap();
+    assert_eq!(i, &10);
 }

[evanlinjin]

This is the exact same thing as Wallet::derivation_of_spk:

bdk/crates/bdk/src/wallet/mod.rs

Lines 822 to 827 in ba76247

	/// Finds how the wallet derived the script pubkey `spk`.
	///
	/// Will only return `Some(_)` if the wallet has given out the spk.
	pub fn derivation_of_spk(&self, spk: &Script) -> Option<(KeychainKind, u32)> {
	self.indexed_graph.index.index_of_spk(spk)
	}