feat: add support for BIP-388 wallet policies by trevarj · Pull Request #898 · rust-bitcoin/rust-miniscript

trevarj · 2026-02-12T12:54:51Z

Implemented BIP-388 by introducing a new type, WalletPolicy, which can be used
to create descriptor templates.

The idea is pretty simple and only really required making a new type that
implements MiniscriptKey, then the existing parser and Translator trait
takes care of the rest.

There are a few edge cases that require validation, which isn't so nice, but
works for now. Test cases that require BIP-390 and BIP-387's sortedmulti_a are
commented out and issues could arise with those test vectors when/if those BIPs
are implemented.

See WalletPolicy's doc and the unit tests for usage.

trevarj · 2026-02-12T13:08:48Z

Closes #899

apoelstra · 2026-02-12T13:17:52Z

concept ACK.

We do plan to implement musig and sortedmulti_a, but no timeline on that, and we can deal with it when we get to it.

We are also working on overhauling our validation framework more broadly, which I think/hope should eliminate the need for your hack. (IIRC there are other instances of this hack, or at least something similar, because of our weird separation between core::str::FromStr and crate::expression::FromTree, which I was able to address on my private branch.)

So I'd be okay to undraft this.

trevarj · 2026-02-12T14:35:04Z

Did a force push to address the incompatibilities with the MSRV.

trevarj · 2026-02-12T14:36:39Z

We do plan to implement musig and sortedmulti_a, but no timeline on that, and we can deal with it when we get to it.

Nice, I got side-tracked and explored adding musig, but got too far down in the muck and wanted to finish this first.

We are also working on overhauling our validation framework more broadly, which I think/hope should eliminate the need for your hack. (IIRC there are other instances of this hack, or at least something similar, because of our weird separation between core::str::FromStr and crate::expression::FromTree, which I was able to address on my private branch.)

I will keep a lookout for this.

So I'd be okay to undraft this.

🫡

tcharding · 2026-02-16T01:55:03Z

Trevor!! Can this be split up a bit mate? The wildcard display stuff, then maybe the XKeyParseError thing, then the rest?

src/descriptor/key.rs

src/descriptor/wallet_policy/key_expression.rs

src/descriptor/wallet_policy/mod.rs

tcharding · 2026-02-16T02:11:26Z

API design suggestion but caveat this is not my repo so feel free to ignore me.

Would it be better to put validation inside from_descriptor, have from_descriptor_unchecked (if needed)?
Perhaps not even have the TryFroms? Or at least put the logic in the type methods and in the TryFrom just call the methods?

As far as semantics, it looks like the unit test prove the PR sufficiently to me.

trevarj · 2026-02-16T07:13:37Z

@tcharding

Trevor!!

TOBIN! Thank you for the review

Can this be split up a bit mate? The wildcard display stuff, then maybe the XKeyParseError thing, then the rest?

Split into four separate commits.

Would it be better to put validation inside from_descriptor, have from_descriptor_unchecked (if needed)?

Seems better to me. Easier to track down the logic than having to find the TryFrom.

Or at least put the logic in the type methods and in the TryFrom just call the methods?

Done

src/descriptor/key.rs

tcharding · 2026-02-16T22:26:28Z

src/descriptor/wallet_policy/mod.rs

+    WalletPolicyParseFromString(String),
+    /// Couldn't set key info on WalletPolicy
+    WalletPolicyInvalidKeyInfo,
+}


I don't know the style here in this repo, leaving for @apoelstra to comment. This is a single big error for the whole module unlike how we do it in rust-bitcoin.

src/descriptor/wallet_policy/mod.rs

tcharding · 2026-02-16T22:43:20Z

src/descriptor/wallet_policy/mod.rs

+impl FromStr for WalletPolicy {
+    type Err = WalletPolicyError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> { s.try_into() }
+}


Flagging that I'm not sure about the policy on this sort of thing in this repo. (by sort of thing I mean what could really be a blanket impl of FromStr using From<&str>.

tcharding · 2026-02-16T22:43:26Z

Apart for the None/Some error thing my review only finds nits. I'm at my knowledge limit now so that is all I can offer I'm afraid.

- Instead of accepting a closure to convert the Key type to a String, added type bounds to use Key: FromStr. - Added new error type XKeyParseError, which will be a wrapper for the error type on a Key's FromStr. XKeyParseError must implement From from that type. - Change visibility of parse_xkey_deriv to pub(crate) for later usage.

- two new derivation_path functions, `derivation_path` and `derivation_paths` that omit the path origin - a `wildcard` accessor function to get the Wildcard value

Implemented BIP-388 by introducing a new type, `WalletPolicy`, which can be used to create descriptor templates. The idea is pretty simple and only really required making a new type that implements `MiniscriptKey`, then the existing parser and `Translator` trait takes care of the rest. There are a few edge cases that require validation, which isn't so nice, but works for now. Test cases that require BIP-390 and BIP-387's sortedmulti_a are commented out and issues could arise with those test vectors when/if those BIPs are implemented. See `WalletPolicy`'s doc and the unit tests for usage.

trevarj mentioned this pull request Feb 12, 2026

BIP-388 wallet policies for descriptors support #899

Open

trevarj force-pushed the bip-388-wallet-policy branch from 215e52e to 4a729f8 Compare February 12, 2026 14:33

trevarj marked this pull request as ready for review February 12, 2026 14:36