Allow `no_std` use of `incrementalmerkletree`

Cargo.lock

@@ -64,9 +64,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "either"
-version = "1.9.0"
+version = "1.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a26ae43d7bcc3b814de94796a5e736d4029efb0ee900c12e2d54c993ad1a1e07"
+checksum = "60b1af1c220855b6ceac025d3f6ecdd2b7c4894bfe9cd9bda4fbb4bc7c0d4cf0"
 
 [[package]]
 name = "errno"

incrementalmerkletree/CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to Rust's notion of
 
 ## Unreleased
 
+### Added
+- `no-std` support, via a default-enabled `std` feature flag.
+
 ## [0.7.0] - 2024-09-25
 
 ### Changed

incrementalmerkletree/Cargo.toml

@@ -18,7 +18,7 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
-either = "1.8"
+either = { version = "1.8", default-features = false }
 proptest = { workspace = true, optional = true }
 rand = { version = "0.8", optional = true }
 rand_core = { version = "0.6", optional = true }
@@ -30,10 +30,12 @@ rand_core = "0.6"
 rand_chacha = "0.3"
 
 [features]
+default = ["std"]
+std = []
 # The legacy-api feature guards types and functions that were previously
 # part of the `zcash_primitives` crate. Those types were removed in the
 # `zcash_primitives` 0.12 release and are now maintained here.
 legacy-api = []
 # The test-dependencies feature guards types and functions that are
 # useful for testing incremental Merkle trees and Merkle tree frontiers.
-test-dependencies = ["dep:proptest", "dep:rand", "dep:rand_core"]
+test-dependencies = ["dep:proptest", "dep:rand", "dep:rand_core", "std"]

incrementalmerkletree/src/frontier.rs

@@ -1,17 +1,18 @@
-use std::mem::size_of;
+use alloc::vec::Vec;
+use core::mem::size_of;
 
 use crate::{Address, Hashable, Level, MerklePath, Position, Source};
 
 #[cfg(feature = "legacy-api")]
-use {std::collections::VecDeque, std::iter::repeat};
+use {alloc::boxed::Box, alloc::collections::VecDeque, core::iter::repeat};
 
 #[cfg(any(test, feature = "test-dependencies"))]
 use {
+    core::num::{NonZeroU64, NonZeroU8},
     rand::{
         distributions::{Distribution, Standard},
         Rng, RngCore,
     },
-    std::num::{NonZeroU64, NonZeroU8},
 };
 
 /// Validation errors that can occur during reconstruction of a Merkle frontier from
@@ -195,7 +196,7 @@ where
         NonEmptyFrontier::from_parts(
             position,
             rng.gen(),
-            std::iter::repeat_with(|| rng.gen())
+            core::iter::repeat_with(|| rng.gen())
                 .take(position.past_ommer_count().into())
                 .collect(),
         )
@@ -209,7 +210,7 @@ where
     ) -> (Vec<H>, Self) {
         let prior_subtree_count: u64 = u64::from(tree_size) >> u8::from(subtree_depth);
         if prior_subtree_count > 0 {
-            let prior_roots: Vec<H> = std::iter::repeat_with(|| rng.gen())
+            let prior_roots: Vec<H> = core::iter::repeat_with(|| rng.gen())
                 .take(prior_subtree_count as usize)
                 .collect();
 
@@ -673,12 +674,13 @@ impl<H: Hashable + Clone, const DEPTH: u8> CommitmentTree<H, DEPTH> {
     }
 }
 
-#[cfg(any(test, feature = "test-dependencies"))]
+#[cfg(any(all(test, feature = "std"), feature = "test-dependencies"))]
 pub mod testing {
     use core::fmt::Debug;
     use proptest::collection::vec;
     use proptest::prelude::*;
     use rand::{distributions::Standard, prelude::Distribution};
+
     use std::collections::hash_map::DefaultHasher;
     use std::hash::Hasher;
 
@@ -762,9 +764,9 @@ pub mod testing {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, feature = "std"))]
 mod tests {
-
+    use alloc::string::{String, ToString};
     use rand::SeedableRng;
     use rand_chacha::ChaChaRng;
 

incrementalmerkletree/src/lib.rs

@@ -44,13 +44,21 @@
 //! context `ommers` refers to the node's ommer, plus each ancestor's ommer.
 
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![no_std]
 
+#[cfg(feature = "std")]
+extern crate std;
+
+#[macro_use]
+extern crate alloc;
+use alloc::vec::Vec;
+
+use core::cmp::Ordering;
+use core::convert::{TryFrom, TryInto};
+use core::fmt;
+use core::num::TryFromIntError;
+use core::ops::{Add, AddAssign, Range, Sub};
 use either::Either;
-use std::cmp::Ordering;
-use std::convert::{TryFrom, TryInto};
-use std::fmt;
-use std::num::TryFromIntError;
-use std::ops::{Add, AddAssign, Range, Sub};
 
 pub mod frontier;
 
@@ -445,7 +453,7 @@ impl Address {
         let level_delta = (u64::BITS - index_delta.leading_zeros()) as u8;
         Address {
             level: higher.level + level_delta,
-            index: std::cmp::max(higher.index, lower_ancestor_idx) >> level_delta,
+            index: core::cmp::max(higher.index, lower_ancestor_idx) >> level_delta,
         }
     }
 
@@ -672,12 +680,14 @@ pub trait Hashable: fmt::Debug {
 
 #[cfg(test)]
 pub(crate) mod tests {
-    use crate::MerklePath;
+    use alloc::string::{String, ToString};
-
+    use alloc::vec::Vec;
-    use super::{Address, Level, Position, Source};
     use core::ops::Range;
     use either::Either;
 
+    use super::{Address, Level, Position, Source};
+    use crate::MerklePath;
+
     #[test]
     fn position_is_complete_subtree() {
         assert!(Position(0).is_complete_subtree(Level(0)));

incrementalmerkletree/src/testing.rs

@@ -1,4 +1,5 @@
 use crate::{Hashable, Level};
+use alloc::string::{String, ToString};
 
 /// A possibly-empty incremental Merkle frontier.
 pub trait Frontier<H> {

incrementalmerkletree/src/witness.rs

@@ -1,5 +1,6 @@
-use std::convert::TryInto;
+use alloc::vec::Vec;
-use std::iter::repeat;
+use core::convert::TryInto;
+use core::iter::repeat;
 
 use crate::{
     frontier::{CommitmentTree, PathFiller},
@@ -241,7 +242,10 @@ impl<H: Hashable + Clone, const DEPTH: u8> IncrementalWitness<H, DEPTH> {
 
 #[cfg(test)]
 mod tests {
+    use alloc::string::{String, ToString};
+
     use crate::{frontier::CommitmentTree, witness::IncrementalWitness, Position};
+
     #[test]
     fn witness_tip_position() {
         let mut base_tree = CommitmentTree::<String, 6>::empty();