Enable no_std support via a default-enabled std feature flag.

.github/workflows/main.yml

@@ -18,3 +18,38 @@ jobs:
       with:
         command: test
         args: --all-features
+
+  build-nostd:
+    name: Build target ${{ matrix.target }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target:
+          - wasm32-wasi
+          - thumbv7em-none-eabihf
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          path: crate_root
+      # We use a synthetic crate to ensure no dev-dependencies are enabled, which can
+      # be incompatible with some of these targets.
+      - name: Create synthetic crate for testing
+        run: cargo init --lib ci-build
+      - name: Copy Rust version into synthetic crate
+        run: cp crate_root/rust-toolchain.toml ci-build/
+      - name: Copy patch directives into synthetic crate
+        run: |
+          echo "[patch.crates-io]" >> ./ci-build/Cargo.toml
+          cat ./crate_root/Cargo.toml | sed "0,/.\+\(patch.crates.\+\)/d" >> ./ci-build/Cargo.toml
+      - name: Add no_std pragma to lib.rs
+        run: |
+          echo "#![no_std]" > ./ci-build/src/lib.rs
+      - name: Add redjubjub as a dependency of the synthetic crate
+        working-directory: ./ci-build
+        run: cargo add --no-default-features --path ../crate_root
+      - name: Add target
+        working-directory: ./ci-build
+        run: rustup target add ${{ matrix.target }}
+      - name: Build for target
+        working-directory: ./ci-build
+        run: cargo build --verbose --target ${{ matrix.target }}

CHANGELOG.md

@@ -2,9 +2,14 @@
 
 Entries are listed in reverse chronological order.
 
+## Unreleased
+
+* Enable `no_std` use via a default-enabled `std` feature flag.
+
 ## 0.7.0
 
 * Update the `reddsa` dependency to version 0.5.0.
+* MSRV is now 1.65
 
 ## 0.6.0
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "redjubjub"
-edition = "2018"
+edition = "2021"
 # When releasing to crates.io:
 # - Update CHANGELOG.md
 # - Create git tag.
@@ -17,10 +17,10 @@ description = "A standalone implementation of the RedJubjub signature scheme."
 features = ["nightly"]
 
 [dependencies]
-reddsa = "0.5.0"
-rand_core = "0.6"
-serde = { version = "1", optional = true, features = ["derive"] }
-thiserror = "1.0"
+reddsa = { version = "0.5.0", default-features = false, features = ["alloc"] }
+rand_core = { version = "0.6", default-features = false }
+serde = { version = "1", optional = true, default-features = false, features = ["derive"] }
+thiserror = { version = "1.0", optional = true }
 zeroize = { version = "1", default-features = false, features = ["zeroize_derive"] }
 
 [dev-dependencies]
@@ -34,7 +34,8 @@ serde_json = "1.0"
 
 [features]
 nightly = []
-default = ["serde"]
+default = ["serde", "std"]
+std = ["dep:thiserror", "reddsa/std"]
 
 [[bench]]
 name = "bench"

src/error.rs

@@ -8,19 +8,21 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
+#[cfg(feature = "std")]
 use thiserror::Error;
 
 /// An error related to RedJubJub signatures.
-#[derive(Error, Debug, Copy, Clone, Eq, PartialEq)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "std", derive(Error))]
 pub enum Error {
     /// The encoding of a signing key was malformed.
-    #[error("Malformed signing key encoding.")]
+    #[cfg_attr(feature = "std", error("Malformed signing key encoding."))]
     MalformedSigningKey,
     /// The encoding of a verification key was malformed.
-    #[error("Malformed verification key encoding.")]
+    #[cfg_attr(feature = "std", error("Malformed verification key encoding."))]
     MalformedVerificationKey,
     /// Signature verification failed.
-    #[error("Invalid signature.")]
+    #[cfg_attr(feature = "std", error("Invalid signature."))]
     InvalidSignature,
 }
 

src/lib.rs

@@ -10,6 +10,10 @@
 
 #![deny(missing_docs)]
 #![doc = include_str!("../README.md")]
+#![no_std]
+
+#[cfg(feature = "std")]
+extern crate std;
 
 pub mod batch;
 mod error;
@@ -53,7 +57,7 @@ impl SigType for SpendAuth {}
 
 pub(crate) mod private {
     use super::*;
-    pub trait Sealed: Copy + Clone + Eq + PartialEq + std::fmt::Debug {
+    pub trait Sealed: Copy + Clone + Eq + PartialEq + core::fmt::Debug {
         type RedDSASigType: reddsa::SigType;
     }
     impl Sealed for Binding {

src/signing_key.rs

@@ -8,7 +8,7 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-use std::convert::{TryFrom, TryInto};
+use core::convert::{TryFrom, TryInto};
 
 use crate::{Error, Randomizer, SigType, Signature, SpendAuth, VerificationKey};
 

src/verification_key.rs

@@ -8,7 +8,7 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-use std::{convert::TryFrom, hash::Hash};
+use core::{convert::TryFrom, hash::Hash};
 
 use crate::{Error, Randomizer, SigType, Signature, SpendAuth};
 
@@ -81,7 +81,7 @@ impl<T: SigType> TryFrom<[u8; 32]> for VerificationKey<T> {
     type Error = Error;
 
     fn try_from(bytes: [u8; 32]) -> Result<Self, Self::Error> {
-        use std::convert::TryInto;
+        use core::convert::TryInto;
         VerificationKeyBytes::from(bytes).try_into()
     }
 }