Add no-std support via a default-enabled std feature flag

Cargo.toml

@@ -24,14 +24,14 @@ rustdoc-args = ["--cfg", "docsrs", "--html-in-header", "katex-header.html"]
 
 [dependencies]
 aes = "0.8"
-bitvec = "1"
-blake2b_simd = "1"
+bitvec = { version = "1", default-features = false }
+blake2b_simd = { version = "1", default-features = false }
 ff = "0.13"
 fpe = "0.6"
 group = { version = "0.13", features = ["wnaf-memuse"] }
-hex = "0.4"
+hex = { version = "0.4", default-features = false }
 lazy_static = "1"
-memuse = { version = "0.2.1", features = ["nonempty"] }
+memuse = { version = "0.2.2", default-features = false }
 pasta_curves = "0.5"
 proptest = { version = "1.0.0", optional = true }
 rand = "0.8"
@@ -57,6 +57,9 @@ getset = "0.1"
 # Logging
 tracing = "0.1"
 
+# No-std support
+core2 = { version = "0.3", default-features = false, features = ["alloc"] }
+
 # Developer tooling dependencies
 image = { version = "0.24", optional = true }
 plotters = { version = "0.3.0", optional = true }
@@ -78,8 +81,9 @@ pprof = { version = "0.11", features = ["criterion", "flamegraph"] }
 bench = false
 
 [features]
-default = ["circuit", "multicore"]
-circuit = ["dep:halo2_gadgets", "dep:halo2_proofs"]
+default = ["circuit", "multicore", "std"]
+std = ["core2/std", "memuse/nonempty"]
+circuit = ["dep:halo2_gadgets", "dep:halo2_proofs", "std"]
 unstable-frost = []
 multicore = ["halo2_proofs?/multicore"]
 dev-graph = ["halo2_proofs?/dev-graph", "image", "plotters"]

src/builder.rs

@@ -1,9 +1,9 @@
 //! Logic for building Orchard components of transactions.
 
+use alloc::collections::BTreeMap;
+use alloc::vec::Vec;
 use core::fmt;
 use core::iter;
-use std::collections::BTreeMap;
-use std::fmt::Display;
 
 use ff::Field;
 use pasta_curves::pallas;
@@ -141,7 +141,7 @@ pub enum BuildError {
     BundleTypeNotSatisfiable,
 }
 
-impl Display for BuildError {
+impl fmt::Display for BuildError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use BuildError::*;
         match self {
@@ -163,6 +163,7 @@ impl Display for BuildError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for BuildError {}
 
 #[cfg(feature = "circuit")]
@@ -189,7 +190,7 @@ pub enum SpendError {
     FvkMismatch,
 }
 
-impl Display for SpendError {
+impl fmt::Display for SpendError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use SpendError::*;
         f.write_str(match self {
@@ -200,18 +201,20 @@ impl Display for SpendError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for SpendError {}
 
 /// The only error that can occur here is if outputs are disabled for this builder.
 #[derive(Debug, PartialEq, Eq)]
 pub struct OutputError;
 
-impl Display for OutputError {
+impl fmt::Display for OutputError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str("Outputs are not enabled for this builder")
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for OutputError {}
 
 /// Information about a specific note to be spent in an [`Action`].

src/bundle.rs

@@ -1,5 +1,7 @@
 //! Structs related to bundles of Orchard actions.
 
+use alloc::vec::Vec;
+
 pub mod commitments;
 
 #[cfg(feature = "circuit")]
@@ -10,10 +12,12 @@ pub use batch::BatchValidator;
 use core::fmt;
 
 use blake2b_simd::Hash as Blake2bHash;
-use memuse::DynamicUsage;
 use nonempty::NonEmpty;
 use zcash_note_encryption::{try_note_decryption, try_output_recovery_with_ovk};
 
+#[cfg(feature = "std")]
+use memuse::DynamicUsage;
+
 use crate::{
     action::Action,
     address::Address,
@@ -472,6 +476,7 @@ impl<V> Bundle<Authorized, V> {
     }
 }
 
+#[cfg(feature = "std")]
 impl<V: DynamicUsage> DynamicUsage for Bundle<Authorized, V> {
     fn dynamic_usage(&self) -> usize {
         self.actions.dynamic_usage()

src/bundle/batch.rs

@@ -1,3 +1,5 @@
+use alloc::vec::Vec;
+
 use halo2_proofs::plonk;
 use pasta_curves::vesta;
 use rand::{CryptoRng, RngCore};

src/circuit.rs

@@ -1,5 +1,7 @@
 //! The Orchard Action circuit implementation.
 
+use alloc::vec::Vec;
+
 use group::{Curve, GroupEncoding};
 use halo2_proofs::{
     circuit::{floor_planner, Layouter, Value},

src/constants/fixed_bases.rs

@@ -1,4 +1,8 @@
 //! Orchard fixed bases.
+
+#[cfg(feature = "circuit")]
+use alloc::vec::Vec;
+
 use super::{L_ORCHARD_SCALAR, L_VALUE};
 
 #[cfg(feature = "circuit")]

src/keys.rs

@@ -1,6 +1,7 @@
 //! Key structures for Orchard.
 
-use std::io::{self, Read, Write};
+use alloc::vec::Vec;
+use core2::io::{self, Read, Write};
 
 use ::zip32::{AccountId, ChildIndex};
 use aes::Aes256;
@@ -405,7 +406,7 @@ impl FullViewingKey {
         Self::from_bytes(&data).ok_or_else(|| {
             io::Error::new(
                 io::ErrorKind::InvalidInput,
-                "Unable to deserialize a valid Orchard FullViewingKey from bytes".to_owned(),
+                "Unable to deserialize a valid Orchard FullViewingKey from bytes",
             )
         })
     }

src/lib.rs

@@ -7,6 +7,7 @@
 //! implicitly mean it is an Orchard payment address (as opposed to e.g. a Sapling payment
 //! address, which is also shielded).
 
+#![no_std]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 // Temporary until we have more of the crate implemented.
 #![allow(dead_code)]
@@ -16,6 +17,14 @@
 #![deny(missing_docs)]
 #![deny(unsafe_code)]
 
+#[macro_use]
+extern crate alloc;
+
+#[cfg(feature = "std")]
+extern crate std;
+
+use alloc::vec::Vec;
+
 mod action;
 mod address;
 pub mod builder;

src/note_encryption.rs

@@ -1,5 +1,6 @@
 //! In-band secret distribution for Orchard bundles.
 
+use alloc::vec::Vec;
 use core::fmt;
 
 use blake2b_simd::{Hash, Params};

src/pczt.rs

@@ -1,7 +1,9 @@
 //! PCZT support for Orchard.
 
-use std::collections::BTreeMap;
-use std::fmt;
+use alloc::collections::BTreeMap;
+use alloc::string::String;
+use alloc::vec::Vec;
+use core::fmt;
 
 use getset::Getters;
 use pasta_curves::pallas;

src/pczt/io_finalizer.rs

@@ -1,3 +1,5 @@
+use alloc::vec::Vec;
+
 use rand::{CryptoRng, RngCore};
 
 use crate::{

src/pczt/parse.rs

@@ -1,4 +1,6 @@
-use std::collections::BTreeMap;
+use alloc::collections::BTreeMap;
+use alloc::string::String;
+use alloc::vec::Vec;
 
 use ff::PrimeField;
 use incrementalmerkletree::Hashable;

src/pczt/prover.rs

@@ -1,3 +1,5 @@
+use alloc::vec::Vec;
+
 use halo2_proofs::plonk;
 use rand::{CryptoRng, RngCore};
 

src/pczt/updater.rs

@@ -1,3 +1,6 @@
+use alloc::string::String;
+use alloc::vec::Vec;
+
 use super::{Action, Bundle, Zip32Derivation};
 
 impl Bundle {

src/tree.rs

@@ -1,5 +1,6 @@
 //! Types related to Orchard note commitment trees and anchors.
 
+use alloc::vec::Vec;
 use core::iter;
 
 use crate::{

src/value.rs

@@ -81,6 +81,7 @@ impl fmt::Display for OverflowError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for OverflowError {}
 
 /// The non-negative value of an individual Orchard note.