zcash_keys: Enable no_std usage via a default-enabled std feature.

Cargo.toml

@@ -65,7 +65,6 @@ redjubjub = "0.7"
 sapling = { package = "sapling-crypto", version = "0.3", default-features = false }
 
 # - Orchard
-nonempty = "0.7"
 orchard = { version = "0.10", default-features = false }
 pasta_curves = "0.5"
 
@@ -77,6 +76,7 @@ transparent = { package = "zcash_transparent", version = "0.0", path = "zcash_tr
 
 # Boilerplate & missing stdlib
 getset = "0.1"
+nonempty = { version = "0.10", default-features = false }
 
 # CSPRNG
 rand = { version = "0.8", default-features = false }
@@ -195,5 +195,6 @@ debug = true
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(zcash_unstable, values("zfuture"))'] }
 
 [patch.crates-io]
-orchard = { git = "https://github.com/zcash/orchard.git", rev = "f99b6565a78763b58dac792d7492c55067bae680" }
+nonempty = { git = "https://github.com/nuttycom/nonempty.git", rev = "38d37189faecb2a0e3d6adc05aa24e1b93c2483b" }
+orchard = { git = "https://github.com/zcash/orchard.git", rev = "159966b80e2d956907f853bb24513ff5bef4087d" }
 sapling-crypto = { git = "https://github.com/zcash/sapling-crypto.git", rev = "e47d57f5c9c46f05740328f8ef9601f6d697cf34" }

zcash_keys/CHANGELOG.md

@@ -6,6 +6,10 @@ and this library adheres to Rust's notion of
 
 ## [Unreleased]
 
+### Added
+- `no-std` compatibility (`alloc` is required). A default-enabled `std` feature
+  flag has been added gating the `std::error::Error` usage.
+
 ### Changed
 - Migrated to `bech32 0.11`.
 - The `UnifiedAddressRequest` argument to the following methods is now optional:

zcash_keys/Cargo.toml

@@ -59,7 +59,7 @@ proptest = { workspace = true, optional = true }
 # Dependencies used internally:
 # (Breaking upgrades to these are usually backwards-compatible, but check MSRVs.)
 # - Documentation
-document-features.workspace = true
+document-features = { workspace = true, optional = true }
 
 # - Encodings
 byteorder = { workspace = true, optional = true }
@@ -76,6 +76,9 @@ zcash_address = { workspace = true, features = ["test-dependencies"] }
 zcash_primitives = { workspace = true, features = ["test-dependencies"] }
 
 [features]
+default = ["std"]
+std = ["dep:document-features"]
+
 ## Enables use of transparent key parts and addresses
 transparent-inputs = ["dep:bip32", "zcash_primitives/transparent-inputs"]
 

zcash_keys/src/encoding.rs

@@ -76,7 +76,7 @@ impl fmt::Display for Bech32DecodeError {
     }
 }
 
-#[cfg(feature = "sapling")]
+#[cfg(all(feature = "sapling", feature = "std"))]
 impl std::error::Error for Bech32DecodeError {}
 
 #[cfg(feature = "sapling")]
@@ -135,6 +135,7 @@ impl fmt::Display for TransparentCodecError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for TransparentCodecError {}
 
 impl<P: consensus::Parameters> AddressCodec<P> for TransparentAddress {

zcash_keys/src/keys.rs

@@ -113,6 +113,7 @@ impl Display for DerivationError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for DerivationError {}
 
 /// A version identifier for the encoding of unified spending keys.
@@ -180,6 +181,7 @@ impl core::fmt::Display for DecodingError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for DecodingError {}
 
 #[cfg(feature = "unstable")]
@@ -547,6 +549,7 @@ impl fmt::Display for AddressGenerationError {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for AddressGenerationError {}
 
 /// Specification for how a unified address should be generated from a unified viewing key.
@@ -1308,7 +1311,6 @@ pub mod testing {
 
 #[cfg(test)]
 mod tests {
-
     use proptest::prelude::proptest;
 
     use {zcash_primitives::consensus::MAIN_NETWORK, zip32::AccountId};

zcash_keys/src/lib.rs

@@ -4,7 +4,8 @@
 //! and viewing keys and addresses.
 //!
 //! ## Feature flags
-#![doc = document_features::document_features!()]
+#![cfg_attr(feature = "std", doc = "## Feature flags")]
+#![cfg_attr(feature = "std", doc = document_features::document_features!())]
 //!
 
 #![no_std]
@@ -19,6 +20,7 @@
 #[macro_use]
 extern crate alloc;
 
+#[cfg(feature = "std")]
 extern crate std;
 
 pub mod address;