Remove std feature (#459)

All of the existing usages of `std` can be replaced with `alloc`.

They are legacy usages from before when liballoc was stabilized.

.github/workflows/rust.yml

@@ -114,10 +114,9 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - uses: dtolnay/rust-toolchain@stable
-    # This filter selects no benchmarks, so we don't run any, only build them.
     - name: Build u32 bench
-      run: env RUSTFLAGS="--cfg curve25519_dalek_bits=\"32\"" cargo bench "nonexistentbenchmark"
+      run: env RUSTFLAGS="--cfg curve25519_dalek_bits=\"32\"" cargo build --benches
     - name: Build u64 bench
-      run: env RUSTFLAGS="--cfg curve25519_dalek_bits=\"64\"" cargo bench "nonexistentbenchmark"
+      run: env RUSTFLAGS="--cfg curve25519_dalek_bits=\"64\"" cargo build --benches
     - name: Build default (host native) bench
-      run: cargo bench "nonexistentbenchmark"
+      run: cargo build --benches

Cargo.toml

@@ -36,11 +36,12 @@ bincode = "1"
 criterion = { version = "0.4.0", features = ["html_reports"] }
 hex = "0.4.2"
 rand = "0.8"
-rand_core = { version = "0.6", default-features = false }
+rand_core = { version = "0.6", default-features = false, features = ["getrandom"] }
 
 [[bench]]
 name = "dalek_benchmarks"
 harness = false
+required-features = ["rand_core"]
 
 [dependencies]
 cfg-if = "1"
@@ -56,8 +57,7 @@ fiat-crypto = { version = "0.1.6", optional = true}
 
 [features]
 nightly = ["subtle/nightly"]
-default = ["std"]
+default = ["alloc"]
-std = ["alloc", "subtle/std", "rand_core/std"]
 alloc = ["zeroize/alloc"]
 
 # fiat-crypto backend with formally-verified field arithmetic

src/backend/serial/scalar_mul/pippenger.rs

@@ -11,6 +11,8 @@
 
 #![allow(non_snake_case)]
 
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::cmp::Ordering;
 
@@ -18,9 +20,6 @@ use crate::edwards::EdwardsPoint;
 use crate::scalar::Scalar;
 use crate::traits::VartimeMultiscalarMul;
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 /// Implements a version of Pippenger's algorithm.
 ///
 /// The algorithm works as follows:
@@ -62,8 +61,6 @@ use crate::prelude::*;
 /// This algorithm is adapted from section 4 of <https://eprint.iacr.org/2012/549.pdf>.
 pub struct Pippenger;
 
-#[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl VartimeMultiscalarMul for Pippenger {
     type Point = EdwardsPoint;
 

src/backend/serial/scalar_mul/precomputed_straus.rs

@@ -11,6 +11,8 @@
 
 #![allow(non_snake_case)]
 
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::cmp::Ordering;
 
@@ -23,9 +25,6 @@ use crate::traits::Identity;
 use crate::traits::VartimePrecomputedMultiscalarMul;
 use crate::window::{NafLookupTable5, NafLookupTable8};
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 #[allow(missing_docs)]
 pub struct VartimePrecomputedStraus {
     static_lookup_tables: Vec<NafLookupTable8<AffineNielsPoint>>,

src/backend/serial/scalar_mul/straus.rs

@@ -13,6 +13,8 @@
 
 #![allow(non_snake_case)]
 
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::cmp::Ordering;
 
@@ -21,9 +23,6 @@ use crate::scalar::Scalar;
 use crate::traits::MultiscalarMul;
 use crate::traits::VartimeMultiscalarMul;
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 /// Perform multiscalar multiplication by the interleaved window
 /// method, also known as Straus' method (since it was apparently
 /// [first published][solution] by Straus in 1964, as a solution to [a

src/backend/vector/ifma/edwards.rs

@@ -11,7 +11,7 @@
 
 use crate::traits::Identity;
 
-use std::ops::{Add, Neg, Sub};
+use core::ops::{Add, Neg, Sub};
 
 use subtle::Choice;
 use subtle::ConditionallySelectable;

src/backend/vector/scalar_mul/mod.rs

@@ -14,13 +14,10 @@ pub mod variable_base;
 pub mod vartime_double_base;
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 pub mod straus;
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 pub mod precomputed_straus;
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 pub mod pippenger;

src/backend/vector/scalar_mul/pippenger.rs

@@ -9,6 +9,8 @@
 
 #![allow(non_snake_case)]
 
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::cmp::Ordering;
 
@@ -17,16 +19,11 @@ use crate::edwards::EdwardsPoint;
 use crate::scalar::Scalar;
 use crate::traits::{Identity, VartimeMultiscalarMul};
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 /// Implements a version of Pippenger's algorithm.
 ///
 /// See the documentation in the serial `scalar_mul::pippenger` module for details.
 pub struct Pippenger;
 
-#[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl VartimeMultiscalarMul for Pippenger {
     type Point = EdwardsPoint;
 

src/backend/vector/scalar_mul/precomputed_straus.rs

@@ -11,6 +11,8 @@
 
 #![allow(non_snake_case)]
 
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::cmp::Ordering;
 
@@ -21,9 +23,6 @@ use crate::traits::Identity;
 use crate::traits::VartimePrecomputedMultiscalarMul;
 use crate::window::{NafLookupTable5, NafLookupTable8};
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 pub struct VartimePrecomputedStraus {
     static_lookup_tables: Vec<NafLookupTable8<CachedPoint>>,
 }

src/backend/vector/scalar_mul/straus.rs

@@ -11,6 +11,8 @@
 
 #![allow(non_snake_case)]
 
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::cmp::Ordering;
 
@@ -22,9 +24,6 @@ use crate::scalar::Scalar;
 use crate::traits::{Identity, MultiscalarMul, VartimeMultiscalarMul};
 use crate::window::{LookupTable, NafLookupTable5};
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 /// Multiscalar multiplication using interleaved window / Straus'
 /// method.  See the `Straus` struct in the serial backend for more
 /// details.

src/edwards.rs

@@ -129,9 +129,6 @@ use crate::window::LookupTableRadix256;
 use crate::window::LookupTableRadix32;
 use crate::window::LookupTableRadix64;
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 use crate::traits::BasepointTable;
 use crate::traits::ValidityCheck;
 use crate::traits::{Identity, IsIdentity};
@@ -710,7 +707,6 @@ impl<'a, 'b> Mul<&'b EdwardsPoint> for &'a Scalar {
 // forward to a specific backend implementation.
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl MultiscalarMul for EdwardsPoint {
     type Point = EdwardsPoint;
 
@@ -743,7 +739,6 @@ impl MultiscalarMul for EdwardsPoint {
 }
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl VartimeMultiscalarMul for EdwardsPoint {
     type Point = EdwardsPoint;
 
@@ -783,11 +778,9 @@ impl VartimeMultiscalarMul for EdwardsPoint {
 // decouple stability of the inner type from the stability of the
 // outer type.
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 pub struct VartimeEdwardsPrecomputation(scalar_mul::precomputed_straus::VartimePrecomputedStraus);
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl VartimePrecomputedMultiscalarMul for VartimeEdwardsPrecomputation {
     type Point = EdwardsPoint;
 
@@ -1126,6 +1119,9 @@ mod test {
     use crate::scalar::Scalar;
     use subtle::ConditionallySelectable;
 
+    #[cfg(feature = "alloc")]
+    use alloc::vec::Vec;
+
     /// X coordinate of the basepoint.
     /// = 15112221349535400772501151409588531511454012693041857206046113283949847762202
     static BASE_X_COORD_BYTES: [u8; 32] = [

src/field.rs

@@ -167,7 +167,6 @@ impl FieldElement {
     ///
     /// When an input `FieldElement` is zero, its value is unchanged.
     #[cfg(feature = "alloc")]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
     pub fn batch_invert(inputs: &mut [FieldElement]) {
         // Montgomery’s Trick and Fast Implementation of Masked AES
         // Genelle, Prouff and Quisquater

src/lib.rs

@@ -32,7 +32,8 @@
 #[macro_use]
 extern crate alloc;
 
-#[cfg(feature = "std")]
+// TODO: move std-dependent tests to `tests/`
+#[cfg(test)]
 #[macro_use]
 extern crate std;
 
@@ -78,10 +79,6 @@ pub mod backend;
 #[cfg(not(docsrs))]
 pub(crate) mod backend;
 
-// Crate-local prelude (for alloc-dependent features like `Vec`)
-
-pub(crate) mod prelude;
-
 // Generic code for window lookups
 pub(crate) mod window;
 

src/montgomery.rs

@@ -374,6 +374,9 @@ mod test {
     use super::*;
     use crate::constants;
 
+    #[cfg(feature = "alloc")]
+    use alloc::vec::Vec;
+
     #[cfg(feature = "rand_core")]
     use rand_core::OsRng;
 
@@ -480,9 +483,9 @@ mod test {
     ];
 
     #[test]
-    #[cfg(feature = "alloc")] // Vec
+    #[cfg(feature = "alloc")]
     fn montgomery_elligator_correct() {
-        let bytes: alloc::vec::Vec<u8> = (0u8..32u8).collect();
+        let bytes: Vec<u8> = (0u8..32u8).collect();
         let bits_in: [u8; 32] = (&bytes[..]).try_into().expect("Range invariant broken");
 
         let fe = FieldElement::from_bytes(&bits_in);

src/prelude.rs

@@ -1,19 +0,0 @@
-// -*- mode: rust; -*-
-//
-// This file is part of curve25519-dalek.
-// Copyright (c) 2016-2021 isis lovecruft
-// Copyright (c) 2016-2019 Henry de Valence
-// See LICENSE for licensing information.
-//
-// Authors:
-// - isis agora lovecruft <isis@patternsinthevoid.net>
-// - Henry de Valence <hdevalence@hdevalence.ca>
-
-//! Crate-local prelude (for alloc-dependent features like `Vec`)
-
-// TODO: switch to alloc::prelude
-#[cfg(all(feature = "alloc", not(feature = "std")))]
-pub use alloc::vec::Vec;
-
-#[cfg(feature = "std")]
-pub use std::vec::Vec;

src/ristretto.rs

@@ -158,6 +158,9 @@
 //! [ristretto_main]:
 //! https://ristretto.group/
 
+#[cfg(feature = "alloc")]
+use alloc::vec::Vec;
+
 use core::borrow::Borrow;
 use core::fmt::Debug;
 use core::iter::Sum;
@@ -186,9 +189,6 @@ use zeroize::Zeroize;
 use crate::edwards::EdwardsBasepointTable;
 use crate::edwards::EdwardsPoint;
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 use crate::scalar::Scalar;
 
 use crate::traits::BasepointTable;
@@ -525,7 +525,6 @@ impl RistrettoPoint {
     /// # }
     /// ```
     #[cfg(feature = "alloc")]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
     pub fn double_and_compress_batch<'a, I>(points: I) -> Vec<CompressedRistretto>
     where
         I: IntoIterator<Item = &'a RistrettoPoint>,
@@ -932,7 +931,6 @@ define_mul_variants!(LHS = Scalar, RHS = RistrettoPoint, Output = RistrettoPoint
 // forward to the EdwardsPoint implementations.
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl MultiscalarMul for RistrettoPoint {
     type Point = RistrettoPoint;
 
@@ -949,7 +947,6 @@ impl MultiscalarMul for RistrettoPoint {
 }
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl VartimeMultiscalarMul for RistrettoPoint {
     type Point = RistrettoPoint;
 
@@ -970,11 +967,9 @@ impl VartimeMultiscalarMul for RistrettoPoint {
 // decouple stability of the inner type from the stability of the
 // outer type.
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 pub struct VartimeRistrettoPrecomputation(scalar_mul::precomputed_straus::VartimePrecomputedStraus);
 
 #[cfg(feature = "alloc")]
-#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
 impl VartimePrecomputedMultiscalarMul for VartimeRistrettoPrecomputation {
     type Point = RistrettoPoint;
 

src/scalar.rs

@@ -150,9 +150,6 @@ use core::ops::{Add, AddAssign};
 use core::ops::{Mul, MulAssign};
 use core::ops::{Sub, SubAssign};
 
-#[allow(unused_imports)]
-use crate::prelude::*;
-
 use cfg_if::cfg_if;
 
 #[cfg(feature = "rand_core")]
@@ -797,7 +794,6 @@ impl Scalar {
     /// # }
     /// ```
     #[cfg(feature = "alloc")]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
     pub fn batch_invert(inputs: &mut [Scalar]) -> Scalar {
         // This code is essentially identical to the FieldElement
         // implementation, and is documented there.  Unfortunately,
@@ -1257,6 +1253,9 @@ mod test {
     use super::*;
     use crate::constants;
 
+    #[cfg(feature = "alloc")]
+    use alloc::vec::Vec;
+
     /// x = 2238329342913194256032495932344128051776374960164957527413114840482143558222
     pub static X: Scalar = Scalar {
         bytes: [