halo2_gadgets: Remove usage of `array::IntoIter::new`

Rust 2021 implements `IntoIterator` for arrays directly, instead of only
references to arrays.

    https://doc.rust-lang.org/edition-guide/rust-2021/IntoIterator-for-arrays.html

halo2_gadgets/benches/primitives.rs

@@ -1,5 +1,3 @@
-use std::array;
-
 use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};
 use ff::Field;
 use halo2_gadgets::primitives::{
@@ -39,7 +37,7 @@ fn bench_primitives(c: &mut Criterion) {
         // - 510 bits for Commit^ivk
         // - 520 bits for MerkleCRH
         // - 1086 bits for NoteCommit
-        for size in array::IntoIter::new([510, 520, 1086]) {
+        for size in [510, 520, 1086] {
             group.bench_function(BenchmarkId::new("hash-to-point", size), |b| {
                 b.iter(|| hasher.hash_to_point(bits[..size].iter().cloned()))
             });

halo2_gadgets/src/ecc/chip/add.rs

@@ -1,5 +1,3 @@
-use std::array;
-
 use super::EccPoint;
 use ff::{BatchInvert, Field};
 use halo2_proofs::{
@@ -71,7 +69,7 @@ impl Config {
     }
 
     pub(crate) fn advice_columns(&self) -> HashSet<Column<Advice>> {
-        core::array::IntoIter::new([
+        [
             self.x_p,
             self.y_p,
             self.x_qr,
@@ -81,12 +79,13 @@ impl Config {
             self.beta,
             self.gamma,
             self.delta,
-        ])
+        ]
+        .into_iter()
         .collect()
     }
 
     pub(crate) fn output_columns(&self) -> HashSet<Column<Advice>> {
-        core::array::IntoIter::new([self.x_qr, self.y_qr]).collect()
+        [self.x_qr, self.y_qr].into_iter().collect()
     }
 
     fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
@@ -206,10 +205,10 @@ impl Config {
 
             Constraints::with_selector(
                 q_add,
-                array::IntoIter::new([
+                [
                     poly1, poly2, poly3, poly4, poly5, poly6, poly7, poly8, poly9, poly10, poly11,
                     poly12,
-                ]),
+                ],
             )
         });
     }

halo2_gadgets/src/ecc/chip/add_incomplete.rs

@@ -1,4 +1,4 @@
-use std::{array, collections::HashSet};
+use std::collections::HashSet;
 
 use super::NonIdentityEccPoint;
 use ff::Field;
@@ -50,7 +50,9 @@ impl Config {
     }
 
     pub(crate) fn advice_columns(&self) -> HashSet<Column<Advice>> {
-        core::array::IntoIter::new([self.x_p, self.y_p, self.x_qr, self.y_qr]).collect()
+        [self.x_p, self.y_p, self.x_qr, self.y_qr]
+            .into_iter()
+            .collect()
     }
 
     fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
@@ -74,10 +76,7 @@ impl Config {
             // (y_r + y_q)(x_p − x_q) − (y_p − y_q)(x_q − x_r) = 0
             let poly2 = (y_r + y_q.clone()) * (x_p - x_q.clone()) - (y_p - y_q) * (x_q - x_r);
 
-            Constraints::with_selector(
-                q_add_incomplete,
-                array::IntoIter::new([("x_r", poly1), ("y_r", poly2)]),
-            )
+            Constraints::with_selector(q_add_incomplete, [("x_r", poly1), ("y_r", poly2)])
         });
     }
 

halo2_gadgets/src/ecc/chip/mul.rs

@@ -153,11 +153,11 @@ impl Config {
 
             Constraints::with_selector(
                 q_mul_lsb,
-                std::array::IntoIter::new([
+                [
                     ("bool_check", bool_check),
                     ("lsb_x", lsb_x),
                     ("lsb_y", lsb_y),
-                ]),
+                ],
             )
         });
     }

halo2_gadgets/src/ecc/chip/mul/complete.rs

@@ -74,7 +74,7 @@ impl Config {
 
                 Constraints::with_selector(
                     q_mul_decompose_var,
-                    std::array::IntoIter::new([("bool_check", bool_check), ("y_switch", y_switch)]),
+                    [("bool_check", bool_check), ("y_switch", y_switch)],
                 )
             },
         );

halo2_gadgets/src/ecc/chip/mul_fixed/short.rs

@@ -1,4 +1,4 @@
-use std::{array, convert::TryInto};
+use std::convert::TryInto;
 
 use super::super::{EccPoint, EccScalarFixedShort, FixedPoints, L_SCALAR_SHORT, NUM_WINDOWS_SHORT};
 use crate::{ecc::chip::MagnitudeSign, utilities::bool_check};
@@ -59,12 +59,12 @@ impl<Fixed: FixedPoints<pallas::Affine>> Config<Fixed> {
 
             Constraints::with_selector(
                 q_mul_fixed_short,
-                array::IntoIter::new([
+                [
                     ("last_window_check", last_window_check),
                     ("sign_check", sign_check),
                     ("y_check", y_check),
                     ("negation_check", negation_check),
-                ]),
+                ],
             )
         });
     }

halo2_gadgets/src/ecc/chip/witness_point.rs

@@ -1,5 +1,3 @@
-use std::array;
-
 use super::{EccPoint, NonIdentityEccPoint};
 
 use group::prime::PrimeCurveAffine;
@@ -68,10 +66,10 @@ impl Config {
             // of the form `q_point * (x * curve_eqn)`, but this was implemented without
             // parentheses, and thus evaluates as `(q_point * x) * curve_eqn`, which is
             // structurally different in the pinned verifying key.
-            array::IntoIter::new([
+            [
                 ("x == 0 v on_curve", q_point.clone() * x * curve_eqn(meta)),
                 ("y == 0 v on_curve", q_point * y * curve_eqn(meta)),
-            ])
+            ]
         });
 
         meta.create_gate("witness non-identity point", |meta| {

halo2_gadgets/src/poseidon.rs

@@ -1,6 +1,5 @@
 //! Gadget and chips for the Poseidon algebraic hash function.
 
-use std::array;
 use std::convert::TryInto;
 use std::fmt;
 use std::marker::PhantomData;
@@ -283,7 +282,8 @@ impl<
         mut layouter: impl Layouter<F>,
         message: [AssignedCell<F, F>; L],
     ) -> Result<AssignedCell<F, F>, Error> {
-        for (i, value) in array::IntoIter::new(message)
+        for (i, value) in message
+            .into_iter()
             .map(PaddedWord::Message)
             .chain(<ConstantLength<L> as Domain<F, RATE>>::padding(L).map(PaddedWord::Padding))
             .enumerate()

halo2_gadgets/src/primitives/poseidon.rs

@@ -1,6 +1,5 @@
 //! The Poseidon algebraic hash function.
 
-use std::array;
 use std::convert::TryInto;
 use std::fmt;
 use std::iter;
@@ -363,8 +362,9 @@ impl<F: FieldExt, S: Spec<F, T, RATE>, const T: usize, const RATE: usize, const
 {
     /// Hashes the given input.
     pub fn hash(mut self, message: [F; L]) -> F {
-        for value in
-            array::IntoIter::new(message).chain(<ConstantLength<L> as Domain<F, RATE>>::padding(L))
+        for value in message
+            .into_iter()
+            .chain(<ConstantLength<L> as Domain<F, RATE>>::padding(L))
         {
             self.sponge.absorb(value);
         }

halo2_gadgets/src/sha256/table16/compression/compression_gates.rs

@@ -1,9 +1,9 @@
 use super::super::{util::*, Gate};
 use halo2_proofs::{
     arithmetic::FieldExt,
-    plonk::{Constraints, Expression},
+    plonk::{Constraint, Constraints, Expression},
 };
-use std::{array, marker::PhantomData};
+use std::marker::PhantomData;
 
 pub struct CompressionGate<F: FieldExt>(PhantomData<F>);
 
@@ -426,23 +426,19 @@ impl<F: FieldExt> CompressionGate<F> {
         lo_3: Expression<F>,
         hi_3: Expression<F>,
         word_3: Expression<F>,
-    ) -> Constraints<
-        F,
-        (&'static str, Expression<F>),
-        impl Iterator<Item = (&'static str, Expression<F>)>,
-    > {
+    ) -> impl IntoIterator<Item = Constraint<F>> {
         let check_lo_hi = |lo: Expression<F>, hi: Expression<F>, word: Expression<F>| {
             lo + hi * F::from(1 << 16) - word
         };
 
         Constraints::with_selector(
             s_digest,
-            array::IntoIter::new([
+            [
                 ("check_lo_hi_0", check_lo_hi(lo_0, hi_0, word_0)),
                 ("check_lo_hi_1", check_lo_hi(lo_1, hi_1, word_1)),
                 ("check_lo_hi_2", check_lo_hi(lo_2, hi_2, word_2)),
                 ("check_lo_hi_3", check_lo_hi(lo_3, hi_3, word_3)),
-            ]),
+            ],
         )
     }
 }

halo2_gadgets/src/sha256/table16/message_schedule/schedule_gates.rs

@@ -1,6 +1,6 @@
 use super::super::Gate;
 use halo2_proofs::{arithmetic::FieldExt, plonk::Expression};
-use std::{array, marker::PhantomData};
+use std::marker::PhantomData;
 
 pub struct ScheduleGate<F: FieldExt>(PhantomData<F>);
 
@@ -29,7 +29,8 @@ impl<F: FieldExt> ScheduleGate<F> {
             + (word * (-F::one()));
         let carry_check = Gate::range_check(carry, 0, 3);
 
-        array::IntoIter::new([("word_check", word_check), ("carry_check", carry_check)])
+        [("word_check", word_check), ("carry_check", carry_check)]
+            .into_iter()
             .map(move |(name, poly)| (name, s_word.clone() * poly))
     }
 
@@ -65,11 +66,12 @@ impl<F: FieldExt> ScheduleGate<F> {
         let range_check_tag_c = Gate::range_check(tag_c, 0, 2);
         let range_check_tag_d = Gate::range_check(tag_d, 0, 4);
 
-        array::IntoIter::new([
+        [
             ("decompose_check", decompose_check),
             ("range_check_tag_c", range_check_tag_c),
             ("range_check_tag_d", range_check_tag_d),
-        ])
+        ]
+        .into_iter()
         .map(move |(name, poly)| (name, s_decompose_1.clone() * poly))
     }
 
@@ -101,11 +103,12 @@ impl<F: FieldExt> ScheduleGate<F> {
         let range_check_tag_d = Gate::range_check(tag_d, 0, 0);
         let range_check_tag_g = Gate::range_check(tag_g, 0, 3);
 
-        array::IntoIter::new([
+        [
             ("decompose_check", decompose_check),
             ("range_check_tag_g", range_check_tag_g),
             ("range_check_tag_d", range_check_tag_d),
-        ])
+        ]
+        .into_iter()
         .map(move |(name, poly)| (name, s_decompose_2.clone() * poly))
     }
 
@@ -130,11 +133,12 @@ impl<F: FieldExt> ScheduleGate<F> {
         let range_check_tag_a = Gate::range_check(tag_a, 0, 1);
         let range_check_tag_d = Gate::range_check(tag_d, 0, 3);
 
-        array::IntoIter::new([
+        [
             ("decompose_check", decompose_check),
             ("range_check_tag_a", range_check_tag_a),
             ("range_check_tag_d", range_check_tag_d),
-        ])
+        ]
+        .into_iter()
         .map(move |(name, poly)| (name, s_decompose_3.clone() * poly))
     }
 

halo2_gadgets/src/sinsemilla/chip.rs

@@ -259,10 +259,7 @@ where
                 lhs - rhs
             };
 
-            Constraints::with_selector(
-                q_s1,
-                std::array::IntoIter::new([("Secant line", secant_line), ("y check", y_check)]),
-            )
+            Constraints::with_selector(q_s1, [("Secant line", secant_line), ("y check", y_check)])
         });
 
         config

halo2_gadgets/src/sinsemilla/merkle/chip.rs

@@ -25,7 +25,6 @@ use crate::{
     },
 };
 use group::ff::PrimeField;
-use std::array;
 
 /// Configuration for the `MerkleChip` implementation.
 #[derive(Clone, Debug)]
@@ -165,12 +164,12 @@ where
 
             Constraints::with_selector(
                 q_decompose,
-                array::IntoIter::new([
+                [
                     ("l_check", l_check),
                     ("left_check", left_check),
                     ("right_check", right_check),
                     ("b1_b2_check", b1_b2_check),
-                ]),
+                ],
             )
         });
 

halo2_gadgets/src/utilities.rs

@@ -6,7 +6,7 @@ use halo2_proofs::{
     plonk::{Advice, Column, Error, Expression},
 };
 use pasta_curves::arithmetic::FieldExt;
-use std::{array, ops::Range};
+use std::ops::Range;
 
 pub mod cond_swap;
 pub mod decompose_running_sum;
@@ -64,7 +64,7 @@ pub(crate) fn transpose_option_array<T: Copy + std::fmt::Debug, const LEN: usize
 ) -> [Option<T>; LEN] {
     let mut ret = [None; LEN];
     if let Some(arr) = option_array {
-        for (entry, value) in ret.iter_mut().zip(array::IntoIter::new(arr)) {
+        for (entry, value) in ret.iter_mut().zip(arr) {
             *entry = Some(value);
         }
     }

halo2_gadgets/src/utilities/cond_swap.rs

@@ -7,7 +7,7 @@ use halo2_proofs::{
     poly::Rotation,
 };
 use pasta_curves::arithmetic::FieldExt;
-use std::{array, marker::PhantomData};
+use std::marker::PhantomData;
 
 /// Instructions for a conditional swap gadget.
 pub trait CondSwapInstructions<F: FieldExt>: UtilitiesInstructions<F> {
@@ -191,11 +191,11 @@ impl<F: FieldExt> CondSwapChip<F> {
 
             Constraints::with_selector(
                 q_swap,
-                array::IntoIter::new([
+                [
                     ("a check", a_check),
                     ("b check", b_check),
                     ("swap is bool", bool_check),
-                ]),
+                ],
             )
         });