Annotate docs with required feature flags

src/arithmetic.rs

@@ -17,6 +17,7 @@ pub use fields::*;
 /// performed. This allows an FFT implementation (for example) to operate
 /// generically over either a field or elliptic curve group.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub trait Group: Copy + Clone + Send + Sync + 'static {
     /// The group is assumed to be of prime order $p$. `Scalar` is the
     /// associated scalar field of size $p$.

src/arithmetic/curves.rs

@@ -23,6 +23,7 @@ use std::{
 /// Currently requires the `std` feature flag because of `hash_to_curve`, and
 /// `CurveAffine::{read, write}`.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub trait CurveExt:
     PrimeCurve<Affine = <Self as CurveExt>::AffineExt>
     + group::Group<Scalar = <Self as CurveExt>::ScalarExt>
@@ -90,6 +91,7 @@ pub trait CurveExt:
 /// This trait is the affine counterpart to `Curve` and is used for
 /// serialization, storage in memory, and inspection of $x$ and $y$ coordinates.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub trait CurveAffine:
     PrimeCurveAffine<
         Scalar = <Self as CurveAffine>::ScalarExt,
@@ -145,6 +147,7 @@ pub trait CurveAffine:
 
 /// The affine coordinates of a point on an elliptic curve.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 #[derive(Clone, Copy, Debug, Default)]
 pub struct Coordinates<C: CurveAffine> {
     pub(crate) x: C::Base,

src/arithmetic/fields.rs

@@ -20,6 +20,7 @@ const_assert!(size_of::<usize>() >= 4);
 /// A trait that exposes additional operations related to calculating square roots of
 /// prime-order finite fields.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub trait SqrtRatio: ff::PrimeField {
     /// The value $(T-1)/2$ such that $2^S \cdot T = p - 1$ with $T$ odd.
     const T_MINUS1_OVER2: [u64; 4];
@@ -65,6 +66,7 @@ pub trait SqrtRatio: ff::PrimeField {
 /// This trait is a common interface for dealing with elements of a finite
 /// field.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub trait FieldExt: SqrtRatio + From<bool> + Ord + Group<Scalar = Self> {
     /// Modulus of the field written as a string for display purposes
     const MODULUS: &'static str;
@@ -119,6 +121,7 @@ pub trait FieldExt: SqrtRatio + From<bool> + Ord + Group<Scalar = Self> {
 ///
 /// `tm1d2` should be set to `(t - 1) // 2`, where `t = (modulus - 1) >> F::S`.
 #[cfg(not(feature = "std"))]
+#[cfg_attr(docsrs, doc(cfg(not(feature = "std"))))]
 pub(crate) fn sqrt_tonelli_shanks<F: ff::PrimeField, S: AsRef<[u64]>>(
     f: &F,
     tm1d2: S,
@@ -165,6 +168,7 @@ pub(crate) fn sqrt_tonelli_shanks<F: ff::PrimeField, S: AsRef<[u64]>>(
 
 /// Parameters for a perfect hash function used in square root computation.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 #[derive(Debug)]
 struct SqrtHasher<F: FieldExt> {
     hash_xor: u32,
@@ -186,6 +190,7 @@ impl<F: FieldExt> SqrtHasher<F> {
 
 /// Tables used for square root computation.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 #[derive(Debug)]
 pub struct SqrtTables<F: FieldExt> {
     hasher: SqrtHasher<F>,

src/curves.rs

@@ -103,6 +103,7 @@ macro_rules! new_curve_impl {
         }
 
         #[cfg(feature = "std")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
         impl group::WnafGroup for $name {
             fn recommended_wnaf_for_num_scalars(num_scalars: usize) -> usize {
                 // Copied from bls12_381::g1, should be updated.

src/fields/fp.rs

@@ -225,6 +225,7 @@ const ROOT_OF_UNITY: Fp = Fp::from_raw([
 /// with t odd. In other words, this
 /// is a t root of unity.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 const DELTA: Fp = Fp::from_raw([
     0x6a6ccd20dd7b9ba2,
     0xf5e4f3f13eee5636,
@@ -464,6 +465,7 @@ impl<'a> From<&'a Fp> for [u8; 32] {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl Group for Fp {
     type Scalar = Fp;
 
@@ -623,6 +625,7 @@ type ReprBits = [u32; 8];
 type ReprBits = [u64; 4];
 
 #[cfg(feature = "bits")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bits")))]
 impl PrimeFieldBits for Fp {
     type ReprBits = ReprBits;
 
@@ -666,10 +669,12 @@ impl PrimeFieldBits for Fp {
 #[cfg(feature = "std")]
 lazy_static! {
     // The perfect hash parameters are found by `squareroottab.sage` in zcash/pasta.
+    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     static ref FP_TABLES: SqrtTables<Fp> = SqrtTables::new(0x11BE, 1098);
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl SqrtRatio for Fp {
     const T_MINUS1_OVER2: [u64; 4] = T_MINUS1_OVER2;
 
@@ -721,6 +726,7 @@ impl SqrtRatio for Fp {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl FieldExt for Fp {
     const MODULUS: &'static str =
         "0x40000000000000000000000000000000224698fc094cf91b992d30ed00000001";

src/fields/fq.rs

@@ -225,6 +225,7 @@ const ROOT_OF_UNITY: Fq = Fq::from_raw([
 /// with t odd. In other words, this
 /// is a t root of unity.
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 const DELTA: Fq = Fq::from_raw([
     0x8494392472d1683c,
     0xe3ac3376541d1140,
@@ -464,6 +465,7 @@ impl<'a> From<&'a Fq> for [u8; 32] {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl Group for Fq {
     type Scalar = Fq;
 
@@ -666,10 +668,12 @@ impl PrimeFieldBits for Fq {
 #[cfg(feature = "std")]
 lazy_static! {
     // The perfect hash parameters are found by `squareroottab.sage` in zcash/pasta.
+    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
     static ref FQ_TABLES: SqrtTables<Fq> = SqrtTables::new(0x116A9E, 1206);
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl SqrtRatio for Fq {
     const T_MINUS1_OVER2: [u64; 4] = T_MINUS1_OVER2;
 
@@ -721,6 +725,7 @@ impl SqrtRatio for Fq {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl FieldExt for Fq {
     const MODULUS: &'static str =
         "0x40000000000000000000000000000000224698fc0994a8dd8c46eb2100000001";