bug: add feature gates for rand

Fails to build without the feature gate `#[cfg(feature = "rand")]`
since rand is optional.  Where ever the feature gate is used, also add
`#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]` which is used by
docs.rs.  Should ensure that the attribute is active when docs.rs is
generating the documentation.

Also, remove `default-features = false` from the optional rand
dependence since `std` is a required feature of rand by this project.

Author: yancyribbens

Cargo.toml

@@ -18,7 +18,7 @@ features = ["rand"]
 
 [dependencies]
 bitcoin = "0.32.7"
-rand = { version = "0.8.5", default-features = false, optional = true }
+rand = { version = "0.8.5", optional = true }
 
 [dev-dependencies]
 bitcoin = "0.32.7"

src/lib.rs

@@ -15,9 +15,13 @@ mod branch_and_bound;
 mod single_random_draw;
 
 use bitcoin::{Amount, FeeRate, SignedAmount, Weight};
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 use rand::thread_rng;
 
 pub use crate::branch_and_bound::select_coins_bnb;
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 pub use crate::single_random_draw::select_coins_srd;
 
 pub(crate) type Return<'a, Utxo> = Option<(u32, Vec<&'a Utxo>)>;

src/single_random_draw.rs

@@ -6,6 +6,8 @@
 
 use bitcoin::blockdata::transaction::effective_value;
 use bitcoin::{Amount, FeeRate};
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 use rand::seq::SliceRandom;
 
 use crate::{Return, WeightedUtxo, CHANGE_LOWER};
@@ -33,6 +35,8 @@ use crate::{Return, WeightedUtxo, CHANGE_LOWER};
 ///     - Not enough potential amount to meet the target
 ///     - Target Amount is zero (no match possible)
 ///     - Search was successful yet no match found
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 pub fn select_coins_srd<'a, R: rand::Rng + ?Sized, Utxo: WeightedUtxo>(
     target: Amount,
     fee_rate: FeeRate,