make rand/getrandom dependency explicit with a feature

In the effort to make the arkworks framework available for compilation
in wasm environment, we need to make ``getrandom`` indirect dependency an
opt-in feature.
``rand/std`` feature triggers the dependency over ``getrandom``, so it can't be
included in the ``std`` feature. It must be separated in an extra
feature that we named ``getrandom``

Cargo.toml

@@ -13,21 +13,21 @@ license = "MIT/Apache-2.0"
 edition = "2018"
 
 [dependencies]
-rand = { version = "0.8", default-features = false, features = ["std_rng"] }
+rand = { version = "0.8", default-features = false, features = ["std_rng"]}
 rayon = { version = "1", optional = true }
 colored = { version = "2", optional = true }
 num-traits = { version = "0.2", default-features = false }
 
+[dev-dependencies]
+rand = { version = "0.8", features = ["std"]}
+
+
 [features]
 default = [ "std" ]
-std = [ "rand/std" ]
+std = []
 parallel = [ "rayon", "std" ]
 print-trace = [ "std", "colored" ]
-
-[profile.release]
-opt-level = 3
-lto = "thin"
-incremental = true
+getrandom = ["rand/std"]
 
 [profile.bench]
 opt-level = 3

src/rand_helper.rs

@@ -4,7 +4,7 @@ use rand::{
     Rng,
 };
 #[cfg(feature = "std")]
-use rand::{prelude::ThreadRng, RngCore};
+use rand::RngCore;
 
 pub use rand;
 
@@ -41,20 +41,28 @@ pub fn test_rng() -> impl rand::Rng {
 /// Should be used only for tests, not for any real world usage.
 #[cfg(feature = "std")]
 pub fn test_rng() -> impl rand::Rng {
-    let is_deterministic =
-        std::env::vars().any(|(key, val)| key == "DETERMINISTIC_TEST_RNG" && val == "1");
-    if is_deterministic {
+    #[cfg(any(feature = "getrandom", test))]
+    {
+        let is_deterministic =
+            std::env::vars().any(|(key, val)| key == "DETERMINISTIC_TEST_RNG" && val == "1");
+        if is_deterministic {
+            RngWrapper::Deterministic(test_rng_helper())
+        } else {
+            RngWrapper::Randomized(rand::thread_rng())
+        }
+    }
+    #[cfg(not(any(feature = "getrandom", test)))]
+    {
         RngWrapper::Deterministic(test_rng_helper())
-    } else {
-        RngWrapper::Randomized(rand::thread_rng())
     }
 }
 
 /// Helper wrapper to enable `test_rng` to return `impl::Rng`.
 #[cfg(feature = "std")]
 enum RngWrapper {
     Deterministic(StdRng),
-    Randomized(ThreadRng),
+    #[cfg(any(feature = "getrandom", test))]
+        Randomized(rand::rngs::ThreadRng),
 }
 
 #[cfg(feature = "std")]
@@ -63,6 +71,7 @@ impl RngCore for RngWrapper {
     fn next_u32(&mut self) -> u32 {
         match self {
             Self::Deterministic(rng) => rng.next_u32(),
+            #[cfg(any(feature = "getrandom", test))]
             Self::Randomized(rng) => rng.next_u32(),
         }
     }
@@ -71,6 +80,7 @@ impl RngCore for RngWrapper {
     fn next_u64(&mut self) -> u64 {
         match self {
             Self::Deterministic(rng) => rng.next_u64(),
+            #[cfg(any(feature = "getrandom", test))]
             Self::Randomized(rng) => rng.next_u64(),
         }
     }
@@ -79,6 +89,7 @@ impl RngCore for RngWrapper {
     fn fill_bytes(&mut self, dest: &mut [u8]) {
         match self {
             Self::Deterministic(rng) => rng.fill_bytes(dest),
+            #[cfg(any(feature = "getrandom", test))]
             Self::Randomized(rng) => rng.fill_bytes(dest),
         }
     }
@@ -87,6 +98,7 @@ impl RngCore for RngWrapper {
     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand::Error> {
         match self {
             Self::Deterministic(rng) => rng.try_fill_bytes(dest),
+            #[cfg(any(feature = "getrandom", test))]
             Self::Randomized(rng) => rng.try_fill_bytes(dest),
         }
     }