Create configuration conditional bench

As we did in rust-bitcoin [0] create a configuration conditional `bench`
that we can use to guard bench mark code. This has the benefit of
making our features additive i.e., we can now test with `--all-features`
with a stable toolchain (currently this fails because of our use of the
`test` crate).

[0] - https://github.com/rust-bitcoin/rust-bitcoin/pull/1092

Cargo.toml

@@ -18,7 +18,6 @@ features = [ "rand", "rand-std", "serde", "bitcoin_hashes", "recovery", "global-
 rustdoc-args = ["--cfg", "docsrs"]
 
 [features]
-unstable = ["recovery"]
 default = ["std"]
 std = ["alloc", "secp256k1-sys/std"]
 # allow use of Secp256k1::new and related API that requires an allocator

README.md

@@ -33,6 +33,11 @@ git config --local core.hooksPath githooks/
 
 Alternatively add symlinks in your `.git/hooks` directory to any of the githooks we provide.
 
+### Benchmarks
+
+We use a custom Rust compiler configuration conditional to guard the bench mark code. To run the
+bench marks use: `RUSTFLAGS='--cfg=bench' cargo +nightly bench --features=recovery`.
+
 ## Fuzzing
 
 If you want to fuzz this library, or any library which depends on it, you will

contrib/test.sh

@@ -98,9 +98,11 @@ if [ "$DO_ASAN" = true ]; then
     cargo run --release --features=alloc --manifest-path=./no_std_test/Cargo.toml | grep -q "Verified alloc Successfully"
 fi
 
-# Bench
-if [ "$DO_BENCH" = true ]; then
-    cargo bench --all --features="unstable"
+
+# Bench if told to, only works with non-stable toolchain (nightly, beta).
+if [ "$DO_BENCH" = true ]
+then
+    RUSTFLAGS='--cfg=bench' cargo bench --features=recovery
 fi
 
 exit 0

src/ecdh.rs

@@ -286,7 +286,7 @@ mod tests {
     }
 }
 
-#[cfg(all(test, feature = "unstable"))]
+#[cfg(bench)]
 mod benches {
     use test::{Bencher, black_box};
 

src/ecdsa/recovery.rs

@@ -452,7 +452,7 @@ mod tests {
     }
 }
 
-#[cfg(all(test, feature = "unstable"))]
+#[cfg(bench)]
 mod benches {
     use rand::{thread_rng, RngCore};
     use test::{Bencher, black_box};

src/key.rs

@@ -2433,7 +2433,7 @@ mod test {
     }
 }
 
-#[cfg(all(test, feature = "unstable"))]
+#[cfg(bench)]
 mod benches {
     use test::Bencher;
     use std::collections::BTreeSet;

src/lib.rs

@@ -155,14 +155,16 @@
 #![allow(clippy::missing_safety_doc)]
 
 #![cfg_attr(all(not(test), not(feature = "std")), no_std)]
-#![cfg_attr(all(test, feature = "unstable"), feature(test))]
+
+// Experimental features we need.
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(bench, feature(test))]
 
 #[cfg(feature = "alloc")]
 extern crate alloc;
 #[cfg(any(test, feature = "std"))]
 extern crate core;
-#[cfg(all(test, feature = "unstable"))]
+#[cfg(bench)]
 extern crate test;
 
 #[macro_use]
@@ -1060,7 +1062,7 @@ mod tests {
     }
 }
 
-#[cfg(all(test, feature = "unstable"))]
+#[cfg(bench)]
 mod benches {
     use test::{Bencher, black_box};