Remove unstable feature

Currently it is not possible to run the test suite with `cargo test
--all-features`, this is because we use a feature called `unstable` to
enable the unstable `test` crate that is used for benchmarking.

There is another way to conditionally enable the test crate and guard
the benchmark code. We can use a custom configuration option `bench`
and then set it using `RUSTFLAGS='--cfg=bench`.

Author: tcharding

Cargo.toml

@@ -17,7 +17,6 @@ no-std = ["hashbrown", "bitcoin/no-std"]
 compiler = []
 trace = []
 
-unstable = []
 serde = ["actual-serde", "bitcoin/serde"]
 rand = ["bitcoin/rand"]
 base64 = ["bitcoin/base64"]

contrib/test.sh

@@ -7,6 +7,12 @@ FEATURES="compiler serde rand base64"
 cargo --version
 rustc --version
 
+# Cache the toolchain we are using.
+NIGHTLY=false
+if cargo --version | grep nightly; then
+    NIGHTLY=true
+fi
+
 # Format if told to
 if [ "$DO_FMT" = true ]
 then
@@ -80,10 +86,18 @@ then
   done
 fi
 
-# Bench if told to (this only works with the nightly toolchain)
+# Bench if told to, only works with non-stable toolchain (nightly, beta).
 if [ "$DO_BENCH" = true ]
 then
-    cargo bench --features="unstable compiler"
+    if [ "$NIGHTLY" = false ]; then
+        if [ -n "$RUSTUP_TOOLCHAIN" ]; then
+            echo "RUSTUP_TOOLCHAIN is set to a non-nightly toolchain but DO_BENCH requires a nightly toolchain"
+        else
+            echo "DO_BENCH requires a nightly toolchain"
+        fi
+        exit 1
+    fi
+    RUSTFLAGS='--cfg=bench' cargo bench
 fi
 
 # Build the docs if told to (this only works with the nightly toolchain)

src/lib.rs

@@ -74,7 +74,8 @@
 //!
 
 #![cfg_attr(all(not(feature = "std"), not(test)), no_std)]
-#![cfg_attr(all(test, feature = "unstable"), feature(test))]
+// Experimental features we need.
+#![cfg_attr(bench, feature(test))]
 // Coding conventions
 #![deny(unsafe_code)]
 #![deny(non_upper_case_globals)]
@@ -107,7 +108,8 @@ extern crate core;
 
 #[cfg(feature = "serde")]
 pub use actual_serde as serde;
-#[cfg(all(test, feature = "unstable"))]
+
+#[cfg(bench)]
 extern crate test;
 
 #[macro_use]

src/policy/compiler.rs

@@ -1601,7 +1601,7 @@ mod tests {
     }
 }
 
-#[cfg(all(test, feature = "unstable"))]
+#[cfg(bench)]
 mod benches {
     use std::str::FromStr;
 

src/policy/mod.rs

@@ -541,7 +541,7 @@ mod tests {
     }
 }
 
-#[cfg(all(test, feature = "compiler", feature = "unstable"))]
+#[cfg(bench)]
 mod benches {
     use core::str::FromStr;