Compiling without min_specialization and stdsimd

[samueldotj]

We are using nightly channel but with limited features which results in compilation failure.

$ export RUSTFLAGS=-Zallow-features=
$ rustup run nightly cargo build

Error message:

error[E0725]: the feature `min_specialization` is not in the list of allowed features                                                                                                
  --> src/lib.rs:42:45                                                                                                                                                               
   |                                                                                                                                                                                 
42 | #![cfg_attr(feature = "specialize", feature(min_specialization))]                                                                                                               
   |                                             ^^^^^^^^^^^^^^^^^^                       
                                                                                                                                                                                     
error[E0725]: the feature `stdsimd` is not in the list of allowed features                                                                                                           
  --> src/lib.rs:43:42                       
   |                                                                                                                                                                                 
43 | #![cfg_attr(feature = "stdsimd", feature(stdsimd))]

https://docs.rs/version_check/latest/version_check/fn.supports_feature.html was proposed by one my colleague to solve this. I tried it and it seems to work.

diff --git a/build.rs b/build.rs
index 8be4964..0738275 100644
--- a/build.rs
+++ b/build.rs
@@ -4,11 +4,11 @@ use std::env;
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
-    if let Some(channel) = version_check::Channel::read() {
-        if channel.supports_features() {
-            println!("cargo:rustc-cfg=feature=\"specialize\"");
-            println!("cargo:rustc-cfg=feature=\"stdsimd\"");
-        }
+    if let Some(true) = version_check::supports_feature("specialize") {
+        println!("cargo:rustc-cfg=feature=\"specialize\"");
+    }
+    if let Some(true) = version_check::supports_feature("stdsimd") {
+        println!("cargo:rustc-cfg=feature=\"stdsimd\"");
     }
     let os = env::var("CARGO_CFG_TARGET_OS").expect("CARGO_CFG_TARGET_OS was not set");
     if os.eq_ignore_ascii_case("linux")

Please make changes to avoid this failure.

[tkaitchuck]

Merged: 76dd8d2