fix warnings

Author: hanabi1224

build.rs

@@ -2,8 +2,14 @@ use rustc_version::{version_meta, Channel};
 
 fn main() {
     match version_meta().unwrap().channel {
-        Channel::Nightly => println!("cargo:rustc-cfg=nightly"),
-        Channel::Beta => println!("cargo:rustc-cfg=beta"),
+        Channel::Nightly => {
+            println!("cargo::rustc-check-cfg=cfg(nightly)");
+            println!("cargo:rustc-cfg=nightly");
+        }
+        Channel::Beta => {
+            println!("cargo::rustc-check-cfg=cfg(beta)");
+            println!("cargo:rustc-cfg=beta");
+        }
         _ => {}
     };
 }

src/lib.rs

@@ -14,6 +14,7 @@ pub use types::*;
 pub mod wasm_exports;
 
 #[cfg(test)]
+#[cfg(nightly)]
 mod tests {
     pub trait RoundTo<T> {
         fn round_to(&self, n: usize) -> T;

src/types/annoy_index_impl.rs

@@ -4,7 +4,6 @@ use crate::internals::storage_ext::*;
 use crate::types::node::*;
 use crate::Storage;
 use std::error::Error;
-use std::vec::Vec;
 
 impl AnnoyIndex {
     #[cfg(not(target_arch = "wasm32"))]