Fix build with use_alloc+use_std.

.travis.yml

@@ -13,6 +13,8 @@ matrix:
       env: FEATURES='use_collections'
     - rust: nightly
       env: FEATURES='use_alloc use_collections'
+    - rust: nightly
+      env: FEATURES='use_std use_alloc use_collections'
 script:
    - cargo build --features "$FEATURES"
 notifications:

src/lib.rs

@@ -1,12 +1,12 @@
 #![no_std]
-#![cfg_attr(feature = "use_alloc", feature(alloc))]
-#![cfg_attr(feature = "use_collections", feature(collections))]
+#![cfg_attr(all(feature = "use_alloc", not(feature = "use_std")), feature(alloc))]
+#![cfg_attr(all(feature = "use_collections", not(feature = "use_std")), feature(collections))]
 
 #[cfg(feature = "use_std")]
 extern crate std;
-#[cfg(feature = "use_alloc")]
+#[cfg(all(feature = "use_alloc", not(feature = "use_std")))]
 extern crate alloc;
-#[cfg(feature = "use_collections")]
+#[cfg(all(feature = "use_collections", not(feature = "use_std")))]
 extern crate collections;
 
 mod object;

src/object.rs

@@ -3,11 +3,11 @@ use core::fmt;
 
 #[cfg(feature = "use_std")]
 use std::boxed::Box;
-#[cfg(feature = "use_alloc")]
+#[cfg(all(feature = "use_alloc", not(feature = "use_std")))]
 use alloc::boxed::Box;
 #[cfg(feature = "use_std")]
 use std::vec::Vec;
-#[cfg(all(feature = "use_alloc", feature = "use_collections"))]
+#[cfg(all(feature = "use_alloc", feature = "use_collections", not(feature = "use_std")))]
 use collections::vec::Vec;
 
 /// A managed object.

src/slice.rs

@@ -3,7 +3,7 @@ use core::fmt;
 
 #[cfg(feature = "use_std")]
 use std::vec::Vec;
-#[cfg(feature = "use_collections")]
+#[cfg(all(feature = "use_collections", not(feature = "use_std")))]
 use collections::vec::Vec;
 
 /// A managed slice.