Make tower-layer no_std compatible.

tower-layer/src/identity.rs

@@ -1,5 +1,5 @@
 use super::Layer;
-use std::fmt;
+use core::fmt;
 
 /// A no-op middleware.
 ///

tower-layer/src/layer_fn.rs

@@ -1,5 +1,5 @@
 use super::Layer;
-use std::fmt;
+use core::fmt;
 
 /// Returns a new [`LayerFn`] that implements [`Layer`] by calling the
 /// given function.
@@ -13,10 +13,10 @@ use std::fmt;
 /// # Example
 /// ```rust
 /// # use tower::Service;
-/// # use std::task::{Poll, Context};
+/// # use core::task::{Poll, Context};
 /// # use tower_layer::{Layer, layer_fn};
-/// # use std::fmt;
-/// # use std::convert::Infallible;
+/// # use core::fmt;
+/// # use core::convert::Infallible;
 /// #
 /// // A middleware that logs requests before forwarding them to another service
 /// pub struct LogService<S> {
@@ -88,7 +88,7 @@ where
 impl<F> fmt::Debug for LayerFn<F> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("LayerFn")
-            .field("f", &format_args!("{}", std::any::type_name::<F>()))
+            .field("f", &format_args!("{}", core::any::type_name::<F>()))
             .finish()
     }
 }

tower-layer/src/lib.rs

@@ -16,6 +16,8 @@
 //!
 //! [`Service`]: https://docs.rs/tower/*/tower/trait.Service.html
 
+#![no_std]
+
 mod identity;
 mod layer_fn;
 mod stack;
@@ -41,9 +43,9 @@ pub use self::{
 ///
 /// ```rust
 /// # use tower_service::Service;
-/// # use std::task::{Poll, Context};
+/// # use core::task::{Poll, Context};
 /// # use tower_layer::Layer;
-/// # use std::fmt;
+/// # use core::fmt;
 ///
 /// pub struct LogLayer {
 ///     target: &'static str,

tower-layer/src/stack.rs

@@ -1,5 +1,5 @@
 use super::Layer;
-use std::fmt;
+use core::fmt;
 
 /// Two middlewares chained together.
 #[derive(Clone)]

tower-service/src/lib.rs

@@ -21,7 +21,6 @@ extern crate std;
 
 use alloc::boxed::Box;
 
-
 use core::future::Future;
 use core::marker::Sized;
 use core::result::Result;