Update minimum Rust version to 1.78 (#3412)

axum/Cargo.toml

@@ -62,7 +62,6 @@ memchr = "2.4.1"
 mime = "0.3.16"
 percent-encoding = "2.1"
 pin-project-lite = "0.2.7"
-rustversion = "1.0.9"
 serde = "1.0"
 sync_wrapper = "1.0.0"
 tower = { version = "0.5.2", default-features = false, features = ["util"] }

axum/README.md

@@ -104,7 +104,7 @@ This crate uses `#![forbid(unsafe_code)]` to ensure everything is implemented in
 
 ## Minimum supported Rust version
 
-axum's MSRV is 1.75.
+axum's MSRV is 1.78.
 
 ## Examples
 

axum/src/handler/mod.rs

@@ -125,11 +125,8 @@ pub use self::service::HandlerService;
 ///     )));
 /// # let _: Router = app;
 /// ```
-#[rustversion::attr(
-    since(1.78),
-    diagnostic::on_unimplemented(
-        note = "Consider using `#[axum::debug_handler]` to improve the error message"
-    )
+#[diagnostic::on_unimplemented(
+    note = "Consider using `#[axum::debug_handler]` to improve the error message"
 )]
 pub trait Handler<T, S>: Clone + Send + Sync + Sized + 'static {
     /// The type of future calling this handler returns.