Enable diagnostic attributes for Rust 1.78+ (#2693)

axum/Cargo.toml

@@ -54,6 +54,7 @@ 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 = "0.4.13", default-features = false, features = ["util"] }
@@ -109,16 +110,12 @@ features = [
     "validate-request",
 ]
 
-[build-dependencies]
-rustversion = "1.0.9"
-
 [dev-dependencies]
 anyhow = "1.0"
 axum-macros = { path = "../axum-macros", version = "0.4.1", features = ["__private"] }
 quickcheck = "1.0"
 quickcheck_macros = "1.0"
 reqwest = { version = "0.12", default-features = false, features = ["json", "stream", "multipart"] }
-rustversion = "1.0.9"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 time = { version = "0.3", features = ["serde-human-readable"] }

axum/build.rs

@@ -1,7 +0,0 @@
-#[rustversion::nightly]
-fn main() {
-    println!("cargo:rustc-cfg=nightly_error_messages");
-}
-
-#[rustversion::not(nightly)]
-fn main() {}

axum/src/handler/mod.rs

@@ -125,8 +125,8 @@ pub use self::service::HandlerService;
 ///     )));
 /// # let _: Router = app;
 /// ```
-#[cfg_attr(
-    nightly_error_messages,
+#[rustversion::attr(
+    since(1.78),
     diagnostic::on_unimplemented(
         note = "Consider using `#[axum::debug_handler]` to improve the error message"
     )