build: simplify use of nightly features

We use some features that are already stable in later versions of Rust,
but only available as unstable features in older Rust versions that the
kernel needs to support.

Instead of checking if a feature is already stable, simply enable them
and allow the warning if the feature is already stable. This avoids the
need of hardcoding whether a feature has been stabilized at a given
version.

`#[feature(...)]` is used when cfg `USE_RUSTC_FEATURES` is enabled. The
build script automatically does this when a nightly compiler is detected
or `RUSTC_BOOTSTRAP` is set.

Signed-off-by: Gary Guo <gary@garyguo.net>

Author: nbdd0121

Cargo.toml

@@ -37,6 +37,7 @@ macrotest = "1.0"
 prettyplease = { version = "0.2.37", features = ["verbatim"] }
 
 [lints.rust]
+stable_features = "allow"
 non_ascii_idents = "deny"
 unexpected_cfgs = { level = "warn", check-cfg = [
     'cfg(UI_TESTS)',

build.rs

@@ -1,18 +1,20 @@
-use rustc_version::{version, Version};
+use rustc_version::{version_meta, Channel, Version};
 
 fn main() {
-    println!("cargo::rustc-check-cfg=cfg(RUSTC_LINT_REASONS_IS_STABLE)");
-    println!("cargo::rustc-check-cfg=cfg(RUSTC_NEW_UNINIT_IS_STABLE)");
+    println!("cargo::rustc-check-cfg=cfg(USE_RUSTC_FEATURES)");
     println!("cargo::rustc-check-cfg=cfg(CONFIG_RUSTC_HAS_UNSAFE_PINNED)");
-    if version().unwrap() >= Version::parse("1.81.0").unwrap()
-        || version().unwrap() >= Version::parse("1.81.0-nightly").unwrap()
-    {
-        println!("cargo:rustc-cfg=RUSTC_LINT_REASONS_IS_STABLE");
-    }
-    if version().unwrap() >= Version::parse("1.82.0").unwrap() {
-        println!("cargo:rustc-cfg=RUSTC_NEW_UNINIT_IS_STABLE");
+
+    let meta = version_meta().unwrap();
+
+    let use_feature = meta.channel == Channel::Nightly || std::env::var("RUSTC_BOOTSTRAP").is_ok();
+    if use_feature {
+        // Use this cfg option to control whether we should enable features that are already stable
+        // in some new Rust versions, but are available as unstable features in older Rust versions
+        // that needs to be supported by the Linux kernel.
+        println!("cargo:rustc-cfg=USE_RUSTC_FEATURES");
     }
-    if version().unwrap() >= Version::parse("1.89.0-nightly").unwrap() {
+
+    if meta.semver >= Version::parse("1.89.0-nightly").unwrap() && use_feature {
         println!("cargo:rustc-cfg=CONFIG_RUSTC_HAS_UNSAFE_PINNED");
     }
 }

examples/big_struct_in_place.rs

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
 
 use pin_init::*;
 

examples/linked_list.rs

@@ -2,7 +2,7 @@
 
 #![allow(clippy::undocumented_unsafe_blocks)]
 #![cfg_attr(feature = "alloc", feature(allocator_api))]
-#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
 
 use core::{
     cell::Cell,

examples/mutex.rs

@@ -2,7 +2,7 @@
 
 #![allow(clippy::undocumented_unsafe_blocks)]
 #![cfg_attr(feature = "alloc", feature(allocator_api))]
-#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
 #![allow(clippy::missing_safety_doc)]
 
 use core::{

examples/pthread_mutex.rs

@@ -3,7 +3,7 @@
 // inspired by <https://github.com/nbdd0121/pin-init/blob/trunk/examples/pthread_mutex.rs>
 #![allow(clippy::undocumented_unsafe_blocks)]
 #![cfg_attr(feature = "alloc", feature(allocator_api))]
-#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
 
 #[cfg(not(windows))]
 mod pthread_mtx {

examples/static_init.rs

@@ -2,7 +2,7 @@
 
 #![allow(clippy::undocumented_unsafe_blocks)]
 #![cfg_attr(feature = "alloc", feature(allocator_api))]
-#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
 #![allow(unused_imports)]
 
 use core::{

internal/Cargo.toml

@@ -21,4 +21,5 @@ syn = { version = "2.0.86", features = ["full", "parsing", "visit-mut"] }
 rustc_version = "0.4"
 
 [lints.rust]
+stable_features = "allow"
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(kernel)'] }

internal/build.rs

@@ -1,10 +1,12 @@
-use rustc_version::{version, Version};
+use rustc_version::{version_meta, Channel};
 
 fn main() {
-    println!("cargo::rustc-check-cfg=cfg(RUSTC_LINT_REASONS_IS_STABLE)");
-    if version().unwrap() >= Version::parse("1.81.0").unwrap()
-        || version().unwrap() >= Version::parse("1.81.0-nightly").unwrap()
-    {
-        println!("cargo:rustc-cfg=RUSTC_LINT_REASONS_IS_STABLE");
+    println!("cargo::rustc-check-cfg=cfg(USE_RUSTC_FEATURES)");
+
+    let meta = version_meta().unwrap();
+
+    let use_feature = meta.channel == Channel::Nightly || std::env::var("RUSTC_BOOTSTRAP").is_ok();
+    if use_feature {
+        println!("cargo:rustc-cfg=USE_RUSTC_FEATURES");
     }
 }

internal/src/lib.rs

@@ -6,7 +6,7 @@
 
 //! `pin-init` proc macros.
 
-#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+#![cfg_attr(USE_RUSTC_FEATURES, feature(lint_reasons))]
 // Documentation is done in the pin-init crate instead.
 #![allow(missing_docs)]