From 47cb6bf7860ce33bdd000198f8b65cf9fb3324b4 Mon Sep 17 00:00:00 2001 From: Xiangfei Ding Date: Wed, 4 Dec 2024 04:47:49 +0800 Subject: rust: use derive(CoercePointee) on rustc >= 1.84.0 The `kernel` crate relies on both `coerce_unsized` and `dispatch_from_dyn` unstable features. Alice Ryhl has proposed [1] the introduction of the unstable macro `SmartPointer` to reduce such dependence, along with a RFC patch [2]. Since Rust 1.81.0 this macro, later renamed to `CoercePointee` in Rust 1.84.0 [3], has been fully implemented with the naming discussion resolved. This feature is now on track to stabilization in the language. In order to do so, we shall start using this macro in the `kernel` crate to prove the functionality and utility of the macro as the justification of its stabilization. This patch makes this switch in such a way that the crate remains backward compatible with older Rust compiler versions, via the new Kconfig option `RUSTC_HAS_COERCE_POINTEE`. A minimal demonstration example is added to the `samples/rust/rust_print_main.rs` module. Link: https://rust-lang.github.io/rfcs/3621-derive-smart-pointer.html [1] Link: https://lore.kernel.org/all/20240823-derive-smart-pointer-v1-1-53769cd37239@google.com/ [2] Link: https://github.com/rust-lang/rust/pull/131284 [3] Signed-off-by: Xiangfei Ding Reviewed-by: Fiona Behrens Reviewed-by: Alice Ryhl Link: https://lore.kernel.org/r/20241203205050.679106-2-dingxiangfei2009@gmail.com [ Fixed version to 1.84. Renamed option to `RUSTC_HAS_COERCE_POINTEE` to match `CC_HAS_*` ones. Moved up new config option, closer to the `CC_HAS_*` ones. Simplified Kconfig line. Fixed typos and slightly reworded example and commit. Added Link to PR. - Miguel ] Signed-off-by: Miguel Ojeda --- samples/rust/rust_print_main.rs | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'samples/rust/rust_print_main.rs') diff --git a/samples/rust/rust_print_main.rs b/samples/rust/rust_print_main.rs index 7935b4772ec6..7e8af5f176a3 100644 --- a/samples/rust/rust_print_main.rs +++ b/samples/rust/rust_print_main.rs @@ -34,6 +34,24 @@ fn arc_print() -> Result { // Uses `dbg` to print, will move `c` (for temporary debugging purposes). dbg!(c); + { + // `Arc` can be used to delegate dynamic dispatch and the following is an example. + // Both `i32` and `&str` implement `Display`. This enables us to express a unified + // behaviour, contract or protocol on both `i32` and `&str` into a single `Arc` of + // type `Arc`. + + use core::fmt::Display; + fn arc_dyn_print(arc: &Arc) { + pr_info!("Arc says {arc}"); + } + + let a_i32_display: Arc = Arc::new(42i32, GFP_KERNEL)?; + let a_str_display: Arc = a.clone(); + + arc_dyn_print(&a_i32_display); + arc_dyn_print(&a_str_display); + } + // Pretty-prints the debug formatting with lower-case hexadecimal integers. pr_info!("{:#x?}", a); -- cgit v1.2.3