feat(core): add CfgStatic

> The new blanket-implemented `CfgStatic` trait can be used to simplify
> some trait bounds of configuration functions.

Author: yvt

src/r3/src/bind/mod.rs

@@ -119,7 +119,7 @@
 /// ```
 )]
 #![doc = include_str!("../common.md")]
-use r3_core::kernel::{cfg, raw, raw_cfg};
+use r3_core::kernel::{cfg, raw_cfg};
 
 pub use r3_core::bind::{
     fn_bind_map, Bind, BindBorrow, BindBorrowMut, BindDefiner, BindRef, BindTable, BindTake,
@@ -196,8 +196,8 @@ pub const fn bind_uninit<'pool, T, C>(
 ) -> Bind<'pool, C::System, core::mem::MaybeUninit<T>>
 where
     T: 'static,
-    C: ~const raw_cfg::CfgBase,
-    C::System: raw::KernelBase + cfg::KernelStatic,
+    // `~const CfgBase` not implied due to [ref:const_supertraits]
+    C: ~const raw_cfg::CfgBase + ~const cfg::CfgStatic,
 {
     // Safety: `MaybeUninit` is safe to leave uninitialized
     unsafe { Bind::define().uninit_unchecked().finish(cfg) }
@@ -234,8 +234,8 @@ where
 pub const fn bind_default<'pool, T, C>(cfg: &mut cfg::Cfg<'pool, C>) -> Bind<'pool, C::System, T>
 where
     T: Default + 'static,
-    C: ~const raw_cfg::CfgBase,
-    C::System: raw::KernelBase + cfg::KernelStatic,
+    // `~const CfgBase` not implied due to [ref:const_supertraits]
+    C: ~const raw_cfg::CfgBase + ~const cfg::CfgStatic,
 {
     Bind::define().init(Default::default).finish(cfg)
 }

src/r3_core/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+- The new blanket-implemented `CfgStatic` trait can be used to simplify some trait bounds of configuration functions.
+
 ### Fixed
 
 - The `Cfg*` traits now imply the corresponding `Kernel*` traits (e.g., `C: CfgTimer` implies `C::System: KernelTimer`), making some trait bounds in configuration functions unnecessary.

src/r3_core/src/bind.rs

@@ -686,8 +686,8 @@ impl<'pool, System, T> DivideBind<'pool, System, T> {
 ///
 /// const fn configure_app<C>(cfg: &mut Cfg<C>)
 /// where
-///     C: ~const traits::CfgBase,
-///     C::System: traits::KernelBase + traits::KernelStatic,
+// `~const CfgBase` not implied due to [ref:const_supertraits]
+///     C: ~const traits::CfgBase + ~const traits::CfgStatic,
 /// {
 ///     let values = Bind::define().init(|| (12, 34)).finish(cfg);
 ///     let (value0, value1) = values.unzip();

src/r3_core/src/kernel/cfg.rs

@@ -725,3 +725,51 @@ macro array_item_from_fn($(
         unsafe { mem::transmute(values) }
     };
 )*}
+
+/// A subtrait of [`raw_cfg::CfgBase`][] that implies
+/// `Self::System: `[`KernelStatic`][].
+///
+/// This trait by itself has no function, but it may help you keep your
+/// configuration functions clean by getting rid of trait bounds on
+/// `C::System`.
+///
+/// # Example
+///
+/// ```rust
+/// # #![feature(const_trait_impl)]
+/// # #![feature(const_mut_refs)]
+/// # use r3_core::kernel::traits;
+/// #
+/// const fn configure<C>(cfg: &mut C)
+/// where
+// `~const CfgBase` not implied due to [ref:const_supertraits]
+///     C: ~const traits::CfgBase + ~const traits::CfgStatic,
+/// {
+///     todo!()   
+/// }
+/// ```
+///
+/// The above is equivalent to:
+///
+/// ```rust
+/// # #![feature(const_trait_impl)]
+/// # #![feature(const_mut_refs)]
+/// # use r3_core::kernel::traits;
+/// #
+/// const fn configure<C>(cfg: &mut C)
+/// where
+///     C: ~const traits::CfgBase,
+///     C::System: traits::KernelStatic,
+/// {
+///     todo!()   
+/// }
+/// ```
+// The supertrait can't be `~const` due to [ref:const_supertraits]
+pub trait CfgStatic: raw_cfg::CfgBase<System: KernelStatic> {}
+
+impl<C> const CfgStatic for C
+where
+    C: ~const raw_cfg::CfgBase,
+    C::System: KernelStatic,
+{
+}

src/r3_core/src/kernel/mod.rs

@@ -72,7 +72,7 @@ pub mod prelude {
 pub mod traits {
     #[doc(no_inline)]
     pub use super::{
-        cfg::KernelStatic,
+        cfg::{CfgStatic, KernelStatic},
         event_group::{EventGroupHandle, EventGroupMethods},
         mutex::{MutexHandle, MutexMethods},
         raw::{

src/r3_support_rp2040/src/usbstdio.rs

@@ -79,8 +79,8 @@ pub const fn configure<'pool, C, TOptions: Options>(
     rp2040_resets: Bind<'pool, C::System, rp2040_pac::RESETS>,
     rp2040_usbctrl_regs: Bind<'pool, C::System, rp2040_pac::USBCTRL_REGS>,
 ) where
-    C: ~const traits::CfgBase + ~const traits::CfgInterruptLine,
-    C::System: traits::KernelStatic,
+    // `~const CfgBase` not implied due to [ref:const_supertraits]
+    C: ~const traits::CfgBase + ~const traits::CfgStatic + ~const traits::CfgInterruptLine,
 {
     bind(
         (rp2040_resets.borrow_mut(), rp2040_usbctrl_regs.take()),