feat(core): use #![feature(associated_type_bounds)]

This feature is tracked by [rust-lang/rust#52662][1].

Fixes `[ref:trait_constraints_on_associated_types_do_not_propagate]`.
That is, when you have `C: ~const CfgTimer`, you don't need `C::System:
KernelTimer` anymore.

[1]: rust-lang/rust#52662

Author: yvt

doc/toolchain_limitations.md

@@ -38,29 +38,6 @@ impl<T> StGeneric<for<'a> fn(&'a T)> {
 ```
 
 
-### `[tag:trait_constraints_on_associated_types_do_not_propagate]` Trait constraints on associated types do not propagate to the trait's use sites
-
-*Upstream issue:* [rust-lang/rust#32722](https://github.com/rust-lang/rust/issues/32722)
-
-According to [this comment](https://github.com/rust-lang/rust/issues/32722#issuecomment-618044689), this is a symptom of [rust-lang/rust#20671](https://github.com/rust-lang/rust/issues/20671).
-
-```rust,compile_fail,E0277
-trait KernelMutex {}
-
-trait CfgBase {
-    type System;
-}
-
-trait CfgMutex: CfgBase
-where
-    Self::System: KernelMutex,
-{}
-
-// error[E0277]: the trait bound `<C as CfgBase>::System: KernelMutex` is not satisfied
-fn foo<C: CfgMutex>() {}
-```
-
-
 ### `[tag:impl_trait_false_type_alias_bounds]` `type_alias_bounds` misfires when `impl Trait` is used in a portion of a type alias
 
 *Upstream issue:* [rust-lang/rust#94395](https://github.com/rust-lang/rust/issues/94395)

src/r3_core/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### 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.
+
 ## [0.1.2] - 2022-03-30
 
 ### Changed

src/r3_core/src/bind.rs

@@ -820,7 +820,7 @@ impl<'pool, const LEN: usize, System, T> const UnzipBind for Bind<'pool, System,
 /// where
 ///     C: ~const traits::CfgBase +
 ///        ~const traits::CfgTask,
-///     C::System: traits::KernelBase + traits::KernelStatic,
+///     C::System: traits::KernelStatic,
 /// {
 ///     let foo = Bind::define().init(|| {
 ///         // `BindTable::get()` will fail because some bindings might not

src/r3_core/src/kernel/mutex.rs

@@ -54,9 +54,6 @@ define_object! {
 /// const fn configure<C>(cfg: &mut Cfg<C>) -> Objects<C::System>
 /// where
 ///     C: ~const traits::CfgMutex,
-// The following bound is necessary becauase of a bug in the compiler
-// [ref:trait_constraints_on_associated_types_do_not_propagate]
-///     C::System: traits::KernelMutex,
 /// {
 ///     let mutex = StaticMutex::define()
 ///         .protocol(MutexProtocol::Ceiling(1))

src/r3_core/src/kernel/raw_cfg.rs

@@ -116,10 +116,7 @@ pub struct TaskDescriptor<System> {
 /// [3]: self#stability
 /// [4]: self#safety
 // The supertrait can't be `~const` due to [ref:const_supertraits]
-pub unsafe trait CfgEventGroup: CfgBase
-where
-    Self::System: raw::KernelEventGroup,
-{
+pub unsafe trait CfgEventGroup: CfgBase<System: raw::KernelEventGroup> {
     fn event_group_define<Properties: ~const Bag>(
         &mut self,
         descriptor: EventGroupDescriptor<Self::System>,
@@ -151,10 +148,7 @@ pub struct EventGroupDescriptor<System> {
 /// [3]: self#stability
 /// [4]: self#safety
 // The supertrait can't be `~const` due to [ref:const_supertraits]
-pub unsafe trait CfgMutex: CfgBase
-where
-    Self::System: raw::KernelMutex,
-{
+pub unsafe trait CfgMutex: CfgBase<System: raw::KernelMutex> {
     fn mutex_define<Properties: ~const Bag>(
         &mut self,
         descriptor: MutexDescriptor<Self::System>,
@@ -185,10 +179,7 @@ pub struct MutexDescriptor<System> {
 /// [3]: self#stability
 /// [4]: self#safety
 // The supertrait can't be `~const` due to [ref:const_supertraits]
-pub unsafe trait CfgSemaphore: CfgBase
-where
-    Self::System: raw::KernelSemaphore,
-{
+pub unsafe trait CfgSemaphore: CfgBase<System: raw::KernelSemaphore> {
     fn semaphore_define<Properties: ~const Bag>(
         &mut self,
         descriptor: SemaphoreDescriptor<Self::System>,
@@ -221,10 +212,7 @@ pub struct SemaphoreDescriptor<System> {
 /// [3]: self#stability
 /// [4]: self#safety
 // The supertrait can't be `~const` due to [ref:const_supertraits]
-pub unsafe trait CfgTimer: CfgBase
-where
-    Self::System: raw::KernelTimer,
-{
+pub unsafe trait CfgTimer: CfgBase<System: raw::KernelTimer> {
     fn timer_define<Properties: ~const Bag>(
         &mut self,
         descriptor: TimerDescriptor<Self::System>,
@@ -258,10 +246,7 @@ pub struct TimerDescriptor<System> {
 /// [3]: self#stability
 /// [4]: self#safety
 // The supertrait can't be `~const` due to [ref:const_supertraits]
-pub unsafe trait CfgInterruptLine: CfgBase
-where
-    Self::System: raw::KernelInterruptLine,
-{
+pub unsafe trait CfgInterruptLine: CfgBase<System: raw::KernelInterruptLine> {
     fn interrupt_line_define<Properties: ~const Bag>(
         &mut self,
         descriptor: InterruptLineDescriptor<Self::System>,

src/r3_core/src/kernel/timer.rs

@@ -279,9 +279,6 @@ define_object! {
 /// const fn configure<C>(b: &mut Cfg<C>) -> StaticTimer<C::System>
 /// where
 ///     C: ~const traits::CfgTimer,
-// The following bound is necessary becauase of a bug in the compiler
-// [ref:trait_constraints_on_associated_types_do_not_propagate]
-///     C::System: traits::KernelTimer,
 /// {
 ///     StaticTimer::define()
 ///         .delay(Duration::from_millis(70))
@@ -319,9 +316,6 @@ define_object! {
 /// const fn configure<C>(b: &mut Cfg<C>) -> StaticTimer<C::System>
 /// where
 ///     C: ~const traits::CfgTimer,
-// The following bound is necessary becauase of a bug in the compiler
-// [ref:trait_constraints_on_associated_types_do_not_propagate]
-///     C::System: traits::KernelTimer,
 /// {
 ///     StaticTimer::define()
 ///         .active(true)

src/r3_core/src/lib.rs

@@ -13,6 +13,7 @@
 #![feature(const_precise_live_drops)]
 #![feature(const_raw_ptr_comparison)]
 #![feature(generic_associated_types)]
+#![feature(associated_type_bounds)]
 #![feature(const_slice_first_last)]
 #![feature(cfg_target_has_atomic)] // `#[cfg(target_has_atomic_load_store)]`
 #![feature(const_cell_into_inner)]

src/r3_support_rp2040/src/usbstdio.rs

@@ -80,7 +80,7 @@ pub const fn configure<'pool, C, TOptions: Options>(
     rp2040_usbctrl_regs: Bind<'pool, C::System, rp2040_pac::USBCTRL_REGS>,
 ) where
     C: ~const traits::CfgBase + ~const traits::CfgInterruptLine,
-    C::System: traits::KernelInterruptLine + traits::KernelStatic,
+    C::System: traits::KernelStatic,
 {
     bind(
         (rp2040_resets.borrow_mut(), rp2040_usbctrl_regs.take()),