Use a mod _export for macro reexports.

This avoids having to do `#[doc(hidden)] pub mod critical_section` which is a bit strange.

Author: Dirbaio

src/critical_section.rs

@@ -1,27 +1,22 @@
-#[cfg(all(cortex_m, feature = "critical-section-single-core"))]
-mod single_core_critical_section {
-    use critical_section::{set_impl, Impl, RawRestoreState};
+use critical_section::{set_impl, Impl, RawRestoreState};
 
-    use crate::interrupt;
-    use crate::register::primask;
+use crate::interrupt;
+use crate::register::primask;
 
-    struct SingleCoreCriticalSection;
-    set_impl!(SingleCoreCriticalSection);
+struct SingleCoreCriticalSection;
+set_impl!(SingleCoreCriticalSection);
 
-    unsafe impl Impl for SingleCoreCriticalSection {
-        unsafe fn acquire() -> RawRestoreState {
-            let was_active = primask::read().is_active();
-            interrupt::disable();
-            was_active
-        }
+unsafe impl Impl for SingleCoreCriticalSection {
+    unsafe fn acquire() -> RawRestoreState {
+        let was_active = primask::read().is_active();
+        interrupt::disable();
+        was_active
+    }
 
-        unsafe fn release(was_active: RawRestoreState) {
-            // Only re-enable interrupts if they were enabled before the critical section.
-            if was_active {
-                interrupt::enable()
-            }
+    unsafe fn release(was_active: RawRestoreState) {
+        // Only re-enable interrupts if they were enabled before the critical section.
+        if was_active {
+            interrupt::enable()
         }
     }
 }
-
-pub use critical_section::with;

src/lib.rs

@@ -49,10 +49,6 @@ mod macros;
 pub mod asm;
 #[cfg(armv8m)]
 pub mod cmse;
-// This is only public so the `singleton` macro does not require depending on
-// the `critical-section` crate separately.
-#[doc(hidden)]
-pub mod critical_section;
 pub mod delay;
 pub mod interrupt;
 #[cfg(all(not(armv6m), not(armv8m_base)))]
@@ -61,3 +57,13 @@ pub mod peripheral;
 pub mod register;
 
 pub use crate::peripheral::Peripherals;
+
+#[cfg(all(cortex_m, feature = "critical-section-single-core"))]
+mod critical_section;
+
+/// Used to reexport items for use in macros. Do not use directly.
+/// Not covered by semver guarantees.
+#[doc(hidden)]
+pub mod _export {
+    pub use critical_section;
+}

src/macros.rs

@@ -65,7 +65,7 @@ macro_rules! iprintln {
 #[macro_export]
 macro_rules! singleton {
     ($name:ident: $ty:ty = $expr:expr) => {
-        $crate::critical_section::with(|_| {
+        $crate::_export::critical_section::with(|_| {
             // this is a tuple of a MaybeUninit and a bool because using an Option here is
             // problematic:  Due to niche-optimization, an Option could end up producing a non-zero
             // initializer value which would move the entire static from `.bss` into `.data`...