Merge pull request rust-embedded#522 from quartiq/singleton-meta

singleton: forward attributes

Author: adamgreig

cortex-m/CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added the ability to name the statics generated by `singleton!()` for better debuggability (#364, #380).
 - Added `critical-section-single-core` feature which provides an implementation for the `critical_section` crate for single-core systems, based on disabling all interrupts. (#447)
 - Added support for `embedded-hal` version 1 delay traits, requiring rust 1.60.
+- `singleton!()` now forwards attributes (#522).
 
 ### Fixed
 - Fixed `singleton!()` statics sometimes ending up in `.data` instead of `.bss` (#364, #380).

cortex-m/src/macros.rs

@@ -64,11 +64,12 @@ macro_rules! iprintln {
 /// ```
 #[macro_export]
 macro_rules! singleton {
-    ($name:ident: $ty:ty = $expr:expr) => {
+    ($(#[$meta:meta])* $name:ident: $ty:ty = $expr:expr) => {
         $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`...
+            $(#[$meta])*
             static mut $name: (::core::mem::MaybeUninit<$ty>, bool) =
                 (::core::mem::MaybeUninit::uninit(), false);
 
@@ -82,14 +83,13 @@ macro_rules! singleton {
                 #[allow(unsafe_code)]
                 unsafe {
                     $name.1 = true;
-                    $name.0 = ::core::mem::MaybeUninit::new(expr);
-                    Some(&mut *$name.0.as_mut_ptr())
+                    Some($name.0.write(expr))
                 }
             }
         })
     };
-    (: $ty:ty = $expr:expr) => {
-        $crate::singleton!(VAR: $ty = $expr)
+    ($(#[$meta:meta])* : $ty:ty = $expr:expr) => {
+        $crate::singleton!($(#[$meta])* VAR: $ty = $expr)
     };
 }
 
@@ -115,3 +115,15 @@ const CFAIL: () = ();
 /// ```
 #[allow(dead_code)]
 const CPASS: () = ();
+
+/// ```
+/// use cortex_m::singleton;
+///
+/// fn foo() {
+///     // check that attributes are forwarded
+///     singleton!(#[link_section = ".bss"] FOO: u8 = 0);
+///     singleton!(#[link_section = ".bss"]: u8 = 1);
+/// }
+/// ```
+#[allow(dead_code)]
+const CPASS_ATTR: () = ();