Merge #390

390: Spawn and schedule from anywhere r=AfoHT a=korken89

This PR moves RTIC to the spawn and schedule from anywhere syntax.

Notable changes:
 * We do no longer support non-`Send` types.
 * Some extra code is generated as any task may spawn/schedule any task. However Rust/LLVM does a great job optimizing away non used instantiations (no real code-size difference observed).
 * Worst case priority inversion has increased, but it is now predictable.

Upsides:
 * With this we should be able to support async/await.
 * RTIC tasks can now be callbacks (spawned and scheduled).
 * RTIC tasks can be stored.

Needs the following PR to land first: https://github.com/rtic-rs/rtic-syntax/pull/34

The following now works:

```rust
#[rtic::app(device = lm3s6965, monotonic = rtic::cyccnt::CYCCNT)]
mod app {
    #[init]
    fn init(mut cx: init::Context) -> init::LateResources {
        // Init stuff...

        // New spawn syntax
        foo::spawn().unwrap();

        // New schedule syntax
        bar::schedule(now + 4_000_000.cycles()).unwrap();

        init::LateResources {}
    }

    #[task]
    fn foo(_: foo::Context) {}

    #[task]
    fn bar(_: bar::Context) {}

    extern "C" {
        fn SSI0();
    }
}

```

Co-authored-by: Per Lindgren <per.lindgren@ltu.se>
Co-authored-by: Emil Fresk <emil.fresk@gmail.com>

1 files changed, 12 insertions, 12 deletions

diff --git a/examples/message.rs b/examples/message.rs
index f9736728..5ff6288a 100644
--- a/examples/message.rs
+++ b/examples/message.rs
@@ -10,39 +10,39 @@ use panic_semihosting as _;
 
 #[rtic::app(device = lm3s6965)]
 mod app {
-    #[init(spawn = [foo])]
-    fn init(c: init::Context) -> init::LateResources {
-        c.spawn.foo(/* no message */).unwrap();
+    #[init]
+    fn init(_: init::Context) -> init::LateResources {
+        foo::spawn(/* no message */).unwrap();
 
         init::LateResources {}
     }
 
-    #[task(spawn = [bar])]
-    fn foo(c: foo::Context) {
+    #[task]
+    fn foo(_: foo::Context) {
         static mut COUNT: u32 = 0;
 
         hprintln!("foo").unwrap();
 
-        c.spawn.bar(*COUNT).unwrap();
+        bar::spawn(*COUNT).unwrap();
         *COUNT += 1;
     }
 
-    #[task(spawn = [baz])]
-    fn bar(c: bar::Context, x: u32) {
+    #[task]
+    fn bar(_: bar::Context, x: u32) {
         hprintln!("bar({})", x).unwrap();
 
-        c.spawn.baz(x + 1, x + 2).unwrap();
+        baz::spawn(x + 1, x + 2).unwrap();
     }
 
-    #[task(spawn = [foo])]
-    fn baz(c: baz::Context, x: u32, y: u32) {
+    #[task]
+    fn baz(_: baz::Context, x: u32, y: u32) {
         hprintln!("baz({}, {})", x, y).unwrap();
 
         if x + y > 4 {
             debug::exit(debug::EXIT_SUCCESS);
         }
 
-        c.spawn.foo().unwrap();
+        foo::spawn().unwrap();
     }
 
     // RTIC requires that unused interrupts are declared in an extern block when