Merge #466

466: Fix for type aliases in `mod app`, UB in `spawn_at`, and `#[cfg]` in hardware tasks r=AfoHT a=korken89

Type aliases such as the following did not work in `0.6-alpha`:

```rust
use rtic::app;

#[app(device = lm3s6965, dispatchers = [SSI0])]
mod app {
    type Test = u32;

    #[task]
    fn t1(_: t1::Context, _val: Test) {}
}
```

Plus that accessing associated constants of monotonic timers was not working as it should dues to the syntax and codegen transforming:

```rust
    #[monotonic(binds = SysTick, default = true)]
    type MyMono = DwtSystick<8_000_000>; // 8 MHz
```

into

```rust
    mod MyMono {
        // ...
    }
```

causing the original `type MyMono` to not exist anymore.

This PR fixes this and adds test to check for this by doing the following expansion instead:

 ```rust
    #[monotonic(binds = SysTick, default = true)]
    type MyMono = DwtSystick<8_000_000>; // 8 MHz
```

into

```rust
    type MyMono = DwtSystick<8_000_000>;

    mod monotonics {
        mod MyMono {
            // ...
        }

        // And other monotonics go here as well
    }
```

**Breaking change**

This causes a breaking change in accessing the `MyMono::now()` method which now exists under `monotonics::MyMono::now()`.

---

Moreover a UB issue was found and fixed in `spawn_at` and hardware tasks properly propagate `#[cfg]`s.

Closes #460
Closes #462
Closes #463

Co-authored-by: Emil Fresk <emil.fresk@gmail.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/macros/src/codegen.rs b/macros/src/codegen.rs
index c5d95687..cf728a7d 100644
--- a/macros/src/codegen.rs
+++ b/macros/src/codegen.rs
@@ -112,8 +112,6 @@ pub fn app(app: &App, analysis: &Analysis, extra: &Extra) -> TokenStream2 {
             let user_imports = &app.user_imports;
 
             quote! {
-                pub use rtic::Monotonic as _;
-
                 #[doc = #doc]
                 #[allow(non_snake_case)]
                 pub mod #name {
@@ -143,6 +141,18 @@ pub fn app(app: &App, analysis: &Analysis, extra: &Extra) -> TokenStream2 {
         })
         .collect();
 
+    let monotonics = if !monotonic_parts.is_empty() {
+        quote!(
+            pub use rtic::Monotonic as _;
+
+            /// Holds static methods for each monotonic.
+            pub mod monotonics {
+                #(#monotonic_parts)*
+            }
+        )
+    } else {
+        quote!()
+    };
     let rt_err = util::rt_err_ident();
 
     quote!(
@@ -151,7 +161,7 @@ pub fn app(app: &App, analysis: &Analysis, extra: &Extra) -> TokenStream2 {
             /// Always include the device crate which contains the vector table
             use #device as #rt_err;
 
-            #(#monotonic_parts)*
+            #monotonics
 
             #(#user_imports)*