Merge #767

767: allow #[init] and #[idle] to be externed r=korken89 a=wiktorwieclaw

I updated `rtic-macros` to a allow init and idle to be externally defined.

## Design notes
* Updated `extern_binds` example to include external #[init] and #[idle] functions.
* Added docs to Local and Shared structs. The `extern_binds` example has a `#![deny(missing_docs)]` which caused some issues.

## Testing
Apart from building the example, I also used this feature in one of my projects and ran it on a MCU [here](https://github.com/grupacosmo/cansat/blob/98ca7bd42e737adfb140a548da1ade01beb495da/crates/cansat-stm32f4/src/main.rs#L59-L74)

## Related issues
* https://github.com/rtic-rs/rtic/issues/505

## Related PRs
* https://github.com/rtic-rs/rtic-syntax/pull/71

Co-authored-by: Vixu <lonevixu@gmail.com>

2 files changed, 28 insertions, 18 deletions

diff --git a/rtic-macros/src/codegen/idle.rs b/rtic-macros/src/codegen/idle.rs
index 0c833ef..9e608cb 100644
--- a/rtic-macros/src/codegen/idle.rs
+++ b/rtic-macros/src/codegen/idle.rs
@@ -34,16 +34,20 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
         let attrs = &idle.attrs;
         let context = &idle.context;
         let stmts = &idle.stmts;
-        let user_idle = Some(quote!(
-            #(#attrs)*
-            #[allow(non_snake_case)]
-            fn #name(#context: #name::Context) -> ! {
-                use rtic::Mutex as _;
-                use rtic::mutex::prelude::*;
-
-                #(#stmts)*
-            }
-        ));
+        let user_idle = if !idle.is_extern {
+            Some(quote!(
+                #(#attrs)*
+                #[allow(non_snake_case)]
+                fn #name(#context: #name::Context) -> ! {
+                    use rtic::Mutex as _;
+                    use rtic::mutex::prelude::*;
+
+                    #(#stmts)*
+                }
+            ))
+        } else {
+            None
+        };
 
         quote!(
             #(#mod_app)*
diff --git a/rtic-macros/src/codegen/init.rs b/rtic-macros/src/codegen/init.rs
index b667ae0..f6bb43d 100644
--- a/rtic-macros/src/codegen/init.rs
+++ b/rtic-macros/src/codegen/init.rs
@@ -54,10 +54,12 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
         .collect();
 
     root_init.push(quote! {
+        #[doc = r"Shared resources"]
         #shared_vis struct #shared {
             #(#shared_resources)*
         }
 
+        #[doc = r"Local resources"]
         #local_vis struct #local {
             #(#local_resources)*
         }
@@ -67,14 +69,18 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
 
     let user_init_return = quote! {#shared, #local};
 
-    let user_init = quote!(
-        #(#attrs)*
-        #[inline(always)]
-        #[allow(non_snake_case)]
-        fn #name(#context: #name::Context) -> (#user_init_return) {
-            #(#stmts)*
-        }
-    );
+    let user_init = if !init.is_extern {
+        Some(quote!(
+            #(#attrs)*
+            #[inline(always)]
+            #[allow(non_snake_case)]
+            fn #name(#context: #name::Context) -> (#user_init_return) {
+                #(#stmts)*
+            }
+        ))
+    } else {
+        None
+    };
 
     let mut mod_app = None;