validate unused dispatchers

closes #521

macros/src/codegen/pre_init.rs

@@ -31,6 +31,13 @@ pub fn codegen(app: &App, analysis: &Analysis, extra: &Extra) -> Vec<TokenStream
     let device = &extra.device;
     let nvic_prio_bits = quote!(#device::NVIC_PRIO_BITS);
 
+    // check that all dispatchers exists in the `Interrupt` enumeration regardless of whether
+    // they are used or not 
+    let interrupt = util::interrupt_ident();
+    for name in app.args.extern_interrupts.keys() {
+        stmts.push(quote!(let _ = #rt_err::#interrupt::#name;));
+    }
+
     let interrupt_ids = analysis.interrupts.iter().map(|(p, (id, _))| (p, id));
 
     // Unmask interrupts and set their priorities
@@ -45,8 +52,6 @@ pub fn codegen(app: &App, analysis: &Analysis, extra: &Extra) -> Vec<TokenStream
         // Compile time assert that this priority is supported by the device
         stmts.push(quote!(let _ = [(); ((1 << #nvic_prio_bits) - #priority as usize)];));
 
-        // NOTE this also checks that the interrupt exists in the `Interrupt` enumeration
-        let interrupt = util::interrupt_ident();
         stmts.push(quote!(
             core.NVIC.set_priority(
                 #rt_err::#interrupt::#name,
@@ -100,8 +105,6 @@ pub fn codegen(app: &App, analysis: &Analysis, extra: &Extra) -> Vec<TokenStream
                 }
             ));
         } else {
-            // NOTE this also checks that the interrupt exists in the `Interrupt` enumeration
-            let interrupt = util::interrupt_ident();
             stmts.push(quote!(
                 core.NVIC.set_priority(
                     #rt_err::#interrupt::#binds,

ui/unknown-interrupt.rs

@@ -0,0 +1,15 @@
+#![no_main]
+
+#[rtic::app(device = lm3s6965, dispatchers = [UnknownInterrupt])]
+mod app {
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
+        (Shared {}, Local {}, init::Monotonics())
+    }
+}

ui/unknown-interrupt.stderr

@@ -0,0 +1,5 @@
+error[E0599]: no variant or associated item named `UnknownInterrupt` found for enum `Interrupt` in the current scope
+ --> examples/unknown-interrupt.rs:3:47
+  |
+3 | #[rtic::app(device = lm3s6965, dispatchers = [UnknownInterrupt])]
+  |                                               ^^^^^^^^^^^^^^^^ variant or associated item not found in `Interrupt`