refactor(embassy): Allow building net without a backend for docs and …

…linting

src/riot-rs-embassy/src/lib.rs

@@ -68,11 +68,18 @@ pub mod reexports {
 
 pub use embassy_executor::Spawner;
 
-#[cfg(feature = "usb-ethernet")]
-use usb::ethernet::NetworkDevice;
-
-#[cfg(feature = "wifi")]
-use wifi::NetworkDevice;
+#[cfg(feature = "net")]
+cfg_if::cfg_if! {
+    if #[cfg(feature = "usb-ethernet")] {
+        use usb::ethernet::NetworkDevice;
+    } else if #[cfg(feature = "wifi")] {
+        use wifi::NetworkDevice;
+    } else if #[cfg(context = "riot-rs")] {
+        compile_error!("no backend for net is active");
+    } else {
+        type NetworkDevice = network::DummyDriver;
+    }
+}
 
 #[cfg(feature = "net")]
 pub use network::NetworkStack;
@@ -264,6 +271,9 @@ async fn init_task(mut peripherals: arch::OptionalPeripherals) {
     #[cfg(feature = "wifi-esp")]
     let device = arch::wifi::esp_wifi::init(&mut peripherals, spawner);
 
+    #[cfg(not(any(feature = "wifi-esp", feature = "wifi-cyw43", feature = "usb-ethernet")))]
+    let device = panic!();
+
     #[cfg(feature = "net")]
     {
         use embassy_net::StackResources;

src/riot-rs-embassy/src/network.rs

@@ -34,3 +34,61 @@ pub(crate) fn config() -> embassy_net::Config {
         unsafe { riot_rs_network_config() }
     }
 }
+
+/// An uninhabited type that stands in for a network driver in documentation and linting.
+///
+/// It also doubles as the infallible type for its own associated types.
+// FIXME: This should be core::convert::Infallible as soon as embassy-net implements the traits on
+// that.
+pub(crate) enum DummyDriver {}
+
+impl embassy_net::driver::Driver for DummyDriver {
+    type RxToken<'a> = Self
+    where
+        Self: 'a;
+
+    type TxToken<'a> = Self
+    where
+        Self: 'a;
+
+    fn receive(
+        &mut self,
+        _cx: &mut core::task::Context,
+    ) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
+        match *self {}
+    }
+
+    fn transmit(&mut self, _cx: &mut core::task::Context) -> Option<Self::TxToken<'_>> {
+        match *self {}
+    }
+
+    fn link_state(&mut self, _cx: &mut core::task::Context) -> embassy_net::driver::LinkState {
+        match *self {}
+    }
+
+    fn capabilities(&self) -> embassy_net::driver::Capabilities {
+        match *self {}
+    }
+
+    fn hardware_address(&self) -> embassy_net::driver::HardwareAddress {
+        match *self {}
+    }
+}
+
+impl embassy_net::driver::TxToken for DummyDriver {
+    fn consume<R, F>(self, _len: usize, _f: F) -> R
+    where
+        F: FnOnce(&mut [u8]) -> R,
+    {
+        match self {}
+    }
+}
+
+impl embassy_net::driver::RxToken for DummyDriver {
+    fn consume<R, F>(self, _f: F) -> R
+    where
+        F: FnOnce(&mut [u8]) -> R,
+    {
+        match self {}
+    }
+}