LED: Add fallible initialization, deprecate new for new_unchecked

src/led.rs

@@ -9,11 +9,54 @@ use core::convert::Infallible;
 /// LEDs are accessible safely; any not implemented on a board are silently ignored.
 pub struct LED<const I: u8>(());
 
+/// The indicated LED is not present on the current board.
+#[derive(Debug)]
+pub struct LedNotPresent;
+
 impl<const I: u8> LED<I> {
+    #[deprecated(
+        note = "Use new_unchecked() to retain the behavior this function has always had; future versions of `.new()` will panic when used with a board that does not have that LED.",
+        since = "0.9.1"
+    )]
     pub const fn new() -> Self {
+        Self::new_unchecked()
+    }
+
+    /// Accesses the LED numbered `I`.
+    ///
+    /// It is not an error if this board does not have a LED with that number; the resulting struct
+    /// will be available but its methods have no effect.
+    pub const fn new_unchecked() -> Self {
         assert!(I < 8, "RIOT only defines LED0..7");
         Self(())
     }
+
+    /// Accesses the LED numbered `I`.
+    ///
+    /// An LED is returned if present on the board, which is known at build time.
+    pub const fn new_checked() -> Result<Self, LedNotPresent> {
+        if Self::is_present() {
+            Ok(Self(()))
+        } else {
+            Err(LedNotPresent)
+        }
+    }
+
+    const fn is_present() -> bool {
+        unsafe {
+            match I {
+                0 => riot_sys::macro_LED0_IS_PRESENT() != -1,
+                1 => riot_sys::macro_LED1_IS_PRESENT() != -1,
+                2 => riot_sys::macro_LED2_IS_PRESENT() != -1,
+                3 => riot_sys::macro_LED3_IS_PRESENT() != -1,
+                4 => riot_sys::macro_LED4_IS_PRESENT() != -1,
+                5 => riot_sys::macro_LED5_IS_PRESENT() != -1,
+                6 => riot_sys::macro_LED6_IS_PRESENT() != -1,
+                7 => riot_sys::macro_LED7_IS_PRESENT() != -1,
+                _ => panic!("RIOT only defines LED0..7"),
+            }
+        }
+    }
 }
 
 impl<const I: u8> switch_hal::OutputSwitch for LED<I> {