Rename embassy-hal-common to embassy-hal-internal, document it's for internal use only. (#1700)

embassy-hal-internal/src/drop.rs

@@ -0,0 +1,51 @@
+use core::mem;
+use core::mem::MaybeUninit;
+
+#[must_use = "to delay the drop handler invokation to the end of the scope"]
+pub struct OnDrop<F: FnOnce()> {
+    f: MaybeUninit<F>,
+}
+
+impl<F: FnOnce()> OnDrop<F> {
+    pub fn new(f: F) -> Self {
+        Self { f: MaybeUninit::new(f) }
+    }
+
+    pub fn defuse(self) {
+        mem::forget(self)
+    }
+}
+
+impl<F: FnOnce()> Drop for OnDrop<F> {
+    fn drop(&mut self) {
+        unsafe { self.f.as_ptr().read()() }
+    }
+}
+
+/// An explosive ordinance that panics if it is improperly disposed of.
+///
+/// This is to forbid dropping futures, when there is absolutely no other choice.
+///
+/// To correctly dispose of this device, call the [defuse](struct.DropBomb.html#method.defuse)
+/// method before this object is dropped.
+#[must_use = "to delay the drop bomb invokation to the end of the scope"]
+pub struct DropBomb {
+    _private: (),
+}
+
+impl DropBomb {
+    pub fn new() -> Self {
+        Self { _private: () }
+    }
+
+    /// Defuses the bomb, rendering it safe to drop.
+    pub fn defuse(self) {
+        mem::forget(self)
+    }
+}
+
+impl Drop for DropBomb {
+    fn drop(&mut self) {
+        panic!("boom")
+    }
+}