Add DefensiveTruncateFrom (#12515)

* Add DefensiveTruncateFrom

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Add tests

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Fix tests

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Map_err in preimage

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Map_err in beefy

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Make test dependant in debug-assertions

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: parity-processbot <>

substrate/primitives/core/src/bounded/bounded_vec.rs

@@ -47,6 +47,12 @@ pub struct BoundedVec<T, S>(
 	#[cfg_attr(feature = "std", serde(skip_serializing))] PhantomData<S>,
 );
 
+/// Create an object through truncation.
+pub trait TruncateFrom<T> {
+	/// Create an object through truncation.
+	fn truncate_from(unbound: T) -> Self;
+}
+
 #[cfg(feature = "std")]
 impl<'de, T, S: Get<u32>> Deserialize<'de> for BoundedVec<T, S>
 where
@@ -234,12 +240,12 @@ impl<'a, T: Ord, Bound: Get<u32>> Ord for BoundedSlice<'a, T, Bound> {
 }
 
 impl<'a, T, S: Get<u32>> TryFrom<&'a [T]> for BoundedSlice<'a, T, S> {
-	type Error = ();
+	type Error = &'a [T];
 	fn try_from(t: &'a [T]) -> Result<Self, Self::Error> {
 		if t.len() <= S::get() as usize {
 			Ok(BoundedSlice(t, PhantomData))
 		} else {
-			Err(())
+			Err(t)
 		}
 	}
 }
@@ -250,12 +256,28 @@ impl<'a, T, S> From<BoundedSlice<'a, T, S>> for &'a [T] {
 	}
 }
 
+impl<'a, T, S: Get<u32>> TruncateFrom<&'a [T]> for BoundedSlice<'a, T, S> {
+	fn truncate_from(unbound: &'a [T]) -> Self {
+		BoundedSlice::<T, S>::truncate_from(unbound)
+	}
+}
+
 impl<'a, T, S> Clone for BoundedSlice<'a, T, S> {
 	fn clone(&self) -> Self {
 		BoundedSlice(self.0, PhantomData)
 	}
 }
 
+impl<'a, T, S> sp_std::fmt::Debug for BoundedSlice<'a, T, S>
+where
+	&'a [T]: sp_std::fmt::Debug,
+	S: Get<u32>,
+{
+	fn fmt(&self, f: &mut sp_std::fmt::Formatter<'_>) -> sp_std::fmt::Result {
+		f.debug_tuple("BoundedSlice").field(&self.0).field(&S::get()).finish()
+	}
+}
+
 // Since a reference `&T` is always `Copy`, so is `BoundedSlice<'a, T, S>`.
 impl<'a, T, S> Copy for BoundedSlice<'a, T, S> {}
 
@@ -692,6 +714,12 @@ impl<T, S: Get<u32>> TryFrom<Vec<T>> for BoundedVec<T, S> {
 	}
 }
 
+impl<T, S: Get<u32>> TruncateFrom<Vec<T>> for BoundedVec<T, S> {
+	fn truncate_from(unbound: Vec<T>) -> Self {
+		BoundedVec::<T, S>::truncate_from(unbound)
+	}
+}
+
 // It is okay to give a non-mutable reference of the inner vec to anyone.
 impl<T, S> AsRef<Vec<T>> for BoundedVec<T, S> {
 	fn as_ref(&self) -> &Vec<T> {
@@ -809,6 +837,12 @@ where
 	}
 }
 
+impl<'a, T: PartialEq, S: Get<u32>> PartialEq<&'a [T]> for BoundedSlice<'a, T, S> {
+	fn eq(&self, other: &&'a [T]) -> bool {
+		&self.0 == other
+	}
+}
+
 impl<T: PartialEq, S: Get<u32>> PartialEq<Vec<T>> for BoundedVec<T, S> {
 	fn eq(&self, other: &Vec<T>) -> bool {
 		&self.0 == other
@@ -1219,6 +1253,18 @@ pub mod test {
 		assert!(b2.is_err());
 	}
 
+	#[test]
+	fn bounded_vec_debug_works() {
+		let bound = BoundedVec::<u32, ConstU32<5>>::truncate_from(vec![1, 2, 3]);
+		assert_eq!(format!("{:?}", bound), "BoundedVec([1, 2, 3], 5)");
+	}
+
+	#[test]
+	fn bounded_slice_debug_works() {
+		let bound = BoundedSlice::<u32, ConstU32<5>>::truncate_from(&[1, 2, 3]);
+		assert_eq!(format!("{:?}", bound), "BoundedSlice([1, 2, 3], 5)");
+	}
+
 	#[test]
 	fn bounded_vec_sort_by_key_works() {
 		let mut v: BoundedVec<i32, ConstU32<5>> = bounded_vec![-5, 4, 1, -3, 2];
@@ -1226,4 +1272,27 @@ pub mod test {
 		v.sort_by_key(|k| k.abs());
 		assert_eq!(v, vec![1, 2, -3, 4, -5]);
 	}
+
+	#[test]
+	fn bounded_vec_truncate_from_works() {
+		let unbound = vec![1, 2, 3, 4, 5];
+		let bound = BoundedVec::<u32, ConstU32<3>>::truncate_from(unbound.clone());
+		assert_eq!(bound, vec![1, 2, 3]);
+	}
+
+	#[test]
+	fn bounded_slice_truncate_from_works() {
+		let unbound = [1, 2, 3, 4, 5];
+		let bound = BoundedSlice::<u32, ConstU32<3>>::truncate_from(&unbound);
+		assert_eq!(bound, &[1, 2, 3][..]);
+	}
+
+	#[test]
+	fn bounded_slice_partialeq_slice_works() {
+		let unbound = [1, 2, 3];
+		let bound = BoundedSlice::<u32, ConstU32<3>>::truncate_from(&unbound);
+
+		assert_eq!(bound, &unbound[..]);
+		assert!(bound == &unbound[..]);
+	}
 }