Required weight is returned in case it exceeds limit.

runtime/parachains/src/ump.rs

@@ -73,7 +73,7 @@ impl<XcmExecutor: xcm::v0::ExecuteXcm<Call>, Call> UmpSink for XcmSink<XcmExecut
 					let xcm_location: MultiLocation = xcm_junction.into();
 					match XcmExecutor::execute_xcm(xcm_location, xcm_message, max_weight) {
 						Outcome::Complete(w) | Outcome::Incomplete(w, _) => Some(w),
-						Outcome::Error(XcmError::WeightLimitReached) => None,
+						Outcome::Error(XcmError::WeightLimitReached(..)) => None,
 						Outcome::Error(_) => Some(0),
 					}
 				}

xcm/src/v0/multi_location.rs

@@ -578,7 +578,7 @@ impl MultiLocation {
 		let self_parents = self.parent_count();
 		let prefix_rest = prefix.len() - prefix.parent_count();
 		let skipped = self_parents.min(prefix_rest);
-		if self.len() + prefix.len() - 2 * skipped > 4 {
+		if self.len() + prefix.len() - 2 * skipped > 8 {
 			return Err(prefix);
 		}
 

xcm/src/v0/traits.rs

@@ -43,7 +43,9 @@ pub enum Error {
 	BadOrigin,
 	ExceedsMaxMessageSize,
 	FailedToTransactAsset(#[codec(skip)] &'static str),
-	WeightLimitReached,
+	/// Execution of the XCM would potentially result in a greater weight used than the pre-specified
+	/// weight limit. The amount that is potentially required is the parameter.
+	WeightLimitReached(Weight),
 	Wildcard,
 	/// The case where an XCM message has specified a optional weight limit and the weight required for
 	/// processing is too great.

xcm/xcm-executor/src/lib.rs

@@ -54,10 +54,10 @@ impl<Config: config::Config> ExecuteXcm<Config::Call> for XcmExecutor<Config> {
 		};
 		let maximum_weight = match shallow_weight.checked_add(deep_weight) {
 			Some(x) => x,
-			None => return Outcome::Error(XcmError::WeightLimitReached),
+			None => return Outcome::Error(XcmError::Overflow),
 		};
 		if maximum_weight > weight_limit {
-			return Outcome::Error(XcmError::WeightLimitReached);
+			return Outcome::Error(XcmError::WeightLimitReached(maximum_weight));
 		}
 		let mut trader = Config::Trader::new();
 		let result = Self::do_execute_xcm(origin, true, message, &mut 0, Some(shallow_weight), &mut trader);