improve MockValidationDataInherentDataProvider to support async back…

…ing (paritytech#4442)

Support async backing in `--dev` mode

This PR improve the relay mock `MockValidationDataInherentDataProvider`
to mach expectations of async backing runtimes.

* Add para_head in the mock relay proof
* Add relay slot in the mock relay proof 

fix paritytech#4437

cumulus/client/parachain-inherent/src/mock.rs

@@ -28,6 +28,9 @@ use std::collections::BTreeMap;
 
 use cumulus_test_relay_sproof_builder::RelayStateSproofBuilder;
 
+/// Relay chain slot duration, in milliseconds.
+pub const RELAY_CHAIN_SLOT_DURATION_MILLIS: u32 = 6000;
+
 /// Inherent data provider that supplies mocked validation data.
 ///
 /// This is useful when running a node that is not actually backed by any relay chain.
@@ -165,11 +168,11 @@ impl<R: Send + Sync + GenerateRandomness<u64>> InherentDataProvider
 		let mut sproof_builder =
 			RelayStateSproofBuilder { para_id: self.xcm_config.para_id, ..Default::default() };
 
-
 		// Calculate the mocked relay block based on the current para block
 		let relay_parent_number =
 			self.relay_offset + self.relay_blocks_per_para_block * self.current_para_block;
-		sproof_builder.current_slot = (relay_parent_number as u64).into();
+		sproof_builder.current_slot =
+			((relay_parent_number / RELAY_CHAIN_SLOT_DURATION_MILLIS) as u64).into();
 
 		// Process the downward messages and set up the correct head
 		let mut downward_messages = Vec::new();

prdoc/pr_4442.prdoc

@@ -0,0 +1,13 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Improve mock relay in --dev mode to support async backing
+
+doc:
+  - audience: Node Dev
+    description: |
+      Support async backing in --dev mode. Improve the relay mock MockValidationDataInherentDataProvider to mach expectations of async backing runtimes.
+
+crates:
+  - name: cumulus-client-parachain-inherent
+    bump: patch