Return the correct block difficulty from the eth-rpc

prdoc/pr_10186.prdoc

@@ -0,0 +1,12 @@
+title: Return the correct block difficulty from the eth-rpc
+doc:
+- audience: Runtime Dev
+  description: |-
+    # Description
+
+    This PR fixes an issue in the eth-rpc/pallet-revive that was causing it to return an incorrect value for the block's difficulty or prevrandao.
+
+    In the VM/interpreter implementation we use a constant for the block difficulty. However, the eth block construction side was unaware of this constant being used and therefore the RPC was always returning a block difficulty of zero.
+crates:
+- name: pallet-revive
+  bump: patch

substrate/frame/revive/src/evm/block_hash/block_builder.rs

@@ -169,6 +169,9 @@ impl<T: crate::Config> EthereumBlockBuilder<T> {
 		let tx_hashes = core::mem::replace(&mut self.tx_hashes, Vec::new());
 		let gas_info = core::mem::replace(&mut self.gas_info, Vec::new());
 
+		let difficulty = U256::from(crate::vm::evm::DIFFICULTY);
+		let mix_hash = H256(difficulty.to_big_endian());
+
 		let mut block = Block {
 			number: block_number,
 			parent_hash,
@@ -186,6 +189,8 @@ impl<T: crate::Config> EthereumBlockBuilder<T> {
 			logs_bloom: self.logs_bloom.bloom.into(),
 			transactions: HashesOrTransactionInfos::Hashes(tx_hashes),
 
+			mix_hash,
+
 			..Default::default()
 		};
 

substrate/frame/revive/src/exec/tests.rs

@@ -2842,7 +2842,7 @@ fn block_hash_returns_proper_values() {
 		assert_eq!(
 			ctx.ext.block_hash(U256::from(0)),
 			Some(H256::from(hex_literal::hex!(
-				"b9be84fb00044994dff6b62393b4c8aa8191717c5ea046f270bd2695524e9f85"
+				"c2fed5de763ecfa4cb65e8f57838c5517f69db4ede78a30093bf3fad66c5a8cd"
 			)))
 		);