EIP-4399 preparation

From EIP-4399 spec:

Renaming

The mixHash field SHOULD further be renamed to random.

...

eth.nimble

@@ -74,6 +74,9 @@ task test_db, "Run db tests":
 task test_utp, "Run utp tests":
   runTest("tests/utp/all_utp_tests")
 
+task test_common, "Run common tests":
+  runTest("tests/common/test_eth_types")
+
 task test, "Run all tests":
   for filename in [
       "test_bloom",
@@ -87,6 +90,7 @@ task test, "Run all tests":
   test_trie_task()
   test_db_task()
   test_utp_task()
+  test_common_task()
 
 task test_discv5_full, "Run discovery v5 and its dependencies tests":
   test_keys_task()

eth/common/eth_types.nim

@@ -244,6 +244,14 @@ func baseFee*(h: BlockHeader | BlockHeaderRef): UInt256 =
 template `baseFee=`*(h: BlockHeader | BlockHeaderRef, data: UInt256) =
   h.fee = some(data)
 
+# starting from EIP-4399, `mixHash`/`mixDigest` field will be alled `random`
+# https://github.com/ethereum/EIPs/blob/bd156daf2afa38aa95bc2137d3121ff536e50645/EIPS/eip-4399.md
+template random*(h: BlockHeader | BlockHeaderRef): Hash256 =
+  h.mixDigest
+
+template `random=`*(h: BlockHeader | BlockHeaderRef, hash: Hash256) =
+  h.mixDigest = hash
+
 func toBlockNonce*(n: uint64): BlockNonce =
   n.toBytesBE()
 

tests/common/test_eth_types.nim

@@ -49,3 +49,10 @@ suite "BlockHashOrNumber":
 
     Json.roundtripTest BlockHashOrNumber(isHash: false, number: 1209231231),
                        "\"1209231231\""
+
+  test "EIP-4399 random field":
+    let hash = Hash256.fromHex "0x7a64245f7f95164f6176d90bd4903dbdd3e5433d555dd1385e81787f9672c588"
+    var blk: BlockHeader
+    blk.random = hash
+    let res = blk.random
+    check hash == res