Implement main changes for the Merge / Paris hark fork

- Add ``Paris`` fork VM classes.
- Supplant ``DIFFICULTY`` opcode at ``0x44`` with ``PREVRANDAO``.
- Allow ``mix_hash`` to be retrieved from the execution context and add ``mixhash`` opcode logic function to be used in new ``PREVRANDAO`` opcode.
- Some renaming of "Mining" nomenclature found within more general classes / methods - created an issue at ethereum#2079 to track more of these changes in a separate PR.
- Minor cleanups along the way.

eth/abc.py

@@ -91,6 +91,7 @@ def mining_hash(self) -> Hash32:
         """
 
     @property
+    @abstractmethod
     def hex_hash(self) -> str:
         """
         Return the hash as a hex string.
@@ -1718,6 +1719,14 @@ def difficulty(self) -> int:
         """
         ...
 
+    @property
+    @abstractmethod
+    def mix_hash(self) -> Hash32:
+        """
+        Return the mix hash of the block
+        """
+        ...
+
     @property
     @abstractmethod
     def gas_limit(self) -> int:
@@ -2662,6 +2671,14 @@ def difficulty(self) -> int:
         """
         ...
 
+    @property
+    @abstractmethod
+    def mix_hash(self) -> Hash32:
+        """
+        Return the current ``mix_hash`` from the current :attr:`~execution_context`
+        """
+        ...
+
     @property
     @abstractmethod
     def gas_limit(self) -> int:
@@ -2686,7 +2703,7 @@ def get_gas_price(self, transaction: SignedTransactionAPI) -> int:
         """
         Return the gas price of the given transaction.
 
-        Factor in the current block's base gase price, if appropriate. (See EIP-1559)
+        Factor in the current block's base gas price, if appropriate. (See EIP-1559)
         """
         ...
 

eth/chains/mainnet/__init__.py

@@ -12,6 +12,7 @@
 
 from .constants import (
     MAINNET_CHAIN_ID,
+    PARIS_MAINNET_BLOCK,
     GRAY_GLACIER_MAINNET_BLOCK,
     ARROW_GLACIER_MAINNET_BLOCK,
     LONDON_MAINNET_BLOCK,
@@ -46,6 +47,7 @@
     IstanbulVM,
     LondonVM,
     MuirGlacierVM,
+    ParisVM,
     PetersburgVM,
     SpuriousDragonVM,
     TangerineWhistleVM,
@@ -106,8 +108,9 @@ class MainnetHomesteadVM(MainnetDAOValidatorVM):
     LONDON_MAINNET_BLOCK,
     ARROW_GLACIER_MAINNET_BLOCK,
     GRAY_GLACIER_MAINNET_BLOCK,
+    PARIS_MAINNET_BLOCK,
 )
-MAINNET_VMS = (
+MINING_MAINNET_VMS = (
     FrontierVM,
     MainnetHomesteadVM,
     TangerineWhistleVM,
@@ -121,7 +124,11 @@ class MainnetHomesteadVM(MainnetDAOValidatorVM):
     ArrowGlacierVM,
     GrayGlacierVM,
 )
+POS_MAINNET_VMS = (
+    ParisVM,
+)
 
+MAINNET_VMS = MINING_MAINNET_VMS + POS_MAINNET_VMS
 MAINNET_VM_CONFIGURATION = tuple(zip(MAINNET_FORK_BLOCKS, MAINNET_VMS))
 
 

eth/chains/mainnet/constants.py

@@ -72,3 +72,8 @@
 # Gray Glacier Block
 #
 GRAY_GLACIER_MAINNET_BLOCK = BlockNumber(15050000)
+
+#
+# Paris Block (block height at which TTD was reached)
+#
+PARIS_MAINNET_BLOCK = BlockNumber(15537394)

eth/constants.py

@@ -1,7 +1,11 @@
 from eth_typing import (
     Address,
     BlockNumber,
-    Hash32
+    Hash32,
+)
+from typing import (
+    List,
+    Optional,
 )
 
 from eth._warnings import catch_and_ignore_import_warning
@@ -184,3 +188,13 @@
 DEFAULT_SPOOF_Y_PARITY = 1
 DEFAULT_SPOOF_R = 1
 DEFAULT_SPOOF_S = 1
+
+
+#
+# Merge / EIP-3675 constants
+#
+POST_MERGE_OMMERS_HASH = EMPTY_UNCLE_HASH
+POST_MERGE_DIFFICULTY = 0
+POST_MERGE_MIX_HASH = ZERO_HASH32
+POST_MERGE_NONCE = b"\x00\x00\x00\x00\x00\x00\x00\x00"
+POST_MERGE_OMMERS: List[Optional[Hash32]] = []

eth/tools/builder/chain/builders.py

@@ -76,6 +76,7 @@
     LondonVM,
     ArrowGlacierVM,
     GrayGlacierVM,
+    ParisVM,
 )
 
 
@@ -248,8 +249,9 @@ def dao_fork_at(dao_fork_block_number: BlockNumber,
 london_at = fork_at(LondonVM)
 arrow_glacier_at = fork_at(ArrowGlacierVM)
 gray_glacier_at = fork_at(GrayGlacierVM)
+paris_at = fork_at(ParisVM)
 
-latest_mainnet_at = gray_glacier_at
+latest_mainnet_at = paris_at
 
 GENESIS_DEFAULTS = cast(
     Tuple[Tuple[str, Union[BlockNumber, int, None, bytes, Address, Hash32]], ...],

eth/vm/base.py

@@ -97,11 +97,13 @@ class VM(Configurable, VirtualMachineAPI):
 
     cls_logger = logging.getLogger('eth.vm.base.VM')
 
-    def __init__(self,
-                 header: BlockHeaderAPI,
-                 chaindb: ChainDatabaseAPI,
-                 chain_context: ChainContextAPI,
-                 consensus_context: ConsensusContextAPI) -> None:
+    def __init__(
+        self,
+        header: BlockHeaderAPI,
+        chaindb: ChainDatabaseAPI,
+        chain_context: ChainContextAPI,
+        consensus_context: ConsensusContextAPI
+    ) -> None:
         self.chaindb = chaindb
         self.chain_context = chain_context
         self.consensus_context = consensus_context
@@ -168,10 +170,12 @@ def apply_transaction(self,
         return receipt, computation
 
     @classmethod
-    def create_execution_context(cls,
-                                 header: BlockHeaderAPI,
-                                 prev_hashes: Iterable[Hash32],
-                                 chain_context: ChainContextAPI) -> ExecutionContextAPI:
+    def create_execution_context(
+        cls,
+        header: BlockHeaderAPI,
+        prev_hashes: Iterable[Hash32],
+        chain_context: ChainContextAPI
+    ) -> ExecutionContextAPI:
         fee_recipient = cls.consensus_class.get_fee_recipient(header)
         try:
             base_fee = header.base_fee_per_gas
@@ -181,6 +185,7 @@ def create_execution_context(cls,
                 timestamp=header.timestamp,
                 block_number=header.block_number,
                 difficulty=header.difficulty,
+                mix_hash=header.mix_hash,
                 gas_limit=header.gas_limit,
                 prev_hashes=prev_hashes,
                 chain_id=chain_context.chain_id,
@@ -191,6 +196,7 @@ def create_execution_context(cls,
                 timestamp=header.timestamp,
                 block_number=header.block_number,
                 difficulty=header.difficulty,
+                mix_hash=header.mix_hash,
                 gas_limit=header.gas_limit,
                 prev_hashes=prev_hashes,
                 chain_id=chain_context.chain_id,
@@ -283,7 +289,7 @@ def apply_all_transactions(
         return result_header, receipts_tuple, computations_tuple
 
     #
-    # Mining
+    # Importing blocks
     #
     def import_block(self, block: BlockAPI) -> BlockAndMetaWitness:
         if self.get_block().number != block.number:
@@ -307,7 +313,8 @@ def import_block(self, block: BlockAPI) -> BlockAndMetaWitness:
         )
 
         execution_context = self.create_execution_context(
-            block.header, self.previous_hashes, self.chain_context)
+            block.header, self.previous_hashes, self.chain_context
+        )
 
         # Zero out the gas_used before applying transactions. Each applied transaction will
         #   increase the gas used in the final new_header.
@@ -329,7 +336,6 @@ def import_block(self, block: BlockAPI) -> BlockAndMetaWitness:
 
     def mine_block(self, block: BlockAPI, *args: Any, **kwargs: Any) -> BlockAndMetaWitness:
         packed_block = self.pack_block(block, *args, **kwargs)
-
         block_result = self.finalize_block(packed_block)
 
         # Perform validation

eth/vm/execution_context.py

@@ -15,29 +15,32 @@
 
 class ExecutionContext(ExecutionContextAPI):
     _coinbase = None
-
     _timestamp = None
     _number = None
     _difficulty = None
+    _mix_hash = None
     _gas_limit = None
     _prev_hashes = None
     _chain_id = None
     _base_fee_per_gas = None
 
     def __init__(
-            self,
-            coinbase: Address,
-            timestamp: int,
-            block_number: BlockNumber,
-            difficulty: int,
-            gas_limit: int,
-            prev_hashes: Iterable[Hash32],
-            chain_id: int,
-            base_fee_per_gas: Optional[int] = None) -> None:
+        self,
+        coinbase: Address,
+        timestamp: int,
+        block_number: BlockNumber,
+        difficulty: int,
+        mix_hash: Hash32,
+        gas_limit: int,
+        prev_hashes: Iterable[Hash32],
+        chain_id: int,
+        base_fee_per_gas: Optional[int] = None
+    ) -> None:
         self._coinbase = coinbase
         self._timestamp = timestamp
         self._block_number = block_number
         self._difficulty = difficulty
+        self._mix_hash = mix_hash
         self._gas_limit = gas_limit
         self._prev_hashes = CachedIterable(prev_hashes)
         self._chain_id = chain_id
@@ -59,6 +62,10 @@ def block_number(self) -> BlockNumber:
     def difficulty(self) -> int:
         return self._difficulty
 
+    @property
+    def mix_hash(self) -> Hash32:
+        return self._mix_hash
+
     @property
     def gas_limit(self) -> int:
         return self._gas_limit

eth/vm/forks/__init__.py

@@ -37,3 +37,6 @@
 from .gray_glacier import (  # noqa: F401
     GrayGlacierVM,
 )
+from .paris import (  # noqa: F401
+    ParisVM,
+)

eth/vm/forks/byzantium/headers.py

@@ -98,7 +98,13 @@ def configure_header(difficulty_fn: Callable[[BlockHeaderAPI, int], int],
     validate_header_params_for_configuration(header_params)
 
     with vm.get_header().build_changeset(**header_params) as changeset:
-        if 'timestamp' in header_params and changeset.block_number > 0:
+        if (
+            'timestamp' in header_params
+            and changeset.block_number > 0
+
+            # check that we are pre-PoS and not using a constant for the difficulty
+            and not isinstance(difficulty_fn, int)
+        ):
             parent_header = get_parent_header(changeset.build_rlp(), vm.chaindb)
             changeset.difficulty = difficulty_fn(
                 parent_header,

eth/vm/forks/frontier/state.py

@@ -178,7 +178,7 @@ def finalize_computation(self,
 
             self.vm_state.delta_balance(computation.msg.sender, gas_refund_amount)
 
-        # Miner Fees
+        # Beneficiary Fees
         gas_used = transaction.gas - gas_remaining - gas_refund
         transaction_fee = gas_used * self.vm_state.get_tip(transaction)
         self.vm_state.logger.debug2(
@@ -190,13 +190,7 @@ def finalize_computation(self,
 
         # Process Self Destructs
         for account, _ in computation.get_accounts_for_deletion():
-            # TODO: need to figure out how we prevent multiple selfdestructs from
-            # the same account and if this is the right place to put this.
             self.vm_state.logger.debug2('DELETING ACCOUNT: %s', encode_hex(account))
-
-            # TODO: this balance setting is likely superflous and can be
-            # removed since `delete_account` does this.
-            self.vm_state.set_balance(account, 0)
             self.vm_state.delete_account(account)
 
         return computation

eth/vm/forks/paris/__init__.py

@@ -0,0 +1,67 @@
+from typing import (
+    Type,
+)
+
+from eth.abc import BlockAPI, BlockHeaderAPI
+from eth.constants import (
+    POST_MERGE_DIFFICULTY,
+    POST_MERGE_NONCE,
+    POST_MERGE_OMMERS_HASH,
+)
+from eth.rlp.blocks import BaseBlock
+from eth.vm.forks.gray_glacier import GrayGlacierVM
+from eth.vm.state import BaseState
+from eth_utils import (
+    ValidationError,
+)
+
+from .blocks import ParisBlock
+from .headers import (
+    configure_paris_header,
+    create_paris_header_from_parent,
+)
+from .state import ParisState
+
+
+class ParisVM(GrayGlacierVM):
+    # fork name
+    fork = 'paris'
+
+    # classes
+    block_class: Type[BaseBlock] = ParisBlock
+    _state_class: Type[BaseState] = ParisState
+
+    # Methods
+    create_header_from_parent = staticmethod(  # type: ignore
+        create_paris_header_from_parent(POST_MERGE_DIFFICULTY)
+    )
+    configure_header = configure_paris_header
+
+    def _assign_block_rewards(self, block: BlockAPI) -> None:
+        # No block reward or uncles / uncle rewards in PoS
+        pass
+
+    @classmethod
+    def validate_header(
+        cls,
+        header: BlockHeaderAPI,
+        parent_header: BlockHeaderAPI
+    ) -> None:
+        super().validate_header(header, parent_header)
+
+        difficulty, nonce, uncles_hash = (
+            header.difficulty, header.nonce, header.uncles_hash
+        )
+
+        if difficulty != POST_MERGE_DIFFICULTY:
+            raise ValidationError(
+                f"Difficulty must be {POST_MERGE_DIFFICULTY}, got {difficulty}."
+            )
+        if nonce != POST_MERGE_NONCE:
+            raise ValidationError(
+                f"Nonce must be {POST_MERGE_NONCE !r}, got {nonce !r}."
+            )
+        if uncles_hash != POST_MERGE_OMMERS_HASH:
+            raise ValidationError(
+                f"Uncles hash must be {POST_MERGE_OMMERS_HASH !r}, got {uncles_hash !r}."
+            )