Change inheritance order for chain_class_without_seal_validation (#1723)

* Change inheritance order for chain_class_without_seal_validation to prevent MRO errors

* Add tests for disabling an already pow disabled chain

Author: Bhargavasomu

eth/tools/builder/chain/builders.py

@@ -290,11 +290,15 @@ def validate_seal(cls, header: BlockHeader) -> None:
 @to_tuple
 def _mix_in_disable_seal_validation(vm_configuration: VMConfiguration) -> Iterable[VMFork]:
     for fork_block, vm_class in vm_configuration:
-        vm_class_without_seal_validation = type(
-            vm_class.__name__,
-            (NoVMSealValidationMixin, vm_class),
-            {},
-        )
+        if issubclass(vm_class, NoVMSealValidationMixin):
+            # Seal validation already disabled, hence nothing to change
+            vm_class_without_seal_validation = vm_class
+        else:
+            vm_class_without_seal_validation = type(
+                vm_class.__name__,
+                (NoVMSealValidationMixin, vm_class),
+                {},
+            )
         yield fork_block, vm_class_without_seal_validation
 
 
@@ -312,11 +316,15 @@ def disable_pow_check(chain_class: Type[BaseChain]) -> Type[BaseChain]:
     if not chain_class.vm_configuration:
         raise ValidationError("Chain class has no vm_configuration")
 
-    chain_class_without_seal_validation = type(
-        chain_class.__name__,
-        (NoChainSealValidationMixin, chain_class),
-        {},
-    )
+    if issubclass(chain_class, NoChainSealValidationMixin):
+        # Seal validation already disabled, hence nothing to change
+        chain_class_without_seal_validation = chain_class
+    else:
+        chain_class_without_seal_validation = type(
+            chain_class.__name__,
+            (chain_class, NoChainSealValidationMixin),
+            {},
+        )
     return chain_class_without_seal_validation.configure(  # type: ignore
         vm_configuration=_mix_in_disable_seal_validation(
             chain_class_without_seal_validation.vm_configuration  # type: ignore

tests/core/builder-tools/test_chain_builder.py

@@ -2,6 +2,11 @@
 
 from eth_utils import ValidationError
 
+from eth.chains import (
+    MainnetChain,
+    MainnetTesterChain,
+    RopstenChain,
+)
 from eth.chains.base import (
     Chain,
     MiningChain,
@@ -19,6 +24,9 @@
     mine_block,
     mine_blocks,
 )
+from eth.tools.builder.chain.builders import (
+    NoChainSealValidationMixin,
+)
 
 
 MINING_CHAIN_PARAMS = (
@@ -229,3 +237,18 @@ def test_chain_builder_chain_split(mining_chain):
 
     head_b = chain_b.get_canonical_head()
     assert head_b.block_number == 3
+
+
+@pytest.mark.parametrize(
+    "chain",
+    (
+        MainnetChain,
+        MainnetTesterChain,
+        RopstenChain,
+    )
+)
+def test_disabling_pow_for_already_pow_disabled_chain(chain):
+    pow_disabled_chain = disable_pow_check(chain)
+    assert issubclass(pow_disabled_chain, NoChainSealValidationMixin)
+    again_pow_disabled_chain = disable_pow_check(pow_disabled_chain)
+    assert issubclass(again_pow_disabled_chain, NoChainSealValidationMixin)