Ensure difficulty/hash/epoch overrides change the ChainSpec (#2798)

* Unify loading of eth2_network_config

* Apply overrides at lighthouse binary level

* Remove duplicate override values

* Add merge values to existing net configs

* Make override flags global

* Add merge fields to testing config

* Add one to TTD

* Fix failing engine tests

* Fix test compile error

* Remove TTD flags

* Move get_eth2_network_config

* Fix warn

* Address review comments

lighthouse/environment/src/lib.rs

@@ -249,7 +249,7 @@ impl<E: EthSpec> EnvironmentBuilder<E> {
             log: self.log.ok_or("Cannot build environment without log")?,
             eth_spec_instance: self.eth_spec_instance,
             eth2_config: self.eth2_config,
-            eth2_network_config: self.eth2_network_config,
+            eth2_network_config: self.eth2_network_config.map(Arc::new),
         })
     }
 }
@@ -263,6 +263,7 @@ pub struct RuntimeContext<E: EthSpec> {
     pub executor: TaskExecutor,
     pub eth_spec_instance: E,
     pub eth2_config: Eth2Config,
+    pub eth2_network_config: Option<Arc<Eth2NetworkConfig>>,
 }
 
 impl<E: EthSpec> RuntimeContext<E> {
@@ -274,6 +275,7 @@ impl<E: EthSpec> RuntimeContext<E> {
             executor: self.executor.clone_with_name(service_name),
             eth_spec_instance: self.eth_spec_instance.clone(),
             eth2_config: self.eth2_config.clone(),
+            eth2_network_config: self.eth2_network_config.clone(),
         }
     }
 
@@ -301,7 +303,7 @@ pub struct Environment<E: EthSpec> {
     log: Logger,
     eth_spec_instance: E,
     pub eth2_config: Eth2Config,
-    pub eth2_network_config: Option<Eth2NetworkConfig>,
+    pub eth2_network_config: Option<Arc<Eth2NetworkConfig>>,
 }
 
 impl<E: EthSpec> Environment<E> {
@@ -324,6 +326,7 @@ impl<E: EthSpec> Environment<E> {
             ),
             eth_spec_instance: self.eth_spec_instance.clone(),
             eth2_config: self.eth2_config.clone(),
+            eth2_network_config: self.eth2_network_config.clone(),
         }
     }
 
@@ -338,6 +341,7 @@ impl<E: EthSpec> Environment<E> {
             ),
             eth_spec_instance: self.eth_spec_instance.clone(),
             eth2_config: self.eth2_config.clone(),
+            eth2_network_config: self.eth2_network_config.clone(),
         }
     }
 

lighthouse/environment/tests/testnet_dir/config.yaml

@@ -3,6 +3,14 @@
 # Extends the mainnet preset
 PRESET_BASE: 'mainnet'
 
+# Transition
+# ---------------------------------------------------------------
+# TBD, 2**256-2**10 is a placeholder
+TERMINAL_TOTAL_DIFFICULTY: 115792089237316195423570985008687907853269984665640564039457584007913129638912
+# By default, don't use these params
+TERMINAL_BLOCK_HASH: 0x0000000000000000000000000000000000000000000000000000000000000000
+TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH: 18446744073709551615
+
 # Genesis
 # ---------------------------------------------------------------
 # CUSTOMISED FOR TEST