Fix and document some usages of defaultRuntimeConfig (#4147)

Other changes:

* Make the light client store compatible with phase0-only networks
  and simulations

beacon_chain/consensus_object_pools/blockchain_dag_light_client.nim

@@ -434,10 +434,14 @@ proc cacheLightClientData(
   if dag.lcDataStore.cache.data.hasKeyOrPut(bid, cachedData):
     doAssert false, "Redundant `cacheLightClientData` call"
 
+func shouldImportLcData(dag: ChainDAGref): bool =
+  dag.lcDataStore.importMode != LightClientDataImportMode.None and
+  dag.cfg.ALTAIR_FORK_EPOCH != FAR_FUTURE_EPOCH
+
 proc deleteLightClientData*(dag: ChainDAGRef, bid: BlockId) =
   ## Delete cached light client data for a given block. This needs to be called
   ## when a block becomes unreachable due to finalization of a different fork.
-  if dag.lcDataStore.importMode == LightClientDataImportMode.None:
+  if not dag.shouldImportLcData:
     return
 
   dag.lcDataStore.cache.data.del bid
@@ -604,7 +608,7 @@ proc createLightClientUpdates(
 
 proc initLightClientDataCache*(dag: ChainDAGRef) =
   ## Initialize cached light client data
-  if dag.lcDataStore.importMode == LightClientDataImportMode.None:
+  if not dag.shouldImportLcData:
     return
 
   # Prune non-finalized data
@@ -709,7 +713,7 @@ proc processNewBlockForLightClient*(
     signedBlock: ForkyTrustedSignedBeaconBlock,
     parentBid: BlockId) =
   ## Update light client data with information from a new block.
-  if dag.lcDataStore.importMode == LightClientDataImportMode.None:
+  if not dag.shouldImportLcData:
     return
   if signedBlock.message.slot < dag.lcDataStore.cache.tailSlot:
     return
@@ -731,7 +735,7 @@ proc processNewBlockForLightClient*(
 proc processHeadChangeForLightClient*(dag: ChainDAGRef) =
   ## Update light client data to account for a new head block.
   ## Note that `dag.finalizedHead` is not yet updated when this is called.
-  if dag.lcDataStore.importMode == LightClientDataImportMode.None:
+  if not dag.shouldImportLcData:
     return
   if dag.head.slot < dag.lcDataStore.cache.tailSlot:
     return
@@ -766,7 +770,7 @@ proc processFinalizationForLightClient*(
   ## Prune cached data that is no longer useful for creating future
   ## `LightClientUpdate` and `LightClientBootstrap` instances.
   ## This needs to be called whenever `finalized_checkpoint` changes.
-  if dag.lcDataStore.importMode == LightClientDataImportMode.None:
+  if not dag.shouldImportLcData:
     return
   let finalizedSlot = dag.finalizedHead.slot
   if finalizedSlot < dag.lcDataStore.cache.tailSlot:

beacon_chain/spec/presets.nim

@@ -103,8 +103,12 @@ when const_preset == "mainnet":
   # TODO Move this to RuntimeConfig
   const SECONDS_PER_SLOT* {.intdefine.}: uint64 = 12
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.2.0-rc.1/configs/mainnet.yaml
-  # TODO Read these from yaml file
+  # The default run-time config specifies the default configuration values
+  # that will be used if a particular run-time config is missing specific
+  # confugration values (which will be then taken from this config object).
+  # It mostly matches the mainnet config with the exception of few properties
+  # such as `CONFIG_NAME`, `TERMINAL_TOTAL_DIFFICULTY`, `*_FORK_EPOCH`, etc
+  # which must be effectively overriden in all network (including mainnet).
   const defaultRuntimeConfig* = RuntimeConfig(
     # Mainnet config
 
@@ -118,7 +122,7 @@ when const_preset == "mainnet":
     # * 'ropsten' - testnet
     # * 'sepolia' - testnet
     # Must match the regex: [a-z0-9\-]
-    CONFIG_NAME: "mainnet",
+    CONFIG_NAME: "",
 
     # Transition
     # ---------------------------------------------------------------
@@ -130,8 +134,6 @@ when const_preset == "mainnet":
       "0x0000000000000000000000000000000000000000000000000000000000000000"),
     # TODO TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH: Epoch(uint64.high),
 
-
-
     # Genesis
     # ---------------------------------------------------------------
     # `2**14` (= 16,384)
@@ -143,7 +145,6 @@ when const_preset == "mainnet":
     # 604800 seconds (7 days)
     GENESIS_DELAY: 604800,
 
-
     # Forking
     # ---------------------------------------------------------------
     # Some forks are disabled for now:
@@ -152,17 +153,16 @@ when const_preset == "mainnet":
 
     # Altair
     ALTAIR_FORK_VERSION: Version [byte 0x01, 0x00, 0x00, 0x00],
-    ALTAIR_FORK_EPOCH: Epoch(74240), # Oct 27, 2021, 10:56:23am UTC
+    ALTAIR_FORK_EPOCH: FAR_FUTURE_EPOCH,
     # Bellatrix
     BELLATRIX_FORK_VERSION: Version [byte 0x02, 0x00, 0x00, 0x00],
-    BELLATRIX_FORK_EPOCH: Epoch(uint64.high),
+    BELLATRIX_FORK_EPOCH: FAR_FUTURE_EPOCH,
     # Capella
     CAPELLA_FORK_VERSION: Version [byte 0x03, 0x00, 0x00, 0x00],
-    CAPELLA_FORK_EPOCH: Epoch(uint64.high),
+    CAPELLA_FORK_EPOCH: FAR_FUTURE_EPOCH,
     # Sharding
     SHARDING_FORK_VERSION: Version [byte 0x04, 0x00, 0x00, 0x00],
-    SHARDING_FORK_EPOCH: Epoch(uint64.high),
-
+    SHARDING_FORK_EPOCH: FAR_FUTURE_EPOCH,
 
     # Time parameters
     # ---------------------------------------------------------------

research/block_sim.nim

@@ -590,7 +590,7 @@ cli do(slots = SLOTS_PER_EPOCH * 6,
 
     while true:
       let nextBlockTime = lastEth1BlockAt +
-                          max(1.0, gauss(r, float defaultRuntimeConfig.SECONDS_PER_ETH1_BLOCK, 3.0))
+                          max(1.0, gauss(r, float cfg.SECONDS_PER_ETH1_BLOCK, 3.0))
       if nextBlockTime > now:
         break
 

research/simutils.nim

@@ -76,7 +76,6 @@ proc loadGenesis*(validators: Natural, validate: bool):
       &"deposit_contract_snapshot_{const_preset}_{validators}_{SPEC_VERSION}.ssz"
     cfg = defaultRuntimeConfig
 
-
   if fileExists(genesisFn) and fileExists(contractSnapshotFn):
     let res = newClone(readSszForkedHashedBeaconState(
       cfg, readAllBytes(genesisFn).tryGet()))