`--era-dir` option (#3895)

* `--era-dir` option

hidden, while the feature is under development

* Update beacon_chain/conf.nim

Co-authored-by: zah <zahary@gmail.com>

beacon_chain/conf.nim

@@ -153,6 +153,11 @@ type
       desc: "A directory containing wallet files"
       name: "wallets-dir" .}: Option[InputDir]
 
+    eraDirFlag* {.
+      hidden
+      desc: "A directory containing era files"
+      name: "era-dir" .}: Option[InputDir]
+
     web3Urls* {.
       desc: "One or more execution layer Web3 provider URLs"
       name: "web3-url" .}: seq[string]
@@ -1018,10 +1023,11 @@ func secretsDir*[Conf](config: Conf): string =
   string config.secretsDirFlag.get(InputDir(config.dataDir / "secrets"))
 
 func walletsDir*(config: BeaconNodeConf): string =
-  if config.walletsDirFlag.isSome:
-    config.walletsDirFlag.get.string
-  else:
-    config.dataDir / "wallets"
+  string config.walletsDirFlag.get(InputDir(config.dataDir / "wallets"))
+
+func eraDir*(config: BeaconNodeConf): string =
+  # The era directory should be shared between networks of the same type..
+  string config.eraDirFlag.get(InputDir(config.dataDir / "era"))
 
 func outWalletName*(config: BeaconNodeConf): Option[WalletName] =
   proc fail {.noreturn.} =
@@ -1063,10 +1069,6 @@ func databaseDir*(config: AnyConf): string =
 func runAsService*(config: BeaconNodeConf): bool =
   config.cmd == noCommand and config.runAsServiceFlag
 
-func eraDir*(config: AnyConf): string =
-  # TODO this should be shared between all instances of the same network
-  config.dataDir / "era"
-
 template writeValue*(writer: var JsonWriter,
                      value: TypedInputFile|InputFile|InputDir|OutPath|OutDir|OutFile) =
   writer.writeValue(string value)