Add support for multiple testnet flags (#1396)

## Issue Addressed

NA

## Proposed Changes

Allows for multiple "hardcoded" testnets.

## Additional Info

This PR is incomplete.

## TODO

- [x] Add flag to CLI, integrate with rest of Lighthouse.


Co-authored-by: Pawan Dhananjay <pawandhananjay@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>

common/clap_utils/src/lib.rs

@@ -14,20 +14,24 @@ pub const BAD_TESTNET_DIR_MESSAGE: &str = "The hard-coded testnet directory was
 
 /// Attempts to load the testnet dir at the path if `name` is in `matches`, returning an error if
 /// the path cannot be found or the testnet dir is invalid.
-///
-/// If `name` is not in `matches`, attempts to return the "hard coded" testnet dir.
-pub fn parse_testnet_dir_with_hardcoded_default<E: EthSpec>(
+pub fn parse_testnet_dir<E: EthSpec>(
     matches: &ArgMatches,
     name: &'static str,
 ) -> Result<Option<Eth2TestnetConfig<E>>, String> {
-    if let Some(path) = parse_optional::<PathBuf>(matches, name)? {
-        Eth2TestnetConfig::load(path.clone())
-            .map_err(|e| format!("Unable to open testnet dir at {:?}: {}", path, e))
-            .map(Some)
-    } else {
-        Eth2TestnetConfig::hard_coded()
-            .map_err(|e| format!("{} Error : {}", BAD_TESTNET_DIR_MESSAGE, e))
-    }
+    let path = parse_required::<PathBuf>(matches, name)?;
+    Eth2TestnetConfig::load(path.clone())
+        .map_err(|e| format!("Unable to open testnet dir at {:?}: {}", path, e))
+        .map(Some)
+}
+
+/// Attempts to load a hardcoded network config if `name` is in `matches`, returning an error if
+/// the name is not a valid network name.
+pub fn parse_hardcoded_network<E: EthSpec>(
+    matches: &ArgMatches,
+    name: &str,
+) -> Result<Option<Eth2TestnetConfig<E>>, String> {
+    let network_name = parse_required::<String>(matches, name)?;
+    Eth2TestnetConfig::constant(network_name.as_str())
 }
 
 /// If `name` is in `matches`, parses the value as a path. Otherwise, attempts to find the user's
@@ -52,7 +56,7 @@ pub fn parse_path_with_default_in_home_dir(
 
 /// Returns the value of `name` or an error if it is not in `matches` or does not parse
 /// successfully using `std::string::FromStr`.
-pub fn parse_required<T>(matches: &ArgMatches, name: &'static str) -> Result<T, String>
+pub fn parse_required<T>(matches: &ArgMatches, name: &str) -> Result<T, String>
 where
     T: FromStr,
     <T as FromStr>::Err: std::fmt::Display,
@@ -62,7 +66,7 @@ where
 
 /// Returns the value of `name` (if present) or an error if it does not parse successfully using
 /// `std::string::FromStr`.
-pub fn parse_optional<T>(matches: &ArgMatches, name: &'static str) -> Result<Option<T>, String>
+pub fn parse_optional<T>(matches: &ArgMatches, name: &str) -> Result<Option<T>, String>
 where
     T: FromStr,
     <T as FromStr>::Err: std::fmt::Display,