Add more detail to bad hardcoded dir warning (#1069)

Cargo.lock

@@ -250,6 +250,7 @@ version = "0.2.0"
 dependencies = [
  "beacon_chain 0.2.0",
  "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "clap_utils 0.1.0",
  "client 0.2.0",
  "ctrlc 3.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "dirs 2.0.2 (registry+https://github.com/rust-lang/crates.io-index)",

beacon_node/Cargo.toml

@@ -41,3 +41,4 @@ eth2-libp2p = { path = "./eth2-libp2p" }
 eth2_ssz = { path = "../eth2/utils/ssz" }
 toml = "0.5.4"
 serde = "1.0.102"
+clap_utils = { path = "../eth2/utils/clap_utils" }

beacon_node/src/config.rs

@@ -1,5 +1,6 @@
 use beacon_chain::builder::PUBKEY_CACHE_FILENAME;
 use clap::ArgMatches;
+use clap_utils::BAD_TESTNET_DIR_MESSAGE;
 use client::{config::DEFAULT_DATADIR, ClientConfig, ClientGenesis};
 use eth2_libp2p::{Enr, Multiaddr};
 use eth2_testnet_config::Eth2TestnetConfig;
@@ -385,14 +386,8 @@ pub fn get_eth2_testnet_config<E: EthSpec>(
         Eth2TestnetConfig::load(testnet_dir.clone())
             .map_err(|e| format!("Unable to open testnet dir at {:?}: {}", testnet_dir, e))?
     } else {
-        Eth2TestnetConfig::hard_coded().map_err(|e| {
-            format!(
-                "The hard-coded testnet directory was invalid. \
-                 This happens when Lighthouse is migrating between spec versions. \
-                 Error : {}",
-                e
-            )
-        })?
+        Eth2TestnetConfig::hard_coded()
+            .map_err(|e| format!("{} Error : {}", BAD_TESTNET_DIR_MESSAGE, e))?
     })
 }
 

eth2/utils/clap_utils/src/lib.rs

@@ -8,6 +8,11 @@ use std::path::PathBuf;
 use std::str::FromStr;
 use types::EthSpec;
 
+pub const BAD_TESTNET_DIR_MESSAGE: &str = "The hard-coded testnet directory was invalid. \
+                                        This happens when Lighthouse is migrating between spec versions \
+                                        or when there is no default public network to connect to. \
+                                        During these times you must specify a --testnet-dir.";
+
 /// 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.
 ///
@@ -20,14 +25,8 @@ pub fn parse_testnet_dir_with_hardcoded_default<E: EthSpec>(
         Eth2TestnetConfig::load(path.clone())
             .map_err(|e| format!("Unable to open testnet dir at {:?}: {}", path, e))
     } else {
-        Eth2TestnetConfig::hard_coded().map_err(|e| {
-            format!(
-                "The hard-coded testnet directory was invalid. \
-                 This happens when Lighthouse is migrating between spec versions. \
-                 Error : {}",
-                e
-            )
-        })
+        Eth2TestnetConfig::hard_coded()
+            .map_err(|e| format!("{} Error : {}", BAD_TESTNET_DIR_MESSAGE, e))
     }
 }