Fix new clippy lints (#2036)

## Issue Addressed

NA

## Proposed Changes

Fixes new clippy lints in the whole project (mainly [manual_strip](https://rust-lang.github.io/rust-clippy/master/index.html#manual_strip) and [unnecessary_lazy_evaluations](https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_lazy_evaluations)). Furthermore, removes `to_string()` calls on literals when used with the `?`-operator.

common/account_utils/src/validator_definitions.rs

@@ -86,14 +86,12 @@ impl ValidatorDefinition {
         let voting_keystore_path = voting_keystore_path.as_ref().into();
         let keystore =
             Keystore::from_json_file(&voting_keystore_path).map_err(Error::UnableToOpenKeystore)?;
-        let voting_public_key = keystore
-            .public_key()
-            .ok_or_else(|| Error::InvalidKeystorePubkey)?;
+        let voting_public_key = keystore.public_key().ok_or(Error::InvalidKeystorePubkey)?;
 
         Ok(ValidatorDefinition {
             enabled: true,
             voting_public_key,
-            description: keystore.description().unwrap_or_else(|| "").to_string(),
+            description: keystore.description().unwrap_or("").to_string(),
             signing_definition: SigningDefinition::LocalKeystore {
                 voting_keystore_path,
                 voting_keystore_password_path: None,
@@ -214,7 +212,7 @@ impl ValidatorDefinitions {
                 Some(ValidatorDefinition {
                     enabled: true,
                     voting_public_key,
-                    description: keystore.description().unwrap_or_else(|| "").to_string(),
+                    description: keystore.description().unwrap_or("").to_string(),
                     signing_definition: SigningDefinition::LocalKeystore {
                         voting_keystore_path,
                         voting_keystore_password_path,

common/clap_utils/src/lib.rs

@@ -101,8 +101,8 @@ pub fn parse_ssz_optional<T: Decode>(
     matches
         .value_of(name)
         .map(|val| {
-            if val.starts_with("0x") {
-                let vec = hex::decode(&val[2..])
+            if let Some(stripped) = val.strip_prefix("0x") {
+                let vec = hex::decode(stripped)
                     .map_err(|e| format!("Unable to parse {} as hex: {:?}", name, e))?;
 
                 T::from_ssz_bytes(&vec)

common/deposit_contract/build.rs

@@ -86,7 +86,7 @@ pub fn download_deposit_contract(
 
                 let abi = contract
                     .get("abi")
-                    .ok_or_else(|| "Response does not contain key: abi".to_string())?
+                    .ok_or("Response does not contain key: abi")?
                     .to_string();
 
                 verify_checksum(abi.as_bytes(), abi_checksum);
@@ -97,7 +97,7 @@ pub fn download_deposit_contract(
 
                 let bytecode = contract
                     .get("bytecode")
-                    .ok_or_else(|| "Response does not contain key: bytecode".to_string())?
+                    .ok_or("Response does not contain key: bytecode")?
                     .to_string();
 
                 verify_checksum(bytecode.as_bytes(), bytecode_checksum);

common/deposit_contract/src/lib.rs

@@ -55,8 +55,7 @@ pub fn decode_eth1_tx_data(
 ) -> Result<(DepositData, Hash256), DecodeError> {
     let abi = Contract::load(ABI)?;
     let function = abi.function("deposit")?;
-    let mut tokens =
-        function.decode_input(bytes.get(4..).ok_or_else(|| DecodeError::InadequateBytes)?)?;
+    let mut tokens = function.decode_input(bytes.get(4..).ok_or(DecodeError::InadequateBytes)?)?;
 
     macro_rules! decode_token {
         ($type: ty, $to_fn: ident) => {

common/eth2/src/lighthouse_vc/http_client.rs

@@ -79,7 +79,7 @@ impl ValidatorClientHttpClient {
         let sig = response
             .headers()
             .get("Signature")
-            .ok_or_else(|| Error::MissingSignatureHeader)?
+            .ok_or(Error::MissingSignatureHeader)?
             .to_str()
             .map_err(|_| Error::InvalidSignatureHeader)?
             .to_string();
@@ -96,7 +96,7 @@ impl ValidatorClientHttpClient {
                 Some(secp256k1::verify(&message, &sig, &self.server_pubkey))
             })
             .filter(|is_valid| *is_valid)
-            .ok_or_else(|| Error::InvalidSignatureHeader)?;
+            .ok_or(Error::InvalidSignatureHeader)?;
 
         Ok(body)
     }

common/eth2_interop_keypairs/src/lib.rs

@@ -106,8 +106,8 @@ impl TryInto<Keypair> for YamlKeypair {
 }
 
 fn string_to_bytes(string: &str) -> Result<Vec<u8>, String> {
-    let string = if string.starts_with("0x") {
-        &string[2..]
+    let string = if let Some(stripped) = string.strip_prefix("0x") {
+        stripped
     } else {
         string
     };

common/eth2_testnet_config/src/lib.rs

@@ -122,7 +122,7 @@ impl Eth2TestnetConfig {
         let genesis_state_bytes = self
             .genesis_state_bytes
             .as_ref()
-            .ok_or_else(|| "Genesis state is unknown".to_string())?;
+            .ok_or("Genesis state is unknown")?;
 
         BeaconState::from_ssz_bytes(genesis_state_bytes)
             .map_err(|e| format!("Genesis state SSZ bytes are invalid: {:?}", e))
@@ -156,8 +156,8 @@ impl Eth2TestnetConfig {
                         //
                         // This allows us to play nice with other clients that are expecting
                         // plain-text, not YAML.
-                        let no_doc_header = if yaml.starts_with("---\n") {
-                            &yaml[4..]
+                        let no_doc_header = if let Some(stripped) = yaml.strip_prefix("---\n") {
+                            stripped
                         } else {
                             &yaml
                         };

common/validator_dir/src/builder.rs

@@ -138,7 +138,7 @@ impl<'a> Builder<'a> {
     pub fn build(self) -> Result<ValidatorDir, Error> {
         let (voting_keystore, voting_password) = self
             .voting_keystore
-            .ok_or_else(|| Error::UninitializedVotingKeystore)?;
+            .ok_or(Error::UninitializedVotingKeystore)?;
 
         let dir = self
             .base_validators_dir

common/validator_dir/src/validator_dir.rs

@@ -167,8 +167,8 @@ impl ValidatorDir {
             .map_err(Error::UnableToReadDepositData)
             .and_then(|hex_bytes| {
                 let hex = std::str::from_utf8(&hex_bytes).map_err(|_| Error::DepositDataNotUtf8)?;
-                if hex.starts_with("0x") {
-                    hex::decode(&hex[2..]).map_err(Error::DepositDataInvalidHex)
+                if let Some(stripped) = hex.strip_prefix("0x") {
+                    hex::decode(stripped).map_err(Error::DepositDataInvalidHex)
                 } else {
                     Err(Error::DepositDataMissing0xPrefix)
                 }