Modify genesis processing process.

- Removed BeaconStateBuilder
- Added genesis code to `state_processing`.

eth2/state_processing/src/get_genesis_state.rs

@@ -0,0 +1,59 @@
+use super::per_block_processing::{errors::BlockProcessingError, process_deposits};
+use ssz::TreeHash;
+use types::*;
+
+pub enum GenesisError {
+    BlockProcessingError(BlockProcessingError),
+    BeaconStateError(BeaconStateError),
+}
+
+/// Returns the genesis `BeaconState`
+///
+/// Spec v0.5.0
+pub fn get_genesis_state(
+    genesis_validator_deposits: &[Deposit],
+    genesis_time: u64,
+    genesis_eth1_data: Eth1Data,
+    spec: &ChainSpec,
+) -> Result<(), BlockProcessingError> {
+    // Get the genesis `BeaconState`
+    let mut state = BeaconState::genesis(genesis_time, genesis_eth1_data, spec);
+
+    // Process genesis deposits.
+    process_deposits(&mut state, genesis_validator_deposits, spec)?;
+
+    // Process genesis activations.
+    for i in 0..state.validator_registry.len() {
+        if state.get_effective_balance(i, spec)? >= spec.max_deposit_amount {
+            state.validator_registry[i].activation_epoch = spec.genesis_epoch;
+        }
+    }
+
+    // Ensure the current epoch cache is built.
+    state.build_epoch_cache(RelativeEpoch::Current, spec)?;
+
+    // Set all the active index roots to be the genesis active index root.
+    let active_validator_indices = state
+        .get_active_validator_indices(spec.genesis_epoch, spec)?
+        .to_vec();
+    let genesis_active_index_root = Hash256::from_slice(&active_validator_indices.hash_tree_root());
+    state.latest_active_index_roots =
+        vec![genesis_active_index_root; spec.latest_active_index_roots_length as usize];
+
+    // Generate the current shuffling seed.
+    state.current_shuffling_seed = state.generate_seed(spec.genesis_epoch, spec)?;
+
+    Ok(())
+}
+
+impl From<BlockProcessingError> for GenesisError {
+    fn from(e: BlockProcessingError) -> GenesisError {
+        GenesisError::BlockProcessingError(e)
+    }
+}
+
+impl From<BeaconStateError> for GenesisError {
+    fn from(e: BeaconStateError) -> GenesisError {
+        GenesisError::BeaconStateError(e)
+    }
+}