You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: hash_agg.rs
    path of file: ./repos/risinglight/src/executor
    
    the code of the file until where you have to start completion: // Copyright 2024 RisingLight Project Authors. Licensed under Apache-2.0.

use std::collections::HashMap;

use iter_chunks::IterChunks;
use smallvec::SmallVec;

use super::*;
use crate::array::DataChunkBuilder;
use crate::types::DataValue;

/// The executor of hash aggregation.
pub struct HashAggExecutor {
    pub aggs: RecExpr,
    pub group_keys: RecExpr,
    pub types: Vec<DataType>,
}

pub type Group
    
    pub async fn execute(self, child: BoxedExecutor) {
        let mut states = HashMap::<GroupKeys, AggValue>::new();

        #[for_await]
        for chunk in child {
            let chunk = chunk?;
            let keys_chunk = Evaluator::new(&self.group_keys).eval_list(&chunk)?;
            let args_chunk = Evaluator::new(&self.aggs).eval_list(&chunk)?;

            for i in 0..chunk.cardinality() {
                let keys = keys_chunk.row(i).values().collect();
                let states = states
                    .entry(keys)
                    .or_insert_with(|| Evaluator::new(&self.aggs).init_agg_states());
                Evaluator::new(&self.aggs).agg_list_append(states, args_chunk.row(i).values());
            }
        }

        let mut batches = IterChunks::chunks(states.into_iter(), PROCESSING_WINDOW_SIZE);
        while let Some(batch) = batches.next() {
            let mut builder = DataChunkBuilder::new(&self.types, PROCESSING_WINDOW_SIZE);
            for (key, aggs) in batch {
                if let Some(chunk) = builder.push_row(aggs.into_iter().chain(key.into_iter())) {
                    yield chunk;
                }
            }
            if let Some(chunk) = builder.take() {
                yield chunk;
            }
        }
    }