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: change.rs
    path of file: ./repos/rust-analyzer/crates/hir-expand/src
    
    the code of the file until where you have to start completion: //! Defines a unit of change that can applied to the database to get the next
//! state. Changes are transactional.
use base_db::{
    salsa::Durability, CrateGraph, CrateId, FileChange, SourceDatabaseExt, SourceRoot,
    TargetLayoutLoadResult, Version,
};
use la_arena::RawIdx;
use span::FileId;
use triomphe::Arc;

use crate::{db::ExpandDatabase, proc_macro::ProcMacros};

#[derive(Debug, Default)]
pub struct ChangeWithProcMacros {
    pub source_change: FileChange,
    pub proc_macros: Option<ProcMacros>,
    pub toolchains: Option<Vec<Option<Version>>>,
    pub target_data_layouts: Option<Vec<TargetLayoutLoadResult>>,
}

impl
    
    pub fn apply(self, db: &mut (impl ExpandDatabase + SourceDatabaseExt)) {
        self.source_change.apply(db);
        if let Some(proc_macros) = self.proc_macros {
            db.set_proc_macros_with_durability(Arc::new(proc_macros), Durability::HIGH);
        }
        if let Some(target_data_layouts) = self.target_data_layouts {
            for (id, val) in target_data_layouts.into_iter().enumerate() {
                db.set_data_layout_with_durability(
                    CrateId::from_raw(RawIdx::from(id as u32)),
                    val,
                    Durability::HIGH,
                );
            }
        }
        if let Some(toolchains) = self.toolchains {
            for (id, val) in toolchains.into_iter().enumerate() {
                db.set_toolchain_with_durability(
                    CrateId::from_raw(RawIdx::from(id as u32)),
                    val,
                    Durability::HIGH,
                );
            }
        }
    }