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: traits.rs
    path of file: ./repos/rust-analyzer/crates/syntax/src/ast
    
    the code of the file until where you have to start completion: //! Various traits that are implemented by ast nodes.
//!
//! The implementations are usually trivial, and live in generated.rs
use either::Either;

use crate::{
    ast::{self, support, AstChildren, AstNode, AstToken},
    syntax_node::SyntaxElemen
    
    pub fn doc_comment_text(self) -> Option<String> {
        let docs = itertools::Itertools::join(
            &mut self.filter_map(|comment| comment.doc_comment().map(ToOwned::to_owned)),
            "\n",
        );
        if docs.is_empty() {
            None
        } else {
            Some(docs)
        }
    }