rust-analyzer/crates/tools/src/lib.rs

extern crate itertools;

use itertools::Itertools;

#[derive(Debug)]
pub struct Test {
    pub name: String,
    pub text: String,
}

pub fn collect_tests(s: &str) -> Vec<(usize, Test)> {
    let mut res = vec![];
    let prefix = "// ";
    let comment_blocks = s
        .lines()
        .map(str::trim_left)
        .enumerate()
        .group_by(|(_idx, line)| line.starts_with(prefix));

    'outer: for (is_comment, block) in comment_blocks.into_iter() {
        if !is_comment {
            continue;
        }
        let mut block = block.map(|(idx, line)| (idx, &line[prefix.len()..]));

        let (start_line, name) = loop {
            match block.next() {
                Some((idx, line)) if line.starts_with("test ") => {
                    break (idx, line["test ".len()..].to_string())
                }
                Some(_) => (),
                None => continue 'outer,
            }
        };
        let text: String = itertools::join(
            block.map(|(_, line)| line).chain(::std::iter::once("")),
            "\n",
        );
        assert!(!text.trim().is_empty() && text.ends_with("\n"));
        res.push((start_line, Test { name, text }))
    }
    res
}