fn main() {
    make_menagerie();
}

async fn make_menagerie() -> Vec<String> {
    vec![
        "monster".to_string(), // <=== repeat this line 1000 to 10000 times.
    ]
}

Build with cargo build. I'm using Rust 1.72 on aarch64-apple-darwin.

In addition to the slow compilation time, I also see large memory usage. With 2500 lines, my OS reported rustc as consuming 20GB.

Exploration

Different versions

There was no obvious correlation.

Different numbers of lines

This appears to show time is proportional to (number of lines)^2

String slices

Switching to returning a &'static str instead of String resulted in fast compilation (<250 ms).

Using a function

Creating a helper function and calling it inside of vec![] resulted in fast compilation (<250 ms).

fn make_string() -> String { "monster".to_string() }

Using another method

Switching to returning a usize instead of a String has reduced compilation time but still surprisingly slow (2.5 sec).

vec![
    "monster".len(),
]

Avoiding async fn

Removing async from make_menagerie has reduced compilation time (<750 ms)

Test case generation

For trying different things, I used two files

main.rs

fn main() {
    make_menagerie();
}

async fn make_menagerie() -> Vec<String> {
    include!("repeat.rs")
}

And to generate 2500 lines:

(echo 'vec!['; yes '"monster".to_string(),' | head -n 2500; echo ']') > src/repeat.rs