How do I generate a text file during compile time and include its content in the output?

Question

I'm trying to do almost the same as How to create a static string at compile time.

build.rs

use std::{env};
use std::path::Path;
use std::io::{Write, BufWriter};
use std::fs::File;

fn main() {
    let out_dir = env::var("OUT_DIR").unwrap();
    let dest_path = Path::new(&out_dir).join("file_path.txt");
    let mut f = BufWriter::new(File::create(&dest_path).unwrap());

    let long_string = dest_path.display();
    write!(f, "{}", long_string).unwrap();
}

main.rs

fn main() {

    static LONG_STRING: &'static str = include_str!("file_path.txt");
    println!("{}", LONG_STRING);
}

Upon cargo build I'm getting the error:

error: couldn't read src\file_path.txt: The system cannot find the file specified. (os error 2)
 --> src\main.rs:3:40
  |
3 |     static LONG_STRING: &'static str = include_str!("file_path.txt");
  |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I can see that the file is generated at

X:\source\github\rust-build-script-example\target\debug\build\rust-build-script-example-f2a03ef7abfd6b23\out\file_path.txt

1. What is the environment variable I have to use instead of OUT_DIR in order to get the file_path.txt to be output to the src directory?
2. If #1 is not possible, then how do I include_str! the generated file in the above directory without hardcoding it in code (since the path seems to have a randomly generated partial rust-build-script-example-f2a03ef7abfd6b23 in it)

My GitHub repository

Answer 1

The trick was

concat!(env!("OUT_DIR"), "/file_path.txt")

I changed my main.rs as follows and it worked.

fn main() {

    static LONG_STRING: &'static str = include_str!(concat!(env!("OUT_DIR"), "/file_path.txt"));

    println!("{}", LONG_STRING);
}

The following crates.io documentation helped

http://doc.crates.io/build-script.html

https://doc.rust-lang.org/cargo/reference/environment-variables.html