gen/build/src/target.rs

use std::env;
use std::ffi::OsStr;
use std::path::{Path, PathBuf};

pub(crate) enum TargetDir {
    Path(PathBuf),
    Unknown,
}

pub(crate) fn find_target_dir(out_dir: &Path) -> TargetDir {
    if let Some(target_dir) = env::var_os("CARGO_TARGET_DIR") {
        let target_dir = PathBuf::from(target_dir);
        if target_dir.is_absolute() {
            return TargetDir::Path(target_dir);
        } else {
            return TargetDir::Unknown;
        };
    }

    // fs::canonicalize on Windows produces UNC paths which cl.exe is unable to
    // handle in includes.
    // https://github.com/rust-lang/rust/issues/42869
    // https://github.com/alexcrichton/cc-rs/issues/169
    let mut also_try_canonical = cfg!(not(windows));

    let mut dir = out_dir.to_owned();
    loop {
        if dir.join(".rustc_info.json").exists()
            || dir.join("CACHEDIR.TAG").exists()
            || dir.file_name() == Some(OsStr::new("target"))
                && dir
                    .parent()
                    .map_or(false, |parent| parent.join("Cargo.toml").exists())
        {
            return TargetDir::Path(dir);
        }
        if dir.pop() {
            continue;
        }
        if also_try_canonical {
            if let Ok(canonical_dir) = out_dir.canonicalize() {
                dir = canonical_dir;
                also_try_canonical = false;
                continue;
            }
        }
        return TargetDir::Unknown;
    }
}