惯用地扩展 Rust Path 中的波浪号 [英] Expand tilde in Rust Path idiomatically

问题描述

有时，例如在读取某个配置文件时，您会读取用户输入的文件路径，而无需通过 shell(例如，您得到 ~/test).

Sometimes, for instance when reading some configuration file, you read a file path entered by the user without going through the shell (for instance, you get ~/test).

由于下面的 Option 2 没有写入用户主目录中的测试文件，我想知道是否有比 Option 1 更惯用的东西.

As Option 2 below doesn’t write to test file in user home directory, I’m wondering if there is something more idiomatic than Option 1.

use std::env::var;
use std::fs::File;
use std::io::prelude::*;
use std::path::Path;

fn write_to(path: &Path) {
    let mut f = File::create(path).unwrap();
    f.write_all("Hi".as_bytes()).unwrap();
}

fn main() {
    // Option 1
    let from_env = format!("{}/test", var("HOME").unwrap());
    let with_var = Path::new(&from_env);
    // Create $HOME/test
    write_to(with_var);

    // Option 2
    let with_tilde = Path::new("~/test");
    // Create the test file in current directory, provided a directory ./~ exists
    write_to(with_tilde);
}

注意:此处使用 unwrap() 以保持示例简短.生产代码中应该有一些错误处理.

Note: unwrap() is used here to keep the example short. There should be some error handling in production code.

推荐答案

1. 最惯用的方法是使用现有的 crate，在本例中为 shellexpand (github、crates.io) 似乎可以满足您的需求:>

1. The most idiomatic way would be to just use an existing crate, in this case shellexpand (github, crates.io) seems to do what you want:

extern crate shellexpand; // 1.0.0

#[test]
fn test_shellexpand() {
    let home = std::env::var("HOME").unwrap();
    assert_eq!(shellexpand::tilde("~/foo"), format!("{}/foo", home));
}

或者，您可以尝试使用 dirs (crates.io).这是草图:

extern crate dirs; // 1.0.4

use std::path::{Path, PathBuf};

fn expand_tilde<P: AsRef<Path>>(path_user_input: P) -> Option<PathBuf> {
    let p = path_user_input.as_ref();
    if !p.starts_with("~") {
        return Some(p.to_path_buf());
    }
    if p == Path::new("~") {
        return dirs::home_dir();
    }
    dirs::home_dir().map(|mut h| {
        if h == Path::new("/") {
            // Corner case: `h` root directory;
            // don't prepend extra `/`, just drop the tilde.
            p.strip_prefix("~").unwrap().to_path_buf()
        } else {
            h.push(p.strip_prefix("~/").unwrap());
            h
        }
    })
}

使用示例:

#[test]
fn test_expand_tilde() {
    // Should work on your linux box during tests, would fail in stranger
    // environments!
    let home = std::env::var("HOME").unwrap();
    let projects = PathBuf::from(format!("{}/Projects", home));
    assert_eq!(expand_tilde("~/Projects"), Some(projects));
    assert_eq!(expand_tilde("/foo/bar"), Some("/foo/bar".into()));
    assert_eq!(
        expand_tilde("~alice/projects"),
        Some("~alice/projects".into())
    );
}

一些说明:

• P:AsRef 输入类型模仿标准图书馆.这就是为什么该方法接受所有 Path-like输入，例如 &str、&OsStr 和 &Path.
• Path::new 不分配任何东西，它指向与 &str 完全相同的字节.
• strip_prefix("~/").unwrap() 不应该在这里失败，因为我们检查了路径是否以 ~ 开头并且不仅仅是~.唯一的办法就是路径以 ~/ 开头(因为 starts_with已定义).

• The P: AsRef<Path> input type imitates what the standard library does. This is why the method accepts all Path-like inputs, like &str, &OsStr, and &Path.
• Path::new doesn't allocate anything, it points to exactly the same bytes as the &str.
• strip_prefix("~/").unwrap() should never fail here, because we checked that the path starts with ~ and is not just ~. The only way how this can be is that the path starts with ~/ (because of how starts_with is defined).

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