Unreadable io::Error debug strings

[liigo]

While trying to open a non-existing file (on Windows 10, Chinese):

use std::fs::File;
fn main() {
    File::open("no-such-file.rs").unwrap();
}

It panicked with a message:

thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 2, message: "\u{7cfb}\u{7edf}\u{627e}\u{4e0d}\u{5230}\u{6307}\u{5b9a}\u{7684}\u{6587}\u{4ef6}\u{3002}" } }', ../src/libcore\result.rs:746
note: Run with `RUST_BACKTRACE=1` for a backtrace.

The OS native error message here is unreadable for human being.

The message ("\u{7cfb}\u{7edf}\u{627e}\u{4e0d}\u{5230}...") is the escaped result of "No such file or directory" in Chinese ("系统找不到指定的文件")。impl fmt::Debug for str do this escape.

I can read Chinese, which is my mother tongue, but I can't read \u{7cfb}....

Possible solutions:

• Don't use local language (Chinese here) OS error string, use English instead.
• Change impl fmt::Debug for str to not escape most Unicode chars. (breaking-change?)

---

fn main() {
    let s = "Hello δεΣ❤ 日月";
    println!("{}", s);   // prints "Hello δεΣ❤ 日月"
    println!("{:?}", s); // prints "Hello \u{3b4}\u{3b5}\u{3a3}\u{2764} \u{65e5}\u{6708}"
}

Run it on play.rust-lang.org

Is impl fmt::Debug for str really friendly enough for debug purpose? Is there possibility that we change its implementation as similar as impl fmt::Display for str?

[retep998]

I think printing escapes is very useful for debugging strings, since often consoles will be either incapable of displaying the character (the WIndows console is notorious for this), or it is something like the wrong kind of whitespace slipping in which can be really hard to notice otherwise. I feel any solution for this issue should be targeted at Debug for io::Error specifically and not strings in general.

[bluss]

I'd prefer to output printable characters as they are, escaping is inconvenient for everything that's not in English.

[liigo]

since often consoles will be either incapable of displaying the character (the WIndows console is notorious for this)

Which morden console don't support printing Unicode strings? Do you means that very old one? (Windows 10 console do its job perfectly.)

[retep998]

@liigo While the Windows console is capable of storing arbitrary unicode text, its unicode text rendering abilities are far more limited. It only displays unicode glyphs when the font supports it (it doesn't use font fallback) and it also doesn't work for anything outside the BMP, nor does it support combining characters. It's a simple wchar -> glyph mapping. Here is your chinese error string in the Windows 10 console:

Granted I can easily copy the text from the console and paste it into another program to view it, unless I choose a raster font for the console, in which case the Windows console actually limits itself to u8 instead of u16, completely ruining unicode and the ability to copy paste unicode text, and the only characters you can rely on are ascii.

[liigo]

Yes. It's the same when you println! something. I don't think we should implement println! to escape almost all unicode characters. If the (old) consoles can't display unicode properly, things should be changed to consoles.

[liigo]

Here is your chinese error string in the Windows 10 console:

For the specific issue, the os error string is returned at runtime by os as local language, I'm sure it has full support to be displayed properly by the os itself.

[liigo]

This issue is still exists in nightly. Could you reopen it? @brson @alexcrichton

@tbu- (the author of #34485)
cc #35068

---

pub fn main() {
    println!("{:?}", "In Chinese: 文件不存在");
    // still prints: "In Chinese: \u{6587}\u{4ef6}\u{4e0d}\u{5b58}\u{5728}"
    // expected: "In Chinese: 文件不存在"
}

[liigo]

Fixed in nightly by #37855. Many thans to @tbu- !