Implement Debug for EncodeWide

[thaliaarchi]

Since std::os::windows::ffi::EncodeWide is reexported from std::sys_common::wtf8::EncodeWide, which has #![allow(missing_debug_implementations)] in the parent module, it does not implement Debug. Implement it akin to core::str::Chars.

The only question is how to format each WTF-16 code unit. We can't format it like char, because \u escape sequences for surrogate halves are invalid syntax in Rust. It would be nice to format them as hex integers, but I am not aware of other instances of that pattern for Debug in std. Settle for decimal.

This becomes insta-stable.

r? libs-api

[bjorn3]

We can't format it like char, because \u escape sequences for surrogate halves are invalid syntax in Rust.

Even if rust doesn't accept \u for surrogate halves, we can still format them as \u. Debug isn't guaranteed to be valid rust source code anyway.

[thaliaarchi]

Here are the options, as I see them. I think formatting them as chars when not surrogates is the most readable for most texts. Rust style seems to lean towards uppercase hex.

1. EncodeWide([97, 233, 32, 55357, 55357, 56489]): decimal
2. EncodeWide([0x61, 0xE9, 0x20, 0xD83D, 0xD83D, 0xDCA9]): hex, zero-pad min 2, upper
3. EncodeWide([0x61, 0xe9, 0x20, 0xd83d, 0xd83d, 0xdca9]): hex, zero-pad min 2, lower
4. EncodeWide([0x0061, 0x00E9, 0x0020, 0xD83D, 0xD83D, 0xDCA9]): hex, zero-pad min 4, upper
5. EncodeWide([0x0061, 0x00e9, 0x0020, 0xd83d, 0xd83d, 0xdca9]): hex, zero-pad min 4, lower
6. EncodeWide(['a', 'é', ' ', '\u{D83D}', '\u{D83D}', '\u{DCA9}']): pseudo-char, escaped surrogates, upper
7. EncodeWide(['a', 'é', ' ', '\u{d83d}', '\u{d83d}', '\u{dca9}']): pseudo-char, escaped surrogates, lower