Tracking issue for const char conversions

[est31]

This is a tracking issue for const char conversions. List of functions belonging to !#[feature(const_char_from_u32_unchecked)]:

impl char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

// Available through core::char and std::char
mod char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

List of functions belonging to stable #![feature(const_char_convert)]:

Details

impl char {
    pub const fn from_u32(self, i: u32) -> Option<char>;
    pub const fn from_digit(self, num: u32, radix: u32) -> Option<char>;
    pub const fn to_digit(self, radix: u32) -> Option<u32>;
}

// Available through core::char and std::char
mod char {
    pub const fn from_u32(i: u32) -> Option<char>;
    pub const fn from_digit(num: u32, radix: u32) -> Option<char>;
}

Steps:

• Introduced by Make char conversion functions unstably const #89258
• Partially stabilized by Stabilize const char convert #102470 , const_char_from_u32_unchecked is still unstable.
• Stabilization is probably blocked by const panicing. Edit: const panic is stable now!
• Stabilization is blocked by Option::unwrap const stability, which is blocked by Tracking issue for #![feature(const_precise_live_drops)] #73255.
• Stabilize const unchecked conversion from u32 to char #126958

[leonardo-m]

We could keep a percentage counter somewhere that tells how much of stdlib is areweconstyet :)

[Nugine]

Hi! Is there any plan of stabilization?

[est31]

@Nugine I've made a stabilization PR, let's see where this goes: #102470

[ChrisDenton]

Stabilization is blocked by #67441 const stability, which is blocked by #73255.

Could we not manually write out a match statement instead of using unwrap?

[est31]

I think the idea was that there should be no extra hacks done just to get things compatible with const fn, but I don't remember it fully any more.

[ChrisDenton]

I've opened #118979 to see what T-libs thinks about it.