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Auto merge of #130511 - bjoernager:const-char-encode-utf8, r=dtolnay

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Support `char::encode_utf8` in const scenarios.

This PR implements [`rust-lang/rfcs#3696`](https://github.com/rust-lang/rfcs/pull/3696/).

This assumes [`const_slice_from_raw_parts_mut`](https://github.com/rust-lang/rust/issues/67456/).
This commit is contained in:
bors 2024-09-19 04:17:04 +00:00
parent df7f77811c fb475e4759
commit f8192ba0d0
2 changed files with 15 additions and 18 deletions
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32
library/core/src/char/methods.rs
View file

@ -672,8 +672,9 @@ pub const fn len_utf16(self) -> usize {
/// 'ß'.encode_utf8(&mut b);
/// ```
#[stable(feature = "unicode_encode_char", since = "1.15.0")]
#[rustc_const_unstable(feature = "const_char_encode_utf8", issue = "130512")]
#[inline]
pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
pub const fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
// SAFETY: `char` is not a surrogate, so this is valid UTF-8.
unsafe { from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
}
@ -1735,14 +1736,11 @@ impl EscapeDebugExtArgs {
#[inline]
const fn len_utf8(code: u32) -> usize {
if code < MAX_ONE_B {
1
} else if code < MAX_TWO_B {
2
} else if code < MAX_THREE_B {
3
} else {
4
match code {
..MAX_ONE_B => 1,
..MAX_TWO_B => 2,
..MAX_THREE_B => 3,
_ => 4,
}
}
@ -1760,11 +1758,12 @@ const fn len_utf8(code: u32) -> usize {
/// Panics if the buffer is not large enough.
/// A buffer of length four is large enough to encode any `char`.
#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
#[rustc_const_unstable(feature = "const_char_encode_utf8", issue = "130512")]
#[doc(hidden)]
#[inline]
pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
pub const fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
let len = len_utf8(code);
match (len, &mut dst[..]) {
match (len, &mut *dst) {
(1, [a, ..]) => {
*a = code as u8;
}
@ -1783,14 +1782,11 @@ pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
*c = (code >> 6 & 0x3F) as u8 | TAG_CONT;
*d = (code & 0x3F) as u8 | TAG_CONT;
}
_ => panic!(
"encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
len,
code,
dst.len(),
),
// Note that we cannot format in constant expressions.
_ => panic!("encode_utf8: buffer does not have enough bytes to encode code point"),
};
&mut dst[..len]
// SAFETY: `<&mut [u8]>::as_mut_ptr` is guaranteed to return a valid pointer and `len` has been tested to be within bounds.
unsafe { slice::from_raw_parts_mut(dst.as_mut_ptr(), len) }
}
/// Encodes a raw u32 value as UTF-16 into the provided `u16` buffer,

1
library/core/src/lib.rs
View file

@ -119,6 +119,7 @@
#![feature(const_bigint_helper_methods)]
#![feature(const_black_box)]
#![feature(const_cell_into_inner)]
#![feature(const_char_encode_utf8)]
#![feature(const_eval_select)]
#![feature(const_exact_div)]
#![feature(const_float_classify)]