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Auto merge of #130511 - bjoernager:const-char-encode-utf8, r=dtolnay
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/).
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commit
f8192ba0d0
@ -672,8 +672,9 @@ impl char {
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/// 'ß'.encode_utf8(&mut b);
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/// ```
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#[stable(feature = "unicode_encode_char", since = "1.15.0")]
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#[rustc_const_unstable(feature = "const_char_encode_utf8", issue = "130512")]
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#[inline]
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pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
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pub const fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
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// SAFETY: `char` is not a surrogate, so this is valid UTF-8.
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unsafe { from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
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}
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@ -1735,14 +1736,11 @@ impl EscapeDebugExtArgs {
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#[inline]
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const fn len_utf8(code: u32) -> usize {
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if code < MAX_ONE_B {
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1
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} else if code < MAX_TWO_B {
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2
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} else if code < MAX_THREE_B {
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3
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} else {
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4
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match code {
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..MAX_ONE_B => 1,
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..MAX_TWO_B => 2,
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..MAX_THREE_B => 3,
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_ => 4,
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}
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}
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@ -1760,11 +1758,12 @@ const fn len_utf8(code: u32) -> usize {
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/// Panics if the buffer is not large enough.
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/// A buffer of length four is large enough to encode any `char`.
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#[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
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#[rustc_const_unstable(feature = "const_char_encode_utf8", issue = "130512")]
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#[doc(hidden)]
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#[inline]
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pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
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pub const fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
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let len = len_utf8(code);
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match (len, &mut dst[..]) {
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match (len, &mut *dst) {
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(1, [a, ..]) => {
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*a = code as u8;
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}
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@ -1783,14 +1782,11 @@ pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
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*c = (code >> 6 & 0x3F) as u8 | TAG_CONT;
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*d = (code & 0x3F) as u8 | TAG_CONT;
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}
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_ => panic!(
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"encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
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len,
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code,
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dst.len(),
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),
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// Note that we cannot format in constant expressions.
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_ => panic!("encode_utf8: buffer does not have enough bytes to encode code point"),
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};
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&mut dst[..len]
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// SAFETY: `<&mut [u8]>::as_mut_ptr` is guaranteed to return a valid pointer and `len` has been tested to be within bounds.
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unsafe { slice::from_raw_parts_mut(dst.as_mut_ptr(), len) }
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}
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/// Encodes a raw u32 value as UTF-16 into the provided `u16` buffer,
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@ -119,6 +119,7 @@
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#![feature(const_bigint_helper_methods)]
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#![feature(const_black_box)]
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#![feature(const_cell_into_inner)]
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#![feature(const_char_encode_utf8)]
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#![feature(const_eval_select)]
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#![feature(const_exact_div)]
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#![feature(const_float_classify)]
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