Rollup merge of #120580 - HTGAzureX1212:HTGAzureX1212/issue-45795, r=m-ou-se

Add `MAX_LEN_UTF8` and `MAX_LEN_UTF16` Constants

This pull request adds the `MAX_LEN_UTF8` and `MAX_LEN_UTF16` constants as per #45795, gated behind the `char_max_len` feature.

The constants are currently applied in the `alloc`, `core` and `std` libraries.

4 files changed, 10 insertions, 7 deletions

diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index 8e307f57cf9..1a266f71965 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -1,5 +1,6 @@
 use rand::RngCore;
 
+use crate::char::MAX_LEN_UTF8;
 use crate::fs::{self, File, FileTimes, OpenOptions};
 use crate::io::prelude::*;
 use crate::io::{BorrowedBuf, ErrorKind, SeekFrom};
@@ -155,7 +156,7 @@ fn file_test_io_non_positional_read() {
 #[test]
 fn file_test_io_seek_and_tell_smoke_test() {
     let message = "ten-four";
-    let mut read_mem = [0; 4];
+    let mut read_mem = [0; MAX_LEN_UTF8];
     let set_cursor = 4 as u64;
     let tell_pos_pre_read;
     let tell_pos_post_read;
@@ -356,7 +357,7 @@ fn file_test_io_seek_shakedown() {
     let chunk_one: &str = "qwer";
     let chunk_two: &str = "asdf";
     let chunk_three: &str = "zxcv";
-    let mut read_mem = [0; 4];
+    let mut read_mem = [0; MAX_LEN_UTF8];
     let tmpdir = tmpdir();
     let filename = &tmpdir.join("file_rt_io_file_test_seek_shakedown.txt");
     {
@@ -621,7 +622,7 @@ fn file_test_directoryinfo_readdir() {
         check!(w.write(msg));
     }
     let files = check!(fs::read_dir(dir));
-    let mut mem = [0; 4];
+    let mut mem = [0; MAX_LEN_UTF8];
     for f in files {
         let f = f.unwrap().path();
         {
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 750116c6269..0661b3d770e 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -284,6 +284,7 @@
 #![feature(cfg_sanitizer_cfi)]
 #![feature(cfg_target_thread_local)]
 #![feature(cfi_encoding)]
+#![feature(char_max_len)]
 #![feature(concat_idents)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
diff --git a/library/std/src/sys/pal/windows/stdio.rs b/library/std/src/sys/pal/windows/stdio.rs
index fd3f559ba19..1b245991aa7 100644
--- a/library/std/src/sys/pal/windows/stdio.rs
+++ b/library/std/src/sys/pal/windows/stdio.rs
@@ -1,5 +1,6 @@
 #![unstable(issue = "none", feature = "windows_stdio")]
 
+use core::char::MAX_LEN_UTF8;
 use core::str::utf8_char_width;
 
 use super::api::{self, WinError};
@@ -426,7 +427,7 @@ fn utf16_to_utf8(utf16: &[u16], utf8: &mut [u8]) -> io::Result<usize> {
 
 impl IncompleteUtf8 {
     pub const fn new() -> IncompleteUtf8 {
-        IncompleteUtf8 { bytes: [0; 4], len: 0 }
+        IncompleteUtf8 { bytes: [0; MAX_LEN_UTF8], len: 0 }
     }
 }
 
diff --git a/library/std/src/sys_common/wtf8.rs b/library/std/src/sys_common/wtf8.rs
index 6c60d901ee9..a7704a65fc9 100644
--- a/library/std/src/sys_common/wtf8.rs
+++ b/library/std/src/sys_common/wtf8.rs
@@ -18,7 +18,7 @@
 #[cfg(test)]
 mod tests;
 
-use core::char::{encode_utf8_raw, encode_utf16_raw};
+use core::char::{MAX_LEN_UTF8, MAX_LEN_UTF16, encode_utf8_raw, encode_utf16_raw};
 use core::clone::CloneToUninit;
 use core::str::next_code_point;
 
@@ -240,7 +240,7 @@ impl Wtf8Buf {
     /// Copied from String::push
     /// This does **not** include the WTF-8 concatenation check or `is_known_utf8` check.
     fn push_code_point_unchecked(&mut self, code_point: CodePoint) {
-        let mut bytes = [0; 4];
+        let mut bytes = [0; MAX_LEN_UTF8];
         let bytes = encode_utf8_raw(code_point.value, &mut bytes);
         self.bytes.extend_from_slice(bytes)
     }
@@ -1001,7 +1001,7 @@ impl<'a> Iterator for EncodeWide<'a> {
             return Some(tmp);
         }
 
-        let mut buf = [0; 2];
+        let mut buf = [0; MAX_LEN_UTF16];
         self.code_points.next().map(|code_point| {
             let n = encode_utf16_raw(code_point.value, &mut buf).len();
             if n == 2 {