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-rw-r--r--library/alloc/src/string.rs85
1 files changed, 57 insertions, 28 deletions
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 9236f5cb8d1..9a161d057db 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -1043,7 +1043,7 @@ impl String {
     #[inline]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
     pub const fn into_bytes(self) -> Vec<u8> {
         self.vec
@@ -1062,7 +1062,7 @@ impl String {
     #[must_use]
     #[stable(feature = "string_as_str", since = "1.7.0")]
     #[rustc_diagnostic_item = "string_as_str"]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     pub const fn as_str(&self) -> &str {
         // SAFETY: String contents are stipulated to be valid UTF-8, invalid contents are an error
         // at construction.
@@ -1085,7 +1085,7 @@ impl String {
     #[must_use]
     #[stable(feature = "string_as_str", since = "1.7.0")]
     #[rustc_diagnostic_item = "string_as_mut_str"]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     pub const fn as_mut_str(&mut self) -> &mut str {
         // SAFETY: String contents are stipulated to be valid UTF-8, invalid contents are an error
         // at construction.
@@ -1134,7 +1134,7 @@ impl String {
     /// assert_eq!(string, "abcdecdeabecde");
     /// ```
     #[cfg(not(no_global_oom_handling))]
-    #[stable(feature = "string_extend_from_within", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "string_extend_from_within", since = "1.87.0")]
     pub fn extend_from_within<R>(&mut self, src: R)
     where
         R: RangeBounds<usize>,
@@ -1159,7 +1159,7 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     pub const fn capacity(&self) -> usize {
         self.vec.capacity()
     }
@@ -1401,11 +1401,14 @@ impl String {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn push(&mut self, ch: char) {
-        match ch.len_utf8() {
-            1 => self.vec.push(ch as u8),
-            _ => {
-                self.vec.extend_from_slice(ch.encode_utf8(&mut [0; char::MAX_LEN_UTF8]).as_bytes())
-            }
+        let len = self.len();
+        let ch_len = ch.len_utf8();
+        self.reserve(ch_len);
+
+        // SAFETY: Just reserved capacity for at least the length needed to encode `ch`.
+        unsafe {
+            core::char::encode_utf8_raw_unchecked(ch as u32, self.vec.as_mut_ptr().add(self.len()));
+            self.vec.set_len(len + ch_len);
         }
     }
 
@@ -1425,7 +1428,7 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     pub const fn as_bytes(&self) -> &[u8] {
         self.vec.as_slice()
     }
@@ -1702,24 +1705,31 @@ impl String {
     #[rustc_confusables("set")]
     pub fn insert(&mut self, idx: usize, ch: char) {
         assert!(self.is_char_boundary(idx));
-        let mut bits = [0; char::MAX_LEN_UTF8];
-        let bits = ch.encode_utf8(&mut bits).as_bytes();
 
+        let len = self.len();
+        let ch_len = ch.len_utf8();
+        self.reserve(ch_len);
+
+        // SAFETY: Move the bytes starting from `idx` to their new location `ch_len`
+        // bytes ahead. This is safe because sufficient capacity was reserved, and `idx`
+        // is a char boundary.
         unsafe {
-            self.insert_bytes(idx, bits);
+            ptr::copy(
+                self.vec.as_ptr().add(idx),
+                self.vec.as_mut_ptr().add(idx + ch_len),
+                len - idx,
+            );
         }
-    }
 
-    #[cfg(not(no_global_oom_handling))]
-    unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
-        let len = self.len();
-        let amt = bytes.len();
-        self.vec.reserve(amt);
+        // SAFETY: Encode the character into the vacated region if `idx != len`,
+        // or into the uninitialized spare capacity otherwise.
+        unsafe {
+            core::char::encode_utf8_raw_unchecked(ch as u32, self.vec.as_mut_ptr().add(idx));
+        }
 
+        // SAFETY: Update the length to include the newly added bytes.
         unsafe {
-            ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
-            ptr::copy_nonoverlapping(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
-            self.vec.set_len(len + amt);
+            self.vec.set_len(len + ch_len);
         }
     }
 
@@ -1749,8 +1759,27 @@ impl String {
     pub fn insert_str(&mut self, idx: usize, string: &str) {
         assert!(self.is_char_boundary(idx));
 
+        let len = self.len();
+        let amt = string.len();
+        self.reserve(amt);
+
+        // SAFETY: Move the bytes starting from `idx` to their new location `amt` bytes
+        // ahead. This is safe because sufficient capacity was just reserved, and `idx`
+        // is a char boundary.
+        unsafe {
+            ptr::copy(self.vec.as_ptr().add(idx), self.vec.as_mut_ptr().add(idx + amt), len - idx);
+        }
+
+        // SAFETY: Copy the new string slice into the vacated region if `idx != len`,
+        // or into the uninitialized spare capacity otherwise. The borrow checker
+        // ensures that the source and destination do not overlap.
+        unsafe {
+            ptr::copy_nonoverlapping(string.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
+        }
+
+        // SAFETY: Update the length to include the newly added bytes.
         unsafe {
-            self.insert_bytes(idx, string.as_bytes());
+            self.vec.set_len(len + amt);
         }
     }
 
@@ -1779,7 +1808,7 @@ impl String {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     pub const unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
         &mut self.vec
     }
@@ -1801,7 +1830,7 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     #[rustc_confusables("length", "size")]
     pub const fn len(&self) -> usize {
         self.vec.len()
@@ -1821,7 +1850,7 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "const_vec_string_slice", since = "1.87.0")]
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
@@ -3140,7 +3169,7 @@ impl From<String> for Vec<u8> {
     }
 }
 
-#[stable(feature = "try_from_vec_u8_for_string", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "try_from_vec_u8_for_string", since = "1.87.0")]
 impl TryFrom<Vec<u8>> for String {
     type Error = FromUtf8Error;
     /// Converts the given [`Vec<u8>`] into a  [`String`] if it contains valid UTF-8 data.
generated by cgit-pink 1.4.1-3-g733a5 (git 2.37.1) at 2026-09-11 21:14:21 +0000