3 files changed, 37 insertions, 4 deletions
diff --git a/library/core/src/char/decode.rs b/library/core/src/char/decode.rs
index dc8ea66cc..11f1c30f6 100644
--- a/library/core/src/char/decode.rs
+++ b/library/core/src/char/decode.rs
@@ -1,6 +1,5 @@
 //! UTF-8 and UTF-16 decoding iterators
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 
@@ -124,7 +123,6 @@ impl fmt::Display for DecodeUtf16Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "decode_utf16", since = "1.9.0")]
 impl Error for DecodeUtf16Error {
     #[allow(deprecated)]
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index b7a63b7c6..bb8359936 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -597,9 +597,14 @@ impl char {
     /// Returns the number of 16-bit code units this `char` would need if
     /// encoded in UTF-16.
     ///
+    /// That number of code units is always either 1 or 2, for unicode scalar values in
+    /// the [basic multilingual plane] or [supplementary planes] respectively.
+    ///
     /// See the documentation for [`len_utf8()`] for more explanation of this
     /// concept. This function is a mirror, but for UTF-16 instead of UTF-8.
     ///
+    /// [basic multilingual plane]: http://www.unicode.org/glossary/#basic_multilingual_plane
+    /// [supplementary planes]: http://www.unicode.org/glossary/#supplementary_planes
     /// [`len_utf8()`]: #method.len_utf8
     ///
     /// # Examples
@@ -1444,6 +1449,38 @@ impl char {
         matches!(*self, '0'..='9')
     }
 
+    /// Checks if the value is an ASCII octal digit:
+    /// U+0030 '0' ..= U+0037 '7'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_ascii_octdigit)]
+    ///
+    /// let uppercase_a = 'A';
+    /// let a = 'a';
+    /// let zero = '0';
+    /// let seven = '7';
+    /// let nine = '9';
+    /// let percent = '%';
+    /// let lf = '\n';
+    ///
+    /// assert!(!uppercase_a.is_ascii_octdigit());
+    /// assert!(!a.is_ascii_octdigit());
+    /// assert!(zero.is_ascii_octdigit());
+    /// assert!(seven.is_ascii_octdigit());
+    /// assert!(!nine.is_ascii_octdigit());
+    /// assert!(!percent.is_ascii_octdigit());
+    /// assert!(!lf.is_ascii_octdigit());
+    /// ```
+    #[must_use]
+    #[unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[rustc_const_unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[inline]
+    pub const fn is_ascii_octdigit(&self) -> bool {
+        matches!(*self, '0'..='7')
+    }
+
     /// Checks if the value is an ASCII hexadecimal digit:
     ///
     /// - U+0030 '0' ..= U+0039 '9', or
diff --git a/library/core/src/char/mod.rs b/library/core/src/char/mod.rs
index 72d63ac4b..b34a71216 100644
--- a/library/core/src/char/mod.rs
+++ b/library/core/src/char/mod.rs
@@ -38,7 +38,6 @@ pub use self::methods::encode_utf16_raw;
 #[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
 pub use self::methods::encode_utf8_raw;
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt::{self, Write};
 use crate::iter::FusedIterator;
@@ -587,6 +586,5 @@ impl fmt::Display for TryFromCharError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "u8_from_char", since = "1.59.0")]
 impl Error for TryFromCharError {}