News and compat annotation for #29153 (ncodeunits(::Char)).

Author: fredrikekre

NEWS.md

@@ -73,6 +73,7 @@ Standard library changes
   * `Base.@kwdef` can now be used for parametric structs, and for structs with supertypes ([#29316]).
   * `merge(::NamedTuple, ::NamedTuple...)` can now be used with more than 2 `NamedTuple`s ([#29259]).
   * `Future.copy!` has been moved to `Base` ([#29178]).
+  * New `ncodeunits(c::Char)` method as a fast equivalent to `ncodeunits(string(c))` ([#29153]).
 
 Compiler/Runtime improvements
 -----------------------------

base/char.jl

@@ -56,6 +56,10 @@ Char
 Return the number of code units required to encode a character as UTF-8.
 This is the number of bytes which will be printed if the character is written
 to an output stream, or `ncodeunits(string(c))` but computed efficiently.
+
+!!! compat "Julia 1.1"
+    This method requires at least Julia 1.1. In Julia 1.0 consider
+    using `ncodeunits(string(c))`.
 """
 ncodeunits(c::Char) = write(devnull, c) # this is surprisingly efficient