feat: add String::write_utf8_uninit (denoland#1019)

src/string.rs

@@ -1,6 +1,7 @@
 use std::convert::TryInto;
 use std::default::Default;
 use std::mem::forget;
+use std::mem::MaybeUninit;
 use std::slice;
 
 use crate::support::char;
@@ -264,6 +265,28 @@ impl String {
  buffer: &mut [u8],
  nchars_ref: Option<&mut usize>,
  options: WriteOptions,
+ ) -> usize {
+ unsafe {
+ // SAFETY:
+ // We assume that v8 will overwrite the buffer without de-initializing any byte in it.
+ // So the type casting of the buffer is safe.
+
+ let buffer = {
+ let len = buffer.len();
+ let data = buffer.as_mut_ptr().cast();
+ slice::from_raw_parts_mut(data, len)
+ };
+ self.write_utf8_uninit(scope, buffer, nchars_ref, options)
+ }
+ }
+
+ /// Writes the contents of the string to an external buffer, as UTF-8.
+ pub fn write_utf8_uninit(
+ &self,
+ scope: &mut Isolate,
+ buffer: &mut [MaybeUninit<u8>],
+ nchars_ref: Option<&mut usize>,
+ options: WriteOptions,
  ) -> usize {
  let mut nchars_ref_int: int = 0;
  let bytes = unsafe {