Rollup merge of rust-lang#136749 - mzeitlin11:extend-asciichar, r=scottmcm

Implement Extend<AsciiChar> for String

Implement `Extend<AsciiChar>` for `String` as suggested in rust-lang#110998 (comment). Also implements `Extend<&AsciiChar>` since there's an analogous impl for `Extend<&char>`, but happy to remove if not thought useful.

r? `@scottmcm`
since you requested it, but no pressure to review!

Author: jhpratt

library/alloc/src/string.rs

@@ -2442,6 +2442,32 @@ impl<'a> Extend<Cow<'a, str>> for String {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
+#[unstable(feature = "ascii_char", issue = "110998")]
+impl Extend<core::ascii::Char> for String {
+    fn extend<I: IntoIterator<Item = core::ascii::Char>>(&mut self, iter: I) {
+        self.vec.extend(iter.into_iter().map(|c| c.to_u8()));
+    }
+
+    #[inline]
+    fn extend_one(&mut self, c: core::ascii::Char) {
+        self.vec.push(c.to_u8());
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[unstable(feature = "ascii_char", issue = "110998")]
+impl<'a> Extend<&'a core::ascii::Char> for String {
+    fn extend<I: IntoIterator<Item = &'a core::ascii::Char>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned());
+    }
+
+    #[inline]
+    fn extend_one(&mut self, c: &'a core::ascii::Char) {
+        self.vec.push(c.to_u8());
+    }
+}
+
 /// A convenience impl that delegates to the impl for `&str`.
 ///
 /// # Examples

library/coretests/tests/ascii_char.rs

@@ -26,3 +26,15 @@ fn test_debug_control() {
         assert_eq!(want, format!("{chr:?}"), "byte: {byte}");
     }
 }
+
+/// Tests Extend implementation for ascii::Char.
+#[test]
+fn test_extend() {
+    let mut s = String::from("abc");
+    s.extend_one(Char::SmallD);
+    assert_eq!(s, String::from("abcd"));
+
+    let mut s = String::from("abc");
+    s.extend(Char::CapitalA..=Char::CapitalC);
+    assert_eq!(s, String::from("abcABC"));
+}

library/coretests/tests/lib.rs

@@ -27,6 +27,7 @@
 #![feature(duration_constructors)]
 #![feature(error_generic_member_access)]
 #![feature(exact_size_is_empty)]
+#![feature(extend_one)]
 #![feature(extern_types)]
 #![feature(float_minimum_maximum)]
 #![feature(flt2dec)]