From d566b5db9bacd68c696d456a6d18569a50e7cb58 Mon Sep 17 00:00:00 2001
From: Matthew Zeitlin <37011898+mzeitlin11@users.noreply.github.com>
Date: Sat, 8 Feb 2025 16:51:04 -0500
Subject: [PATCH] Implement Extend<AsciiChar> for String

---
 library/alloc/src/string.rs           | 26 ++++++++++++++++++++++++++
 library/coretests/tests/ascii_char.rs | 12 ++++++++++++
 library/coretests/tests/lib.rs        |  1 +
 3 files changed, 39 insertions(+)

diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index b29f740ef0f2a..154da69107884 100644
--- a/library/alloc/src/string.rs
+++ b/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
diff --git a/library/coretests/tests/ascii_char.rs b/library/coretests/tests/ascii_char.rs
index 75b5fd4b9e61d..f5a15a9469f3f 100644
--- a/library/coretests/tests/ascii_char.rs
+++ b/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"));
+}
diff --git a/library/coretests/tests/lib.rs b/library/coretests/tests/lib.rs
index f1bbed3de3017..03527f237c151 100644
--- a/library/coretests/tests/lib.rs
+++ b/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)]