Added tests for Add<char> & AddAssign<char> for String.

Made previous code tidy friendly.

Author: Ruster-a11y

src/liballoc/string.rs

@@ -2072,7 +2072,8 @@ impl Add<&&String> for String {
 /// // `a` is moved and can no longer be used here.
 /// ```
 ///
-/// If you want to keep using the initial `String`, you can clone it and append to the clone instead:
+/// If you want to keep using the initial `String`, you can clone it and append to the
+/// clone instead:
 ///
 /// ```
 /// let a = String::from("hello world! ");

src/liballoc/tests/string.rs

@@ -195,8 +195,15 @@ fn test_add_assign() {
     assert_eq!(s.as_str(), "");
     s += "abc";
     assert_eq!(s.as_str(), "abc");
-    s += "ประเทศไทย中华Việt Nam";
-    assert_eq!(s.as_str(), "abcประเทศไทย中华Việt Nam");
+    s += "ประเทศไทย中华Việt Nam ";
+    assert_eq!(s.as_str(), "abcประเทศไทย中华Việt Nam ");
+
+    let s2 = "OPS ".to_string();
+    s += &s2;
+    assert_eq!(s.as_str(), "abcประเทศไทย中华Việt Nam OPS ");
+
+    s += '👋';
+    assert_eq!(s.as_str(), "abcประเทศไทย中华Việt Nam 👋");
 }
 
 #[test]
@@ -304,9 +311,10 @@ fn test_str_clear() {
 fn test_str_add() {
     let a = String::from("12345");
     let b = a + "2";
-    let b = b + "2";
-    assert_eq!(b.len(), 7);
-    assert_eq!(b, "1234522");
+    let b = b + "2 ";
+    let b = b + '👋';
+    assert_eq!(b.len(), 12);
+    assert_eq!(b, "1234522 👋");
 }
 
 #[test]

src/libsyntax/parse/parser/expr.rs

@@ -1084,7 +1084,8 @@ impl<'a> Parser<'a> {
                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix })
                         = next_token.kind {
                     if self.token.span.hi() == next_token.span.lo() {
-                        // FIXME: Should just be `&symbol.as_str()` but can't as of now due to Deref coercion
+                        // FIXME: Should just be `&symbol.as_str()` but can't as of now due to
+                        // Deref coercion.
                         // Issue: https://github.com/rust-lang/rust/issues/51916
                         let s = String::from("0.") + &symbol.as_str().get_str();
                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);

src/libsyntax_pos/symbol.rs

@@ -1129,9 +1129,8 @@ impl !Sync for SymbolStr {}
 /// - `&*ss` is a `&str`;
 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
 ///   function expecting a `&str`.
-/// 
-/// FIXME: This has no meaning anymore since the addition of implementations
-/// of `Add<char> for String`, `Add<&&str> for String`, and `Add<&&String> for String`.
+///
+/// FIXME: This has no meaning anymore since the addition of `impl Add<char> for String`.
 /// Due to the outstanding Deref coercion issue this Deref implementation gets ignored.
 /// Issue: https://github.com/rust-lang/rust/issues/51916
 impl std::ops::Deref for SymbolStr {