Auto merge of #52486 - kennytm:rollup, r=kennytm

Rollup of 13 pull requests

Successful merges:

 - #51628 (use checked write in `LineWriter` example)
 - #52116 (Handle array manually in str case conversion methods)
 - #52218 (Amend option.take examples)
 - #52418 (Do not use desugared ident when suggesting adding a type)
 - #52439 (Revert some changes from #51917 to fix custom libdir)
 - #52455 (Fix doc comment: use `?` instead of `.unwrap()`)
 - #52458 (rustc: Fix a suggestion for the `proc_macro` feature)
 - #52464 (Allow clippy to be installed with make install)
 - #52472 (rustc: Enable `use_extern_macros` in 2018 edition)
 - #52477 (Clarify short-circuiting behvaior of Iterator::zip.)
 - #52480 (Cleanup #24958)
 - #52487 (Don't build twice the sanitizers on Linux)
 - #52510 (rustdoc: remove FIXME about macro redirects)

Failed merges:

r? @ghost

1 files changed, 27 insertions, 2 deletions

diff --git a/src/liballoc/str.rs b/src/liballoc/str.rs
index bb99d0401d3..4d6434c378e 100644
--- a/src/liballoc/str.rs
+++ b/src/liballoc/str.rs
@@ -45,6 +45,7 @@ use core::str::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
 use core::mem;
 use core::ptr;
 use core::iter::FusedIterator;
+use core::unicode::conversions;
 
 use borrow::{Borrow, ToOwned};
 use boxed::Box;
@@ -369,7 +370,18 @@ impl str {
                 // See https://github.com/rust-lang/rust/issues/26035
                 map_uppercase_sigma(self, i, &mut s)
             } else {
-                s.extend(c.to_lowercase());
+                match conversions::to_lower(c) {
+                    [a, '\0', _] => s.push(a),
+                    [a, b, '\0'] => {
+                        s.push(a);
+                        s.push(b);
+                    }
+                    [a, b, c] => {
+                        s.push(a);
+                        s.push(b);
+                        s.push(c);
+                    }
+                }
             }
         }
         return s;
@@ -423,7 +435,20 @@ impl str {
     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
     pub fn to_uppercase(&self) -> String {
         let mut s = String::with_capacity(self.len());
-        s.extend(self.chars().flat_map(|c| c.to_uppercase()));
+        for c in self[..].chars() {
+            match conversions::to_upper(c) {
+                [a, '\0', _] => s.push(a),
+                [a, b, '\0'] => {
+                    s.push(a);
+                    s.push(b);
+                }
+                [a, b, c] => {
+                    s.push(a);
+                    s.push(b);
+                    s.push(c);
+                }
+            }
+        }
         return s;
     }