Auto merge of #56557 - pietroalbini:rollup, r=pietroalbini

Rollup of 11 pull requests

Successful merges:

 - #56315 (Rustdoc inline macro reexport)
 - #56332 ([rustdoc] Specific crate search)
 - #56362 (Stabilise exhaustive integer patterns)
 - #56426 (libsyntax_pos: A few tweaks)
 - #56441 (rustbuild: Fix issues with compiler docs)
 - #56446 (pass the parameter environment to `traits::find_associated_item`)
 - #56500 (cleanup: remove static lifetimes from consts)
 - #56525 (Avoid extra copy and syscall in std::env::current_exe)
 - #56528 (Remove unused dependency (rustc_lint -> rustc_mir))
 - #56548 (Optimized string FromIterator + Extend impls)
 - #56553 (Don't print the profiling summary to stdout when -Zprofile-json is set)

Failed merges:

r? @ghost

1 files changed, 30 insertions, 19 deletions

diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index 662f8ae614f..006c602649b 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -577,7 +577,7 @@ impl String {
             return Cow::Borrowed("");
         };
 
-        const REPLACEMENT: &'static str = "\u{FFFD}";
+        const REPLACEMENT: &str = "\u{FFFD}";
 
         let mut res = String::with_capacity(v.len());
         res.push_str(first_valid);
@@ -1732,18 +1732,37 @@ impl<'a> FromIterator<&'a str> for String {
 #[stable(feature = "extend_string", since = "1.4.0")]
 impl FromIterator<String> for String {
     fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
-        let mut buf = String::new();
-        buf.extend(iter);
-        buf
+        let mut iterator = iter.into_iter();
+
+        // Because we're iterating over `String`s, we can avoid at least
+        // one allocation by getting the first string from the iterator
+        // and appending to it all the subsequent strings.
+        match iterator.next() {
+            None => String::new(),
+            Some(mut buf) => {
+                buf.extend(iterator);
+                buf
+            }
+        }
     }
 }
 
 #[stable(feature = "herd_cows", since = "1.19.0")]
 impl<'a> FromIterator<Cow<'a, str>> for String {
     fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
-        let mut buf = String::new();
-        buf.extend(iter);
-        buf
+        let mut iterator = iter.into_iter();
+
+        // Because we're iterating over CoWs, we can (potentially) avoid at least
+        // one allocation by getting the first item and appending to it all the
+        // subsequent items.
+        match iterator.next() {
+            None => String::new(),
+            Some(cow) => {
+                let mut buf = cow.into_owned();
+                buf.extend(iterator);
+                buf
+            }
+        }
     }
 }
 
@@ -1753,9 +1772,7 @@ impl Extend<char> for String {
         let iterator = iter.into_iter();
         let (lower_bound, _) = iterator.size_hint();
         self.reserve(lower_bound);
-        for ch in iterator {
-            self.push(ch)
-        }
+        iterator.for_each(move |c| self.push(c));
     }
 }
 
@@ -1769,27 +1786,21 @@ impl<'a> Extend<&'a char> for String {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Extend<&'a str> for String {
     fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
-        for s in iter {
-            self.push_str(s)
-        }
+        iter.into_iter().for_each(move |s| self.push_str(s));
     }
 }
 
 #[stable(feature = "extend_string", since = "1.4.0")]
 impl Extend<String> for String {
     fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
-        for s in iter {
-            self.push_str(&s)
-        }
+        iter.into_iter().for_each(move |s| self.push_str(&s));
     }
 }
 
 #[stable(feature = "herd_cows", since = "1.19.0")]
 impl<'a> Extend<Cow<'a, str>> for String {
     fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
-        for s in iter {
-            self.push_str(&s)
-        }
+        iter.into_iter().for_each(move |s| self.push_str(&s));
     }
 }