Auto merge of #40889 - frewsxcv:rollup, r=frewsxcv

Rollup of 5 pull requests

- Successful merges: #40682, #40731, #40783, #40838, #40864
- Failed merges:

src/libcollections/str.rs

@@ -10,9 +10,28 @@
 
 //! Unicode string slices.
 //!
+//! The `&str` type is one of the two main string types, the other being `String`.
+//! Unlike its `String` counterpart, its contents are borrowed.
+//!
+//! # Basic Usage
+//!
+//! A basic string declaration of `&str` type:
+//!
+//! ```
+//! let hello_world = "Hello, World!";
+//! ```
+//!
+//! Here we have declared a string literal, also known as a string slice.
+//! String literals have a static lifetime, which means the string `hello_world`
+//! is guaranteed to be valid for the duration of the entire program.
+//! We can explicitly specify `hello_world`'s lifetime as well:
+//!
+//! ```
+//! let hello_world: &'static str = "Hello, world!";
+//! ```
+//!
 //! *[See also the `str` primitive type](../../std/primitive.str.html).*
 
-
 #![stable(feature = "rust1", since = "1.0.0")]
 
 // Many of the usings in this module are only used in the test configuration.

src/libcollections/vec.rs

@@ -1563,7 +1563,7 @@ impl<T> ops::DerefMut for Vec<T> {
 impl<T> FromIterator<T> for Vec<T> {
     #[inline]
     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
-        <Self as SpecExtend<_, _>>::from_iter(iter.into_iter())
+        <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
     }
 }
 
@@ -1631,7 +1631,7 @@ impl<'a, T> IntoIterator for &'a mut Vec<T> {
 impl<T> Extend<T> for Vec<T> {
     #[inline]
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
-        self.spec_extend(iter.into_iter())
+        <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
     }
 }
 
@@ -1662,7 +1662,7 @@ impl<T, I> SpecExtend<T, I> for Vec<T>
                 vector
             }
         };
-        vector.spec_extend(iterator);
+        <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
         vector
     }
 
@@ -1674,7 +1674,7 @@ impl<T, I> SpecExtend<T, I> for Vec<T>
 impl<T, I> SpecExtend<T, I> for Vec<T>
     where I: TrustedLen<Item=T>,
 {
-    fn from_iter(iterator: I) -> Self {
+    default fn from_iter(iterator: I) -> Self {
         let mut vector = Vec::new();
         vector.spec_extend(iterator);
         vector
@@ -1706,6 +1706,27 @@ impl<T, I> SpecExtend<T, I> for Vec<T>
     }
 }
 
+impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
+    fn from_iter(iterator: IntoIter<T>) -> Self {
+        // A common case is passing a vector into a function which immediately
+        // re-collects into a vector. We can short circuit this if the IntoIter
+        // has not been advanced at all.
+        if *iterator.buf == iterator.ptr as *mut T {
+            unsafe {
+                let vec = Vec::from_raw_parts(*iterator.buf as *mut T,
+                                              iterator.len(),
+                                              iterator.cap);
+                mem::forget(iterator);
+                vec
+            }
+        } else {
+            let mut vector = Vec::new();
+            vector.spec_extend(iterator);
+            vector
+        }
+    }
+}
+
 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
     where I: Iterator<Item=&'a T>,
           T: Clone,

src/libcollectionstest/vec.rs

@@ -680,3 +680,19 @@ fn test_placement_panic() {
     let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { vec.place_back() <- mkpanic(); }));
     assert_eq!(vec.len(), 3);
 }
+
+#[test]
+fn from_into_inner() {
+    let vec = vec![1, 2, 3];
+    let ptr = vec.as_ptr();
+    let vec = vec.into_iter().collect::<Vec<_>>();
+    assert_eq!(vec, [1, 2, 3]);
+    assert_eq!(vec.as_ptr(), ptr);
+
+    let ptr = &vec[1] as *const _;
+    let mut it = vec.into_iter();
+    it.next().unwrap();
+    let vec = it.collect::<Vec<_>>();
+    assert_eq!(vec, [2, 3]);
+    assert!(ptr != vec.as_ptr());
+}

src/libstd/io/cursor.rs

@@ -89,6 +89,10 @@ pub struct Cursor<T> {
 impl<T> Cursor<T> {
     /// Creates a new cursor wrapping the provided underlying I/O object.
     ///
+    /// Cursor initial position is `0` even if underlying object (e.
+    /// g. `Vec`) is not empty. So writing to cursor starts with
+    /// overwriting `Vec` content, not with appending to it.
+    ///
     /// # Examples
     ///
     /// ```