Auto merge of #28665 - steveklabnik:rollup, r=steveklabnik

- Successful merges: #28319, #28588, #28637, #28652, #28654, #28655
- Failed merges: #28621

Author: bors

src/doc/trpl/closures.md

@@ -411,8 +411,9 @@ fn factory() -> &(Fn(i32) -> i32) {
 ```
 
 Right. Because we have a reference, we need to give it a lifetime. But
-our `factory()` function takes no arguments, so elision doesn’t kick in
-here. What lifetime can we choose? `'static`:
+our `factory()` function takes no arguments, so
+[elision](lifetimes.html#lifetime-elision) doesn’t kick in here. Then what
+choices do we have? Try `'static`:
 
 ```rust,ignore
 fn factory() -> &'static (Fn(i32) -> i32) {
@@ -432,7 +433,7 @@ But we get another error:
 ```text
 error: mismatched types:
  expected `&'static core::ops::Fn(i32) -> i32`,
-    found `[closure <anon>:7:9: 7:20]`
+    found `[closure@<anon>:7:9: 7:20]`
 (expected &-ptr,
     found closure) [E0308]
          |x| x + num
@@ -441,21 +442,17 @@ error: mismatched types:
 ```
 
 This error is letting us know that we don’t have a `&'static Fn(i32) -> i32`,
-we have a `[closure <anon>:7:9: 7:20]`. Wait, what?
+we have a `[closure@<anon>:7:9: 7:20]`. Wait, what?
 
 Because each closure generates its own environment `struct` and implementation
 of `Fn` and friends, these types are anonymous. They exist just solely for
-this closure. So Rust shows them as `closure <anon>`, rather than some
+this closure. So Rust shows them as `closure@<anon>`, rather than some
 autogenerated name.
 
-But why doesn’t our closure implement `&'static Fn`? Well, as we discussed before,
-closures borrow their environment. And in this case, our environment is based
-on a stack-allocated `5`, the `num` variable binding. So the borrow has a lifetime
-of the stack frame. So if we returned this closure, the function call would be
-over, the stack frame would go away, and our closure is capturing an environment
-of garbage memory!
-
-So what to do? This _almost_ works:
+The error also points out that the return type is expected to be a reference,
+but what we are trying to return is not. Further, we cannot directly assign a
+`'static` lifetime to an object. So we'll take a different approach and return
+a "trait object" by `Box`ing up the `Fn`. This _almost_ works:
 
 ```rust,ignore
 fn factory() -> Box<Fn(i32) -> i32> {
@@ -471,7 +468,7 @@ assert_eq!(6, answer);
 # }
 ```
 
-We use a trait object, by `Box`ing up the `Fn`. There’s just one last problem:
+There’s just one last problem:
 
 ```text
 error: closure may outlive the current function, but it borrows `num`,
@@ -480,8 +477,12 @@ Box::new(|x| x + num)
          ^~~~~~~~~~~
 ```
 
-We still have a reference to the parent stack frame. With one last fix, we can
-make this work:
+Well, as we discussed before, closures borrow their environment. And in this
+case, our environment is based on a stack-allocated `5`, the `num` variable
+binding. So the borrow has a lifetime of the stack frame. So if we returned
+this closure, the function call would be over, the stack frame would go away,
+and our closure is capturing an environment of garbage memory! With one last
+fix, we can make this work:
 
 ```rust
 fn factory() -> Box<Fn(i32) -> i32> {

src/doc/trpl/lifetimes.md

@@ -349,9 +349,9 @@ fn frob<'a, 'b>(s: &'a str, t: &'b str) -> &str; // Expanded: Output lifetime is
 fn get_mut(&mut self) -> &mut T; // elided
 fn get_mut<'a>(&'a mut self) -> &'a mut T; // expanded
 
-fn args<T:ToCStr>(&mut self, args: &[T]) -> &mut Command // elided
-fn args<'a, 'b, T:ToCStr>(&'a mut self, args: &'b [T]) -> &'a mut Command // expanded
+fn args<T:ToCStr>(&mut self, args: &[T]) -> &mut Command; // elided
+fn args<'a, 'b, T:ToCStr>(&'a mut self, args: &'b [T]) -> &'a mut Command; // expanded
 
 fn new(buf: &mut [u8]) -> BufWriter; // elided
-fn new<'a>(buf: &'a mut [u8]) -> BufWriter<'a> // expanded
+fn new<'a>(buf: &'a mut [u8]) -> BufWriter<'a>; // expanded
 ```

src/libcore/mem.rs

@@ -434,6 +434,11 @@ pub fn replace<T>(dest: &mut T, mut src: T) -> T {
 /// While this does call the argument's implementation of `Drop`, it will not
 /// release any borrows, as borrows are based on lexical scope.
 ///
+/// This effectively does nothing for
+/// [types which implement `Copy`](../../book/ownership.html#copy-types),
+/// e.g. integers. Such values are copied and _then_ moved into the function,
+/// so the value persists after this function call.
+///
 /// # Examples
 ///
 /// Basic usage:
@@ -486,6 +491,21 @@ pub fn replace<T>(dest: &mut T, mut src: T) -> T {
 /// let borrow = x.borrow();
 /// println!("{}", *borrow);
 /// ```
+///
+/// Integers and other types implementing `Copy` are unaffected by `drop()`
+///
+/// ```
+/// #[derive(Copy, Clone)]
+/// struct Foo(u8);
+///
+/// let x = 1;
+/// let y = Foo(2);
+/// drop(x); // a copy of `x` is moved and dropped
+/// drop(y); // a copy of `y` is moved and dropped
+///
+/// println!("x: {}, y: {}", x, y.0); // still available
+/// ```
+///
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn drop<T>(_x: T) { }

src/libcore/slice.rs

@@ -1410,15 +1410,15 @@ impl<'a, T> ExactSizeIterator for ChunksMut<'a, T> {}
 // Free functions
 //
 
-/// Converts a pointer to A into a slice of length 1 (without copying).
+/// Converts a reference to A into a slice of length 1 (without copying).
 #[unstable(feature = "ref_slice", issue = "27774")]
 pub fn ref_slice<A>(s: &A) -> &[A] {
     unsafe {
         from_raw_parts(s, 1)
     }
 }
 
-/// Converts a pointer to A into a slice of length 1 (without copying).
+/// Converts a reference to A into a slice of length 1 (without copying).
 #[unstable(feature = "ref_slice", issue = "27774")]
 pub fn mut_ref_slice<A>(s: &mut A) -> &mut [A] {
     unsafe {

src/libcore/str/mod.rs

@@ -115,8 +115,8 @@ impl Utf8Error {
     /// Returns the index in the given string up to which valid UTF-8 was
     /// verified.
     ///
-    /// Starting at the index provided, but not necessarily at it precisely, an
-    /// invalid UTF-8 encoding sequence was found.
+    /// It is the maximum index such that `from_utf8(input[..index])`
+    /// would return `Some(_)`.
     #[unstable(feature = "utf8_error", reason = "method just added",
                issue = "27734")]
     pub fn valid_up_to(&self) -> usize { self.valid_up_to }

src/libstd/macros.rs

@@ -98,7 +98,7 @@ macro_rules! print {
     ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
 }
 
-/// Macro for printing to the standard output.
+/// Macro for printing to the standard output, with a newline.
 ///
 /// Use the `format!` syntax to write data to the standard output.
 /// See `std::fmt` for more information.