Auto merge of #30916 - steveklabnik:rollup, r=steveklabnik

- Successful merges: #30712, #30895, #30902, #30903, #30909, #30910, #30911, #30912, #30914
- Failed merges:

9 files changed, 76 insertions, 101 deletions

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c3851dcc8f1..e864172e813 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -174,7 +174,7 @@ labels to triage issues:
 * Yellow, **A**-prefixed labels state which **area** of the project an issue
   relates to.
 
-* Magenta, **B**-prefixed labels identify bugs which **belong** elsewhere.
+* Magenta, **B**-prefixed labels identify bugs which are **blockers**.
 
 * Green, **E**-prefixed labels explain the level of **experience** necessary
   to fix the issue.
diff --git a/src/doc/book/SUMMARY.md b/src/doc/book/SUMMARY.md
index 3df791fd51b..fe5e1c3990c 100644
--- a/src/doc/book/SUMMARY.md
+++ b/src/doc/book/SUMMARY.md
@@ -51,6 +51,7 @@
     * [FFI](ffi.md)
     * [Borrow and AsRef](borrow-and-asref.md)
     * [Release Channels](release-channels.md)
+    * [Using Rust without the standard library](using-rust-without-the-standard-library.md)
 * [Nightly Rust](nightly-rust.md)
     * [Compiler Plugins](compiler-plugins.md)
     * [Inline Assembly](inline-assembly.md)
diff --git a/src/doc/book/error-handling.md b/src/doc/book/error-handling.md
index 1556caaf993..9b1d16170b9 100644
--- a/src/doc/book/error-handling.md
+++ b/src/doc/book/error-handling.md
@@ -1795,6 +1795,10 @@ To convert this to proper error handling, we need to do the following:
 Let's try it:
 
 ```rust,ignore
+use std::error::Error;
+
+// The rest of the code before this is unchanged
+
 fn search<P: AsRef<Path>>
          (file_path: P, city: &str)
          -> Result<Vec<PopulationCount>, Box<Error+Send+Sync>> {
@@ -1903,8 +1907,13 @@ let city = if !matches.free.is_empty() {
 	return;
 };
 
-for pop in search(&data_file, &city) {
-	println!("{}, {}: {:?}", pop.city, pop.country, pop.count);
+match search(&data_file, &city) {
+    Ok(pops) => {
+        for pop in pops {
+            println!("{}, {}: {:?}", pop.city, pop.country, pop.count);
+        }
+    }
+    Err(err) => println!("{}", err)
 }
 ...
 ```
@@ -1927,6 +1936,10 @@ that it is generic on some type parameter `R` that satisfies
 `io::Read`. Another way is to use trait objects:
 
 ```rust,ignore
+use std::io;
+
+// The rest of the code before this is unchanged
+
 fn search<P: AsRef<Path>>
          (file_path: &Option<P>, city: &str)
          -> Result<Vec<PopulationCount>, Box<Error+Send+Sync>> {
diff --git a/src/doc/book/no-stdlib.md b/src/doc/book/no-stdlib.md
index 0b7eec72c91..65beaed2fc7 100644
--- a/src/doc/book/no-stdlib.md
+++ b/src/doc/book/no-stdlib.md
@@ -1,8 +1,15 @@
 % No stdlib
 
-By default, `std` is linked to every Rust crate. In some contexts,
-this is undesirable, and can be avoided with the `#![no_std]`
-attribute attached to the crate.
+Rust’s standard library provides a lot of useful functionality, but assumes
+support for various features of its host system: threads, networking, heap
+allocation, and others. There are systems that do not have these features,
+however, and Rust can work with those too! To do so, we tell Rust that we
+don’t want to use the standard library via an attribute: `#![no_std]`.
+
+> Note: This feature is technically stable, but there are some caveats. For
+> one, you can build a `#![no_std]` _library_ on stable, but not a _binary_.
+> For details on libraries without the standard library, see [the chapter on
+> `#![no_std]`](using-rust-without-the-standard-library.html)
 
 Obviously there's more to life than just libraries: one can use
 `#[no_std]` with an executable, controlling the entry point is
@@ -77,89 +84,3 @@ personality function (see the
 information), but crates which do not trigger a panic can be assured
 that this function is never called. The second function, `panic_fmt`, is
 also used by the failure mechanisms of the compiler.
-
-## Using libcore
-
-> **Note**: the core library's structure is unstable, and it is recommended to
-> use the standard library instead wherever possible.
-
-With the above techniques, we've got a bare-metal executable running some Rust
-code. There is a good deal of functionality provided by the standard library,
-however, that is necessary to be productive in Rust. If the standard library is
-not sufficient, then [libcore](../core/index.html) is designed to be used
-instead.
-
-The core library has very few dependencies and is much more portable than the
-standard library itself. Additionally, the core library has most of the
-necessary functionality for writing idiomatic and effective Rust code. When
-using `#![no_std]`, Rust will automatically inject the `core` crate, like
-we do for `std` when we’re using it.
-
-As an example, here is a program that will calculate the dot product of two
-vectors provided from C, using idiomatic Rust practices.
-
-```rust
-# #![feature(libc)]
-#![feature(lang_items)]
-#![feature(start)]
-#![feature(raw)]
-#![no_std]
-
-extern crate libc;
-
-use core::mem;
-
-#[no_mangle]
-pub extern fn dot_product(a: *const u32, a_len: u32,
-                          b: *const u32, b_len: u32) -> u32 {
-    use core::raw::Slice;
-
-    // Convert the provided arrays into Rust slices.
-    // The core::raw module guarantees that the Slice
-    // structure has the same memory layout as a &[T]
-    // slice.
-    //
-    // This is an unsafe operation because the compiler
-    // cannot tell the pointers are valid.
-    let (a_slice, b_slice): (&[u32], &[u32]) = unsafe {
-        mem::transmute((
-            Slice { data: a, len: a_len as usize },
-            Slice { data: b, len: b_len as usize },
-        ))
-    };
-
-    // Iterate over the slices, collecting the result
-    let mut ret = 0;
-    for (i, j) in a_slice.iter().zip(b_slice.iter()) {
-        ret += (*i) * (*j);
-    }
-    return ret;
-}
-
-#[lang = "panic_fmt"]
-extern fn panic_fmt(args: &core::fmt::Arguments,
-                    file: &str,
-                    line: u32) -> ! {
-    loop {}
-}
-
-#[lang = "eh_personality"] extern fn eh_personality() {}
-# #[start] fn start(argc: isize, argv: *const *const u8) -> isize { 0 }
-# #[lang = "eh_unwind_resume"] extern fn rust_eh_unwind_resume() {}
-# #[no_mangle] pub extern fn rust_eh_register_frames () {}
-# #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
-# fn main() {}
-```
-
-Note that there is one lang item here whose signature differs from the examples
-above, `panic_fmt`. This must be defined by consumers of libcore because the
-core library declares panics, but it does not define it. The `panic_fmt`
-lang item is this crate's definition of panic, and it must be guaranteed to
-never return.
-
-As can be seen in this example, the core library is intended to provide the
-power of Rust in all circumstances, regardless of platform requirements. Further
-libraries, such as liballoc, add functionality to libcore which make other
-platform-specific assumptions, but continue to be more portable than the
-standard library itself.
-
diff --git a/src/doc/book/the-stack-and-the-heap.md b/src/doc/book/the-stack-and-the-heap.md
index 3be4096e971..a7b6faccd8d 100644
--- a/src/doc/book/the-stack-and-the-heap.md
+++ b/src/doc/book/the-stack-and-the-heap.md
@@ -185,7 +185,7 @@ After `italic()` is over, its frame is deallocated, leaving only `bold()` and
 | **3**   | **c**|**1**  |
 | **2**   | **b**|**100**|
 | **1**   | **a**| **5** |
-| 0       | x    | 42    | 
+| 0       | x    | 42    |
 
 And then `bold()` ends, leaving only `main()`:
 
@@ -554,8 +554,8 @@ Managing the memory for the stack is trivial: The machine
 increments or decrements a single value, the so-called “stack pointer”.
 Managing memory for the heap is non-trivial: heap-allocated memory is freed at
 arbitrary points, and each block of heap-allocated memory can be of arbitrary
-size, the memory manager must generally work much harder to identify memory for
-reuse.
+size, so the memory manager must generally work much harder to
+identify memory for reuse.
 
 If you’d like to dive into this topic in greater detail, [this paper][wilson]
 is a great introduction.
@@ -579,4 +579,3 @@ comes at the cost of either significant runtime support (e.g. in the form of a
 garbage collector) or significant programmer effort (in the form of explicit
 memory management calls that require verification not provided by the Rust
 compiler).
-
diff --git a/src/doc/book/using-rust-without-the-standard-library.md b/src/doc/book/using-rust-without-the-standard-library.md
new file mode 100644
index 00000000000..59182e1a4ef
--- /dev/null
+++ b/src/doc/book/using-rust-without-the-standard-library.md
@@ -0,0 +1,41 @@
+% Using Rust Without the Standard Library
+
+Rust’s standard library provides a lot of useful functionality, but assumes
+support for various features of its host system: threads, networking, heap
+allocation, and others. There are systems that do not have these features,
+however, and Rust can work with those too! To do so, we tell Rust that we
+don’t want to use the standard library via an attribute: `#![no_std]`.
+
+> Note: This feature is technically stable, but there are some caveats. For
+> one, you can build a `#![no_std]` _library_ on stable, but not a _binary_.
+> For details on binaries without the standard library, see [the nightly
+> chapter on `#![no_std]`](no-stdlib.html)
+
+To use `#![no_std]`, add a it to your crate root:
+
+```rust
+#![no_std]
+
+fn plus_one(x: i32) -> i32 {
+    x + 1
+}
+```
+
+Much of the functionality that’s exposed in the standard library is also
+available via the [`core` crate](../core/). When we’re using the standard
+library, Rust automatically brings `std` into scope, allowing you to use
+its features without an explicit import. By the same token, when using
+`!#[no_std]`, Rust will bring `core` into scope for you, as well as [its
+prelude](../core/prelude/v1/). This means that a lot of code will Just Work:
+
+```rust
+#![no_std]
+
+fn may_fail(failure: bool) -> Result<(), &'static str> {
+    if failure {
+        Err("this didn’t work!")
+    } else {
+        Ok(())
+    }
+}
+```
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index efc28be92a4..be140469eb6 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -222,12 +222,12 @@ impl<T: ?Sized> Drop for IntermediateBox<T> {
 }
 
 impl<T> Box<T> {
-    /// Allocates memory on the heap and then moves `x` into it.
+    /// Allocates memory on the heap and then places `x` into it.
     ///
     /// # Examples
     ///
     /// ```
-    /// let x = Box::new(5);
+    /// let five = Box::new(5);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline(always)]
@@ -266,7 +266,7 @@ impl<T: ?Sized> Box<T> {
     /// # Examples
     ///
     /// ```
-    /// let seventeen = Box::new(17u32);
+    /// let seventeen = Box::new(17);
     /// let raw = Box::into_raw(seventeen);
     /// let boxed_again = unsafe { Box::from_raw(raw) };
     /// ```
diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index ee6e708ea32..fb6dac40798 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -130,7 +130,7 @@ pub fn size_of<T>() -> usize {
     unsafe { intrinsics::size_of::<T>() }
 }
 
-/// Returns the size of the type that `val` points to in bytes.
+/// Returns the size of the given value in bytes.
 ///
 /// # Examples
 ///
diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index 259f0d390b4..7f57d6dc650 100644
--- a/src/libstd/num/f32.rs
+++ b/src/libstd/num/f32.rs
@@ -62,7 +62,7 @@ mod cmath {
         pub fn hypotf(x: c_float, y: c_float) -> c_float;
     }
 
-    // See the comments in `core::float::Float::floor` for why MSVC is special
+    // See the comments in the `floor` function for why MSVC is special
     // here.
     #[cfg(not(target_env = "msvc"))]
     extern {