Auto merge of #26844 - steveklabnik:rollup, r=steveklabnik

- Successful merges: #26599, #26761, #26807, #26809, #26825, #26827, #26828, #26832, #26834, #26835
- Failed merges: #26796

Author: bors

CONTRIBUTING.md

@@ -83,6 +83,21 @@ feature. We use the 'fork and pull' model described there.
 
 Please make pull requests against the `master` branch.
 
+Compiling all of `make check` can take a while. When testing your pull request,
+consider using one of the more specialized `make` targets to cut down on the
+amount of time you have to wait. You need to have built the compiler at least
+once before running these will work, but that’s only one full build rather than
+one each time.
+
+    $ make -j8 rustc-stage1 && make check-stage1
+
+is one such example, which builds just `rustc`, and then runs the tests. If
+you’re adding something to the standard library, try
+
+    $ make -j8 check-stage1-std NO_REBUILD=1
+
+This will not rebuild the compiler, but will run the tests.
+
 All pull requests are reviewed by another person. We have a bot,
 @rust-highfive, that will automatically assign a random person to review your
 request.
@@ -108,6 +123,10 @@ will run all the tests on every platform we support. If it all works out,
 
 [merge-queue]: http://buildbot.rust-lang.org/homu/queue/rust
 
+Speaking of tests, Rust has a comprehensive test suite. More information about
+it can be found
+[here](https://github.com/rust-lang/rust-wiki-backup/blob/master/Note-testsuite.md).
+
 ## Writing Documentation
 
 Documentation improvements are very welcome. The source of `doc.rust-lang.org`

src/doc/reference.md

@@ -2515,9 +2515,8 @@ Here are some examples:
 #### Moved and copied types
 
 When a [local variable](#variables) is used as an
-[rvalue](#lvalues,-rvalues-and-temporaries) the variable will either be moved
-or copied, depending on its type. All values whose type implements `Copy` are
-copied, all others are moved.
+[rvalue](#lvalues,-rvalues-and-temporaries), the variable will be copied
+if its type implements `Copy`. All others are moved.
 
 ### Literal expressions
 
@@ -2882,7 +2881,6 @@ operand.
 ```
 # let mut x = 0;
 # let y = 0;
-
 x = y;
 ```
 

src/doc/trpl/ffi.md

@@ -533,19 +533,10 @@ attribute turns off Rust's name mangling, so that it is easier to link to.
 
 # FFI and panics
 
-It’s important to be mindful of `panic!`s when working with FFI. This code,
-when called from C, will `abort`:
-
-```rust
-#[no_mangle]
-pub extern fn oh_no() -> ! {
-    panic!("Oops!");
-}
-# fn main() {}
-```
-
-If you’re writing code that may panic, you should run it in another thread,
-so that the panic doesn’t bubble up to C:
+It’s important to be mindful of `panic!`s when working with FFI. A `panic!`
+across an FFI boundary is undefined behavior. If you’re writing code that may
+panic, you should run it in another thread, so that the panic doesn’t bubble up
+to C:
 
 ```rust
 use std::thread;

src/doc/trpl/patterns.md

@@ -282,6 +282,38 @@ This ‘destructuring’ behavior works on any compound data type, like
 [tuples]: primitive-types.html#tuples
 [enums]: enums.html
 
+# Ignoring bindings
+
+You can use `_` in a pattern to disregard the value. For example, here’s a
+`match` against a `Result<T, E>`:
+
+```rust
+# let some_value: Result<i32, &'static str> = Err("There was an error");
+match some_value {
+    Ok(value) => println!("got a value: {}", value),
+    Err(_) => println!("an error occurred"),
+}
+```
+
+In the first arm, we bind the value inside the `Ok` variant to `value`. But
+in the `Err` arm, we use `_` to disregard the specific error, and just print
+a general error message.
+
+`_` is valid in any pattern that creates a binding. This can be useful to
+ignore parts of a larger structure:
+
+```rust
+fn coordinate() -> (i32, i32, i32) {
+    // generate and return some sort of triple tuple
+# (1, 2, 3)
+}
+
+let (x, _, z) = coordinate();
+```
+
+Here, we bind the first and last element of the tuple to `x` and `z`, but
+ignore the middle element.
+
 # Mix and Match
 
 Whew! That’s a lot of different ways to match things, and they can all be