---

yaml
---
r: 273739
b: refs/heads/beta
c: 161c541
h: refs/heads/master
i:
  273737: 3492f59
  273735: 5c3d49e

Author: bors

[refs]

@@ -23,7 +23,7 @@ refs/tags/0.9: 36870b185fc5f5486636d4515f0e22677493f225
 refs/tags/0.10: ac33f2b15782272ae348dbd7b14b8257b2148b5a
 refs/tags/0.11.0: e1247cb1d0d681be034adb4b558b5a0c0d5720f9
 refs/tags/0.12.0: f0c419429ef30723ceaf6b42f9b5a2aeb5d2e2d1
-refs/heads/beta: f611e446624d288da7def4ad175405579c8bc310
+refs/heads/beta: 161c541afdd18423940e97c7a02b517b1f6d61be
 refs/tags/1.0.0-alpha: e42bd6d93a1d3433c486200587f8f9e12590a4d7
 refs/heads/tmp: e06d2ad9fcd5027bcaac5b08fc9aa39a49d0ecd3
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f

branches/beta/CONTRIBUTING.md

@@ -132,8 +132,8 @@ Some common make targets are:
 - `make check-stage1-std NO_REBUILD=1` - test the standard library without
   rebuilding the entire compiler
 - `make check TESTNAME=<substring-of-test-name>` - Run a matching set of tests.
-  - `TESTNAME` should be a substring of the tests to match against e.g. it could 
-    be the fully qualified test name, or just a part of it. 
+  - `TESTNAME` should be a substring of the tests to match against e.g. it could
+    be the fully qualified test name, or just a part of it.
     `TESTNAME=collections::hash::map::test_map::test_capacity_not_less_than_len`
     or `TESTNAME=test_capacity_not_less_than_len`.
 - `make check-stage1-rpass TESTNAME=<substring-of-test-name>` - Run a single

branches/beta/mk/target.mk

@@ -89,6 +89,7 @@ $$(TLIB$(1)_T_$(2)_H_$(3))/stamp.$(4): \
 		$$(RUSTFLAGS$(1)_$(4)_T_$(2)) \
 		--out-dir $$(@D) \
 		-C extra-filename=-$$(CFG_FILENAME_EXTRA) \
+		-C metadata=$$(CFG_FILENAME_EXTRA) \
 		$$<
 	@touch -r $$@.start_time $$@ && rm $$@.start_time
 	$$(call LIST_ALL_OLD_GLOB_MATCHES, \

branches/beta/src/compiletest/runtest.rs

@@ -727,8 +727,11 @@ fn run_debuginfo_lldb_test(config: &Config, props: &TestProps, testpaths: &TestP
     script_str.push_str("type category enable Rust\n");
 
     // Set breakpoints on every line that contains the string "#break"
+    let source_file_name = testpaths.file.file_name().unwrap().to_string_lossy();
     for line in &breakpoint_lines {
-        script_str.push_str(&format!("breakpoint set --line {}\n", line));
+        script_str.push_str(&format!("breakpoint set --file '{}' --line {}\n",
+                                     source_file_name,
+                                     line));
     }
 
     // Append the other commands

branches/beta/src/doc/book/casting-between-types.md

@@ -17,12 +17,12 @@ function result.
 The most common case of coercion is removing mutability from a reference:
 
  * `&mut T` to `&T`
- 
+
 An analogous conversion is to remove mutability from a
 [raw pointer](raw-pointers.md):
 
  * `*mut T` to `*const T`
- 
+
 References can also be coerced to raw pointers:
 
  * `&T` to `*const T`
@@ -32,7 +32,7 @@ References can also be coerced to raw pointers:
 Custom coercions may be defined using [`Deref`](deref-coercions.md).
 
 Coercion is transitive.
- 
+
 # `as`
 
 The `as` keyword does safe casting:
@@ -64,7 +64,7 @@ A cast `e as U` is also valid in any of the following cases:
     and `U` is an integer type; *enum-cast*
  * `e` has type `bool` or `char` and `U` is an integer type; *prim-int-cast*
  * `e` has type `u8` and `U` is `char`; *u8-char-cast*
- 
+
 For example
 
 ```rust
@@ -98,9 +98,9 @@ The semantics of numeric casts are:
 
 [float-int]: https://github.com/rust-lang/rust/issues/10184
 [float-float]: https://github.com/rust-lang/rust/issues/15536
- 
+
 ## Pointer casts
- 
+
 Perhaps surprisingly, it is safe to cast [raw pointers](raw-pointers.md) to and
 from integers, and to cast between pointers to different types subject to
 some constraints. It is only unsafe to dereference the pointer:
@@ -114,7 +114,7 @@ let b = a as u32;
 
 * `e` has type `*T`, `U` has type `*U_0`, and either `U_0: Sized` or
   `unsize_kind(T) == unsize_kind(U_0)`; a *ptr-ptr-cast*
-  
+
 * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
 
 * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*

branches/beta/src/doc/book/closures.md

@@ -502,5 +502,5 @@ assert_eq!(6, answer);
 ```
 
 By making the inner closure a `move Fn`, we create a new stack frame for our
-closure. By `Box`ing it up, we’ve given it a known size, and allowing it to
+closure. By `Box`ing it up, we’ve given it a known size, allowing it to
 escape our stack frame.

branches/beta/src/doc/book/concurrency.md

@@ -94,6 +94,54 @@ fn main() {
 }
 ```
 
+As closures can capture variables from their environment, we can also try to
+bring some data into the other thread:
+
+```rust,ignore
+use std::thread;
+
+fn main() {
+    let x = 1;
+    thread::spawn(|| {
+        println!("x is {}", x);
+    });
+}
+```
+
+However, this gives us an error:
+
+```text
+5:19: 7:6 error: closure may outlive the current function, but it
+                 borrows `x`, which is owned by the current function
+...
+5:19: 7:6 help: to force the closure to take ownership of `x` (and any other referenced variables),
+          use the `move` keyword, as shown:
+      thread::spawn(move || {
+          println!("x is {}", x);
+      });
+```
+
+This is because by default closures capture variables by reference, and thus the
+closure only captures a _reference to `x`_. This is a problem, because the
+thread may outlive the scope of `x`, leading to a dangling pointer.
+
+To fix this, we use a `move` closure as mentioned in the error message. `move`
+closures are explained in depth [here](closures.html#move-closures); basically
+they move variables from their environment into themselves. This means that `x`
+is now owned by the closure, and cannot be used in `main()` after the call to
+`spawn()`.
+
+```rust
+use std::thread;
+
+fn main() {
+    let x = 1;
+    thread::spawn(move || {
+        println!("x is {}", x);
+    });
+}
+```
+
 Many languages have the ability to execute threads, but it's wildly unsafe.
 There are entire books about how to prevent errors that occur from shared
 mutable state. Rust helps out with its type system here as well, by preventing
@@ -145,23 +193,64 @@ This gives us an error:
 ```
 
 Rust knows this wouldn't be safe! If we had a reference to `data` in each
-thread, and the thread takes ownership of the reference, we'd have three
-owners!
+thread, and the thread takes ownership of the reference, we'd have three owners!
+`data` gets moved out of `main` in the first call to `spawn()`, so subsequent
+calls in the loop cannot use this variable.
+
+So, we need some type that lets us have more than one owning reference to a
+value. Usually, we'd use `Rc<T>` for this, which is a reference counted type
+that provides shared ownership. It has some runtime bookkeeping that keeps track
+of the number of references to it, hence the "reference count" part of its name.
+
+Calling `clone()` on an `Rc<T>` will return a new owned reference and bump the
+internal reference count. We create one of these for each thread:
 
-So, we need some type that lets us have more than one reference to a value and
-that we can share between threads, that is it must implement `Sync`.
 
-We'll use `Arc<T>`, Rust's standard atomic reference count type, which
-wraps a value up with some extra runtime bookkeeping which allows us to
-share the ownership of the value between multiple references at the same time.
+```ignore
+use std::thread;
+use std::time::Duration;
+use std::rc::Rc;
 
-The bookkeeping consists of a count of how many of these references exist to
-the value, hence the reference count part of the name.
+fn main() {
+    let mut data = Rc::new(vec![1, 2, 3]);
+
+    for i in 0..3 {
+        // create a new owned reference
+        let data_ref = data.clone();
+
+        // use it in a thread
+        thread::spawn(move || {
+            data_ref[i] += 1;
+        });
+    }
+
+    thread::sleep(Duration::from_millis(50));
+}
+```
+
+This won't work, however, and will give us the error:
+
+```text
+13:9: 13:22 error: the trait `core::marker::Send` is not
+            implemented for the type `alloc::rc::Rc<collections::vec::Vec<i32>>`
+...
+13:9: 13:22 note: `alloc::rc::Rc<collections::vec::Vec<i32>>`
+            cannot be sent between threads safely
+```
+
+As the error message mentions, `Rc` cannot be sent between threads safely. This
+is because the internal reference count is not maintained in a thread safe
+matter and can have a data race.
+
+To solve this, we'll use `Arc<T>`, Rust's standard atomic reference count type.
 
 The Atomic part means `Arc<T>` can safely be accessed from multiple threads.
 To do this the compiler guarantees that mutations of the internal count use
 indivisible operations which can't have data races.
 
+In essence, `Arc<T>` is a type that lets us share ownership of data _across
+threads_.
+
 
 ```ignore
 use std::thread;
@@ -182,7 +271,7 @@ fn main() {
 }
 ```
 
-We now call `clone()` on our `Arc<T>`, which increases the internal count.
+Similarly to last time, we use `clone()` to create a new owned handle.
 This handle is then moved into the new thread.
 
 And... still gives us an error.
@@ -193,14 +282,21 @@ And... still gives us an error.
                              ^~~~
 ```
 
-`Arc<T>` assumes one more property about its contents to ensure that it is safe
-to share across threads: it assumes its contents are `Sync`. This is true for
-our value if it's immutable, but we want to be able to mutate it, so we need
-something else to persuade the borrow checker we know what we're doing.
+`Arc<T>` by default has immutable contents. It allows the _sharing_ of data
+between threads, but shared mutable data is unsafe and when threads are
+involved can cause data races!
+
 
-It looks like we need some type that allows us to safely mutate a shared value,
-for example a type that can ensure only one thread at a time is able to
-mutate the value inside it at any one time.
+Usually when we wish to make something in an immutable position mutable, we use
+`Cell<T>` or `RefCell<T>` which allow safe mutation via runtime checks or
+otherwise (see also: [Choosing Your Guarantees](choosing-your-guarantees.html)).
+However, similar to `Rc`, these are not thread safe. If we try using these, we
+will get an error about these types not being `Sync`, and the code will fail to
+compile.
+
+It looks like we need some type that allows us to safely mutate a shared value
+across threads, for example a type that can ensure only one thread at a time is
+able to mutate the value inside it at any one time.
 
 For that, we can use the `Mutex<T>` type!
 
@@ -229,7 +325,17 @@ fn main() {
 Note that the value of `i` is bound (copied) to the closure and not shared
 among the threads.
 
-Also note that [`lock`](../std/sync/struct.Mutex.html#method.lock) method of
+We're "locking" the mutex here. A mutex (short for "mutual exclusion"), as
+mentioned, only allows one thread at a time to access a value. When we wish to
+access the value, we use `lock()` on it. This will "lock" the mutex, and no
+other thread will be able to lock it (and hence, do anything with the value)
+until we're done with it. If a thread attempts to lock a mutex which is already
+locked, it will wait until the other thread releases the lock.
+
+The lock "release" here is implicit; when the result of the lock (in this case,
+`data`) goes out of scope, the lock is automatically released.
+
+Note that [`lock`](../std/sync/struct.Mutex.html#method.lock) method of
 [`Mutex`](../std/sync/struct.Mutex.html) has this signature:
 
 ```ignore

branches/beta/src/doc/book/const-and-static.md

@@ -72,7 +72,7 @@ a [`Drop`][drop] implementation.
 # Initializing
 
 Both `const` and `static` have requirements for giving them a value. They must
-be given a value that’s a constant expression. In other words, you cannot use 
+be given a value that’s a constant expression. In other words, you cannot use
 the result of a function call or anything similarly complex or at runtime.
 
 # Which construct should I use?

branches/beta/src/doc/book/getting-started.md

@@ -417,7 +417,7 @@ first. This leaves the top-level project directory (in this case,
 to your code. In this way, using Cargo helps you keep your projects nice and
 tidy. There's a place for everything, and everything is in its place.
 
-Now, copy *main.rs* to the *src* directory, and delete the compiled file you
+Now, move *main.rs* into the *src* directory, and delete the compiled file you
 created with `rustc`. As usual, replace `main` with `main.exe` if you're on
 Windows.
 

branches/beta/src/doc/book/macros.md

@@ -337,8 +337,8 @@ fn main() {
 }
 ```
 
-Instead you need to pass the variable name into the invocation, so it’s tagged
-with the right syntax context.
+Instead you need to pass the variable name into the invocation, so that it’s
+tagged with the right syntax context.
 
 ```rust
 macro_rules! foo {
@@ -470,7 +470,7 @@ which syntactic form it matches.
 * `ty`: a type. Examples: `i32`; `Vec<(char, String)>`; `&T`.
 * `pat`: a pattern. Examples: `Some(t)`; `(17, 'a')`; `_`.
 * `stmt`: a single statement. Example: `let x = 3`.
-* `block`: a brace-delimited sequence of statements. Example:
+* `block`: a brace-delimited sequence of statements and optionally an expression. Example:
   `{ log(error, "hi"); return 12; }`.
 * `item`: an [item][item]. Examples: `fn foo() { }`; `struct Bar;`.
 * `meta`: a "meta item", as found in attributes. Example: `cfg(target_os = "windows")`.

branches/beta/src/doc/book/match.md

@@ -28,8 +28,8 @@ patterns][patterns] that covers all the patterns that are possible here.
 
 [patterns]: patterns.html
 
-One of the many advantages of `match` is it enforces ‘exhaustiveness checking’. 
-For example if we remove the last arm with the underscore `_`, the compiler will 
+One of the many advantages of `match` is it enforces ‘exhaustiveness checking’.
+For example if we remove the last arm with the underscore `_`, the compiler will
 give us an error:
 
 ```text
@@ -58,7 +58,7 @@ let number = match x {
 };
 ```
 
-Sometimes it’s a nice way of converting something from one type to another; in 
+Sometimes it’s a nice way of converting something from one type to another; in
 this example the integers are converted to `String`.
 
 # Matching on enums
@@ -90,7 +90,7 @@ fn process_message(msg: Message) {
 
 Again, the Rust compiler checks exhaustiveness, so it demands that you
 have a match arm for every variant of the enum. If you leave one off, it
-will give you a compile-time error unless you use `_` or provide all possible 
+will give you a compile-time error unless you use `_` or provide all possible
 arms.
 
 Unlike the previous uses of `match`, you can’t use the normal `if`

branches/beta/src/doc/book/ownership.md

@@ -124,7 +124,7 @@ special annotation here, it’s the default thing that Rust does.
 ## The details
 
 The reason that we cannot use a binding after we’ve moved it is subtle, but
-important. 
+important.
 
 When we write code like this:
 
@@ -148,7 +148,7 @@ The first line allocates memory for the vector object `v` on the stack like
 it does for `x` above. But in addition to that it also allocates some memory
 on the [heap][sh] for the actual data (`[1, 2, 3]`). Rust copies the address
 of this heap allocation to an internal pointer, which is part of the vector
-object placed on the stack (let's call it the data pointer). 
+object placed on the stack (let's call it the data pointer).
 
 It is worth pointing out (even at the risk of stating the obvious) that the
 vector object and its data live in separate memory regions instead of being a
@@ -163,7 +163,7 @@ does not create a copy of the heap allocation containing the actual data.
 Which means that there would be two pointers to the contents of the vector
 both pointing to the same memory allocation on the heap. It would violate
 Rust’s safety guarantees by introducing a data race if one could access both
-`v` and `v2` at the same time. 
+`v` and `v2` at the same time.
 
 For example if we truncated the vector to just two elements through `v2`:
 

branches/beta/src/doc/book/primitive-types.md

@@ -164,7 +164,7 @@ copying. For example, you might want to reference only one line of a file read
 into memory. By nature, a slice is not created directly, but from an existing
 variable binding. Slices have a defined length, can be mutable or immutable.
 
-Internally, slices are represented as a pointer to the beginning of the data 
+Internally, slices are represented as a pointer to the beginning of the data
 and a length.
 
 ## Slicing syntax

branches/beta/src/doc/book/vectors.md

@@ -116,7 +116,7 @@ for i in v {
 ```
 
 Note: You cannot use the vector again once you have iterated by taking ownership of the vector.
-You can iterate the vector multiple times by taking a reference to the vector whilst iterating. 
+You can iterate the vector multiple times by taking a reference to the vector whilst iterating.
 For example, the following code does not compile.
 
 ```rust,ignore