Version 1.17.0 (2017-04-27)

Language

The lifetime of statics and consts defaults to 'static. RFC 1623
Fields of structs may be initialized without duplicating the field/variable names. RFC 1682
Self may be included in the where clause of impls. RFC 1647
When coercing to an unsized type lifetimes must be equal. That is, there is no subtyping between T and U when T: Unsize<U>. For example, coercing &mut [&'a X; N] to &mut [&'b X] requires 'a be equal to 'b. Soundness fix.
Values passed to the indexing operator, [], automatically coerce
Static variables may contain references to other statics

Compiler

Exit quickly on only --emit dep-info
Make -C relocation-model more correctly determine whether the linker creates a position-independent executable
Add -C overflow-checks to directly control whether integer overflow panics
The rustc type checker now checks items on demand instead of in a single in-order pass. This is mostly an internal refactoring in support of future work, including incremental type checking, but also resolves RFC 1647, allowing Self to appear in impl where clauses.
Optimize vtable loads
Turn off vectorization for Emscripten targets
Provide suggestions for unknown macros imported with use
Fix ICEs in path resolution
Strip exception handling code on Emscripten when panic=abort
Add clearer error message using &str + &str

Stabilized APIs

Libraries

BTreeMap and BTreeSet can iterate over ranges
Cell can store non-Copy types. RFC 1651
String implements FromIterator<&char>
Box implements a number of new conversions: From<Box<str>> for String, From<Box<[T]>> for Vec<T>, From<Box<CStr>> for CString, From<Box<OsStr>> for OsString, From<Box<Path>> for PathBuf, Into<Box<str>> for String, Into<Box<[T]>> for Vec<T>, Into<Box<CStr>> for CString, Into<Box<OsStr>> for OsString, Into<Box<Path>> for PathBuf, Default for Box<str>, Default for Box<CStr>, Default for Box<OsStr>, From<&CStr> for Box<CStr>, From<&OsStr> for Box<OsStr>, From<&Path> for Box<Path>
ffi::FromBytesWithNulError implements Error and Display
Specialize PartialOrd<A> for [A] where A: Ord
Slightly optimize slice::sort
Add ToString trait specialization for Cow<'a, str> and String
Box<[T]> implements From<&[T]> where T: Copy, Box<str> implements From<&str>
IpAddr implements From for various arrays. SocketAddr implements From<(I, u16)> where I: Into<IpAddr>
format! estimates the needed capacity before writing a string
Support unprivileged symlink creation in Windows
PathBuf implements Default
Implement PartialEq<[A]> for VecDeque<A>
HashMap resizes adaptively to guard against DOS attacks and poor hash functions.

Cargo

Misc

Documentation is rendered with mdbook instead of the obsolete, in-tree rustbook
The "Unstable Book" documents nightly-only features
Improve the style of the sidebar in rustdoc output
Configure build correctly on 64-bit CPU's with the armhf ABI
Fix MSP430 breakage due to i128
Preliminary Solaris/SPARCv9 support
rustc is linked statically on Windows MSVC targets, allowing it to run without installing the MSVC runtime.
rustdoc --test includes file names in test names
This release includes builds of std for sparc64-unknown-linux-gnu, aarch64-unknown-linux-fuchsia, and x86_64-unknown-linux-fuchsia.
Initial support for aarch64-unknown-freebsd
Initial support for i686-unknown-netbsd
This release no longer includes the old makefile build system. Rust is built with a custom build system, written in Rust, and with Cargo.
Add Debug implementations for libcollection structs
TypeId implements PartialOrd and Ord
--test-threads=0 produces an error
rustup installs documentation by default
The Rust source includes NatVis visualizations. These can be used by WinDbg and Visual Studio to improve the debugging experience.

Compatibility Notes

Rust 1.17 does not correctly detect the MSVC 2017 linker. As a workaround, either use MSVC 2015 or run vcvars.bat.
When coercing to an unsized type lifetimes must be equal. That is, disallow subtyping between T and U when T: Unsize<U>, e.g. coercing &mut [&'a X; N] to &mut [&'b X] requires 'a be equal to 'b. Soundness fix.
format! and Display::to_string panic if an underlying formatting implementation returns an error. Previously the error was silently ignored. It is incorrect for write_fmt to return an error when writing to a string.
In-tree crates are verified to be unstable. Previously, some minor crates were marked stable and could be accessed from the stable toolchain.
Rust git source no longer includes vendored crates. Those that need to build with vendored crates should build from release tarballs.
Fix inert attributes from proc_macro_derives
During crate resolution, rustc prefers a crate in the sysroot if two crates are otherwise identical. Unlikely to be encountered outside the Rust build system.
Fixed bugs around how type inference interacts with dead-code. The existing code generally ignores the type of dead-code unless a type-hint is provided; this can cause surprising inference interactions particularly around defaulting. The new code uniformly ignores the result type of dead-code.
Tuple-struct constructors with private fields are no longer visible
Lifetime parameters that do not appear in the arguments are now considered early-bound, resolving a soundness bug (#32330). The hr_lifetime_in_assoc_type future-compatibility lint has been in effect since April of 2016.
rustdoc: fix doctests with non-feature crate attributes
Make transmuting from fn item types to pointer-sized types a hard error