As of yesterday evening, we have a self-hosting Rust compiler, which means that the Rust compiler written in Rust can compile itself. The resulting binary is identical to the compiler built by the Rust bootstrap compiler (which was written in OCaml). This is a big milestone for the project and represents the culmination of many months of focused work.
So the obvious question is: what's next? The short answer is "a lot"! Here are a few areas we'll be focusing on in the next few months.
Compiler performance. Currently, it takes 15 minutes on an Opteron for rustc to compile itself. That's far too slow to be practical. We should be at least 50× faster. This is a tall order, but, especially with the renewed emphasis on compiler performance that clang, GCC, and Go have spearheaded in recent years, we can't afford to ignore this.
Missing features. We have many features that are part of the core language that have yet to be implemented in rustc. Just to name a few, we need destructors, threads, object upcasts, garbage collection, stack growth, alias analysis for safety, and an x86-64 port. Some features are partially working but unfinished, such as pattern matching.
Language additions. Several new language features are under discussion. Most of these are attempts to solve difficulties in the language that we encountered while working on the Rust compiler. (Being able to find these difficulties early is one of the great advantages of writing the compiler in the language itself!) These features include unique pointers, self types, overloading, blocks/lambdas, and macros.
New syntax. This one is contentious, as syntax always is, but the general consensus is that some parts of the syntax are too difficult for their own good. Some of the mutually-agreed-upon facets of the syntax that we'd like to change are (a) to put items and types in different namespaces, (b) to make the switch-case syntax less spiky and verbose, and (c) to use ECMAScript 4-like .<> notation for type parameter instantiation; e.g. map.<int>(...);
It's an exciting time for Rust—there's been lots of forward progress and the language is slowly but surely starting to feel less like a toy. As always, you can find the current state of the compiler on GitHub.