b4502f7c0b
integrate anon dep nodes into trait selection
Use anonymous nodes for trait selection. In all cases, we use the same basic "memoization" strategy:
- Store the `DepNodeIndex` in the slot along with value.
- If value is present, return it, and add a read of the dep-node-index.
- Else, start an anonymous task, and store resulting node.
We apply this strategy to a number of caches in trait selection:
- The "trans" caches of selection and projection
- The "evaluation" cache
- The "candidate selection" cache
In general, for our cache strategy to be "dep-correct", the computation of the value is permitted to rely on the *value in the key* but nothing else. The basic argument is this: in order to look something up, you have to produce the key, and to do that you must have whatever reads were needed to create the key. Then, you get whatever reads were further needed to produce the value. But if the "closure" that produced the value made use of *other* environmental data, not derivable from the key, that would be bad -- but that would **also** suggest that the cache is messed up (though it's not proof).
The structure of these caches do not obviously prove that the correctness criteria are met, and I aim to address that in further refactorings. But I *believe* it to be the case that, if we assume that the existing caches are correct, there are also no dependency failures (in other words, if there's a bug, it's a pre-existing one). Specifically:
- The trans caches: these take as input just a `tcx`, which is "by definition" not leaky, the `trait-ref` etc, which is part of the key, and sometimes a span (doesn't influence the result). So they seem fine.
- The evaluation cache:
- This computation takes as input the "stack" and has access to the infcx.
- The infcx is a problem -- would be better to take the tcx -- and this is exactly one of the things I plan to improve in later PRs. Let's ignore it for now. =)
- The stack itself is also not great, in that the *key* only consists of the top-entry in the stack.
- However, the stack can cause a problem in two ways:
- overflow (we panic)
- cycle check fails (we do not update the cache, I believe)
- The candidate selection cache:
- as before, takes the "stack" and has access to the infcx.
- here it is not as obvious that we avoid caching stack-dependent computations. However, to the extent that we do, this is a pre-existing bug, in that we are making cache entries we shouldn't.
- I aim to resolve this by -- following the chalk-style of evaluation -- merging candidate selection and evaluation.
- The infcx is a problem -- would be better to take the tcx -- and this is exactly one of the things I plan to improve in later PRs. Let's ignore it for now. =)
- The stack itself is also not great, in that the *key* only consists of the top-entry in the stack.
- Moreover, the stack would generally just introduce ambiguities and errors anyhow, so that lessens the risk.
Anyway, the existing approach to handle dependencies in the trait code carries the same risks or worse, so this seems like a strict improvement!
r? @michaelwoerister
cc @arielb1
The Rust Programming Language
This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Quick Start
Read "Installation" from The Book.
Building from Source
-
Make sure you have installed the dependencies:
g++4.7 or later orclang++3.x or laterpython2.7 (but not 3.x)- GNU
make3.81 or later cmake3.4.3 or latercurlgit
-
Clone the source with
git:$ git clone https://github.com/rust-lang/rust.git $ cd rust
-
Build and install:
$ ./x.py build && sudo ./x.py installNote: Install locations can be adjusted by copying the config file from
./src/bootstrap/config.toml.exampleto./config.toml, and adjusting theprefixoption under[install]. Various other options, such as enabling debug information, are also supported, and are documented in the config file.When complete,
sudo ./x.py installwill place several programs into/usr/local/bin:rustc, the Rust compiler, andrustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager, which you may also want to build.
Building on Windows
There are two prominent ABIs in use on Windows: the native (MSVC) ABI used by Visual Studio, and the GNU ABI used by the GCC toolchain. Which version of Rust you need depends largely on what C/C++ libraries you want to interoperate with: for interop with software produced by Visual Studio use the MSVC build of Rust; for interop with GNU software built using the MinGW/MSYS2 toolchain use the GNU build.
MinGW
MSYS2 can be used to easily build Rust on Windows:
-
Grab the latest MSYS2 installer and go through the installer.
-
Run
mingw32_shell.batormingw64_shell.batfrom wherever you installed MSYS2 (i.e.C:\msys64), depending on whether you want 32-bit or 64-bit Rust. (As of the latest version of MSYS2 you have to runmsys2_shell.cmd -mingw32ormsys2_shell.cmd -mingw64from the command line instead) -
From this terminal, install the required tools:
# Update package mirrors (may be needed if you have a fresh install of MSYS2) $ pacman -Sy pacman-mirrors # Install build tools needed for Rust. If you're building a 32-bit compiler, # then replace "x86_64" below with "i686". If you've already got git, python, # or CMake installed and in PATH you can remove them from this list. Note # that it is important that you do **not** use the 'python2' and 'cmake' # packages from the 'msys2' subsystem. The build has historically been known # to fail with these packages. $ pacman -S git \ make \ diffutils \ tar \ mingw-w64-x86_64-python2 \ mingw-w64-x86_64-cmake \ mingw-w64-x86_64-gcc -
Navigate to Rust's source code (or clone it), then build it:
$ ./x.py build && ./x.py install
MSVC
MSVC builds of Rust additionally require an installation of Visual Studio 2013
(or later) so rustc can use its linker. Make sure to check the “C++ tools”
option.
With these dependencies installed, you can build the compiler in a cmd.exe
shell with:
> python x.py build
Currently building Rust only works with some known versions of Visual Studio. If you have a more recent version installed the build system doesn't understand then you may need to force rustbuild to use an older version. This can be done by manually calling the appropriate vcvars file before running the bootstrap.
CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\vcvars64.bat"
python x.py build
Specifying an ABI
Each specific ABI can also be used from either environment (for example, using the GNU ABI in powershell) by using an explicit build triple. The available Windows build triples are:
- GNU ABI (using GCC)
i686-pc-windows-gnux86_64-pc-windows-gnu
- The MSVC ABI
i686-pc-windows-msvcx86_64-pc-windows-msvc
The build triple can be specified by either specifying --build=ABI when
invoking x.py commands, or by copying the config.toml file (as described
in Building From Source), and modifying the build option under the [build]
section.
Configure and Make
While it's not the recommended build system, this project also provides a
configure script and makefile (the latter of which just invokes x.py).
$ ./configure
$ make && sudo make install
When using the configure script, the generated config.mk file may override the
config.toml file. To go back to the config.toml file, delete the generated
config.mk file.
Building Documentation
If you’d like to build the documentation, it’s almost the same:
$ ./x.py doc
The generated documentation will appear under doc in the build directory for
the ABI used. I.e., if the ABI was x86_64-pc-windows-msvc, the directory will be
build\x86_64-pc-windows-msvc\doc.
Notes
Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier state of development). As such, source builds require a connection to the Internet, to fetch snapshots, and an OS that can execute the available snapshot binaries.
Snapshot binaries are currently built and tested on several platforms:
| Platform / Architecture | x86 | x86_64 |
|---|---|---|
| Windows (7, 8, Server 2008 R2) | ✓ | ✓ |
| Linux (2.6.18 or later) | ✓ | ✓ |
| OSX (10.7 Lion or later) | ✓ | ✓ |
You may find that other platforms work, but these are our officially supported build environments that are most likely to work.
Rust currently needs between 600MiB and 1.5GiB to build, depending on platform. If it hits swap, it will take a very long time to build.
There is more advice about hacking on Rust in CONTRIBUTING.md.
Getting Help
The Rust community congregates in a few places:
- Stack Overflow - Direct questions about using the language.
- users.rust-lang.org - General discussion and broader questions.
- /r/rust - News and general discussion.
Contributing
To contribute to Rust, please see CONTRIBUTING.
Rust has an IRC culture and most real-time collaboration happens in a variety of channels on Mozilla's IRC network, irc.mozilla.org. The most popular channel is #rust, a venue for general discussion about Rust. And a good place to ask for help would be #rust-beginners.
License
Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.
See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.