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Rollup merge of rust-lang#57653 - mark-i-m:contrib-doc, r=nikomatsakis
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Make the contribution doc reference the guide more

and also remove a lot of redundant info already in the guide
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@Centril
Centril authored Jan 19, 2019
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250 changes: 21 additions & 229 deletions CONTRIBUTING.md
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Expand Up @@ -19,9 +19,16 @@ hop on [#rust-internals][pound-rust-internals].

As a reminder, all contributors are expected to follow our [Code of Conduct][coc].

The [rustc-guide] is your friend! It describes how the compiler works and how
to contribute to it in more detail than this document.

If this is your first time contributing, the [walkthrough] chapter of the guide
can give you a good example of how a typical contribution would go.

[pound-rust-internals]: https://chat.mibbit.com/?server=irc.mozilla.org&channel=%23rust-internals
[internals]: https://internals.rust-lang.org
[coc]: https://www.rust-lang.org/conduct.html
[walkthrough]: https://rust-lang.github.io/rustc-guide/walkthrough.html

## Feature Requests
[feature-requests]: #feature-requests
Expand Down Expand Up @@ -89,222 +96,14 @@ $ RUST_BACKTRACE=1 rustc ...
```

## The Build System
[the-build-system]: #the-build-system

Rust's build system allows you to bootstrap the compiler, run tests &
benchmarks, generate documentation, install a fresh build of Rust, and more.
It's your best friend when working on Rust, allowing you to compile & test
your contributions before submission.

The build system lives in [the `src/bootstrap` directory][bootstrap] in the
project root. Our build system is itself written in Rust and is based on Cargo
to actually build all the compiler's crates. If you have questions on the build
system internals, try asking in [`#rust-internals`][pound-rust-internals].

[bootstrap]: https://github.com/rust-lang/rust/tree/master/src/bootstrap/

### Configuration
[configuration]: #configuration

Before you can start building the compiler you need to configure the build for
your system. In most cases, that will just mean using the defaults provided
for Rust.

To change configuration, you must copy the file `config.toml.example`
to `config.toml` in the directory from which you will be running the build, and
change the settings provided.

There are large number of options provided in this config file that will alter the
configuration used in the build process. Some options to note:

#### `[llvm]`:
- `assertions = true` = This enables LLVM assertions, which makes LLVM misuse cause an assertion failure instead of weird misbehavior. This also slows down the compiler's runtime by ~20%.
- `ccache = true` - Use ccache when building llvm

#### `[build]`:
- `compiler-docs = true` - Build compiler documentation

#### `[rust]`:
- `debuginfo = true` - Build a compiler with debuginfo. Makes building rustc slower, but then you can use a debugger to debug `rustc`.
- `debuginfo-lines = true` - An alternative to `debuginfo = true` that doesn't let you use a debugger, but doesn't make building rustc slower and still gives you line numbers in backtraces.
- `debuginfo-tools = true` - Build the extended tools with debuginfo.
- `debug-assertions = true` - Makes the log output of `debug!` work.
- `optimize = false` - Disable optimizations to speed up compilation of stage1 rust, but makes the stage1 compiler x100 slower.

For more options, the `config.toml` file contains commented out defaults, with
descriptions of what each option will do.

Note: Previously the `./configure` script was used to configure this
project. It can still be used, but it's recommended to use a `config.toml`
file. If you still have a `config.mk` file in your directory - from
`./configure` - you may need to delete it for `config.toml` to work.

### Building
[building]: #building

A default configuration requires around 3.5 GB of disk space, whereas building a debug configuration may require more than 30 GB.

Dependencies
- [build dependencies](README.md#building-from-source)
- `gdb` 6.2.0 minimum, 7.1 or later recommended for test builds
For info on how to configure and build the compiler, please see [this
chapter][rustcguidebuild] of the rustc-guide. This chapter contains info for
contributions to the compiler and the standard library. It also lists some
really useful commands to the build system (`./x.py`), which could save you a
lot of time.

The build system uses the `x.py` script to control the build process. This script
is used to build, test, and document various parts of the compiler. You can
execute it as:

```sh
python x.py build
```

On some systems you can also use the shorter version:

```sh
./x.py build
```

To learn more about the driver and top-level targets, you can execute:

```sh
python x.py --help
```

The general format for the driver script is:

```sh
python x.py <command> [<directory>]
```

Some example commands are `build`, `test`, and `doc`. These will build, test,
and document the specified directory. The second argument, `<directory>`, is
optional and defaults to working over the entire compiler. If specified,
however, only that specific directory will be built. For example:

```sh
# build the entire compiler
python x.py build

# build all documentation
python x.py doc

# run all test suites
python x.py test

# build only the standard library
python x.py build src/libstd

# test only one particular test suite
python x.py test src/test/rustdoc

# build only the stage0 libcore library
python x.py build src/libcore --stage 0
```

You can explore the build system through the various `--help` pages for each
subcommand. For example to learn more about a command you can run:

```
python x.py build --help
```

To learn about all possible rules you can execute, run:

```
python x.py build --help --verbose
```

Note: Previously `./configure` and `make` were used to build this project.
They are still available, but `x.py` is the recommended build system.

### Useful commands
[useful-commands]: #useful-commands

Some common invocations of `x.py` are:

- `x.py build --help` - show the help message and explain the subcommand
- `x.py build src/libtest --stage 1` - build up to (and including) the first
stage. For most cases we don't need to build the stage2 compiler, so we can
save time by not building it. The stage1 compiler is a fully functioning
compiler and (probably) will be enough to determine if your change works as
expected.
- `x.py build src/rustc --stage 1` - This will build just rustc, without libstd.
This is the fastest way to recompile after you changed only rustc source code.
Note however that the resulting rustc binary won't have a stdlib to link
against by default. You can build libstd once with `x.py build src/libstd`,
but it is only guaranteed to work if recompiled, so if there are any issues
recompile it.
- `x.py test` - build the full compiler & run all tests (takes a while). This
is what gets run by the continuous integration system against your pull
request. You should run this before submitting to make sure your tests pass
& everything builds in the correct manner.
- `x.py test src/libstd --stage 1` - test the standard library without
recompiling stage 2.
- `x.py test src/test/run-pass --test-args TESTNAME` - 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=collections::hash::map::test_map::test_capacity_not_less_than_len`
or `TESTNAME=test_capacity_not_less_than_len`.
- `x.py test src/test/run-pass --stage 1 --test-args <substring-of-test-name>` -
Run a single rpass test with the stage1 compiler (this will be quicker than
running the command above as we only build the stage1 compiler, not the entire
thing). You can also leave off the directory argument to run all stage1 test
types.
- `x.py test src/libcore --stage 1` - Run stage1 tests in `libcore`.
- `x.py test src/tools/tidy` - Check that the source code is in compliance with
Rust's style guidelines. There is no official document describing Rust's full
guidelines as of yet, but basic rules like 4 spaces for indentation and no
more than 99 characters in a single line should be kept in mind when writing
code.

### Using your local build
[using-local-build]: #using-local-build

If you use Rustup to manage your rust install, it has a feature called ["custom
toolchains"][toolchain-link] that you can use to access your newly-built compiler
without having to install it to your system or user PATH. If you've run `python
x.py build`, then you can add your custom rustc to a new toolchain like this:

[toolchain-link]: https://github.com/rust-lang-nursery/rustup.rs#working-with-custom-toolchains-and-local-builds

```
rustup toolchain link <name> build/<host-triple>/stage2
```

Where `<host-triple>` is the build triple for the host (the triple of your
computer, by default), and `<name>` is the name for your custom toolchain. (If you
added `--stage 1` to your build command, the compiler will be in the `stage1`
folder instead.) You'll only need to do this once - it will automatically point
to the latest build you've done.

Once this is set up, you can use your custom toolchain just like any other. For
example, if you've named your toolchain `local`, running `cargo +local build` will
compile a project with your custom rustc, setting `rustup override set local` will
override the toolchain for your current directory, and `cargo +local doc` will use
your custom rustc and rustdoc to generate docs. (If you do this with a `--stage 1`
build, you'll need to build rustdoc specially, since it's not normally built in
stage 1. `python x.py build --stage 1 src/libstd src/tools/rustdoc` will build
rustdoc and libstd, which will allow rustdoc to be run with that toolchain.)

### Out-of-tree builds
[out-of-tree-builds]: #out-of-tree-builds

Rust's `x.py` script fully supports out-of-tree builds - it looks for
the Rust source code from the directory `x.py` was found in, but it
reads the `config.toml` configuration file from the directory it's
run in, and places all build artifacts within a subdirectory named `build`.

This means that if you want to do an out-of-tree build, you can just do it:
```
$ cd my/build/dir
$ cp ~/my-config.toml config.toml # Or fill in config.toml otherwise
$ path/to/rust/x.py build
...
$ # This will use the Rust source code in `path/to/rust`, but build
$ # artifacts will now be in ./build
```

It's absolutely fine to have multiple build directories with different
`config.toml` configurations using the same code.
[rustcguidebuild]: https://rust-lang.github.io/rustc-guide/how-to-build-and-run.html

## Pull Requests
[pull-requests]: #pull-requests
Expand All @@ -320,26 +119,13 @@ bring those changes into the source repository.

Please make pull requests against the `master` branch.

Compiling all of `./x.py test` can take a while. When testing your pull request,
consider using one of the more specialized `./x.py` 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.

$ python x.py test --stage 1

is one such example, which builds just `rustc`, and then runs the tests. If
you’re adding something to the standard library, try

$ python x.py test src/libstd --stage 1

Please make sure your pull request is in compliance with Rust's style
guidelines by running

$ python x.py test src/tools/tidy

Make this check before every pull request (and every new commit in a pull
request) ; you can add [git hooks](https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks)
request); you can add [git hooks](https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks)
before every push to make sure you never forget to make this check.

All pull requests are reviewed by another person. We have a bot,
Expand Down Expand Up @@ -532,6 +318,12 @@ to check small fixes. For example, `rustdoc src/doc/reference.md` will render
reference to `doc/reference.html`. The CSS might be messed up, but you can
verify that the HTML is right.

Additionally, contributions to the [rustc-guide] are always welcome. Contributions
can be made directly at [the
rust-lang/rustc-guide](https://github.com/rust-lang/rustc-guide) repo. The issue
tracker in that repo is also a great way to find things that need doing. There
are issues for beginners and advanced compiler devs alike!

## Issue Triage
[issue-triage]: #issue-triage

Expand Down Expand Up @@ -627,7 +419,7 @@ For people new to Rust, and just starting to contribute, or even for
more seasoned developers, some useful places to look for information
are:

* The [rustc guide] contains information about how various parts of the compiler work
* The [rustc guide] contains information about how various parts of the compiler work and how to contribute to the compiler
* [Rust Forge][rustforge] contains additional documentation, including write-ups of how to achieve common tasks
* The [Rust Internals forum][rif], a place to ask questions and
discuss Rust's internals
Expand Down

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