# Contribution Guide
-If you want to hack on miri yourself, great! Here are some resources you might
+If you want to hack on Miri yourself, great! Here are some resources you might
find useful.
## Getting started
-Check out the issues on this GitHub repository for some ideas. There's lots that
-needs to be done that we haven't documented in the issues yet, however. For more
-ideas or help with hacking on Miri, you can contact us (`oli-obk` and `RalfJ`)
-on the [Rust Zulip].
+Check out the issues on this GitHub repository for some ideas. In particular,
+look for the green `E-*` labels which mark issues that should be rather
+well-suited for onboarding. For more ideas or help with hacking on Miri, you can
+contact us (`oli-obk` and `RalfJ`) on the [Rust Zulip].
[Rust Zulip]: https://rust-lang.zulipchat.com
-### Fixing Miri when rustc changes
+## Preparing the build environment
-Miri is heavily tied to rustc internals, so it is very common that rustc changes
-break Miri. Fixing those is a good way to get starting working on Miri.
-Usually, Miri will require changes similar to the other consumers of the changed
-rustc API, so reading the rustc PR diff is a good way to get an idea for what is
-needed.
+Miri heavily relies on internal and unstable rustc interfaces to execute MIR,
+which means it is important that you install a version of rustc that Miri
+actually works with.
-When submitting a PR against Miri after fixing it for rustc changes, make sure
-you update the `rust-version` file. That file always contains the exact rustc
-git commit with which Miri works, and it is the version that our CI tests Miri
-against.
+The `rust-version` file contains the commit hash of rustc that Miri is currently
+tested against. Other versions will likely not work. After installing
+[`rustup-toolchain-install-master`], you can run the following command to
+install that exact version of rustc as a toolchain:
+```
+./rustup-toolchain
+```
+This will set up a rustup toolchain called `miri` and set it as an override for
+the current directory.
+
+If you want to also have `clippy` installed, you need to run this:
+```
+./rustup-toolchain "" -c clippy
+```
-## Building Miri with a nightly rustc
+[`rustup-toolchain-install-master`]: https://github.com/kennytm/rustup-toolchain-install-master
-Miri heavily relies on internal rustc interfaces to execute MIR. Still, some
-things (like adding support for a new intrinsic or a shim for an external
-function being called) can be done by working just on the Miri side.
+## Building and testing Miri
-To prepare, make sure you are using a nightly Rust compiler. You also need to
-have the `rust-src` and `rustc-dev` components installed, which you can add via
-`rustup component add rust-src rustc-dev`. Then you should be able to just
-`cargo build` Miri.
+Invoking Miri requires getting a bunch of flags right and setting up a custom
+sysroot with xargo. The `miri` script takes care of that for you. With the
+build environment prepared, compiling Miri is just one command away:
-In case this fails, your nightly might be incompatible with Miri master. The
-`rust-version` file contains the commit hash of rustc that Miri is currently
-tested against; you can use that to find a nightly that works or you might have
-to wait for the next nightly to get released. You can also use
-[`rustup-toolchain-install-master`](https://github.com/kennytm/rustup-toolchain-install-master)
-to install that exact version of rustc as a toolchain:
```
-rustup-toolchain-install-master $(cat rust-version) -c rust-src -c rustc-dev
+./miri build
```
-Another common problem is outdated dependencies: Miri does not come with a
-lockfile (it cannot, due to how it gets embedded into the rustc build). So you
-have to run `cargo update` every now and then yourself to make sure you are
-using the latest versions of everything (which is what gets tested on CI).
+Run `./miri` without arguments to see the other commands our build tool
+supports.
-## Testing the Miri driver
-[testing-miri]: #testing-the-miri-driver
+### Testing the Miri driver
-The Miri driver in the `miri` binary is the "heart" of Miri: it is basically a
-version of `rustc` that, instead of compiling your code, runs it. It accepts
-all the same flags as `rustc` (though the ones only affecting code generation
-and linking obviously will have no effect) [and more][miri-flags].
+The Miri driver compiled from `src/bin/miri.rs` is the "heart" of Miri: it is
+basically a version of `rustc` that, instead of compiling your code, runs it.
+It accepts all the same flags as `rustc` (though the ones only affecting code
+generation and linking obviously will have no effect) [and more][miri-flags].
-Running the Miri driver requires some fiddling with environment variables, so
-the `miri` script helps you do that. For example, you can run the driver on a
-particular file by doing
+[miri-flags]: README.md#miri--z-flags-and-environment-variables
+
+For example, you can (cross-)run the driver on a particular file by doing
```sh
-./miri run tests/run-pass/format.rs
-./miri run tests/run-pass/hello.rs --target i686-unknown-linux-gnu
+./miri run tests/pass/format.rs
+./miri run tests/pass/hello.rs --target i686-unknown-linux-gnu
```
-and you can run the test suite using:
+and you can (cross-)run the entire test suite using:
```
./miri test
+MIRI_TEST_TARGET=i686-unknown-linux-gnu ./miri test
```
+If your target doesn't support libstd, you can run miri with
+
+```
+MIRI_NO_STD=1 MIRI_TEST_TARGET=thumbv7em-none-eabihf ./miri test tests/fail/alloc/no_global_allocator.rs
+MIRI_NO_STD=1 ./miri run tests/pass/no_std.rs --target thumbv7em-none-eabihf
+```
+
+to avoid attempting (and failing) to build libstd. Note that almost no tests will pass
+this way, but you can run individual tests.
+
`./miri test FILTER` only runs those tests that contain `FILTER` in their
filename (including the base directory, e.g. `./miri test fail` will run all
compile-fail tests).
`MIRI_LOG` environment variable. For example:
```sh
-MIRI_LOG=info ./miri run tests/run-pass/vecs.rs
+MIRI_LOG=info ./miri run tests/pass/vec.rs
```
Setting `MIRI_LOG` like this will configure logging for Miri itself as well as
-the `rustc::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
+the `rustc_middle::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
can also do more targeted configuration, e.g. the following helps debug the
stacked borrows implementation:
```sh
-MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/run-pass/vecs.rs
+MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/pass/vec.rs
```
In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
evaluation error was originally raised.
-## Testing `cargo miri`
+#### UI testing
+
+We use ui-testing in Miri, meaning we generate `.stderr` and `.stdout` files for the output
+produced by Miri. You can use `./miri bless` to automatically (re)generate these files when
+you add new tests or change how Miri presents certain output.
+
+Note that when you also use `MIRIFLAGS` to change optimizations and similar, the ui output
+will change in unexpected ways. In order to still be able
+to run the other checks while ignoring the ui output, use `MIRI_SKIP_UI_CHECKS=1 ./miri test`.
+
+For more info on how to configure ui tests see [the documentation on the ui test crate][ui_test]
+
+[ui_test]: ui_test/README.md
+
+### Testing `cargo miri`
Working with the driver directly gives you full control, but you also lose all
-the convenience provided by cargo. Once your test case depends on a crate, it
-is probably easier to test it with the cargo wrapper. You can install your
+the convenience provided by cargo. Once your test case depends on a crate, it
+is probably easier to test it with the cargo wrapper. You can install your
development version of Miri using
```
the same toolchain when calling `cargo miri` that you used when installing Miri!
There's a test for the cargo wrapper in the `test-cargo-miri` directory; run
-`./run-test.py` in there to execute it.
+`./run-test.py` in there to execute it. Like `./miri test`, this respects the
+`MIRI_TEST_TARGET` environment variable to execute the test for another target.
+
+### Using a modified standard library
+
+Miri re-builds the standard library into a custom sysroot, so it is fairly easy
+to test Miri against a modified standard library -- you do not even have to
+build Miri yourself, the Miri shipped by `rustup` will work. All you have to do
+is set the `MIRI_LIB_SRC` environment variable to the `library` folder of a
+`rust-lang/rust` repository checkout. Note that changing files in that directory
+does not automatically trigger a re-build of the standard library; you have to
+clear the Miri build cache manually (on Linux, `rm -rf ~/.cache/miri`;
+and on Windows, `rmdir /S "%LOCALAPPDATA%\rust-lang\miri\cache"`).
+
+### Benchmarking
+
+Miri comes with a few benchmarks; you can run `./miri bench` to run them with the locally built
+Miri. Note: this will run `./miri install` as a side-effect. Also requires `hyperfine` to be
+installed (`cargo install hyperfine`).
+
+## Configuring `rust-analyzer`
+
+To configure `rust-analyzer` and VS Code for working on Miri, save the following
+to `.vscode/settings.json` in your local Miri clone:
+
+```json
+{
+ "rust-analyzer.rustc.source": "discover",
+ "rust-analyzer.linkedProjects": [
+ "./Cargo.toml",
+ "./cargo-miri/Cargo.toml"
+ ],
+ "rust-analyzer.checkOnSave.overrideCommand": [
+ "./miri",
+ "check",
+ "--message-format=json"
+ ],
+ "rust-analyzer.buildScripts.overrideCommand": [
+ "./miri",
+ "check",
+ "--message-format=json",
+ ],
+ "rust-analyzer.rustfmt.extraArgs": [
+ "+nightly"
+ ],
+}
+```
-## Building Miri with a locally built rustc
+> #### Note
+>
+> If you are [building Miri with a locally built rustc][], set
+> `rust-analyzer.rustcSource` to the relative path from your Miri clone to the
+> root `Cargo.toml` of the locally built rustc. For example, the path might look
+> like `../rust/Cargo.toml`.
+
+See the rustc-dev-guide's docs on ["Configuring `rust-analyzer` for `rustc`"][rdg-r-a]
+for more information about configuring VS Code and `rust-analyzer`.
+
+[rdg-r-a]: https://rustc-dev-guide.rust-lang.org/building/suggested.html#configuring-rust-analyzer-for-rustc
+
+## Advanced topic: other build environments
+
+We described above the simplest way to get a working build environment for Miri,
+which is to use the version of rustc indicated by `rustc-version`. But
+sometimes, that is not enough.
+
+### Updating `rustc-version`
+
+The `rustc-version` file is regularly updated to keep Miri close to the latest
+version of rustc. Usually, new contributors do not have to worry about this. But
+sometimes a newer rustc is needed for a patch, and sometimes Miri needs fixing
+for changes in rustc. In both cases, `rustc-version` needs updating.
+
+To update the `rustc-version` file and install the latest rustc, you can run:
+```
+./rustup-toolchain HEAD
+```
+
+Now edit Miri until `./miri test` passes, and submit a PR. Generally, it is
+preferred to separate updating `rustc-version` and doing what it takes to get
+Miri working again, from implementing new features that rely on the updated
+rustc. This avoids blocking all Miri development on landing a big PR.
+
+### Building Miri with a locally built rustc
+
+[building Miri with a locally built rustc]: #building-miri-with-a-locally-built-rustc
A big part of the Miri driver lives in rustc, so working on Miri will sometimes
-require using a locally built rustc. The bug you want to fix may actually be on
+require using a locally built rustc. The bug you want to fix may actually be on
the rustc side, or you just need to get more detailed trace of the execution
than what is possible with release builds -- in both cases, you should develop
-miri against a rustc you compiled yourself, with debug assertions (and hence
+Miri against a rustc you compiled yourself, with debug assertions (and hence
tracing) enabled.
The setup for a local rustc works as follows:
```sh
-git clone https://github.com/rust-lang/rust/ rustc
+# Clone the rust-lang/rust repo.
+git clone https://github.com/rust-lang/rust rustc
cd rustc
-cp config.toml.example config.toml
-# Now edit `config.toml` and set `debug-assertions = true`.
-# This step can take 30 minutes and more.
-./x.py build src/rustc
+# Create a config.toml with defaults for working on Miri.
+./x.py setup compiler
+ # Now edit `config.toml` and under `[rust]` set `debug-assertions = true`.
+
+# Build a stage 2 rustc, and build the rustc libraries with that rustc.
+# This step can take 30 minutes or more.
+./x.py build --stage 2 compiler/rustc
# If you change something, you can get a faster rebuild by doing
-./x.py --keep-stage 0 build src/rustc
+./x.py build --keep-stage 0 --stage 2 compiler/rustc
# You may have to change the architecture in the next command
-rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
+rustup toolchain link stage2 build/x86_64-unknown-linux-gnu/stage2
# Now cd to your Miri directory, then configure rustup
-rustup override set custom
+rustup override set stage2
```
-With this, you should now have a working development setup! See
-[above][testing-miri] for how to proceed working with the Miri driver.
+Important: You need to delete the Miri cache when you change the stdlib; otherwise the
+old, chached version will be used. On Linux, the cache is located at `~/.cache/miri`,
+and on Windows, it is located at `%LOCALAPPDATA%\rust-lang\miri\cache`; the exact
+location is printed after the library build: "A libstd for Miri is now available in ...".
+
+Note: `./x.py --stage 2 compiler/rustc` currently errors with `thread 'main'
+panicked at 'fs::read(stamp) failed with No such file or directory (os error 2)`,
+you can simply ignore that error; Miri will build anyway.
+
+For more information about building and configuring a local compiler,
+see <https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html>.
+
+With this, you should now have a working development setup! See
+[above](#building-and-testing-miri) for how to proceed working on Miri.
projects / rust.git / blobdiff