running.md

Running tests

You can run the tests using x.py. The most basic command – which you will almost never want to use! – is as follows:

./x.py test

This will build the stage 1 compiler and then run the whole test suite. You probably don't want to do this very often, because it takes a very long time, and anyway bors / GitHub Actions will do it for you. (Often, I will run this command in the background after opening a PR that I think is done, but rarely otherwise. -nmatsakis)

The test results are cached and previously successful tests are ignored during testing. The stdout/stderr contents as well as a timestamp file for every test can be found under build/ARCH/test/. To force-rerun a test (e.g. in case the test runner fails to notice a change) you can simply remove the timestamp file.

Note that some tests require a Python-enabled gdb. You can test if your gdb install supports Python by using the python command from within gdb. Once invoked you can type some Python code (e.g. print("hi")) followed by return and then CTRL+D to execute it. If you are building gdb from source, you will need to configure with --with-python=<path-to-python-binary>.

Running a subset of the test suites

When working on a specific PR, you will usually want to run a smaller set of tests. For example, a good "smoke test" that can be used after modifying rustc to see if things are generally working correctly would be the following:

./x.py test src/test/ui

This will run the ui test suite. Of course, the choice of test suites is somewhat arbitrary, and may not suit the task you are doing. For example, if you are hacking on debuginfo, you may be better off with the debuginfo test suite:

./x.py test src/test/debuginfo

If you only need to test a specific subdirectory of tests for any given test suite, you can pass that directory to x.py test:

./x.py test src/test/ui/const-generics

Likewise, you can test a single file by passing its path:

./x.py test src/test/ui/const-generics/const-test.rs

Run only the tidy script

./x.py test tidy

Run tests on the standard library

./x.py test --stage 0 library/std

Run the tidy script and tests on the standard library

./x.py test --stage 0 tidy library/std

Run tests on the standard library using a stage 1 compiler

./x.py test library/std

By listing which test suites you want to run you avoid having to run tests for components you did not change at all.

Warning: Note that bors only runs the tests with the full stage 2 build; therefore, while the tests usually work fine with stage 1, there are some limitations.

Run unit tests on the compiler/library

You may want to run unit tests on a specific file with following:

./x.py test compiler/rustc_data_structures/src/thin_vec/tests.rs

But unfortunately, it's impossible. You should invoke following instead:

./x.py test compiler/rustc_data_structures/ --test-args thin_vec

Running an individual test

Another common thing that people want to do is to run an individual test, often the test they are trying to fix. As mentioned earlier, you may pass the full file path to achieve this, or alternatively one may invoke x.py with the --test-args option:

./x.py test src/test/ui --test-args issue-1234

Under the hood, the test runner invokes the standard rust test runner (the same one you get with #[test]), so this command would wind up filtering for tests that include "issue-1234" in the name. (Thus --test-args is a good way to run a collection of related tests.)

Editing and updating the reference files

If you have changed the compiler's output intentionally, or you are making a new test, you can pass --bless to the test subcommand. E.g. if some tests in src/test/ui are failing, you can run

./x.py test src/test/ui --bless

to automatically adjust the .stderr, .stdout or .fixed files of all tests. Of course you can also target just specific tests with the --test-args your_test_name flag, just like when running the tests.

Passing --pass $mode

Pass UI tests now have three modes, check-pass, build-pass and run-pass. When --pass $mode is passed, these tests will be forced to run under the given $mode unless the directive // ignore-pass exists in the test file. For example, you can run all the tests in src/test/ui as check-pass:

./x.py test src/test/ui --pass check

By passing --pass $mode, you can reduce the testing time. For each mode, please see here.

Using incremental compilation

You can further enable the --incremental flag to save additional time in subsequent rebuilds:

./x.py test src/test/ui --incremental --test-args issue-1234

If you don't want to include the flag with every command, you can enable it in the config.toml:

[rust]
incremental = true

Note that incremental compilation will use more disk space than usual. If disk space is a concern for you, you might want to check the size of the build directory from time to time.

Running tests with different "compare modes"

UI tests may have different output depending on certain "modes" that the compiler is in. For example, when in "non-lexical lifetimes" (NLL) mode a test foo.rs will first look for expected output in foo.nll.stderr, falling back to the usual foo.stderr if not found. To run the UI test suite in NLL mode, one would use the following:

./x.py test src/test/ui --compare-mode=nll

Other examples of compare-modes are "noopt", "migrate", and revisions.

Running tests manually

Sometimes it's easier and faster to just run the test by hand. Most tests are just rs files, so you can do something like

rustc +stage1 src/test/ui/issue-1234.rs

This is much faster, but doesn't always work. For example, some tests include directives that specify specific compiler flags, or which rely on other crates, and they may not run the same without those options.