Compiler Test Documentation

In the Rust project, we use a special set of commands embedded in comments to test the Rust compiler. There are two groups of commands:

Header commands
Error info commands

Both types of commands are inside comments, but header commands should be in a comment before any code.

Summary of Error Info Commands

Error commands specify something about certain lines of the program. They tell the test what kind of error and what message you are expecting.

~: Associates the following error level and message with the current line
~|: Associates the following error level and message with the same line as the previous comment
~^: Associates the following error level and message with the previous line. Each caret (^) that you add adds a line to this, so ~^^^^^^^ is seven lines up.

The error levels that you can have are:

ERROR
WARNING
NOTE
HELP and SUGGESTION*

* Note: SUGGESTION must follow immediately after HELP.

Summary of Header Commands

Header commands specify something about the entire test file as a whole. They are normally put right after the copyright comment, e.g.:

// Copyright blah blah blah
// except according to those terms.

// ignore-test This doesn't actually work

Ignoring tests

These are used to ignore the test in some situations, which means the test won't be compiled or run.

ignore-X where X is a target detail or stage will ignore the test accordingly (see below)
ignore-pretty will not compile the pretty-printed test (this is done to test the pretty-printer, but might not always work)
ignore-test always ignores the test
ignore-lldb and ignore-gdb will skip a debuginfo test on that debugger.

only-X is the opposite. The test will run only when X matches.

Some examples of X in ignore-X:

Architecture: aarch64, arm, asmjs, mips, wasm32, x86_64, x86, ...
OS: android, emscripten, freebsd, ios, linux, macos, windows, ...
Environment (fourth word of the target triple): gnu, msvc, musl.
Pointer width: 32bit, 64bit.
Stage: stage0, stage1, stage2.

Other Header Commands

min-{gdb,lldb}-version
min-llvm-version
compile-pass for UI tests, indicates that the test is supposed to compile, as opposed to the default where the test is supposed to error out.
compile-flags passes extra command-line args to the compiler, e.g. compile-flags -g which forces debuginfo to be enabled.
should-fail indicates that the test should fail; used for "meta testing", where we test the compiletest program itself to check that it will generate errors in appropriate scenarios. This header is ignored for pretty-printer tests.
gate-test-X where X is a feature marks the test as "gate test" for feature X. Such tests are supposed to ensure that the compiler errors when usage of a gated feature is attempted without the proper #![feature(X)] tag. Each unstable lang feature is required to have a gate test.

Revisions

Certain classes of tests support "revisions" (as of the time of this writing, this includes run-pass, compile-fail, run-fail, and incremental, though incremental tests are somewhat different). Revisions allow a single test file to be used for multiple tests. This is done by adding a special header at the top of the file:

// revisions: foo bar baz

This will result in the test being compiled (and tested) three times, once with --cfg foo, once with --cfg bar, and once with --cfg baz. You can therefore use #[cfg(foo)] etc within the test to tweak each of these results.

You can also customize headers and expected error messages to a particular revision. To do this, add [foo] (or bar, baz, etc) after the // comment, like so:

// A flag to pass in only for cfg `foo`:
//[foo]compile-flags: -Z verbose

#[cfg(foo)]
fn test_foo() {
    let x: usize = 32_u32; //[foo]~ ERROR mismatched types
}

Note that not all headers have meaning when customized to a revision. For example, the ignore-test header (and all "ignore" headers) currently only apply to the test as a whole, not to particular revisions. The only headers that are intended to really work when customized to a revision are error patterns and compiler flags.

Guide to the UI Tests

The UI tests are intended to capture the compiler's complete output, so that we can test all aspects of the presentation. They work by compiling a file (e.g., ui/hello_world/main.rs), capturing the output, and then applying some normalization (see below). This normalized result is then compared against reference files named ui/hello_world/main.stderr and ui/hello_world/main.stdout. If either of those files doesn't exist, the output must be empty. If the test run fails, we will print out the current output, but it is also saved in build/<target-triple>/test/ui/hello_world/main.stdout (this path is printed as part of the test failure message), so you can run diff and so forth.

Normally, the test-runner checks that UI tests fail compilation. If you want to do a UI test for code that compiles (e.g. to test warnings, or if you have a collection of tests, only some of which error out), you can use the // compile-pass header command to have the test runner instead check that the test compiles successfully.

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 command you used to run the tests. This will then copy over the files from the build directory and use them as the new reference.

Normalization

The normalization applied is aimed at eliminating output difference between platforms, mainly about filenames:

the test directory is replaced with $DIR
all backslashes (\) are converted to forward slashes (/) (for Windows)
all CR LF newlines are converted to LF

Sometimes these built-in normalizations are not enough. In such cases, you may provide custom normalization rules using the header commands, e.g.

// normalize-stdout-test: "foo" -> "bar"
// normalize-stderr-32bit: "fn\(\) \(32 bits\)" -> "fn\(\) \($$PTR bits\)"
// normalize-stderr-64bit: "fn\(\) \(64 bits\)" -> "fn\(\) \($$PTR bits\)"

This tells the test, on 32-bit platforms, whenever the compiler writes fn() (32 bits) to stderr, it should be normalized to read fn() ($PTR bits) instead. Similar for 64-bit. The replacement is performed by regexes using default regex flavor provided by regex crate.

The corresponding reference file will use the normalized output to test both 32-bit and 64-bit platforms:

...
   |
   = note: source type: fn() ($PTR bits)
   = note: target type: u16 (16 bits)
...

Please see ui/transmute/main.rs and .stderr for a concrete usage example.

Besides normalize-stderr-32bit and -64bit, one may use any target information or stage supported by ignore-X here as well (e.g. normalize-stderr-windows or simply normalize-stderr-test for unconditional replacement).

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