Add a section about `rustc_clean`
diff --git a/src/doc/rustc-dev-guide/src/tests/compiletest.md b/src/doc/rustc-dev-guide/src/tests/compiletest.md index c2aee82..a691380 100644 --- a/src/doc/rustc-dev-guide/src/tests/compiletest.md +++ b/src/doc/rustc-dev-guide/src/tests/compiletest.md
@@ -187,8 +187,26 @@ cause an Internal Compiler Error (ICE). This is a highly specialized directive to check that the incremental cache continues to work after an ICE. -[`tests/incremental`]: https://github.com/rust-lang/rust/tree/HEAD/tests/incremental +Incremental tests may use the attribute `#[rustc_clean(...)]` attribute. This attribute compares +the fingerprint from the current compilation session with the previous one. +The first revision should never have an active `rustc_clean` attribute, since it will always be dirty. +In the default mode, it asserts that the fingerprints must be the same. +The attribute takes the following arguments: + +* `cfg="<cond>"` — checks the cfg condition `<cond>`, and only runs the check if the config condition evaluates to true. + This can be used to only run the `rustc_clean` attribute in a specific revision. +* `except="<query1>,<query2>,..."` — asserts that the query results for the listed queries must be different, + rather than the same. +* `loaded_from_disk="<query1>,<query2>,..."` — asserts that the query results for the listed queries + were actually loaded from disk (not just marked green). + This can be useful to ensure that a test is actually exercising the deserialization + logic for a particular query result. This can be combined with `except`. + +A simple example of a test using `rustc_clean` is the [hello_world test]. + +[`tests/incremental`]: https://github.com/rust-lang/rust/tree/7b42543/tests/incremental +[hello_world test]: https://github.com/rust-lang/rust/blob/646a3f8c15baefb98dc6e0c1c1ba3356db702d2a/tests/incremental/hello_world.rs ### Debuginfo tests