rust/tests/run-make/README.md

# The `run-make` test suite

The `run-make` test suite contains tests which are the most flexible out of all
the [rust-lang/rust](https://github.com/rust-lang/rust) test suites. `run-make`
tests can basically contain arbitrary code, and are supported by the
[`run_make_support`] library.

## Infrastructure

There are two kinds of run-make tests:

1. The new `rmake.rs` version: this allows run-make tests to be written in Rust
   (with `rmake.rs` as the main test file).
2. The legacy `Makefile` version: this is what run-make tests were written with
   before support for `rmake.rs` was introduced.

The implementation for collecting and building the `rmake.rs` recipes (or
`Makefile`s) are in
[`src/tools/compiletest/src/runtest.rs`](../../src/tools/compiletest/src/runtest.rs),
in `run_rmake_v2_test` and `run_rmake_legacy_test`.

### Rust-based `run-make` tests: `rmake.rs`

The setup for the `rmake.rs` version is a 3-stage process:

1. First, we build the [`run_make_support`] library in bootstrap as a tool lib.
2. Then, we compile the `rmake.rs` "recipe" linking the support library and its
   dependencies in, and provide a bunch of env vars. We setup a directory
   structure within `build/<target>/test/run-make/`

   ```
   <test-name>/
       rmake.exe              # recipe binary
       rmake_out/             # sources from test sources copied over
   ```

   and copy non-`rmake.rs` input support files over to `rmake_out/`. The
   support library is made available as an [*extern prelude*][extern_prelude].
3. Finally, we run the recipe binary and set `rmake_out/` as the working
   directory.

[`run_make_support`]: ../../src/tools/run-make-support
[extern_prelude]: https://doc.rust-lang.org/reference/names/preludes.html#extern-prelude

### Formatting

Note that files under `tests/` are not formatted by `./x fmt`,
use `rustfmt tests/path/to/file.rs` to format a specific file if desired.