run-make: update test suite README

Author: jieyouxu

tests/run-make/README.md

@@ -1,48 +1,26 @@
 # 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.
+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:
+A `run-make` test is a test recipe source file `rmake.rs` accompanied by its parent directory (e.g. `tests/run-make/foo/rmake.rs` is the `foo` `run-make` test).
 
-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 are in [`src/tools/compiletest/src/runtest.rs`](../../src/tools/compiletest/src/runtest.rs), in `run_rmake_v2_test` and `run_rmake_legacy_test`.
 
-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:
+The setup for the `rmake.rs` can be summarized as 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/`
+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.
+   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.