Auto merge of #33282 - alexcrichton:rustbuild-crate-tests, r=brson

rustbuild: Add support for crate tests + doctests

This commit adds support to rustbuild to run crate unit tests (those defined by
`#[test]`) as well as documentation tests. All tests are powered by `cargo test`
under the hood.

Each step requires the `libtest` library is built for that corresponding stage.
Ideally the `test` crate would be a dev-dependency, but for now it's just easier
to ensure that we sequence everything in the right order.

Currently no filtering is implemented, so there's not actually a method of
testing *only* libstd or *only* libcore, but rather entire swaths of crates are
tested all at once.

A few points of note here are:

* The `coretest` and `collectionstest` crates are just listed as `[[test]]`
  entires for `cargo test` to naturally pick up. This mean that `cargo test -p
  core` actually runs all the tests for libcore.
* Libraries that aren't tested all mention `test = false` in their `Cargo.toml`
* Crates aren't currently allowed to have dev-dependencies due to
  rust-lang/cargo#860, but we can likely alleviate this restriction once
  workspaces are implemented.

cc #31590

2 files changed, 7 insertions, 0 deletions

diff --git a/src/libcore/Cargo.toml b/src/libcore/Cargo.toml
index 98f941f0057..02fe574b81e 100644
--- a/src/libcore/Cargo.toml
+++ b/src/libcore/Cargo.toml
@@ -8,3 +8,7 @@ build = "build.rs"
 name = "core"
 path = "lib.rs"
 test = false
+
+[[test]]
+name = "coretest"
+path = "../libcoretest/lib.rs"
diff --git a/src/libcore/build.rs b/src/libcore/build.rs
index a991ac0de1a..255a367e58b 100644
--- a/src/libcore/build.rs
+++ b/src/libcore/build.rs
@@ -8,7 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![deny(warnings)]
+
 fn main() {
     // Remove this whenever snapshots and rustbuild nightlies are synced.
     println!("cargo:rustc-cfg=cargobuild");
+    println!("cargo:rerun-if-changed=build.rs")
 }