Rollup merge of #148459 - Zalathar:bootstrap-py, r=Kobzol

bootstrap: Split out a separate `./x test bootstrap-py` step

While testing changes to bootstrap, I was annoyed by the fact that `./x test bootstrap` spams a bunch of mysterious output to the console.

That output turns out to come from `bootstrap_test.py`, which runs unit tests for the Python parts of bootstrap. Those tests are (presumably) useful, but they don't add value when working on the Rust parts of bootstrap.

This PR therefore pulls them out into a separate test step that can be run with `./x test bootstrap-py`.

src/bootstrap/src/core/build_steps/test.rs

@@ -3337,6 +3337,42 @@ fn distcheck_rustc_dev(builder: &Builder<'_>, dir: &Path) {
     builder.remove_dir(dir);
 }
 
+/// Runs unit tests in `bootstrap_test.py`, which test the Python parts of bootstrap.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub(crate) struct BootstrapPy;
+
+impl Step for BootstrapPy {
+    type Output = ();
+    const DEFAULT: bool = true;
+    const IS_HOST: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        // Bootstrap tests might not be perfectly self-contained and can depend
+        // on the environment, so only run them by default in CI, not locally.
+        // See `test::Bootstrap::should_run`.
+        let is_ci = run.builder.config.is_running_on_ci;
+        run.alias("bootstrap-py").default_condition(is_ci)
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(BootstrapPy)
+    }
+
+    fn run(self, builder: &Builder<'_>) -> Self::Output {
+        let mut check_bootstrap = command(builder.python());
+        check_bootstrap
+            .args(["-m", "unittest", "bootstrap_test.py"])
+            // Forward command-line args after `--` to unittest, for filtering etc.
+            .args(builder.config.test_args())
+            .env("BUILD_DIR", &builder.out)
+            .env("BUILD_PLATFORM", builder.build.host_target.triple)
+            .env("BOOTSTRAP_TEST_RUSTC_BIN", &builder.initial_rustc)
+            .env("BOOTSTRAP_TEST_CARGO_BIN", &builder.initial_cargo)
+            .current_dir(builder.src.join("src/bootstrap/"));
+        check_bootstrap.delay_failure().run(builder);
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Bootstrap;
 
@@ -3353,18 +3389,6 @@ impl Step for Bootstrap {
         // Some tests require cargo submodule to be present.
         builder.build.require_submodule("src/tools/cargo", None);
 
-        let mut check_bootstrap = command(builder.python());
-        check_bootstrap
-            .args(["-m", "unittest", "bootstrap_test.py"])
-            .env("BUILD_DIR", &builder.out)
-            .env("BUILD_PLATFORM", builder.build.host_target.triple)
-            .env("BOOTSTRAP_TEST_RUSTC_BIN", &builder.initial_rustc)
-            .env("BOOTSTRAP_TEST_CARGO_BIN", &builder.initial_cargo)
-            .current_dir(builder.src.join("src/bootstrap/"));
-        // NOTE: we intentionally don't pass test_args here because the args for unittest and cargo test are mutually incompatible.
-        // Use `python -m unittest` manually if you want to pass arguments.
-        check_bootstrap.delay_failure().run(builder);
-
         let mut cargo = tool::prepare_tool_cargo(
             builder,
             build_compiler,

src/bootstrap/src/core/builder/mod.rs

@@ -869,6 +869,7 @@ impl<'a> Builder<'a> {
             Kind::Test => describe!(
                 crate::core::build_steps::toolstate::ToolStateCheck,
                 test::Tidy,
+                test::BootstrapPy,
                 test::Bootstrap,
                 test::Ui,
                 test::Crashes,