Unrolled build for rust-lang#123504

Rollup merge of rust-lang#123504 - RalfJung:test-cargo-miri, r=Mark-Simulacrum

bootstrap: split cargo-miri test into separate Step

This makes it easier to test just the driver or the cargo-miri integration.

````@rust-lang/miri```` this means to test both you now need to do `./x.py test miri cargo-miri`.

Author: rust-timer

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

@@ -597,7 +597,7 @@ impl Step for Miri {
         builder.ensure(compile::Std::new(target_compiler, host));
         let host_sysroot = builder.sysroot(target_compiler);
 
-        // # Run `cargo test`.
+        // Run `cargo test`.
         // This is with the Miri crate, so it uses the host compiler.
         let mut cargo = tool::prepare_tool_cargo(
             builder,
@@ -652,15 +652,46 @@ impl Step for Miri {
                 builder.run(&mut cargo);
             }
         }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct CargoMiri {
+    target: TargetSelection,
+}
+
+impl Step for CargoMiri {
+    type Output = ();
+    const ONLY_HOSTS: bool = false;
 
-        // # Run `cargo miri test`.
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("src/tools/miri/cargo-miri")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(CargoMiri { target: run.target });
+    }
+
+    /// Tests `cargo miri test`.
+    fn run(self, builder: &Builder<'_>) {
+        let host = builder.build.build;
+        let target = self.target;
+        let stage = builder.top_stage;
+        if stage == 0 {
+            eprintln!("cargo-miri cannot be tested at stage 0");
+            std::process::exit(1);
+        }
+
+        // This compiler runs on the host, we'll just use it for the target.
+        let compiler = builder.compiler(stage, host);
+
+        // Run `cargo miri test`.
         // This is just a smoke test (Miri's own CI invokes this in a bunch of different ways and ensures
         // that we get the desired output), but that is sufficient to make sure that the libtest harness
         // itself executes properly under Miri, and that all the logic in `cargo-miri` does not explode.
-        // This is running the build `cargo-miri` for the given target, so we need the target compiler.
         let mut cargo = tool::prepare_tool_cargo(
             builder,
-            target_compiler,
+            compiler,
             Mode::ToolStd, // it's unclear what to use here, we're not building anything just doing a smoke test!
             target,
             "miri-test",

src/bootstrap/src/core/builder.rs

@@ -808,6 +808,7 @@ impl<'a> Builder<'a> {
                 test::EditionGuide,
                 test::Rustfmt,
                 test::Miri,
+                test::CargoMiri,
                 test::Clippy,
                 test::RustDemangler,
                 test::CompiletestTest,

src/ci/docker/host-x86_64/x86_64-gnu-tools/checktools.sh

@@ -32,18 +32,18 @@ python3 "$X_PY" test --stage 2 src/tools/rustfmt
 # that bugs which only surface when the GC runs at a specific time are more likely to cause CI to fail.
 # This significantly increases the runtime of our test suite, or we'd do this in PR CI too.
 if [ -z "${PR_CI_JOB:-}" ]; then
-    MIRIFLAGS=-Zmiri-provenance-gc=1 python3 "$X_PY" test --stage 2 src/tools/miri
+    MIRIFLAGS=-Zmiri-provenance-gc=1 python3 "$X_PY" test --stage 2 src/tools/miri src/tools/miri/cargo-miri
 else
-    python3 "$X_PY" test --stage 2 src/tools/miri
+    python3 "$X_PY" test --stage 2 src/tools/miri src/tools/miri/cargo-miri
 fi
 # We natively run this script on x86_64-unknown-linux-gnu and x86_64-pc-windows-msvc.
 # Also cover some other targets via cross-testing, in particular all tier 1 targets.
 case $HOST_TARGET in
   x86_64-unknown-linux-gnu)
     # Only this branch runs in PR CI.
     # Fully test all main OSes, including a 32bit target.
-    python3 "$X_PY" test --stage 2 src/tools/miri --target x86_64-apple-darwin
-    python3 "$X_PY" test --stage 2 src/tools/miri --target i686-pc-windows-msvc
+    python3 "$X_PY" test --stage 2 src/tools/miri src/tools/miri/cargo-miri --target x86_64-apple-darwin
+    python3 "$X_PY" test --stage 2 src/tools/miri src/tools/miri/cargo-miri --target i686-pc-windows-msvc
     # Only run "pass" tests for the remaining targets, which is quite a bit faster.
     python3 "$X_PY" test --stage 2 src/tools/miri --target x86_64-pc-windows-gnu --test-args pass
     python3 "$X_PY" test --stage 2 src/tools/miri --target i686-unknown-linux-gnu --test-args pass