Fix check compiletest with in-tree libstd and add tests for it

Author: Kobzol

src/bootstrap/src/core/build_steps/check.rs

@@ -375,7 +375,7 @@ impl Step for Compiletest {
         );
 
         if mode != Mode::ToolBootstrap {
-            builder.ensure(Rustc::new(self.target, builder));
+            builder.std(compiler, self.target);
         }
 
         let mut cargo = prepare_tool_cargo(
@@ -399,6 +399,10 @@ impl Step for Compiletest {
         let _guard = builder.msg_check("compiletest artifacts", self.target, None);
         run_cargo(builder, cargo, builder.config.free_args.clone(), &stamp, vec![], true, false);
     }
+
+    fn metadata(&self) -> Option<StepMetadata> {
+        Some(StepMetadata::check("compiletest", self.target))
+    }
 }
 
 macro_rules! tool_check_step {

src/bootstrap/src/core/builder/tests.rs

@@ -1391,6 +1391,30 @@ mod snapshot {
         ");
     }
 
+    #[test]
+    fn check_compiletest() {
+        let ctx = TestCtx::new();
+        insta::assert_snapshot!(
+            ctx.config("check")
+                .path("compiletest")
+                .render_steps(), @"[check] compiletest <host>");
+    }
+
+    #[test]
+    fn check_compiletest_stage1_libtest() {
+        let ctx = TestCtx::new();
+        insta::assert_snapshot!(
+            ctx.config("check")
+                .path("compiletest")
+                .args(&["--set", "build.compiletest-use-stage0-libtest=false"])
+                .render_steps(), @r"
+        [build] llvm <host>
+        [build] rustc 0 <host> -> rustc 1 <host>
+        [build] rustc 1 <host> -> std 1 <host>
+        [check] compiletest <host>
+        ");
+    }
+
     #[test]
     fn test_exclude() {
         let ctx = TestCtx::new();