Use stage auto-bump when cross-checking on stage 1

Author: Kobzol

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

@@ -196,11 +196,13 @@ impl Step for Rustc {
         // Build host std for compiling build scripts
         builder.std(build_compiler, build_compiler.host);
 
-        // Build target std so that the checked rustc can link to it during the check
-        // FIXME: maybe we can a way to only do a check of std here?
-        // But for that we would have to copy the stdlib rmetas to the sysroot of the build
-        // compiler, which conflicts with std rlibs, if we also build std.
-        builder.std(build_compiler, target);
+        if build_compiler.host != target {
+            // Build target std so that the checked rustc can link to it during the check
+            // FIXME: maybe we can a way to only do a check of std here?
+            // But for that we would have to copy the stdlib rmetas to the sysroot of the build
+            // compiler, which conflicts with std rlibs, if we also build std.
+            builder.ensure(Std::new(build_compiler, target));
+        }
 
         let mut cargo = builder::Cargo::new(
             builder,
@@ -270,13 +272,19 @@ fn prepare_compiler_for_check(
             build_compiler
         }
         Mode::Rustc => {
-            if builder.top_stage < 2 && host != target {
-                eprintln!("Cannot do a cross-compilation check of rustc on stage 1, use stage 2");
-                exit!(1);
+            // This is a horrible hack, because we actually change the compiler stage numbering
+            // here. If you do `x check --stage 1 --host FOO`, we build stage 1 host rustc,
+            // and use that to check stage 1 FOO rustc (which actually makes that stage 2 FOO
+            // rustc).
+            //
+            // FIXME: remove this and either fix cross-compilation check on stage 2 (which has a
+            // myriad of other problems) or disable cross-checking on stage 1.
+            if host != target {
+                builder.compiler(builder.top_stage, host)
+            } else {
+                // When checking the stage N compiler, we want to do it with the stage N-1 compiler
+                builder.compiler(builder.top_stage - 1, host)
             }
-
-            // When checking the stage N compiler, we want to do it with the stage N-1 compiler
-            builder.compiler(builder.top_stage - 1, host)
         }
         Mode::Std => {
             // When checking std stage N, we want to do it with the stage N compiler

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

@@ -1299,31 +1299,29 @@ mod snapshot {
         let ctx = TestCtx::new();
         insta::assert_snapshot!(
             ctx.config("check")
-                .stage(2)
                 .targets(&[TEST_TRIPLE_1])
                 .hosts(&[TEST_TRIPLE_1])
                 .render_steps(), @r"
         [build] llvm <host>
         [build] rustc 0 <host> -> rustc 1 <host>
         [build] rustc 1 <host> -> std 1 <host>
-        [build] rustc 1 <host> -> std 1 <target1>
-        [build] llvm <target1>
+        [check] rustc 1 <host> -> std 1 <target1>
         [check] rustc 1 <host> -> rustc 2 <target1>
-        [check] rustc 1 <host> -> Rustdoc 2 <target1>
-        [check] rustc 1 <host> -> cranelift 2 <target1>
-        [check] rustc 1 <host> -> gcc 2 <target1>
-        [check] rustc 1 <host> -> Clippy 2 <target1>
-        [check] rustc 1 <host> -> Miri 2 <target1>
-        [check] rustc 1 <host> -> CargoMiri 2 <target1>
+        [check] rustc 0 <host> -> std 0 <target1>
+        [build] llvm <target1>
+        [check] rustc 0 <host> -> rustc 1 <target1>
+        [check] rustc 0 <host> -> Rustdoc 1 <target1>
+        [check] rustc 0 <host> -> cranelift 1 <target1>
+        [check] rustc 0 <host> -> gcc 1 <target1>
+        [check] rustc 0 <host> -> Clippy 1 <target1>
+        [check] rustc 0 <host> -> Miri 1 <target1>
+        [check] rustc 0 <host> -> CargoMiri 1 <target1>
         [check] rustc 0 <host> -> MiroptTestTools 1 <target1>
-        [check] rustc 1 <host> -> Rustfmt 2 <target1>
-        [check] rustc 1 <host> -> rust-analyzer 2 <target1>
-        [build] rustc 1 <host> -> rustc 2 <host>
-        [build] rustc 2 <host> -> std 2 <host>
-        [build] rustc 2 <host> -> std 2 <target1>
-        [check] rustc 2 <host> -> TestFloatParse 3 <target1>
+        [check] rustc 0 <host> -> Rustfmt 1 <target1>
+        [check] rustc 0 <host> -> rust-analyzer 1 <target1>
+        [build] rustc 1 <host> -> std 1 <target1>
+        [check] rustc 1 <host> -> TestFloatParse 2 <target1>
         [check] rustc 0 <host> -> FeaturesStatusDump 1 <target1>
-        [check] rustc 2 <host> -> std 2 <target1>
         ");
     }