do not build additional stage on compiler paths

When calling `x build compiler (or rustc) --stage N` bootstrap builds stage N+1 compiler,
which is clearly not what we requested. This doesn't happen when running `x build --stage N`
without explicitly targeting the compiler.

The changes applied fix this issue.

Signed-off-by: onur-ozkan <[email protected]>

Author: onur-ozkan

src/bootstrap/src/core/build_steps/compile.rs

@@ -993,7 +993,9 @@ impl Step for Rustc {
     fn make_run(run: RunConfig<'_>) {
         let crates = run.cargo_crates_in_set();
         run.builder.ensure(Rustc {
-            compiler: run.builder.compiler(run.builder.top_stage, run.build_triple()),
+            compiler: run
+                .builder
+                .compiler(run.builder.top_stage.saturating_sub(1), run.build_triple()),
             target: run.target,
             crates,
         });
@@ -1902,7 +1904,7 @@ impl Step for Assemble {
 
     fn make_run(run: RunConfig<'_>) {
         run.builder.ensure(Assemble {
-            target_compiler: run.builder.compiler(run.builder.top_stage + 1, run.target),
+            target_compiler: run.builder.compiler(run.builder.top_stage, run.target),
         });
     }
 

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

@@ -664,15 +664,13 @@ mod dist {
                 std!(TEST_TRIPLE_1 => TEST_TRIPLE_3, stage = 2),
             ]
         );
-        assert_eq!(builder.cache.all::<compile::Assemble>().len(), 5);
+        assert_eq!(builder.cache.all::<compile::Assemble>().len(), 4);
         assert_eq!(
             first(builder.cache.all::<compile::Rustc>()),
             &[
                 rustc!(TEST_TRIPLE_1 => TEST_TRIPLE_1, stage = 0),
                 rustc!(TEST_TRIPLE_1 => TEST_TRIPLE_1, stage = 1),
-                rustc!(TEST_TRIPLE_1 => TEST_TRIPLE_1, stage = 2),
                 rustc!(TEST_TRIPLE_1 => TEST_TRIPLE_2, stage = 1),
-                rustc!(TEST_TRIPLE_1 => TEST_TRIPLE_2, stage = 2),
             ]
         );
     }