Simplify LLVM bitcode linker in bootstrap and add tests for it

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

@@ -2059,7 +2059,7 @@ impl Step for Assemble {
                 trace!("llvm-bitcode-linker enabled, installing");
                 let llvm_bitcode_linker =
                     builder.ensure(crate::core::build_steps::tool::LlvmBitcodeLinker {
-                        compiler,
+                        build_compiler: compiler,
                         target: target_compiler.host,
                     });
 

src/bootstrap/src/core/build_steps/dist.rs

@@ -2374,7 +2374,8 @@ impl Step for LlvmBitcodeLinker {
 
         builder.ensure(compile::Rustc::new(compiler, target));
 
-        let llbc_linker = builder.ensure(tool::LlvmBitcodeLinker { compiler, target });
+        let llbc_linker =
+            builder.ensure(tool::LlvmBitcodeLinker { build_compiler: compiler, target });
 
         let self_contained_bin_dir = format!("lib/rustlib/{}/bin/self-contained", target.triple);
 

src/bootstrap/src/core/build_steps/tool.rs

@@ -1014,7 +1014,7 @@ impl Step for RustAnalyzerProcMacroSrv {
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
 pub struct LlvmBitcodeLinker {
-    pub compiler: Compiler,
+    pub build_compiler: Compiler,
     pub target: TargetSelection,
 }
 
@@ -1031,7 +1031,9 @@ impl Step for LlvmBitcodeLinker {
 
     fn make_run(run: RunConfig<'_>) {
         run.builder.ensure(LlvmBitcodeLinker {
-            compiler: run.builder.compiler(run.builder.top_stage, run.builder.config.host_target),
+            build_compiler: run
+                .builder
+                .compiler(run.builder.top_stage, run.builder.config.host_target),
             target: run.target,
         });
     }
@@ -1042,7 +1044,7 @@ impl Step for LlvmBitcodeLinker {
     )]
     fn run(self, builder: &Builder<'_>) -> ToolBuildResult {
         builder.ensure(ToolBuild {
-            compiler: self.compiler,
+            compiler: self.build_compiler,
             target: self.target,
             tool: "llvm-bitcode-linker",
             mode: Mode::ToolRustc,
@@ -1054,6 +1056,10 @@ impl Step for LlvmBitcodeLinker {
             artifact_kind: ToolArtifactKind::Binary,
         })
     }
+
+    fn metadata(&self) -> Option<StepMetadata> {
+        Some(StepMetadata::build("LlvmBitcodeLinker", self.target).built_by(self.build_compiler))
+    }
 }
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]

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

@@ -757,6 +757,27 @@ mod snapshot {
         ");
     }
 
+    #[test]
+    fn build_compiler_tools() {
+        let ctx = TestCtx::new();
+        insta::assert_snapshot!(
+            ctx
+                .config("build")
+                .stage(2)
+                .args(&["--set", "rust.llvm-bitcode-linker=true"])
+                .render_steps(), @r"
+        [build] llvm <host>
+        [build] rustc 0 <host> -> rustc 1 <host>
+        [build] rustc 1 <host> -> LlvmBitcodeLinker 2 <host>
+        [build] rustc 1 <host> -> std 1 <host>
+        [build] rustc 1 <host> -> rustc 2 <host>
+        [build] rustc 2 <host> -> LlvmBitcodeLinker 3 <host>
+        [build] rustc 2 <host> -> std 2 <host>
+        [build] rustdoc 1 <host>
+        "
+        );
+    }
+
     #[test]
     fn build_library_no_explicit_stage() {
         let ctx = TestCtx::new();
@@ -1040,6 +1061,7 @@ mod snapshot {
         [build] rustc 0 <host> -> cargo-clippy 1 <host>
         [build] rustc 0 <host> -> miri 1 <host>
         [build] rustc 0 <host> -> cargo-miri 1 <host>
+        [build] rustc 1 <host> -> LlvmBitcodeLinker 2 <host>
         ");
     }
 
@@ -1230,6 +1252,7 @@ mod snapshot {
         [build] rustc 0 <host> -> cargo-clippy 1 <target1>
         [build] rustc 0 <host> -> miri 1 <target1>
         [build] rustc 0 <host> -> cargo-miri 1 <target1>
+        [build] rustc 1 <host> -> LlvmBitcodeLinker 2 <target1>
         ");
     }