Make WasmComponentLd a ToolTarget tool

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

@@ -5,7 +5,8 @@ use crate::core::build_steps::compile::{
 };
 use crate::core::build_steps::tool;
 use crate::core::build_steps::tool::{
-    COMPILETEST_ALLOW_FEATURES, SourceType, get_compiler_for_target, prepare_tool_cargo,
+    COMPILETEST_ALLOW_FEATURES, SourceType, ToolTargetBuildMode, get_tool_target_compiler,
+    prepare_tool_cargo,
 };
 use crate::core::builder::{
     self, Alias, Builder, Kind, RunConfig, ShouldRun, Step, StepMetadata, crate_description,
@@ -252,7 +253,7 @@ fn prepare_compiler_for_check(
 
     match mode {
         Mode::ToolBootstrap => builder.compiler(0, host),
-        Mode::ToolTarget => get_compiler_for_target(builder, target),
+        Mode::ToolTarget => get_tool_target_compiler(builder, ToolTargetBuildMode::Build(target)),
         Mode::ToolStd => {
             // These tools require the local standard library to be checked
             let build_compiler = builder.compiler(builder.top_stage, host);

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

@@ -2286,15 +2286,13 @@ impl Step for Assemble {
         }
 
         // In addition to `rust-lld` also install `wasm-component-ld` when
-        // LLD is enabled. This is a relatively small binary that primarily
-        // delegates to the `rust-lld` binary for linking and then runs
-        // logic to create the final binary. This is used by the
-        // `wasm32-wasip2` target of Rust.
+        // is enabled. This is used by the `wasm32-wasip2` target of Rust.
         if builder.tool_enabled("wasm-component-ld") {
-            let wasm_component = builder.ensure(crate::core::build_steps::tool::WasmComponentLd {
-                compiler: build_compiler,
-                target: target_compiler.host,
-            });
+            let wasm_component =
+                builder.ensure(crate::core::build_steps::tool::WasmComponentLd::for_compiler(
+                    builder,
+                    target_compiler,
+                ));
             builder.copy_link(
                 &wasm_component.tool_path,
                 &libdir_bin.join(wasm_component.tool_path.file_name().unwrap()),

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

@@ -365,12 +365,36 @@ pub(crate) fn get_tool_rustc_compiler(
     builder.compiler(target_compiler.stage.saturating_sub(1), builder.config.host_target)
 }
 
-/// Returns the smallest stage compiler that is able to compile code for the given `target`.
-pub(crate) fn get_compiler_for_target(builder: &Builder<'_>, target: TargetSelection) -> Compiler {
+/// Determines how to build a `ToolTarget`, i.e. which compiler should be used to compile it.
+/// The compiler stage is automatically auto-bumped if we need to cross-compile a stage 1 tool.
+pub enum ToolTargetBuildMode {
+    /// Build the tool using rustc that corresponds to the selected CLI stage.
+    Build(TargetSelection),
+    /// Build the tool so that it can be attached to the sysroot of the passed compiler.
+    /// Since we always dist stage 2+, the compiler that builds the tool in this case has to be
+    /// stage 1+.
+    Dist(Compiler),
+}
+
+/// Returns compiler that is able to compile a `ToolTarget` tool with the given `mode`.
+pub(crate) fn get_tool_target_compiler(
+    builder: &Builder<'_>,
+    mode: ToolTargetBuildMode,
+) -> Compiler {
+    let (target, min_build_compiler_stage) = match mode {
+        ToolTargetBuildMode::Build(target) => {
+            assert!(builder.top_stage > 0);
+            (target, builder.top_stage - 1)
+        }
+        ToolTargetBuildMode::Dist(target_compiler) => {
+            assert!(target_compiler.stage > 0);
+            (target_compiler.host, target_compiler.stage - 1)
+        }
+    };
     let compiler = if builder.host_target == target {
-        builder.compiler(0, builder.host_target)
+        builder.compiler(min_build_compiler_stage, builder.host_target)
     } else {
-        builder.compiler(1, builder.host_target)
+        builder.compiler(min_build_compiler_stage.max(1), builder.host_target)
     };
     builder.std(compiler, target);
     compiler
@@ -533,7 +557,6 @@ bootstrap_tool!(
     // rustdoc-gui-test has a crate dependency on compiletest, so it needs the same unstable features.
     RustdocGUITest, "src/tools/rustdoc-gui-test", "rustdoc-gui-test", is_unstable_tool = true, allow_features = COMPILETEST_ALLOW_FEATURES;
     CoverageDump, "src/tools/coverage-dump", "coverage-dump";
-    WasmComponentLd, "src/tools/wasm-component-ld", "wasm-component-ld", is_unstable_tool = true, allow_features = "min_specialization";
     UnicodeTableGenerator, "src/tools/unicode-table-generator", "unicode-table-generator";
     FeaturesStatusDump, "src/tools/features-status-dump", "features-status-dump";
     OptimizedDist, "src/tools/opt-dist", "opt-dist", submodules = &["src/tools/rustc-perf"];
@@ -661,7 +684,10 @@ impl Step for RemoteTestServer {
 
     fn make_run(run: RunConfig<'_>) {
         run.builder.ensure(RemoteTestServer {
-            build_compiler: get_compiler_for_target(run.builder, run.target),
+            build_compiler: get_tool_target_compiler(
+                run.builder,
+                ToolTargetBuildMode::Build(run.target),
+            ),
             target: run.target,
         });
     }
@@ -935,6 +961,75 @@ impl Step for LldWrapper {
     }
 }
 
+/// Builds the `wasm-component-ld` linker wrapper, which is shipped with rustc to be executed on the
+/// host platform where rustc runs.
+#[derive(Debug, Clone, Hash, PartialEq, Eq)]
+pub struct WasmComponentLd {
+    build_compiler: Compiler,
+    target: TargetSelection,
+}
+
+impl WasmComponentLd {
+    /// Returns `WasmComponentLd` that should be **used** by the passed compiler.
+    pub fn for_compiler(builder: &Builder<'_>, target_compiler: Compiler) -> Self {
+        Self {
+            build_compiler: get_tool_target_compiler(
+                builder,
+                ToolTargetBuildMode::Dist(target_compiler),
+            ),
+            target: target_compiler.host,
+        }
+    }
+}
+
+impl Step for WasmComponentLd {
+    type Output = ToolBuildResult;
+
+    const ONLY_HOSTS: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("src/tools/wasm-component-ld")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(WasmComponentLd {
+            build_compiler: get_tool_target_compiler(
+                run.builder,
+                ToolTargetBuildMode::Build(run.target),
+            ),
+            target: run.target,
+        });
+    }
+
+    #[cfg_attr(
+        feature = "tracing",
+        instrument(
+            level = "debug",
+            name = "WasmComponentLd::run",
+            skip_all,
+            fields(build_compiler = ?self.build_compiler),
+        ),
+    )]
+    fn run(self, builder: &Builder<'_>) -> ToolBuildResult {
+        builder.ensure(ToolBuild {
+            build_compiler: self.build_compiler,
+            target: self.target,
+            tool: "wasm-component-ld",
+            mode: Mode::ToolTarget,
+            path: "src/tools/wasm-component-ld",
+            source_type: SourceType::InTree,
+            extra_features: vec![],
+            allow_features: "min-specialization",
+            cargo_args: vec![],
+            artifact_kind: ToolArtifactKind::Binary,
+        })
+    }
+
+    fn metadata(&self) -> Option<StepMetadata> {
+        Some(StepMetadata::build("WasmComponentLd", self.target).built_by(self.build_compiler))
+    }
+}
+
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
 pub struct RustAnalyzer {
     pub compiler: Compiler,

src/bootstrap/src/core/builder/mod.rs

@@ -981,6 +981,7 @@ impl<'a> Builder<'a> {
                 tool::CoverageDump,
                 tool::LlvmBitcodeLinker,
                 tool::RustcPerf,
+                tool::WasmComponentLd
             ),
             Kind::Clippy => describe!(
                 clippy::Std,