Rename and document `ONLY_HOSTS` in bootstrap

13 files changed, 119 insertions, 114 deletions

diff --git a/src/bootstrap/src/core/build_steps/check.rs b/src/bootstrap/src/core/build_steps/check.rs
index 6d393446d45..1e08e8547dc 100644
--- a/src/bootstrap/src/core/build_steps/check.rs
+++ b/src/bootstrap/src/core/build_steps/check.rs
@@ -172,7 +172,7 @@ impl Rustc {
 
 impl Step for Rustc {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -324,7 +324,7 @@ pub struct CodegenBackend {
 
 impl Step for CodegenBackend {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -410,7 +410,7 @@ macro_rules! tool_check_step {
 
         impl Step for $name {
             type Output = ();
-            const ONLY_HOSTS: bool = true;
+            const IS_HOST: bool = true;
             /// Most of the tool-checks using this macro are run by default.
             const DEFAULT: bool = true $( && $default )?;
 
diff --git a/src/bootstrap/src/core/build_steps/clippy.rs b/src/bootstrap/src/core/build_steps/clippy.rs
index 23d9a032eb9..3c4aa0886c2 100644
--- a/src/bootstrap/src/core/build_steps/clippy.rs
+++ b/src/bootstrap/src/core/build_steps/clippy.rs
@@ -256,7 +256,7 @@ impl Rustc {
 
 impl Step for Rustc {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
diff --git a/src/bootstrap/src/core/build_steps/compile.rs b/src/bootstrap/src/core/build_steps/compile.rs
index 2a236de0192..c04f42ab055 100644
--- a/src/bootstrap/src/core/build_steps/compile.rs
+++ b/src/bootstrap/src/core/build_steps/compile.rs
@@ -995,7 +995,7 @@ impl Step for Rustc {
     /// uplifting it from stage Y, causing the other stage to fail when attempting to link with
     /// stage X which was never actually built.
     type Output = u32;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = false;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -1559,7 +1559,7 @@ pub struct GccCodegenBackend {
 impl Step for GccCodegenBackend {
     type Output = GccCodegenBackendOutput;
 
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("rustc_codegen_gcc").alias("cg_gcc")
@@ -1644,7 +1644,7 @@ pub struct CraneliftCodegenBackend {
 
 impl Step for CraneliftCodegenBackend {
     type Output = BuildStamp;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("rustc_codegen_cranelift").alias("cg_clif")
@@ -2008,7 +2008,7 @@ pub struct Assemble {
 
 impl Step for Assemble {
     type Output = Compiler;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("compiler/rustc").path("compiler")
diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index 7fdfeabe29d..64c2cdd2ec7 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -140,7 +140,7 @@ pub struct RustcDocs {
 impl Step for RustcDocs {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -402,7 +402,7 @@ pub struct Rustc {
 impl Step for Rustc {
     type Output = GeneratedTarball;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("rustc")
@@ -794,7 +794,7 @@ pub struct RustcDev {
 impl Step for RustcDev {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("rustc-dev")
@@ -1024,7 +1024,7 @@ impl Step for Src {
     /// The output path of the src installer tarball
     type Output = GeneratedTarball;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("rust-src")
@@ -1085,7 +1085,7 @@ impl Step for PlainSourceTarball {
     /// Produces the location of the tarball generated
     type Output = GeneratedTarball;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1233,7 +1233,7 @@ pub struct Cargo {
 impl Step for Cargo {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = should_build_extended_tool(run.builder, "cargo");
@@ -1287,7 +1287,7 @@ pub struct RustAnalyzer {
 impl Step for RustAnalyzer {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = should_build_extended_tool(run.builder, "rust-analyzer");
@@ -1330,7 +1330,7 @@ pub struct Clippy {
 impl Step for Clippy {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = should_build_extended_tool(run.builder, "clippy");
@@ -1378,7 +1378,7 @@ pub struct Miri {
 impl Step for Miri {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = should_build_extended_tool(run.builder, "miri");
@@ -1428,7 +1428,7 @@ pub struct CraneliftCodegenBackend {
 impl Step for CraneliftCodegenBackend {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         // We only want to build the cranelift backend in `x dist` if the backend was enabled
@@ -1519,7 +1519,7 @@ pub struct Rustfmt {
 impl Step for Rustfmt {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = should_build_extended_tool(run.builder, "rustfmt");
@@ -1564,7 +1564,7 @@ pub struct Extended {
 impl Step for Extended {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -2301,7 +2301,7 @@ pub struct LlvmTools {
 
 impl Step for LlvmTools {
     type Output = Option<GeneratedTarball>;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -2406,7 +2406,7 @@ pub struct LlvmBitcodeLinker {
 impl Step for LlvmBitcodeLinker {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = should_build_extended_tool(run.builder, "llvm-bitcode-linker");
@@ -2458,7 +2458,7 @@ pub struct RustDev {
 impl Step for RustDev {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("rust-dev")
@@ -2561,7 +2561,7 @@ pub struct Bootstrap {
 impl Step for Bootstrap {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = false;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("bootstrap")
@@ -2601,7 +2601,7 @@ pub struct BuildManifest {
 impl Step for BuildManifest {
     type Output = GeneratedTarball;
     const DEFAULT: bool = false;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("build-manifest")
@@ -2633,7 +2633,7 @@ pub struct ReproducibleArtifacts {
 impl Step for ReproducibleArtifacts {
     type Output = Option<GeneratedTarball>;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("reproducible-artifacts")
diff --git a/src/bootstrap/src/core/build_steps/doc.rs b/src/bootstrap/src/core/build_steps/doc.rs
index 6f0d5203d11..f6b27d83120 100644
--- a/src/bootstrap/src/core/build_steps/doc.rs
+++ b/src/bootstrap/src/core/build_steps/doc.rs
@@ -830,7 +830,7 @@ impl Rustc {
 impl Step for Rustc {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -975,7 +975,7 @@ macro_rules! tool_doc {
         impl Step for $tool {
             type Output = ();
             const DEFAULT: bool = true;
-            const ONLY_HOSTS: bool = true;
+            const IS_HOST: bool = true;
 
             fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
                 let builder = run.builder;
@@ -1139,7 +1139,7 @@ pub struct ErrorIndex {
 impl Step for ErrorIndex {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1181,7 +1181,7 @@ pub struct UnstableBookGen {
 impl Step for UnstableBookGen {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1248,7 +1248,7 @@ impl RustcBook {
 impl Step for RustcBook {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
diff --git a/src/bootstrap/src/core/build_steps/gcc.rs b/src/bootstrap/src/core/build_steps/gcc.rs
index 389afaecea3..2b36b0f2e27 100644
--- a/src/bootstrap/src/core/build_steps/gcc.rs
+++ b/src/bootstrap/src/core/build_steps/gcc.rs
@@ -47,7 +47,7 @@ impl GccOutput {
 impl Step for Gcc {
     type Output = GccOutput;
 
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/gcc").alias("gcc")
diff --git a/src/bootstrap/src/core/build_steps/install.rs b/src/bootstrap/src/core/build_steps/install.rs
index 666f2715224..4457258e9cd 100644
--- a/src/bootstrap/src/core/build_steps/install.rs
+++ b/src/bootstrap/src/core/build_steps/install.rs
@@ -163,7 +163,7 @@ macro_rules! install {
        $($name:ident,
        $condition_name: ident = $path_or_alias: literal,
        $default_cond:expr,
-       only_hosts: $only_hosts:expr,
+       IS_HOST: $IS_HOST:expr,
        $run_item:block $(, $c:ident)*;)+) => {
         $(
             #[derive(Debug, Clone, Hash, PartialEq, Eq)]
@@ -183,7 +183,7 @@ macro_rules! install {
         impl Step for $name {
             type Output = ();
             const DEFAULT: bool = true;
-            const ONLY_HOSTS: bool = $only_hosts;
+            const IS_HOST: bool = $IS_HOST;
             $(const $c: bool = true;)*
 
             fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -206,11 +206,11 @@ macro_rules! install {
 }
 
 install!((self, builder, _config),
-    Docs, path = "src/doc", _config.docs, only_hosts: false, {
+    Docs, path = "src/doc", _config.docs, IS_HOST: false, {
         let tarball = builder.ensure(dist::Docs { host: self.target }).expect("missing docs");
         install_sh(builder, "docs", self.compiler.stage, Some(self.target), &tarball);
     };
-    Std, path = "library/std", true, only_hosts: false, {
+    Std, path = "library/std", true, IS_HOST: false, {
         // `expect` should be safe, only None when host != build, but this
         // only runs when host == build
         let tarball = builder.ensure(dist::Std {
@@ -219,13 +219,13 @@ install!((self, builder, _config),
         }).expect("missing std");
         install_sh(builder, "std", self.compiler.stage, Some(self.target), &tarball);
     };
-    Cargo, alias = "cargo", Self::should_build(_config), only_hosts: true, {
+    Cargo, alias = "cargo", Self::should_build(_config), IS_HOST: true, {
         let tarball = builder
             .ensure(dist::Cargo { build_compiler: self.compiler, target: self.target })
             .expect("missing cargo");
         install_sh(builder, "cargo", self.compiler.stage, Some(self.target), &tarball);
     };
-    RustAnalyzer, alias = "rust-analyzer", Self::should_build(_config), only_hosts: true, {
+    RustAnalyzer, alias = "rust-analyzer", Self::should_build(_config), IS_HOST: true, {
         if let Some(tarball) =
             builder.ensure(dist::RustAnalyzer { build_compiler: self.compiler, target: self.target })
         {
@@ -236,13 +236,13 @@ install!((self, builder, _config),
             );
         }
     };
-    Clippy, alias = "clippy", Self::should_build(_config), only_hosts: true, {
+    Clippy, alias = "clippy", Self::should_build(_config), IS_HOST: true, {
         let tarball = builder
             .ensure(dist::Clippy { build_compiler: self.compiler, target: self.target })
             .expect("missing clippy");
         install_sh(builder, "clippy", self.compiler.stage, Some(self.target), &tarball);
     };
-    Miri, alias = "miri", Self::should_build(_config), only_hosts: true, {
+    Miri, alias = "miri", Self::should_build(_config), IS_HOST: true, {
         if let Some(tarball) = builder.ensure(dist::Miri { build_compiler: self.compiler, target: self.target }) {
             install_sh(builder, "miri", self.compiler.stage, Some(self.target), &tarball);
         } else {
@@ -252,7 +252,7 @@ install!((self, builder, _config),
             );
         }
     };
-    LlvmTools, alias = "llvm-tools", _config.llvm_tools_enabled && _config.llvm_enabled(_config.host_target), only_hosts: true, {
+    LlvmTools, alias = "llvm-tools", _config.llvm_tools_enabled && _config.llvm_enabled(_config.host_target), IS_HOST: true, {
         if let Some(tarball) = builder.ensure(dist::LlvmTools { target: self.target }) {
             install_sh(builder, "llvm-tools", self.compiler.stage, Some(self.target), &tarball);
         } else {
@@ -261,7 +261,7 @@ install!((self, builder, _config),
             );
         }
     };
-    Rustfmt, alias = "rustfmt", Self::should_build(_config), only_hosts: true, {
+    Rustfmt, alias = "rustfmt", Self::should_build(_config), IS_HOST: true, {
         if let Some(tarball) = builder.ensure(dist::Rustfmt {
             build_compiler: self.compiler,
             target: self.target
@@ -273,13 +273,13 @@ install!((self, builder, _config),
             );
         }
     };
-    Rustc, path = "compiler/rustc", true, only_hosts: true, {
+    Rustc, path = "compiler/rustc", true, IS_HOST: true, {
         let tarball = builder.ensure(dist::Rustc {
             compiler: builder.compiler(builder.top_stage, self.target),
         });
         install_sh(builder, "rustc", self.compiler.stage, Some(self.target), &tarball);
     };
-    RustcCodegenCranelift, alias = "rustc-codegen-cranelift", Self::should_build(_config), only_hosts: true, {
+    RustcCodegenCranelift, alias = "rustc-codegen-cranelift", Self::should_build(_config), IS_HOST: true, {
         if let Some(tarball) = builder.ensure(dist::CraneliftCodegenBackend {
             build_compiler: self.compiler,
             target: self.target
@@ -292,7 +292,7 @@ install!((self, builder, _config),
             );
         }
     };
-    LlvmBitcodeLinker, alias = "llvm-bitcode-linker", Self::should_build(_config), only_hosts: true, {
+    LlvmBitcodeLinker, alias = "llvm-bitcode-linker", Self::should_build(_config), IS_HOST: true, {
         if let Some(tarball) = builder.ensure(dist::LlvmBitcodeLinker { build_compiler: self.compiler, target: self.target }) {
             install_sh(builder, "llvm-bitcode-linker", self.compiler.stage, Some(self.target), &tarball);
         } else {
@@ -311,7 +311,7 @@ pub struct Src {
 impl Step for Src {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let config = &run.builder.config;
diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index 16941a32bb1..c476d1c1a2d 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -255,7 +255,7 @@ pub struct Llvm {
 impl Step for Llvm {
     type Output = LlvmResult;
 
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/llvm-project").path("src/llvm-project/llvm")
@@ -908,7 +908,7 @@ pub struct Enzyme {
 
 impl Step for Enzyme {
     type Output = PathBuf;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/enzyme/enzyme")
@@ -1013,7 +1013,7 @@ pub struct Lld {
 
 impl Step for Lld {
     type Output = PathBuf;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/llvm-project/lld")
diff --git a/src/bootstrap/src/core/build_steps/run.rs b/src/bootstrap/src/core/build_steps/run.rs
index 7475a777dad..7f1a7d00257 100644
--- a/src/bootstrap/src/core/build_steps/run.rs
+++ b/src/bootstrap/src/core/build_steps/run.rs
@@ -22,7 +22,7 @@ pub struct BuildManifest;
 
 impl Step for BuildManifest {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/build-manifest")
@@ -61,7 +61,7 @@ pub struct BumpStage0;
 
 impl Step for BumpStage0 {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/bump-stage0")
@@ -83,7 +83,7 @@ pub struct ReplaceVersionPlaceholder;
 
 impl Step for ReplaceVersionPlaceholder {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/replace-version-placeholder")
@@ -174,7 +174,7 @@ pub struct CollectLicenseMetadata;
 
 impl Step for CollectLicenseMetadata {
     type Output = PathBuf;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/collect-license-metadata")
@@ -205,7 +205,7 @@ pub struct GenerateCopyright;
 
 impl Step for GenerateCopyright {
     type Output = Vec<PathBuf>;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/generate-copyright")
@@ -269,7 +269,7 @@ pub struct GenerateWindowsSys;
 
 impl Step for GenerateWindowsSys {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/generate-windows-sys")
@@ -331,7 +331,7 @@ pub struct UnicodeTableGenerator;
 
 impl Step for UnicodeTableGenerator {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/unicode-table-generator")
@@ -353,7 +353,7 @@ pub struct FeaturesStatusDump;
 
 impl Step for FeaturesStatusDump {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/features-status-dump")
@@ -415,7 +415,7 @@ impl Step for CoverageDump {
     type Output = ();
 
     const DEFAULT: bool = false;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/coverage-dump")
@@ -437,7 +437,7 @@ pub struct Rustfmt;
 
 impl Step for Rustfmt {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/rustfmt")
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index 24530a1bf9c..9bf1f889f76 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -51,7 +51,7 @@ pub struct CrateBootstrap {
 
 impl Step for CrateBootstrap {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -109,7 +109,7 @@ pub struct Linkcheck {
 
 impl Step for Linkcheck {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     /// Runs the `linkchecker` tool as compiled in `stage` by the `host` compiler.
@@ -189,7 +189,7 @@ pub struct HtmlCheck {
 impl Step for HtmlCheck {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -236,7 +236,7 @@ pub struct Cargotest {
 
 impl Step for Cargotest {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/cargotest")
@@ -313,7 +313,7 @@ impl Cargo {
 
 impl Step for Cargo {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path(Self::CRATE_PATH)
@@ -410,7 +410,7 @@ pub struct RustAnalyzer {
 
 impl Step for RustAnalyzer {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -469,7 +469,7 @@ pub struct Rustfmt {
 
 impl Step for Rustfmt {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/rustfmt")
@@ -809,7 +809,7 @@ pub struct Clippy {
 
 impl Step for Clippy {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = false;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -909,7 +909,7 @@ pub struct RustdocTheme {
 impl Step for RustdocTheme {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/rustdoc-themes")
@@ -946,7 +946,7 @@ pub struct RustdocJSStd {
 impl Step for RustdocJSStd {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = run.builder.config.nodejs.is_some();
@@ -1006,7 +1006,7 @@ pub struct RustdocJSNotStd {
 impl Step for RustdocJSNotStd {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let default = run.builder.config.nodejs.is_some();
@@ -1061,7 +1061,7 @@ pub struct RustdocGUI {
 impl Step for RustdocGUI {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1154,7 +1154,7 @@ pub struct Tidy;
 impl Step for Tidy {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     /// Runs the `tidy` tool.
     ///
@@ -1272,7 +1272,7 @@ macro_rules! test {
             mode: $mode:expr,
             suite: $suite:expr,
             default: $default:expr
-            $( , only_hosts: $only_hosts:expr )? // default: false
+            $( , IS_HOST: $IS_HOST:expr )? // default: false
             $( , compare_mode: $compare_mode:expr )? // default: None
             $( , )? // optional trailing comma
         }
@@ -1287,10 +1287,10 @@ macro_rules! test {
         impl Step for $name {
             type Output = ();
             const DEFAULT: bool = $default;
-            const ONLY_HOSTS: bool = (const {
+            const IS_HOST: bool = (const {
                 #[allow(unused_assignments, unused_mut)]
                 let mut value = false;
-                $( value = $only_hosts; )?
+                $( value = $IS_HOST; )?
                 value
             });
 
@@ -1338,7 +1338,7 @@ pub struct CrateRunMakeSupport {
 
 impl Step for CrateRunMakeSupport {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/run-make-support")
@@ -1375,7 +1375,7 @@ pub struct CrateBuildHelper {
 
 impl Step for CrateBuildHelper {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/build_helper")
@@ -1443,7 +1443,7 @@ test!(UiFullDeps {
     mode: "ui",
     suite: "ui-fulldeps",
     default: true,
-    only_hosts: true,
+    IS_HOST: true,
 });
 
 test!(Rustdoc {
@@ -1451,14 +1451,14 @@ test!(Rustdoc {
     mode: "rustdoc",
     suite: "rustdoc",
     default: true,
-    only_hosts: true,
+    IS_HOST: true,
 });
 test!(RustdocUi {
     path: "tests/rustdoc-ui",
     mode: "ui",
     suite: "rustdoc-ui",
     default: true,
-    only_hosts: true,
+    IS_HOST: true,
 });
 
 test!(RustdocJson {
@@ -1466,7 +1466,7 @@ test!(RustdocJson {
     mode: "rustdoc-json",
     suite: "rustdoc-json",
     default: true,
-    only_hosts: true,
+    IS_HOST: true,
 });
 
 test!(Pretty {
@@ -1474,7 +1474,7 @@ test!(Pretty {
     mode: "pretty",
     suite: "pretty",
     default: true,
-    only_hosts: true,
+    IS_HOST: true,
 });
 
 test!(RunMake { path: "tests/run-make", mode: "run-make", suite: "run-make", default: true });
@@ -1505,7 +1505,7 @@ impl Step for Coverage {
     type Output = ();
     const DEFAULT: bool = true;
     /// Compiletest will automatically skip the "coverage-run" tests if necessary.
-    const ONLY_HOSTS: bool = false;
+    const IS_HOST: bool = false;
 
     fn should_run(mut run: ShouldRun<'_>) -> ShouldRun<'_> {
         // Support various invocation styles, including:
@@ -1584,7 +1584,7 @@ test!(CoverageRunRustdoc {
     mode: "coverage-run",
     suite: "coverage-run-rustdoc",
     default: true,
-    only_hosts: true,
+    IS_HOST: true,
 });
 
 // For the mir-opt suite we do not use macros, as we need custom behavior when blessing.
@@ -2273,7 +2273,7 @@ struct BookTest {
 
 impl Step for BookTest {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.never()
@@ -2439,7 +2439,7 @@ macro_rules! test_book {
             impl Step for $name {
                 type Output = ();
                 const DEFAULT: bool = $default;
-                const ONLY_HOSTS: bool = true;
+                const IS_HOST: bool = true;
 
                 fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
                     run.path($path)
@@ -2499,7 +2499,7 @@ pub struct ErrorIndex {
 impl Step for ErrorIndex {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         // Also add `error-index` here since that is what appears in the error message
@@ -2595,7 +2595,7 @@ pub struct CrateLibrustc {
 impl Step for CrateLibrustc {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.crate_or_deps("rustc-main").path("compiler")
@@ -2880,7 +2880,7 @@ pub struct CrateRustdoc {
 impl Step for CrateRustdoc {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.paths(&["src/librustdoc", "src/tools/rustdoc"])
@@ -2972,7 +2972,7 @@ pub struct CrateRustdocJsonTypes {
 impl Step for CrateRustdocJsonTypes {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/rustdoc-json-types")
@@ -3161,7 +3161,7 @@ pub struct Bootstrap;
 impl Step for Bootstrap {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     /// Tests the build system itself.
     fn run(self, builder: &Builder<'_>) {
@@ -3231,7 +3231,7 @@ pub struct TierCheck {
 impl Step for TierCheck {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/tier-check")
@@ -3285,7 +3285,7 @@ pub struct LintDocs {
 impl Step for LintDocs {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/lint-docs")
@@ -3311,7 +3311,7 @@ pub struct RustInstaller;
 
 impl Step for RustInstaller {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     /// Ensure the version placeholder replacement tool builds
@@ -3431,7 +3431,7 @@ pub struct CodegenCranelift {
 impl Step for CodegenCranelift {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.paths(&["compiler/rustc_codegen_cranelift"])
@@ -3559,7 +3559,7 @@ pub struct CodegenGCC {
 impl Step for CodegenGCC {
     type Output = ();
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.paths(&["compiler/rustc_codegen_gcc"])
@@ -3692,7 +3692,7 @@ pub struct TestFloatParse {
 
 impl Step for TestFloatParse {
     type Output = ();
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -3758,7 +3758,7 @@ pub struct CollectLicenseMetadata;
 
 impl Step for CollectLicenseMetadata {
     type Output = PathBuf;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/collect-license-metadata")
diff --git a/src/bootstrap/src/core/build_steps/tool.rs b/src/bootstrap/src/core/build_steps/tool.rs
index 793e6b629c9..d7afe1ff7db 100644
--- a/src/bootstrap/src/core/build_steps/tool.rs
+++ b/src/bootstrap/src/core/build_steps/tool.rs
@@ -687,7 +687,7 @@ impl Step for Rustdoc {
     type Output = PathBuf;
 
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/rustdoc").path("src/librustdoc")
@@ -809,7 +809,7 @@ impl Cargo {
 impl Step for Cargo {
     type Output = ToolBuildResult;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -885,7 +885,7 @@ impl LldWrapper {
 impl Step for LldWrapper {
     type Output = BuiltLldWrapper;
 
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/lld-wrapper")
@@ -986,7 +986,7 @@ impl WasmComponentLd {
 impl Step for WasmComponentLd {
     type Output = ToolBuildResult;
 
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.path("src/tools/wasm-component-ld")
@@ -1049,7 +1049,7 @@ impl RustAnalyzer {
 impl Step for RustAnalyzer {
     type Output = ToolBuildResult;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1102,7 +1102,7 @@ impl Step for RustAnalyzerProcMacroSrv {
     type Output = ToolBuildResult;
 
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1192,7 +1192,7 @@ impl LlvmBitcodeLinker {
 impl Step for LlvmBitcodeLinker {
     type Output = ToolBuildResult;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         let builder = run.builder;
@@ -1246,7 +1246,7 @@ pub enum LibcxxVersion {
 impl Step for LibcxxVersionTool {
     type Output = LibcxxVersion;
     const DEFAULT: bool = false;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.never()
@@ -1407,7 +1407,7 @@ macro_rules! tool_rustc_extended {
         impl Step for $name {
             type Output = ToolBuildResult;
             const DEFAULT: bool = true; // Overridden by `should_run_tool_build_step`
-            const ONLY_HOSTS: bool = true;
+            const IS_HOST: bool = true;
 
             fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
                 should_run_extended_rustc_tool(
@@ -1575,7 +1575,7 @@ impl TestFloatParse {
 
 impl Step for TestFloatParse {
     type Output = ToolBuildResult;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
     const DEFAULT: bool = false;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
diff --git a/src/bootstrap/src/core/build_steps/vendor.rs b/src/bootstrap/src/core/build_steps/vendor.rs
index 0caeb328811..7b860ceb943 100644
--- a/src/bootstrap/src/core/build_steps/vendor.rs
+++ b/src/bootstrap/src/core/build_steps/vendor.rs
@@ -53,7 +53,7 @@ pub(crate) struct Vendor {
 impl Step for Vendor {
     type Output = VendorOutput;
     const DEFAULT: bool = true;
-    const ONLY_HOSTS: bool = true;
+    const IS_HOST: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("placeholder").default_condition(true)
diff --git a/src/bootstrap/src/core/builder/mod.rs b/src/bootstrap/src/core/builder/mod.rs
index 54bf1842ab3..7462d549d08 100644
--- a/src/bootstrap/src/core/builder/mod.rs
+++ b/src/bootstrap/src/core/builder/mod.rs
@@ -100,8 +100,13 @@ pub trait Step: 'static + Clone + Debug + PartialEq + Eq + Hash {
     /// by `Step::should_run`.
     const DEFAULT: bool = false;
 
-    /// If true, then this rule should be skipped if --target was specified, but --host was not
-    const ONLY_HOSTS: bool = false;
+    /// If this value is true, then the values of `run.target` passed to the `make_run` function of
+    /// this Step will be determined based on the `--host` flag.
+    /// If this value is false, then they will be determined based on the `--target` flag.
+    ///
+    /// A corollary of the above is that if this is set to true, then the step will be skipped if
+    /// `--target` was specified, but `--host` was explicitly set to '' (empty string).
+    const IS_HOST: bool = false;
 
     /// Primary function to implement `Step` logic.
     ///
@@ -298,7 +303,7 @@ pub fn crate_description(crates: &[impl AsRef<str>]) -> String {
 
 struct StepDescription {
     default: bool,
-    only_hosts: bool,
+    is_host: bool,
     should_run: fn(ShouldRun<'_>) -> ShouldRun<'_>,
     make_run: fn(RunConfig<'_>),
     name: &'static str,
@@ -500,7 +505,7 @@ impl StepDescription {
     fn from<S: Step>(kind: Kind) -> StepDescription {
         StepDescription {
             default: S::DEFAULT,
-            only_hosts: S::ONLY_HOSTS,
+            is_host: S::IS_HOST,
             should_run: S::should_run,
             make_run: S::make_run,
             name: std::any::type_name::<S>(),
@@ -516,7 +521,7 @@ impl StepDescription {
         }
 
         // Determine the targets participating in this rule.
-        let targets = if self.only_hosts { &builder.hosts } else { &builder.targets };
+        let targets = if self.is_host { &builder.hosts } else { &builder.targets };
 
         for target in targets {
             let run = RunConfig { builder, paths: pathsets.clone(), target: *target };