implement x run rustfmt

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/core/build_steps/run.rs

@@ -392,3 +392,55 @@ impl Step for CyclicStep {
         builder.ensure(CyclicStep { n: self.n.saturating_sub(1) })
     }
 }
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Rustfmt;
+
+impl Step for Rustfmt {
+    type Output = ();
+    const ONLY_HOSTS: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("src/tools/rustfmt")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(Rustfmt);
+    }
+
+    fn run(self, builder: &Builder<'_>) {
+        let host = builder.build.build;
+
+        // `x run` uses stage 0 by default but rustfmt does not work well with stage 0.
+        // Change the stage to 1 if it's not set explicitly.
+        let stage = if builder.config.is_explicit_stage() || builder.top_stage >= 1 {
+            builder.top_stage
+        } else {
+            1
+        };
+
+        if stage == 0 {
+            eprintln!("rustfmt cannot be run at stage 0");
+            std::process::exit(1);
+        }
+
+        let compiler = builder.compiler(stage, host);
+        let rustfmt_build = builder.ensure(tool::Rustfmt { compiler, target: host });
+
+        let mut rustfmt = tool::prepare_tool_cargo(
+            builder,
+            rustfmt_build.build_compiler,
+            Mode::ToolRustc,
+            host,
+            Kind::Run,
+            "src/tools/rustfmt",
+            SourceType::InTree,
+            &[],
+        );
+
+        rustfmt.args(["--bin", "rustfmt", "--"]);
+        rustfmt.args(builder.config.args());
+
+        rustfmt.into_cmd().run(builder);
+    }
+}

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

@@ -1114,6 +1114,7 @@ impl<'a> Builder<'a> {
                 run::UnicodeTableGenerator,
                 run::FeaturesStatusDump,
                 run::CyclicStep,
+                run::Rustfmt,
             ),
             Kind::Setup => {
                 describe!(setup::Profile, setup::Hook, setup::Link, setup::Editor)