use in-tree rustfmt if stage > 0 or precompiled one is unavailable

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

Author: onur-ozkan

src/bootstrap/src/core/build_steps/format.rs

@@ -9,6 +9,7 @@ use std::sync::mpsc::SyncSender;
 use build_helper::git::get_git_modified_files;
 use ignore::WalkBuilder;
 
+use crate::core::build_steps::tool;
 use crate::core::builder::Builder;
 use crate::utils::build_stamp::BuildStamp;
 use crate::utils::exec::command;
@@ -237,11 +238,21 @@ pub fn format(build: &Builder<'_>, check: bool, all: bool, paths: &[PathBuf]) {
 
     let override_ = override_builder.build().unwrap(); // `override` is a reserved keyword
 
-    let rustfmt_path = build.initial_rustfmt().unwrap_or_else(|| {
-        eprintln!("fmt error: `x fmt` is not supported on this channel");
-        crate::exit!(1);
-    });
-    assert!(rustfmt_path.exists(), "{}", rustfmt_path.display());
+    // If stage is not explicitly set or is 0, try using the precompiled one first.
+    let rustfmt_path = if build.top_stage == 0
+        // This is useful for `x test tidy`, since `x test` defaults to stage 1,
+        // but we don't actually want to use the in-tree stage 1 rustfmt for that command.
+        || !build.config.is_explicit_stage()
+    {
+        build.initial_rustfmt().unwrap_or_else(|| {
+            let compiler = build.compiler(build.top_stage, build.config.build);
+            build.ensure(tool::Rustfmt { compiler, target: build.config.build }).tool_path
+        })
+    } else {
+        let compiler = build.compiler(build.top_stage, build.config.build);
+        build.ensure(tool::Rustfmt { compiler, target: build.config.build }).tool_path
+    };
+
     let src = build.src.clone();
     let (tx, rx): (SyncSender<PathBuf>, _) = std::sync::mpsc::sync_channel(128);
     let walker = WalkBuilder::new(src.clone()).types(matcher).overrides(override_).build_parallel();