[DO NOT MERGE] debug logging

Author: jieyouxu

src/bootstrap/src/core/build_steps/test.rs

@@ -424,7 +424,8 @@ impl Step for Rustfmt {
 
         let dir = testdir(builder, compiler.host);
         t!(fs::create_dir_all(&dir));
-        cargo.env("RUSTFMT_TEST_DIR", dir);
+        cargo.env("RUSTFMT_TEST_DIR", &dir);
+        eprintln!("RUSTFMT_TEST_DIR = {:?}", dir.display());
 
         cargo.add_rustc_lib_path(builder);
 

src/tools/rustfmt/src/test/mod.rs

@@ -1018,7 +1018,7 @@ fn make_temp_file(file_name: &'static str) -> TempFile {
     let target_dir = var("RUSTFMT_TEST_DIR").unwrap_or_else(|_| ".".to_owned());
     let path = Path::new(&target_dir).join(file_name);
 
-    let mut file = File::create(&path).expect("couldn't create temp file");
+    let mut file = File::create(&path).expect(format!("couldn't create temp file @ path = {:?}", path));
     let content = "fn main() {}\n";
     file.write_all(content.as_bytes())
         .expect("couldn't write temp file");